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Dittmar Hahn, Ph.D.

Dittmar Hahn, Ph.D.


Dittmar Hahn, Ph.D.

Professor of Microbial Ecology

Department Chair

Phone +1 (512) 245 3372

Fax +1 (512) 245 8713

E-mail: dh49@txstate.edu


Department of Biology, Texas State University, 601 University Drive, San Marcos, Texas 78666, USA


Ph.D. in Microbiology, 1989, Wageningen Agricultural University, The Netherlands, Department of Microbiology (Advisors: Antoon D.L. Akkermans, Alexander J.B. Zehnder)

Diploma in Biology, 1984, University of Hamburg, Germany

Research Interests

I am a microbial ecologist using molecular techniques to study uncultured microorganisms in aquatic and terrestrial environments. During the last years, I have mainly addressed questions on the ecology of nitrogen-fixing actinomycetes of the genus Frankia and their host plants, but was also involved in studies on invertebrate-microorganism interactions, the ecophysiology of uncultured purple sulfur and sulfate-reducing bacteria, the role of microorganisms in bioremediation of organic and inorganic contaminants, or the fate of pathogens in the environment.

Current Research Projects

Current research projects fall into two major research areas:

  1.  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.
  2. 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 activities cover projects performed in collaboration with scientists 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.

1. 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).

2. 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.

3. 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.

Courses Taught

BIO 4446 Microbial Ecology

BIO 7360 G Molecular Techniques in Microbial Ecology

BIO 7410 Aquatic Microbial Ecology

Recent Peer-reviewed Publications

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, 92100

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

Gaertner, J.P., Wheeler, P.E., Obafemi, S., Valdez, J., Forstner, M.R.J., Bonner, T.H., Hahn, D. 2008. Detection of salmonellae in fish in a natural river system. J. Aquatic Animal Health 20, 150-157

Gaertner, J.P., Hahn, D., Rose, F.L., Forstner, M.R.J. 2008. Detection of salmonellae in different turtle species within a headwater spring ecosystem. J. Wildl. Dis. 44, 519-526

Gaertner, J.P., Hahn, D., Jackson, J., Forstner, M.R.J., Rose, F.L. 2008. Detection of salmonellae in captive and free-ranging turtles using enrichment culture and polymerase chain reaction. J. Herpetol. 42, 223-231

Welsh, A., Burke, D.J., Hahn, D. 2007. Analysis of nitrogen-fixing members of the ε-subclass of Proteobacteria in salt marsh sediments. Appl. Environ. Microbiol. 73, 7747-7752

Mirza, B.S., Welsh, A., Hahn, D. 2007. Saprophytic growth of inoculated Frankia sp. in soil microcosms. FEMS Microbiol. Ecol. 62, 280-289

Zhang, C., Smirnov, A., Hahn, D., Grebel, H. 2007. Surface enhanced raman scattering of biospecies on anodized aluminum oxide films. Chem. Phys. Lett. 440, 239-243

Suntornvongsakul, K., Burke, D.J., Hahn, D. 2007. Uptake and translocation of heavy metals in salt marsh sediments by Spartina patens. Bull. Environ. Contamin. Toxicol. 78, 275-279

Suntornvongsakul, K., Burke, D.J., Hamerlynck, E.P., Hahn, D. 2007. Fate and effect of heavy metals in salt-marsh sediments. Environ. Pollut. 149, 79-91

Hahn, D., Gaertner, J., Forstner, M.R.J., Rose, F.L. 2007. High resolution analysis of salmonellae from turtles within a headwater spring ecosystem. FEMS Microbiol. Ecol. 60, 148-155

Hahn, D., Cozzolino, A., Piccolo, A., Armenante, P.M. 2007. Reduction of 2,4-dichlorophenol toxicity to Pseudomonas putida after oxidative incubation with humic substances and a biomimetic catalyst. Ecotoxicol. Environ. Safety 66, 335-342

Positions Available

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.