Current Research Projects
Frankia-actinorhizal plant symbiosis (PDF) Activities in this area mainly deal with the assessment of the diversity of frankiae in different soils (in collaboration with Dr. Mark Paschke, CSU), of saprophytic growth of selected Frankia strains and concomitant consequences for root nodule formation on actinorhizal plants (in collaboration with Dr. Jeffrey Dawson, UIUC), and with the development of qPCR assays for the quantification of indigenous and introduced frankiae in soils.
Ecology of pathogens (PDF) Studies on pathogens in the environment have been initiated relatively recently at Texas State University in collaboration with Dr. Michael Forstner (genetics, herpetology), Dr. Francis Rose (herpetology) and Dr. Tim Bonner (ichthyology). Two different organisms are currently investigated: 1. bacteria of the genus Salmonella, a large group of enteric bacteria that are associated with a broad range of hosts including humans, and 2. fungi (Batrachochytrium dendrobatidis) that have been implicated as major contributor for significant declines in populations of amphibians worldwide.
Additional projects on pathogens include the detection of Chagas disease in rat species throughout Texas, and the analyses of mongooses and rats from Costa Rica for Leptospira sp. (both in collaboration with Dr. Ivan Castro-Arellano, Wildlife Ecology).
Other activities cover projects performed in collaboration with scientist of different disciplines (e.g. Identification of microbes in corroding concrete, Jiang Hu [Concrete Technology] and Walter Rudzinski [Chemistry]; Platform development for the detection of biospecies, Haim Grebel [Electronic Imaging Center, NJIT]; Succession of yeasts during mescal production, Claudia Patricia Larralde-Corona [CBG-Instituto Politécnico Nacional, Reynosa, Mexico]).
Additional Research Interests
Research activities and interests in the past have covered additional areas and topics. None of these topics, however, is currently part of major research activities.
- Interactions of microbes in aquatic systems (PDF) Uncultured populations of bacteria were analyzed in aquatic systems and populations related to environmental characteristics for many years. Initially, these studies dealt with the qualitative and quantitative analysis of Archaea in anaerobic sediments of Lake Rotsee (Lucerne, Switzerland), and were subsequently expanded to studies on the interaction of aggregate-forming phototrophic sulfur and sulfate-reducing bacteria in the chemocline of the meromictic Lake Cadagno, Switzerland (in a long-lasting collaboration with Dr. Mauro Tonolla and co-workers, Cantonal Institute of Microbiology, Bellinzona, Switzerland).
- Interactions of microbes in terrestrial systems (PDF) Initial studies on terrestrial systems focused on aquifer material that was analyzed for the significance of toluene-degrading isolates in diesel fuel contaminated aquifer material, for diesel fuel mineralization under methanogenic conditions as well as for interactions between bacteria and protozoa. Diversity and dynamics of microbial communities in natural and contaminated soils were subsequently studied at different levels of resolution. Multi-level analyses were also used in field and greenhouse studies on the interaction between microorganisms (i.e. bacteria, mycorrhizae, protozoa) and plants (Spartina patens) in estuarine environments.
- Microbe-earthworm interactions (PDF) Interactions between bacteria and invertebrates were topic of studies on the effect of passage of bacteria through the gut of the earthworm Lumbricus terrestris. The analysis focused on the use of the whole cell hybridization technique for the in situ analysis of different bacterial populations during gut passage and for studies on the effect of passage on dormant stages (i.e. endospores of Bacillus megaterium and cysts of protozoa). This topic included the development of a detection protocol for endospores by whole cell hybridization.
Recent Peer-reviewed Publications
Samant, S., Dawson, J.O., Hahn, D. 2016. Growth responses of introduced Frankia strains to edaphic factors. Plant Soil 400, 123-132
Samant, S., Huo, T., Dawson, J.O., Hahn, D. 2016. Abundance and relative distribution of Frankia host infection groups under actinorhizal Alnus glutinosa and non-actinorhizal Betula nigra trees. Microb. Ecol. 71, 473-481.
Hussain, K., Hameed, S., Shahid, M., Ali, A., Iqbal, J., Hahn, D. 2015. First report of Providentia vermicola strains characterized for enhanced rapeseed growth attributing parameters. Int. J. Agricult. Biol. 17, 1110-1116.
Samant, S., Dawson, J.O., Hahn, D. 2015. Growth responses of indigenous Frankia populations to edaphic factors in actinorhizal rhizospheres. System. Appl. Microbiol. 38, 501-505.
