Nov 2014-present: Associate Professor at the Research Department for Limnology, Mondsee, University of Innsbruck;
June 2013–Oct. 2014: Assistant Professor at the Research Institute for Limnology, Mondsee, University of Innsbruck
Sept 1, 2012-May 2013: Senior Scientist at the Research Institute for Limnology, Mondsee of the University of Innsbruck and head of working group "Environmental Microbiology"
2005-Aug 31, 2012: Senior Scientist at the Institute for Limnology in Mondsee and head of working group "Environmental Microbiology"
1999-2004: Junior Scientist at the Institute for Limnology in Mondsee and head of working group "Environmental Microbiology"
1997-1998: Postdoctoral Research Associate at Max-Planck-Institute for Limnology, Plön, Germany
2013: venia legendi at Paris Lodron University of Salzburg (Austria)
1997: Ph.D. in Biology/Microbiology at the University of Braunschweig, Germany
1992-1996: Research Associate at the GBF (National Research Center for Biotechnology) in Braunschweig, Germany
1992: M.Sc. (Diplom) in Biology, University of Freiburg
Evolution of obligate endosymbiosis between ciliates (Euplotes spp.) and Polynucleobacter bacteria
Physiology and biogeochemical role of abundant freshwater bacteria
We investigate the ecology, diversity, and evolution of bacterial taxa occurring in freshwater systems with high cell numbers. These abundant bacterioplankton taxa are investigated by an approach combining experimental investigations on cultivated representatives and cultivation-independent in situ methods. Our major model organisms are Polynucleobacter bacteria (e.g., Hahn, 2003; Hahn et al., 2009), freshwater Actinobacteria (e.g. Sharma et al. 2009), and filamentous Bacteroidetes affiliated with the genera Aquirestis and Haliscomenobacter (e.g., Schauer & Hahn, 2005). Polynucleobacter spp. (Betaproteobacteria) represent a major component of bacterioplankton in many freshwater lakes and ponds. For instance, the species P. necessarius has a ubiquitous (Jezberova et al., 2010) and cosmopolitan (Hahn et al., 2009) distribution in standing freshwater systems, and occurs in natural systems with relative abundances of up to 70% of total bacterial numbers (Jezberova et al., 2010). Isolation of > 200 P. necessarius strains from a broad diversity of freshwater systems (pH range 3.5 to 9.0) located on all continents and in all climatic zones (including Antarctic, Arctic and tropical zones) enabled a detailed phylogenetic characterization of this taxon (Fig. 1).
Fig. 1. Diversity of Polynucleobacter bacteria. Phylogenetic tree based on 16S rRNA gene sequences of cultivated and uncultivated (environmental sequences) Polynucleobacter spp. strains (Betaproteobacteria). The tree illustrates the phylogenetic diversity and highlights the close phylogenetic relationship between strains with an obligate free-living (planktonic, black font) and strains with an obligate endosymbiotic lifestyle (red font). The previously designated subclusters (Hahn, 2003) PnecA, PnecB1, PnecB2, PnecC, and PnecD represent the species P. rarus, P. difficilis, P. acidiphobus, P. necessarius, and P. cosmopolitanus, respectively.
Based on these phylogenetic characterization (i.e. 16S-23S ITS sequences), reverse line blot hybridization (RLBH) probes were developed, which enable the specific detection of P. necessarius subgroups in environmental samples (Jezbera et al., 2011). This method was used to test if the ubiquitous and cosmopolitan distribution of the species results from a generalist adaptation or from radiation in specialized lineages differing in environmental adaptations. Investigation of 121 habitats for presence/absence of these subgroups revealed that ubiquity of the species resulted from ecological diversification (Jezbera et al., 2011).
Fig. 2. Pond-1, a small acidic pond located at an altitude of 1300 m in the Austrian Alps. This pond is persistently inhabited by a particular P. necessarius lineage represented by a genome-sequenced strain (strain QLW-P1DMWA-1).
Sequencing of the genome of a free-living representative of a P. necessarius lineage (F10) contributing on average 11% of bacterioplankton in a small pond (Pond-1; Fig. 2) revealed an unexpected small genome size (2.1 Mbp), and comparative genome analyses suggested a highly passive lifestyle of the bacterium (Hahn et al., 2012). This bacterium lacks flagella-mediated motility, quorum sensing, and encodes only a small number of signal transduction genes (Fig. 3). Several other strains also affiliated with the F10 lineage could be isolated from Pond-1 over a period of four years. Interestingly, multilocus sequence analysis of these strains revealed only very minor genetic differences between those strains (only 0.17% polymorphic sites), which indicate a rather low microdiversity of the F10 population persisting in Pond-1. It is surprising that a low-diversity population of a bacterium with a highly passive lifestyle comprises on average 11% to bacterial numbers in a limnologically quite dynamic habitat (Hahn et al., 2012).
