Principal Investigator: John A. Breznak, Michigan State University
Termites are important decomposers of earth's major form of biomass -- lignocellulosic plant material and residues derived from it, e.g. humus. In order to thrive on such relatively refractory, nitrogen-poor food resources, termites are aided by a diverse community of gut microbial symbionts. The nature of the gut microbes, and their role in termite nutrition and vitality, has been an ongoing focus of research in the PI's laboratory for many years. Research supported by the current award is largely an outgrowth of a breakthrough, which led to two major discoveries during the previous funding period. The breakthrough was the isolation in pure culture of a long-recognized, major, and morphologically distinct, but hitherto elusive, component of the termite gut microbial community, i.e. spirochetes. The discoveries were: (a) the recognition of them as novel species of Treponema capable of acetate production from a variety of substrates, including H2+CO2; and (b) the demonstration of nitrogenase structural genes (nifH) and N2 fixation in these (and subsequently in free-living) spirochetes. Inasmuch as microbially-produced acetate supports up to 100% of the daily energy requirement of termites, and N2 fixation by gut microbes can supply up to 60% of the nitrogen for termite growth, the importance of spirochetes in termite nutrition was becoming clearer. Moreover, as neither H2/CO2-acetogenesis nor N2 fixation had ever been recognized in spirochetes before, these discoveries were also providing new insight into the metabolic diversity of these fascinating bacteria.
A combination of physiological, biochemical, and molecular biological methods will now be used to explore these metabolic activities in greater detail. We seek to identify factors affecting their expression and activity, and to assess the importance of spirochetes to H2/CO2-acetogenesis and N2 fixation in situ. Cooperative and antagonistic interactions of spirochetes with other members of the gut microbiota will also be examined, including: the provision of folate compounds (required for growth of termite gut spirochetes) by other gut microbes that utilize spirochete products, e.g. acetate oxidizers; and antagonisms between H2/CO2-acetogenic spirochetes and H2-consuming methanogens - two groups of microbes competing for the same energy source. Studies will also be done to test the hypothesis that many of the (non-spirochetal) gut microbes colonizing the microoxic region of hindguts near the epithelium are microaerophiles that have previously escaped isolation in pure culture, because they will not grow in air or under anoxia. It is hypothesized that such microaerophiles are acetate-oxidizers that consume inwardly diffusing O2, thereby rendering the luminal region of the gut anoxic for the fermentative production (by spirochetes and protozoa) of more acetate. This latter effort is likely to reveal new principles about life under hypoxia, a pervasive but poorly studied condition experienced by many organisms in our biosphere. This research project will involve graduate students and a postdoctoral and, hence, will expand the base of scientists trained to explore two of the most salient features of the microbial world - its enormous, but poorly understood and largely untapped diversity, and its importance to macrobial life on our planet.