Villamizar Gomez, A., Farr, W., Hahn, D., Dixon, J.R., Lazcano, D., Forstner, M.R.J. 2015. Absence of Batrachochytrium dendrobatidis in eighteen species of amphibians from a variety of habitats in Taumalipas, Mexico. Herpetol. Rev. 46, 34-37.
Samant, S., Amann, R.I., Hahn, D. 2014. Evaluation of the 23S rRNA gene as target for qPCR based quantification of Frankia in soils. System. Appl. Microbiol. 37, 229-234
Sha, Q., Vattem, D.A., Forstner, M.R.J., Hahn, D. 2013. Quantifying Salmonella population dynamics in water and biofilms. Microb. Ecol. 65, 60-67
Lee, H.-I., Donati, A.J., Hahn, D., Tisa, L.S., Chang, W.-S. 2013. Alteration of the exopolysaccharide production and the transcriptional profile of free-living Frankia strain CcI3 under nitrogen-fixing conditions. Appl. Microbiol. Biotechnol. 97, 10499-10509
Sha, Q., Forstner, M.R.J., Hahn, D. 2013. Diversity of Salmonella in biofilms and water in a headwater ecosystem. FEMS Microbiol. Ecol. 83, 642-649
Lindsay, M.K., Zhang, Y., Forstner, M.R.J., Hahn, D. 2013. Effects of the freshwater turtle Trachemys scripta elegans on ecosystem functioning: an approach in experimental ponds. Amphibia-Reptilia 34, 75-84
Sha, Q., Forstner, M.R.J., Bonner, T., Hahn, D. 2013. Salmonellae in fish feces analyzed by in situ hybridization and quantitative polymerase chain reaction. J. Aquatic Animal Health 25, 184-190
Samant, S., Sha, Q., Iyer, A., Dhabekar, P., Hahn, D. 2012. Quantification of Frankia in soils using SYBR Green based qPCR. System. Appl. Microbiol. 35, 191-197
Peduzzi, S., Storelli, N., Welsh, A., Peduzzi, R., Hahn, D., Perret, X., Tonolla, M. 2012. Candidatus „Thiodictyon syntrophicum“, sp. nov., a new purple sulfur bacterium isolated from the chemocline of Lake Cadagno forming aggregates and specific associations with Desulfocapsa sp. System. Appl. Microbiol. 35, 139-144
Gaertner, J.P., Brown, D.J., Mendoza, J.A., Forstner, M.R.J., Bonner, T., Hahn, D. 2012. Geographic variation in Batrachochytrium dendrobatidis occurrence among populations of Acris crepitans blanchardi in Texas, USA. Herpetol. Rev. 43, 150-159
Gaertner, J.P., Mendoza, J.A., Neang, T., Forstner, M.R.J., Hahn, D. 2011. Detection of Batrachochytrium dendrobatidis in frogs from different locations in Cambodia. Herpetol. Rev. 42, 546-549
Mendoza, J.A., Gaertner, J.P., Holden, J., Forstner, M.R.J., Hahn, D. 2011. Detection of Batrachochytrium dendrobatidis on amphibians in Pursat Province, Cambodia. Herpetol. Rev. 42, 542-545
Pokharel, A., Mirza, B.S., Dawson, J.O., Hahn, D. 2011. Frankia populations in soil and root nodules of sympatrically grown Alnus taxa. Microb. Ecol. 61, 92-100
Hahn, D., Mirza, B.S., Benagli, C., Vogel, G., Tonolla, M. 2011. Typing of nitrogen-fixing Frankia strains by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry. System. Appl. Microbiol. 34, 63-68
Becker, J.C., Groeger, A.W., Nowlin, W.H., Chumchal, M.M., Hahn, D. 2011. Spatial variability in the speciation and bioaccumulation of mercury in an arid subtropical reservoir ecosystem. Environ. Toxicol. Chem. 30, 2300-2311
Sha, Q., Gunathilake, A., Forstner, M.R.J., Hahn, D. 2011. Temporal analyses of the distribution and diversity of Salmonella in natural biofilms. System. Appl. Microbiol. 34, 353-359
Gaertner, J.P., Mendoza, J.A., Forstner, M.R.J., Hahn, D. 2011. Recovery of Salmonella from biofilms in a headwater spring ecosystem. J. Water Health 9, 458-466
Peduzzi, S., Welsh, A., Demarta, A., Decristophoris, P.M.A., Peduzzi, R., Hahn, D., Tonolla, M. 2011. Thiocystis chemoclinalis sp. nov. and Thiocystis cadagnonensis sp. nov., two new motile purple sulfur bacteria isolated from the chemocline of meromictic Lake Cadagno, Switzerland. Int. J. Syst. Evol. Microbiol. 61, 1682-1687