Fig. 3. Gene number of bacterial genomes versus number of encoded signal transduction genes. The plot depicts the total number of annotated signal transduction genes in particular bacterial genomes versus the total number of genes of the respective genomes. P. necessarius QLW-P1DMWA-1 isolated from Pond-1 is highlighted as a yellow dot. (A) Entire data set consisting of 904 analyzed bacterial genomes. Red dots indicate bacteria obligately associated as symbionts or pathogens with a host; blue dots indicate free-living or facultative host-associated bacteria. (B) Plot of genomes of bacteria classified as free-living or facultative host-associated (shown in (A) as blue dots) with ≤ 100 signal transduction genes. All blue dots represent bacteria either facultatively associated with hosts (e.g., dwelling in the oral cavity or in the intestinal tract) or dwelling as free-living organisms in extreme environments (permanently anoxic, low or high temperature, low pH). The yellow (Polynucleobacter) and the green dots represent the only exclusively free-living taxa inhabiting non-extreme systems. Almost all of them are phototrophic (Synechococcus and Prochlorococcus) or predominantly heterotrophic taxa (Pelagibacter and Puniceispirillum) dwelling as planktonic bacteria in marine systems. (Hahn et al., 2012)
By combining genome analysis, physiological characterization (e.g. substrate assimilation tests), and experimental investigations we could get insights in the ecological role of the F10 lineage bacteria inhabiting Pond-1 (Fig. 4; Hahn et al., 2012). These investigations suggested that this lineage is mostly utilizing low molecular weight photooxidation products of humic substances mainly resulting from the impact of UV light on humic substances contained in the water column of the pond. These findings again reflect the highly passive lifestyle of the F10 lineage bacteria.
Fig. 4. Conceptual model on carbon fluxes utilized by the P. necessarius F10 lineage population in Pond-1. The model suggests origin and transformation of major carbon sources utilized by the F10 lineage population inhabiting Pond-1. Humic substances (HS) leached from soils (1) and floating mats (2) (Schwingrasen, formed mainly of Sphagnum and Carex) are transported by percolating water to the pond. Polynucleobacter bacteria affiliated with the F10 lineage mainly utilize low-molecular-weight (LMW) photooxidation products of HS (3). Direct utilization of aliphatic residues of HS by enzymatic cleavage is also expected to take place (4). Another potential substrate source could be fermentation products released by bioturbation and other processes from the sediment (5) to the water column of the pond. (Hahn et al., 2012)
Future studies will focus on microevolution, genome evolution, biogeography, and physiology of our model bacteria.
Metagenomische Charakterisierung des Bakterioplanktons des Brettersees als Startpunkt für Langzeituntersuchungen zum Einfluss von Umweltveränderungen auf die Evolution der Bakterien in hochalpinen Seen - Glockner-Öko-Fonds, ongoing
Microevolution of a freshwater bacterium, funded by the Austrian Science Fund (FWF), Project no. P27160, finished
Ecological diversification within the subspecies Polynucleobacter necessarius ssp. asymbioticus and environmental ecotype sorting (FWF I 482-B09), funded by the European Science Foundation (ESF), project FREDI, project leader Jakob Pernthaler, University of Zurich, Switzerland, finished Link
Ecological Diversity of Polynucleobacter Bacteria, funded by the Austrian Science Fund (FWF), Project no. P19853, finished
Polynucleobacter Genome Project, funded by the DOE Joint Genome Institute (USA), finished Genome sequencing of a free-living Polynucleobacternecessarius strain Link and a obligately endosymbiotic P. necessarius strain Link
Mechanisms Controlling the Diversity of Bacterioplankton, funded by the Austrian Science Fund (FWF), Project no. P15655-Bio, finished
Interaction of Protists and Bacteria (Jubiläumsfondsprojekt #7767,) funded by the Austrian National Bank, finished
Biogeography and within-taxon ecological differentiation of Polynucleobacter necessarius subsp. asymbioticus and Limnohabitans planctonicus (Betaproteobacteria), Austrian-Czech cooperation project with Jan Jezbera (Czech Republic), funded by the OEAD, finished
Ecological and phylogenetic comparison of bacterial populations inhabiting Antarctic and European lakes, binational Acciones Integradas Projekt with Antonio Camacho (Spain) funded by the OEAD, finished
Eco-physiological characteristics of two important groups of Betaproteobacteria abundant in freshwater bacterioplankton, Austrian-Czech cooperation project with Karel Šimek (Czech Republic), funded by the OEAD, finished
