Physiology and Nutrition ofTreponema primitia, an H2/ CO2-Acetogenic Spirochete from Termite Hindguts

Publisher Website
Google Scholar
Abstract
Treponema primitiastrains ZAS-1 and ZAS-2, the first spirochetes to be isolated from termite hindguts (J. R. Leadbetter, T. M. Schmidt, J. R. Graber, and J. A. Breznak, Science283:686-689, 1999), were examined for nutritional, physiological, and biochemical properties relevant to growth and survival in their natural habitat. In addition to using H2plus CO2as substrates, these strains were capable of homoacetogenic growth on mono- and disaccharides and (in the case of ZAS-2) methoxylated benzenoids. Cells were also capable of mixotrophic growth (i.e., simultaneous utilization of H2and organic substrates). Cell extracts ofT. primitiapossessed enzyme activities of the Wood/Ljungdahl (acetyl coenzyme A) pathway of acetogenesis, including tetrahydrofolate-dependent enzymes of the methyl group-forming branch. However, a folate compound was required in the medium for growth. ZAS-1 and ZAS-2 growing on H2plus CO2displayed H2thresholds of 650 and 490 ppmv, respectively. Anoxic cultures of ZAS-1 and ZAS-2 maintained growth after the addition of as much as 0.5% (vol/vol) O2to the headspace atmosphere. Cell extracts exhibited NADH and NADPH peroxidase and NADH oxidase activities but neither catalase nor superoxide dismutase activity. Results indicate that (i)T. primitiais able to exploit a variety of substrates derived from the food of its termite hosts and in so doing contributes to termite nutrition via acetogenesis, (ii) in situ growth ofT. primitiais likely dependent on secretion of a folate compound(s) by other members of the gut microbiota, and (iii) cells possess enzymatic adaptations to oxidative stress, which is likely to be encountered in peripheral regions of the termite hindgut.