Lab of Dr. Dittmar Hahn

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).

 

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.

Recent Peer-reviewed Publications

 

Benavidez, K.M., Guerra, T., Torres, M., Rodriguez, D., Veech, J.A., Hahn, D., Miller, R.J., Soltero, F.V., Perez Ramirez, A.E., Perez de Leon, A., Castro-Arellano, I. 2019. The prevalence of Leptospira among invasive small mammals on Puerto Rican cattle farms. PLOS Neglected Tropical Diseases 13(5):e0007236.

Vemulapally, S., Guerra, T.M., Hahn, D. 2019. Localization of typical and atypical Frankia isolates from Casuarina sp. in nodules formed on Casuarina equisetifolia. Plant and Soil 435, 385-393.

Marshall, T.L., Baca, C.R., Correa, D.T., Forstner, M.R.J., Hahn, D., Rodriguez, D. 2019. Genetic characterization of chytrids isolated from larval amphibians collected in central and east Texas. Fungal Ecology 39, 55-62.

Gates, A.Y, Guerra, T.M., Morrison, F.B., Forstner, M.R.J., Hardy, T.B., Hahn, D. 2018. Detection of Salmonella in the intestine of Hypostomus plecostomus from the upper San Marcos River, Texas. Journal of Water and Health 16, 460-471.

Ben Tekaya, S., Guerra, T., Rodriguez, D., Dawson, J.O., Hahn, D. 2018. Frankia diversity in host-plant root nodules is independent of abundance or relative diversity of Frankia in corresponding rhizosphere soils. Applied and Environmental Microbiology 84:e02248-17.

Milholland, M.T., Castro-Arellano, I., Arellano, E., Nava-Garcia, E., Rangel-Altamirano, G., Gonzalez-Cozatl, F.X., Suzan, G., Schountz, T., Gonzalez-Padron, S., Vigueras, A., Rubio, A., Maikis, T.J., Westrich, B., Marinez, J.A. III, Esteve-Gassent, M.D., Torres, M., Rodriguez-Ruiz, E.R., Hahn, D., Lacher, T.E. 2017. Species identity supersedes the dilution effect concerning Hantavirus prevalence at sites across Texas and Mexico. ILAR Journal 58, 401-412.

Aleman, A., Guerra, T., Maikis, T.J., Milholland, M.T., Castro-Arellano, I., Forstner, M.R.J., Hahn, D. 2017. The prevalence of Trypanosoma cruzi, the causal agent of Chagas disease, in Texas rodent populations. EcoHealth 14, 130-143.

Ben Tekaya, S., Ganesan, A.S., Guerra, T., Dawson, J.O., Forstner, M.R.J., Hahn, D. 2017. SybrGreen and Taqman-based qPCR approaches allow assessment of the abundance and relative distribution of Frankia clusters in soils. Applied and Environmental Microbiology 83:e02833-16.

Becker, J.C., Rodibaugh, K.J., Hahn, D., Nowlin, W.H. 2017. Bacterial community composition and carbon metabolism in a subtropical riverscape. Hydrobiologia 792, 209-226.

Rodriguez, D., Guerra, T., Forstner, M.R.J., Hahn, D. 2016. Diversity of Frankia in soil assessed by Illumina sequencing of nifH gene fragments. Systematic and Applied Microbiology 39, 391-397.

Samant, S., Dawson, J.O., Hahn, D. 2016. Growth responses of introduced Frankia strains to edaphic factors. Plant and 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. Microbial Ecology 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. International Journal of Agriculture and Biology 17, 1110-1116.

Samant, S., Dawson, J.O., Hahn, D. 2015. Growth responses of indigenous Frankia populations to edaphic factors in actinorhizal rhizospheres. Systematic and Applied Microbiology 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 eigtheen species of amphibians from a variety of habitats in Taumalipas, Mexico. Herpetological Review 46, 34-37.

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.