Hoetzinger M., Hahn M.W., Andersson L.Y., Buckley N., Ramsin C., Buck M., Nuy J.K., Garcia S.L., Puente-Sánchez F., Bertilsson S. (2024). Geographic population structure and distinct intra-population dynamics of globally abundant freshwater bacteria, The ISME Journal 18 (1): wrae113, https://doi.org/10.1093/ismejo/wrae113
Boukheloua R., Mukherjee I., Park H., Šimek K., Kasalický V., Ngochera M., Grossart H.-P., Picazo-Mozo A., Camacho A., Cabello-Yeves P.J., Rodriguez-Valera F., Callieri C., Andrei A.-S., Pernthaler J., Posch T., Alfreider A., Sommaruga R., Hahn M.W., Sonntag B., Lopez-Garcia P., Moreira D., Jardillier L., Lepère C., Biderre-Petit C., Bednarska A., Ślusarczyk M., Tóth V-R., Banciu H.L., Kormas K., Orlic S., Šantić D., Muyzer G., Herlemann D.P.R., Tammert H., Bertilsson S., Langenheder S., Zechmeister T., Salmaso N., Storelli N., Capelli C., Lepori F., Lanta V., Henriques Vieira H., Kostanjšek F., Kabeláčová K., Chiriac M.-C., Haber M., Shabarova T., Fernandes C., Rychtecký P., Znachor P., Szőke-Nagy T., Layoun P., Wong H.L., Silva Kavagutti V., Bulzu P.-A., Salcher M.M., Piwosz K., Ghai R., Global freshwater distribution of Telonemia protists, The ISME Journal, wrae177, https://doi.org/10.1093/ismejo/wrae177
Shah M., Bornemann T.L.V., Nuy J.K., Hahn M.W., Probst A.J., Beisser D., Boenigk J. (2024). Genome-resolved metagenomics reveals the effect of nutrient availability on bacterial genomic properties across 44 European freshwater lakes. Environ Microbiol. 26(6):e16634. doi: 10.1111/1462-2920.16634
He Z., Naganuma T., Nakai R., Uetake J., Hahn M.W. (2024). Microbiomic analysis of bacteria associated with rock tripe lichens from Alpine areas in Eastern Alps and Equatorial Africa. Current Microbiology, 115: 81 (https://doi.org/10.1007/s00284-024-03626-8
Pitt A., Lienbacher S., Schmidt J., Neumann Schaal M., Wolf J., Hahn M.W. (2024). Description of a new freshwater bacterium Aquirufa regiilacus sp. nov., classification of the genera Aquirufa, Arundinibacter, Sandaracinomonas, and Tellurirhabdus to the family Spirosomataceae, classification of the genus Chryseotalea to the family Fulvivirgaceae and Litoribacter to the family Cyclobacteriaceae, as well as classification of Litoribacter alkaliphilus as a later heterotypic synonym of Litoribacter ruber. Archives of Microbiology 206(79), https://link.springer.com/article/10.1007/s00203-023-03801-8
2023
Pitt A., Hahn M. (2023). Wissen schaffen mit Citizen Scientists: Biodiversität und Ökologie von Süßwasserbakterien. Biologie in unserer Zeit, 53(3): 272–279. https://doi.org/10.11576/biuz-6525
2022
Hahn M.W., Pitt A., Schmidt J., Koll U., Wolf J. Whitman W.B., Bodelier P.L.E, Neumann-Schaal M. (2022). Zwartia hollandica gen. nov., sp. nov., Jezberella montanilacus gen. nov., sp. nov. and Sheuella amnicola gen. nov., comb. nov., representing the environmental GKS98 (betIII) cluster. Int. J. Syst. Evol. Microbiol. 72:9, 1-13. https://doi.org/10.1099/ijsem.0.005513
Hahn M.W., Pitt A., Schmidt J., Camacho A. (2022). Fourteen new Polynucleobacter species: P. brandtiae sp. nov., P. kasalickyi sp. nov., P. antarcticus sp. nov., P. arcticus sp. nov., P. tropicus sp. nov., P. bastaniensis sp. nov., P. corsicus sp. nov., P. finlandensis sp. nov., P. ibericus sp. nov., P. hallstattensis sp. nov., P. alcilacus sp. nov., P. nymphae sp. nov., P. paludilacus sp. nov. and P. parvulilacunae sp. nov. Int. J. Syst. Evol. Microbiol.: 72(6):005408. https://doi.org/10.1099/ijsem.0.005408
Pitt A., Koll U., Schmidt J., Neumann-.Schaal M., Wolf J., Krausz S., Hahn M.W. (2022). Aquirufa lenticrescens sp. nov. and Aquirufa aurantiipilula sp. nov.: two new species of a lineage of widespread freshwater bacteria. Arch Microbiol 204: 356, https://doi.org/10.1007/s00203-022-02950-6
2021
Hahn M. (2021) Evolution und Systematik der Prokaryoten. In: Boenigk J (editor). Boenigk, Biologie: Der Begleiter in und durch das Studium. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 859-884. https://www.springer.com/gp/book/9783662612699
Hahn M.W., Pitt A. (2021). Silvanigrella. Bergey's Manual of Systematics of Archaea and Bacteria. pp. 1-9.
Hahn M.W., Huemer A, Pitt A., Hoetzinger M. (2021). Opening a next-generation black box: ecological trends for hundreds of species-like taxa uncovered within a single bacterial >99% 16S rRNA operational taxonomic unit. Molecular Ecology Resources 21:2471–2485.
Hahn M.W., Pitt A., Koll U., Schmidt J., Maresca J.A., Neumann-Schaal M. (2021). Aurantimicrobium photophilum sp. nov., a non-photosynthetic bacterium adjusting its metabolism to the diurnal light cycle and reclassification of Cryobacterium mesophilum as Terrimesophilobacter mesophilus gen. nov., comb. nov. Int J Syst Evol Microbiol 71(8):004975.