Gaertner, J.P, McHenry, D., Forstner, M.R.J., Hahn, D. 2010. Annual variation of Batrachochytrium dendrobatidis in the Houston toad (Bufo houstonensis) and a sympatric congener (Bufo nebulifer). Herpetol. Rev. 41, 456-459
Banerjee, A., Perez-Castillejos, R., Hahn, D., Smirnov, A., Grebel, H. 2010. Micro-fluidic channels on nanopatterned substrates: Monitoring protein binding to lipid bilayers with surface-enhanced Raman spectroscopy. Chem. Phys. Lett. 489, 121-126
Welsh, A.K., Burke, D.J., Hamerlynck, E.P., Hahn, D. 2010. Seasonal analyses of arbuscular mycorrhizae, nitrogen-fixing bacteria and growth performance of the salt marsh grass Spartina patens. Plant Soil 330, 251-266
Welsh, A.K., Dawson, J.O., Gottfried, G.J., Hahn, D. 2009. Diversity of Frankia in root nodules of geographically isolated Arizona alders in central Arizona (USA). Appl. Environ. Microbiol. 75, 6913-6918
Mirza, B.S., Welsh, A.K., Rieder, J.P., Paschke, M.W., Hahn, D. 2009. Diversity of frankiae in soils from five continents. System. Appl. Microbiol. 32, 558-570
Mirza, B.S., Welsh, A.K., Hahn, D. 2009. Growth of Frankia strains in leaf litter-amended soil and the rhizosphere of a non-actinorhizal plant. FEMS Microbiol. Ecol. 70, 132-141
Boonfueng, T., Axe, L., Yee, N., Hahn, D., Ndiba, P.K. 2009. Zn sorption mechanisms onto sheathed Leptothrix discophora and the impact of the nanoparticulate biogenic Mn oxide coating. J. Coll. Inter. Sci. 333, 439–447
Mirza, B.S., Welsh, A., Rasul, G., Rieder, J.P., Paschke, M.W., Hahn, D. 2009. Diversity of Frankia populations in root nodules of different host plant species revealed by nifH gene sequence analysis. Microb. Ecol. 58, 384-393
Welsh, A., Mirza, B.S., Rieder, J.P., Paschke, M.W., Hahn, D. 2009. Diversity of frankiae in root nodules of Morella pensylvanica grown in soils from five continents. System. Appl. Microbiol. 32, 201-210
McCracken, S., Gaertner, J.P., Forstner, M.R.J., Hahn, D. 2009. Detection of Batrachochytrium dendrobatidis in amphibians from the forest floor to the upper canopy of an Ecuadorian amazon lowland rainforest. Herpetol. Rev. 40, 190-195
Gaertner, J.P., Gaston, M.A., Spontak, D., Forstner, M.R.J., Hahn, D. 2009. Seasonal variation in the detection of Batrachochytrium dendrobatidis in a Texas population of Blanchard's cricket frog (Acris crepitans blanchardi). Herpetol. Rev. 40, 184-197
Decristophoris, P.M.A., Peduzzi, S., Ruggeri-Bernardi, N., Hahn, D., Tonolla, M. 2009. Fine scale analysis of shifts in community structure in the chemocline of meromictic Lake Cadagno, Switzerland. J. Limnol. 68, 16-24
Gaertner, J.P., Forstner, M.R.J., O’Donnell, L., Hahn, D. 2009. Detection of Batrachochytrium dendrobatidis in endemic salamander species from Central Texas. EcoHealth 6, 20-26
Gaertner, J.P., Garres, T., Becker, J.C., Jimenez, M.L., Forstner, M.R.J., Hahn, D. 2009. Analyses of salmonellae in a headwater spring ecosystem. J. Water Health 7, 115-121
Positions available in the Hahn Lab
Positions are available for undergraduate, M.S. and Ph.D. students to study 1. the fate of salmonellae outside potential host environments and 2. growth and nitrogen-fixation of the actinomycete Frankia in the rhizosphere of host and non-host plants and in bulk soil, using different molecular tools (e.g., in situ hybridization, qPCR). Ph.D. candidates must have a Masters degree, and preferably hands-on experience in microbiology, the use of molecular techniques and statistics. The ability to work independently but within a team environment is required.