S139: Fermentative biohydrogen from hyperthermophilic Thermotoga species

The order Thermotogales comprises obligate fermentative anaerobes that grow optimally in the range of 65-80°C. These bacteria are of particular interest for their ability to deconstruct a wide range of complex polysaccharides and produce hydrogen at twice the yield of mesophilic bacteria (3-4 vs. 1-2 mol H₂/mol glucose). To probe differences in carbohydrate utilization, transcriptomes were analyzed during growth of T. maritima, T. neapolitana, T. petrophila, and T. sp. RQ2 on glucose as well as on a mixture of complex polysaccharides. Although responses to these growth substrates were mostly conserved from one species to another, certain differences were observed that mapped back to the regulation of glycoside hydrolase (GH) inventories and ABC transporters in the genome of each species. A real-time PCR assay was developed to investigate interactions and population dynamics by tracking the cell densities of the four aforementioned species in mixed culture. For example, under the conditions tested in batch culture, T. sp. RQ2 dominated the population after a relatively short period of time. This observation was attributed to a faster maximum growth rate related to GH inventory, but interspecies interactions between these species was also examined as a factor. The results presented here illustrate that, while hyperthermophilic members of the genus Thermotoga share core genomes and essential metabolic pathways, differences in GH inventory, ABC transporters and the regulation of these gene sets underlie subtle differences in the growth physiology of this group. Furthermore, these differences map to certain competitive advantages for Thermotoga species in specific environmental niches.