Pitt A., Schmidt J., Koll U., Hahn M.W. (2021).Aquiluna borgnonia gen. nov., sp. nov., a member of a Microbacteriaceae lineage of freshwater bacteria with small genome sizes. Int J Syst Evol Microbiol 71:5 https://doi.org/10.1099/ijsem.0.004825
Hoetzinger M., Pitt A., Huemer A., Hahn, M.W. (2021). Continental-scale gene flow prevents allopatric divergence of pelagic freshwater bacteria. Genome Biology and Evolution, 13:3, evab019, https://doi.org/10.1093/gbe/evab019
2020
Waite, D.W., Chuvochina, M., Pelikan, C., Parks, D.H., Yilmaz, P., Wagner, M., Loy, A., Naganuma, T., Nakai, R., Whitman, W.B., Hahn, M.W., Kuever, J., and P. Hugenholtz (2020). Proposal to reclassify the proteobacterial classes Deltaproteobacteria and Oligoflexia, and the phylum Thermodesulfobacteria into four phyla reflecting major functional capabilities. Int J Syst Evol Microbiol 70:5972–6016, doi:10.1099/ijsem.0.004213
Srivastava A., Murugaiyan J., Garcia J.A.L., De Corte D., Hoetzinger M., Eravci M., Weise C., Kumar Y., Roesler U., Hahn M.W., Grossart H.-P. (2020). Combined methylome, transcriptome and proteome analyses document rapid acclimatization of a bacterium to environmental changes. Frontiers in Microbiology 11:544785 https://doi.org/10.3389/fmicb.2020.544785
Pitt A., Koll U., Schmidt J., Hahn M. W. (2020). Aquirufa ecclesiirivi sp. nov. and Aquirufa beregesia sp. nov., isolated from a small creek and classification of Allopseudarcicella aquatilis as a later heterotypic synonym of Aquirufa nivalisilvae. Int J Syst Evol Microbiol 70: 4602–4609. https://doi.org/10.1099/ijsem.0.004319
Pitt A., Koll U., Schmidt J., Hahn M.W. (2020). Fluviispira multicolorata gen. nov., sp. nov. and Silvanigrella paludirubra sp. nov., isolated from freshwater habitats. Int J Syst Evol Microbiol 70: 1630-1638. https://doi.org/10.1099/ijsem.0.003947
Pitt A., Schmidt J., Koll U., Hahn M.W. (2020). Rariglobus hedericola gen. nov., sp. nov., belonging to the Verrucomicrobia, isolated from a temperate freshwater habitat. Int J Syst Evol Microbiol 70:1830-1836, https://doi.org/10.1099/ijsem.0.003980
Nuy J.K., Hoetzinger M., Hahn M.W., Beisser D., Boenigk J. (2020). Ecological differentiation in two major freshwater bacterial taxa along environmental gradients. Front. Microbiol. 11:154. doi.org/10.3389/fmicb.2020.00154
2019
Limberger R., Pitt A., Hahn M. W., Wickham S. A. (2019). Spatial insurance in multi-trophic metacommunities. Ecology Letters 22:1828-1837, doi: 10.1111/ele.13365
Pitt A., Schmidt J., Koll U., Hahn M.W. (2019).Rhodoluna limnophila sp. nov., a bacterium with 1.4 Mbp genome size isolated from freshwater habitats located in Salzburg, Austria. Int J Syst Evol Microbiol 69:3946-3954, doi.org/10.1099/ijsem.0.003720
Pitt A., Schmidt J., Koll U., Hahn M.W. (2019). Aquirufa antheringensis gen. nov., sp. nov. and Aquirufa nivalisilvae sp. nov., representing a new genus of widespread freshwater bacteria, Int J Syst Evol Microbiol 69:2739-2749, doi 10.1099/ijsem.0.003554
Beisser, D., Bock, C., Hahn, M.W., Vos, M., Sures, B., Rahmann, S., and J. Boenigk (2019) Interaction-specific changes in the transcriptome of Polynucleobacter asymbioticus caused by varying protistan communities. Frontiers in Microbiology 10, 1498, doi.10.3389/fmicb.2019.01498
Hahn M.W., Koll U., Schmidt J. (2019). Isolation and Cultivation of Bacteria. Pages 313-351. In: Hurst C. (eds) The Structure and Function of Aquatic Microbial Communities. Advances in Environmental Microbiology, vol 7. Springer, Cham. Link
Maresca J.A., Keffer J. L., Hempel P.P., Polson S.W., Shevchenko O., Bhavsar J., Powell D., Miller K.J., Singh A., Hahn, M.W. (2019). Light modulates the physiology of nonphototrophic Actinobacteria, Journal of Bacteriology, e00740-18, doi: 10.1128/JB.00740-18Commentary by Carolyn E. Lubner
Pitt A., Hahn M.W. (2019). Mikrobiologie in der Schule: Erforschung unbekannter Gewässerbakterien, Biologie in unserer Zeit, 49(2): 131-137 doi:10.1002/biuz.201910672
Hahn, M. W. , Hoetzinger, M. (2019). Polynucleobacter . In Bergey's Manual of Systematics of Archaea and Bacteria (eds W. B. Whitman, F. Rainey, P. Kämpfer, M. Trujillo, J. Chun, P. DeVos, B. Hedlund and S. Dedysh). doi:10.1002/9781118960608.gbm00940.pub2
Hoetzinger M., Schmidt J., Pit, A., Koll U., Lang E., Hahn, M.W. (2019) Polynucleobacter paneuropaeus sp. nov., characterized by six strains isolated from freshwater lakes located along a 3000 km north–south cross-section across Europe. Int J Syst Evol Microbiol 69: 203–213 doi.org/10.1099/ijsem.0.003130
2018
Hahn, M.W., Koll, U., Schmidt, J., Huymann, L.R., Karbon, G., and E. Lang. (2018). Polynucleobacter hirudinilacicola sp. nov. and Polynucleobacter campilacus sp. nov. both isolated from freshwater systems. International Journal of Systematic and Evolutionary Microbiology 68(8): 2593-2601 doi: 10.1099/ijsem.0.002880
Pitt A., Schmidt J., Lang E., Whitman W.B., Woyke T., Hahn M. W. (2018). Polynucleobacter meluiroseus sp. nov., a bacterium isolated from a lake located in the mountains of the Mediterranean island of Corsica. International Journal of Systematic and Evolutionary Microbiology 68: 1975-1985, doi: 10.1099/ijsem.0.002777
Simek K., Grujcic V., Hahn M.W., Hornak K., Jezberova J., Kasalicky V., Nedoma J., Salcher M.M, Shabarova T. (2018). Bacterial prey food characteristics modulate community growth response of freshwater bacterivorous flagellates. Limnol. Oceanogr. 63:484–502, doi:10.1002/lno.10759
2017
Hahn M.W., Schmidt J., Ssanyu G.A., Kyrpides N.C., Whitman W.B. (2017). Reclassification of a Polynucleobacter cosmopolitanus strain isolated from tropical Lake Victoria as Polynucleobacter victoriensis sp. nov. Int. J. Syst. Evol. Microbiol. 67: 5087-5093 DOI:10.1099/ijsem.0.002421
Hahn M.W., Koll U., Karbon G., Schmidt J., Lang E. (2017). Polynucleobacteraenigmaticus sp. nov. isolated from the permanently anoxic monimolimnion of a meromictic lake in Austria. Int. J. Syst. Evol. Microbiol. 67:4646–4654 doi: 10.1099/ijsem.0.002347
Hahn M.W., Karbon G., Koll U., Schmidt J., Lang E. (2017). Polynucleobacter sphagniphilus sp. nov. a planktonic freshwater bacterium isolated from an acidic and humic freshwater habitat. Int. J. Syst. Evol. Microbiol. 67:3261-3267
Hahn M.W., Schmidt J., Koll U., Rohde M., Verbarg S., Pitt A., Nakai R., Naganuma T., Lang E. (2017). Silvanigrella aquatica gen. nov., sp. nov., isolated from a freshwater lake, description of Silvanigrellaceae fam. nov. and Silvanigrellales ord. nov., reclassification of the order Bdellovibrionales in the class Oligoflexia, reclassification of the families Bacteriovoracaceae and Halobacteriovoraceae in the new order Bacteriovoracales ord. nov., and reclassification of the family Pseudobacteriovoracaceae in the order Oligoflexales.Int J Syst Evol Microbiol 67:2555–2568doi: http://dx.doi.org/10.1099/ijsem.0.001965
Vannini C. , Sigona C., Hahn M.W., Petroni G., Fujishima M. (2017). High degree of specificity in the association between symbiotic Betaproteobacteria and the host Euplotes (Ciliophora, Euplotia). Eur. J. Protistol. 59:124–132 https://doi.org/10.1016/j.ejop.2017.04.003
Hahn, M.W., Huymann, L.R., Koll, U., Schmidt, J., Lang, E., Hoetzinger, M. (2017). Polynucleobacter wuianus sp. nov., a free-living freshwater bacterium affiliated with the cryptic species complex PnecC. Int. J. Syst. Evol. Microbiol. 67:379–385
Hoetzinger M., Hahn M.W., Jezberová J., Schmidt J., Koll U. (2017). Microdiversification of a pelagic Polynucleobacter species is mainly driven by acquisition of genomic islands from a partially interspecific gene pool. Applied and Environmental Microbiology (AEM) 83: 3 e02266-16, doi.org/10.1128/aem.02266-16
2016
Hahn M. W. (2016). Rhodoluna, 1–9 DOI: 10.1002/9781118960608.gbm01312, In: Whitman, W.B. (ed.) Bergey's Manual of Systematics of Archaea and Bacteria, Wiley Online ISBN: 9781118960608
Nakamura S., Kikukawa T., Tamogami J., Kamiya M., Aizawa T., Hahn M.W., Ihara K., Kamo N., Demura M. (2016). Photochemical characterization of actinorhodopsin and its functional existence in the natural host. Biochimica et Biophysica Acta-Bioenergetics 1857: 1900–1908.
Hahn M. W., Schmidt J., Pitt A., Taipale S. J., Lang E. (2016). Reclassification of four Polynucleobacter necessarius strains as Polynucleobacter asymbioticus comb. nov., Polynucleobacter duraquae sp. nov., Polynucleobacter yangtzensis sp. nov., and Polynucleobacter sinensis sp. nov., and emended description of the species Polynucleobacter necessarius. Int. J. Syst. Evol. Microbiol. 66: 2883–2892. PDF
Hahn M.W., Jezberová J., Koll U., Saueressig-Beck T., Schmidt J. (2016). Complete ecological isolation and cryptic diversity in Polynucleobacter bacteria not resolved by 16S rRNA gene sequences. The ISME Journal 10:1642-1655. pdf
2015
Taipale, S.J., Peltomaa, E., Hiltunen, M., Jones, R.I., Hahn, M.W., Biasi, C., Brett, M.T. (2015) Inferring phytoplankton, terrestrial plant and bacteria bulk delta C-13 values from compound specific analyses of lipids and fatty acids. PLOS ONE 10(7) e0133974
Keffer J.L., Hahn M.W., Maresca J.A. (2015). Characterization of an unconventional rhodopsin from the freshwater Actinobacterium Rhodoluna lacicola. J. Bacteriol. 197(16) 2704-2712 doi:10.1128/JB.00386-15
Keffer J. L., Sabanayagam C. R., Lee M. E., DeLong E. F.,Hahn M. W., Maresca, J. A. (2015). Identifying rhodopsin-containing cells using TIRF microscopy. Applied and Environmental Microbiology. 81:10 3442-3450.
Hahn, M.W., Koll, U., Jezberova, J. and A. Camacho (2015). Global phylogeography of pelagic Polynucleobacter bacteria: Restricted geographic distribution of subgroups, isolation by distance, and influence of climate. Environ. Microbiol.17(3), 829–840. PDF
2014
Hahn M.W., Schmidt J., Taipale S.J., Doolittle W.F., Koll U. (2014). Rhodoluna lacicolagen. nov., sp. nov., a planktonic freshwater bacterium with stream-lined genome. Int. J. Syst. Evol. Microbiol., 64: 3254–3263. PDF
Taipale, S.J., Brett, M.T., Hahn, M.W., Martin-Creuzburg, D., Yeung, S., Hiltunen, M., Strandberg, U., and P. Kankaala (2014). Differing Daphnia magnaassimilation efficiencies for terrestrial, bacterial and algal carbon and fatty acids. Ecology 95:563–576.
2013
Jezberova, J., Jezbera, J., and Hahn M.W. (2013). Insights into variability of actinorhodopsin genes of the LG1 cluster in two different freshwater habitats. PLoS ONE 8(7): e68542.
Šimek K., Kasalický V., Jezbera J., Horňák K., Nedoma J., Hahn M.W., Bass D., Jost S., Boenigk J. (2013). Differential freshwater flagellate community response to bacterial food quality with a focus on Limnohabitans bacteria. The ISME Journal 7: 1519–1530.
Kasalický V., Jezbera J., Hahn M.W., Šimek K. (2013). The diversity of the Limnohabitans genus, an important group of freshwater bacterioplankton, by characterization of 35 isolated strains. PLoS ONE 8(3): e58209, doi:10.1371/journal.pone.0058209
Jezbera J., Jezberová J., Kasalický V., Šimek K., Hahn M.W. (2013). Patterns of Limnohabitans microdiversity across a large set of freshwater habitats as revealed by Reverse Line Blot Hybridization. PLoS ONE 8(3): e58527, doi:10.1371/journal.pone.0058527
2012
Jezbera J., Jezberová J., Koll U., Hornak K., Simek K., Hahn M.W. (2012). Contrasting trends in distribution of four major planktonic betaproteobacterial groups along a pH gradient of epilimnia of 72 freshwater habitats. FEMS Microbiology Ecology 81: 467-479.
Hahn M.W., Scheuerl T., Jezberová J., Koll U., Jezbera J., Šimek K., Vannini C., Petroni G., Wu Q. L. (2012). The passive yet successful way of planktonic life: Genomic and experimental analysis of the ecology of a free-living Polynucleobacter population. PLoS ONE 7(3): e32772. PDF
Meincke L., Copeland A., Lapidus A., Lucas S., Berry K. W., Glavina Del Rio T., Hammon N., Dalin E., Tice H., Pitluck S., Richardson P., Bruce, D., Goodwin L., Han C., Tapia R., Detter J. C., Schmutz J., Brettin T., Larimer F., Land M., Hauser L., Kyrpides N. C., Ivanova N., Göker M., Woyke T., Wu Q. L., Pöckl M., Hahn M. W., Klenk H.-P. (2012). Complete genome sequence of Polynucleobacter necessarius subsp. asymbioticus type strain (QLW-P1DMWA-1T). Standards in Genomic Sciences 6: 74-83 doi: 10.4056/sigs.2395367
Hahn M.W., Minasyan A., Lang E., Koll U., Spröer, C. (2012). Polynucleobacter difficilis sp. nov., a planktonic freshwater bacterium affiliated with subcluster B1 of the genus Polynucleobacter. Int. J. Syst. Evol. Microbiol. 62: 376 - 383.
2011
Wang, J., Yang, D., Zhang, Y., Shen, J., van der Gast, C., Hahn, M.W., and Q. Wu (2011) Do Patterns of Bacterial Diversity along Salinity Gradients Differ from Those Observed for Macroorganisms? PLoS ONE 6(11): e27597. LINK
Taipale, S., Kankaala, P., Hahn, M. W., Jones, R. I., and Tiirola, M. (2011). Methane oxidizing and photoautotrophic bacteria are major producers in a humic lake with large anoxic hypolimnion. Aquat Microb Ecol. 64: 81–95.
Hahn, M.W., Lang, E., Tarao, M., and Brandt, U. (2011). Polynucleobacter rarus sp. nov., a free-living planktonic bacterium isolated from an acidic lake. Int. J. Syst. Evol. Microbiol. 61: 781-787. PDF
Hahn, M.W., Lang, E., Brandt, U., and Spröer, C. (2011). Polynucleobacter acidiphobus sp. nov., a representative of an abundant group of planktonic freshwater bacteria. Int. J. Syst. Evol. Microbiol. 61: 788-794. PDFSuppl.Mat.
Jezbera, J., Jezberová, J., Brandt, U., and Hahn, M.W. (2011). Ubiquity of Polynucleobacter necessarius subspecies asymbioticus results from ecological diversification. Environ. Microbiol. 13: 922–931. PDF
2010
Kasalický, V, Jezbera, J., Šimek, K., and Hahn, M.W. (2010). Limnohabitans planktonicus sp. nov., and Limnohabitans parvus sp. nov., two novel planktonic Betaproteobacteria isolated from a freshwater reservoir and emended description of the genus Limnohabitans. Int. J. Syst. Evol. Microbiol. 60: 2710-2714.
Hahn, M.W., Kasalický, V., Jezbera, J., Brandt, U., and Šimek, K. (2010). Limnohabitans australis sp. nov., isolated from a freshwater pond, and emended description of the genus Limnohabitans. Int. J. Syst. Evol. Microbiol. 60: 2946-2950. PDF
Hahn, M.W., Kasalický, V., Jezbera, J., Brandt, U., Jezberová, J., and Šimek, K. (2010). Limnohabitans curvus gen. nov., sp. nov., a planktonic bacterium isolated from a freshwater lake. Int. J. Syst. Evol. Microbiol. 60: 1358-1365.
Jezberová, J., Jezbera, J., Brandt, U., Lindström, E.S., Langenheder, S., and Hahn, M.W. (2010). Ubiquity of Polynucleobacter necessarius ssp. asymbioticus in lentic freshwater habitats of a heterogenous 2000 km2 area. Environ. Microbiol. 12: 658-669.
Šimek, K., Kasalický, V, Horňák, K., Hahn M.W., and Weinbauer, M.G. (2010). Assessing niche separation among coexisting Limnohabitans strains through interactions with a competitor, viruses, and a bacterivore. Appl. Environ. Microbiol. 76: 1406–1416.
Šimek, K., Kasalický, V., Jezbera, J., Jezberová, J., Hejzlar, J., and Hahn, M.W. (2010). Broad habitat range of the phylogenetically narrow R-BT065 cluster, representing a core group of the betaproteobacterial genus Limnohabitans. Appl. Environ. Microbiol. 76: 631-639.
Hahn, M.W., Lang, E., Brandt, U., Lünsdorf, H., Wu, Q.L., and E. Stackebrandt. (2010): Polynucleobacter cosmopolitanus sp. nov., free-living planktonic bacteria inhabiting freshwater lakes and rivers. Int. J. Syst. Evol. Microbiol. 60: 166-173.
2009
Xing, P., Hahn, M.W., and Wu, Q.L. (2009): Low taxa richness of bacterioplankton in high-altitude lakes of the Eastern Tibetan Plateau with predominance of Bacteroidetes and Synechococcus. Appl. Environ. Microbiol. 75: 7017–7025
Jezbera, J., Sharma, A.K., Brandt, U., Doolittle, W.F., and M.W. Hahn. (2009): "Candidatus Planktophila limnetica", an actinobacterium representing one of the most numerically important taxa in freshwater bacterioplankton. Int. J. Syst. Evol. Microbiol. 59: 2864-2869.
Hahn, M.W., Lang, E., Brandt, U., Wu, Q.L., and Scheuerl, T. (2009): Emended description of the genus Polynucleobacter and the species P. necessarius and proposal of two subspecies, P. necessarius subspecies necessarius subsp. nov. and P. necessarius subsp. asymbioticus subsp. nov. Int. J. Syst. Evol. Microbiol. 59: 2002-2009.
Tarao, M., Jezbera, J., and Hahn, M.W. (2009): Involvement of cell surface structures in size-independent grazing resistance of freshwater Actinobacteria. Appl. Environ. Microbiol. 75: 4720-4726.
Hahn, M.W. (2009): Real-time evolution observatories in the wild (Crystal ball - 2009). Environ. Microbiol. Reports 1: 8-9.
Sharma, A.K., Sommerfeld, K., Bullerjahn, G.S., Matteson, A.R., Wilhelm, S.W., Jezbera, J., Brandt, U., Doolittle, W.F., and Hahn, M.W. (2009): Actinorhodopsin genes discovered in diverse freshwater habitats and among cultivated freshwater Actinobacteria. The ISME Journal 3: 726–737.
Hahn, M.W. (2009): Description of seven Candidatus species affiliated with the phylum Actinobacteria, representing planktonic freshwater bacteria. Int. J. Syst. Evol. Microbiol. 59: 112-11.
2008
Hahn, W.W. and Wu, Q.L. (2008): Planktonic bacteria in Chinese and European lakes: Are they different? In: Microbes and the Environment: Perspective and Challenges, S.-J. Liu H. L. Drake (eds.), Science Press, Beijing, pp. 73-78.
2007
Wu, Q.L., Zwart, G., Wu, J. , Kamst-van Agterveld, M.P., Liu, S., and Hahn, M.W. (2007): Submersed macrophytes play a key role in structuring bacterioplankton community composition in the large, shallow, subtropical Taihu Lake, China. Environ. Microbiol. 9:2765–2774.
Groben, R., Hahn, M.W., Horňák, K., Mergeay, J., Šimek, K., and Vrb, J.. (2007): Meeting Report: ALTER-Net Workshop about the “Application of Molecular Techniques to Study Biodiversity, Structure and Function of Planktonic Communities in Lakes” at Blanes, Spain, February 15-16, 2007. Protist 158:417-421.
Hahn, M.W. and Schauer, M. (2007): ‘Candidatus Aquirestis calciphila’ and ‘Candidatus Haliscomenobacter calcifugiens’, filamentous, planktonic bacteria inhabiting natural lakes. Int. J. Syst. Evol. Microbiol. 57:936-940.
Wu, Q.L., Chen, Y., Xu, K., Liu, Z., and Hahn, M.W. (2007): Intra-habitat heterogeneity of microbial food web structure under the regime of eutrophication and sediment resuspension in the large subtropical shallow Lake Taihu, China. Hydrobiologia 581:241–254.
Vannini, C., Pöckl, M., Petroni, G., Wu, Q.L., Lang, E., Stackebrandt, E., Schrallhammer, M., Richardson, P.M., and Hahn, M.W. (2007): Endosymbiosis in statu nascendi: Close phylogenetic relationship between obligately endosymbiotic and obligately free-living Polynucleobacter strains (Betaproteobacteria). Environ. Microbiol. 9:347-359.
2006
Wu, Q.L., Zwart, G., Schauer, M., Kamst-van Agterveld, M.P., and Hahn, M.W. (2006): Bacterioplankton community composition along a salinity gradient of sixteen high-mountain lakes located on the Tibetan Plateau, China. Appl. Environ. Microbiol. 72:5478–5485.
Wu, Q.L. and Hahn, M.W. (2006b): High predictability of the seasonal dynamics of a species-like Polynucleobacter population in a freshwater lake. Environ. Microbiol. 8:1660-1666.
Šimek, K., Horňák, K. , Jezbera, J. , Nedoma, J. , Vrba, J., Straškrábová, V. , Macek, M. , Dolan, J. R., and Hahn., M.W. (2006): Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoir. Environ. Microbiol. 8:1613-1624.
Schauer, M., Jing, J., and Hahn, M.W. (2006): Recurrent seasonal variations in abundance and composition of filamentous SOL cluster bacteria (Saprospiraceae, Bacteroidetes) in oligomesotrophic Lake Mondsee (Austria). Appl. Environ. Microbiol. 72:4704-4712.
Hahn, M.W. (2006): The microbial diversity of inland waters. Current Opinion in Biotechnology 17: 256-261.
Wu, Q.L. and Hahn, M.W. (2006): Differences in structure and dynamics of Polynucleobacter communities in a temperate and a subtropical lake revealed at three phylogenetic levels. FEMS Microb. Ecol. 57(1):67.
2005
Schauer, M., Kamenik, C., and Hahn, M.W. (2005): Ecological differentiation within a cosmopolitan group of planktonic freshwater bacteria (SOL cluster, Saprospiraceae, Bacteroidetes). Appl. Environ. Microbiol. 71:5900–5907.
Camacho, A., Rochera, C., Silvestre, J.J., Vicente, E., and Hahn, M.W. (2005): Spatial Dominance and Inorganic Carbon Assimilation by Conspicuous Autotrophic Biofilms in a Physical and Chemical Gradient of a Cold Sulfurous Spring: The Role of Differential Ecological Strategies. Microb. Ecol. 50: 172 - 184. Link
Hahn, M.W., Pöckl, M., and Wu, Q.L. (2005): Low intraspecific diversity in a Polynucleobacter subcluster population numerically dominating bacterioplankton of a freshwater pond. Appl. Environ. Microbiol. 71: 4539–4547. Abstract
Schauer, M. and Hahn, M.W. (2005): Diversity and phylogenetic affiliations of morphologically conspicuous large filamentous bacteria occurring in the pelagic zones of a broad spectrum of freshwater habitats. Appl. Environ. Microbiol. 71: 1931-1940. AbstractPDF
Hahn, M.W. and Pöckl, M. (2005): Ecotypes of planktonic Actinobacteria with identical 16S rRNA genes adapted to thermal niches in temperate, subtropical, and tropical freshwater habitats. Appl. Environ. Microbiol. 71: 766–773. AbstractPDF
2004
Boenigk, J., Stadler, P., Wiedlroither, A., and Hahn, M.W. (2004): Strain-specific differences in the grazing sensitivities of closely related ultramicrobacteria affiliated with the Polynucleobacter cluster. Appl. Environ. Microbiol. 70: 5787-5793.
Hahn, M.W. (2004): Broad diversity of viable bacteria in ‘sterile’ (0.2µm) filtered water. Research in Microbiology 155: 688-691. Abstract
Hahn, M.W., Stadler, P., Wu, Q.L., and Pöckl, M. (2004): The filtration–acclimatization method for isolation of an important fraction of the not readily cultivable bacteria. Journal of Microbiological Methods 57: 379-390. Abstract
Hahn, M.W., Lünsdorf, H., and Janke, L. (2004): Exopolymer production and microcolony formation play an important role in protistan grazing defense of novel bacterial strains isolated from freshwater plankton. Aquat Microb Ecol. 35:297-308. Link
Wu Q.L., Boenigk J., and Hahn M.W. (2004): Successful predation by a nanoflagellate on filamentous bacteria challenges current models on flagellate bacterivory. Appl. Environ. Microbiol. 70: 332–339. AbstractPDF
2003
Hahn, M.W. (2003): Isolation of Strains Belonging to the Cosmopolitan Polynucleobacter necessarius Cluster from Freshwater Habitats Located in Three Climatic Zones. Appl. Environ. Microbiol. 69: 5248-5254. Abstract
Hahn, M.W., Lünsdorf, H., Wu, Q., Schauer, M., Höfle, M. G., Boenigk, J., and Stadler P. (2003): Isolation of novel ultramicrobacteria classified as Actinobacteria from five freshwater habitats in Europe and Asia. Appl. Environ. Microbiol. 69(3): 1442-1451. AbstractPDF
2001
Hahn, M.W. and Höfle, M.G.(2001): Grazing of protozoa and its effect on populations of aquatic bacteria (MiniReview). FEMS Microbiology Ecology 35: 113-121. Abstract Full article: PDF
2000
Hahn, M.W., Moore, E.R.B., and Höfle, M.G. (2000):. Role of microcolony formation in the protistan grazing defense of the aquatic bacterium Pseudomonas sp. MWH1. Microbial Ecology 39: 175-185. Abstract
