Research

We are interested in microbial diversity and ecology, especially as these aspects relate to microbe-microbe and microbe-animal symbiotic interactions. One model system we have been studying for many years is the symbiotic gut microbiota of termites.

Termites are an important group of terrestrial insects, which feed on some of earth's most abundant forms of biomass, i.e. lignocellulosic plant material and residues derived from it (e.g. humus). Their gut microbiota is dense and diverse and includes representatives from all known domains of life, i.e. Eukarya (represented by cellulolytic protozoa), an assortment of Bacteria, and methanogenic Archaea. Many of these have proven to be novel genera and species. We seek to understand how such microbes cooperate with each other and with the insect to bring about digestion and to furnish termites with required nutrients. Recently, we discovered new species of spirochetes in termite guts that can provide the insects with up to 1/3 of their energy source (acetate) by the overall reaction, 4 H2 + 2 CO2 --> CH3COOH + 2 H2O, a process previously unknown in the spirochete phylum of bacteria. We continue to explore reasons why this microbial process, which is of obvious nutritional benefit to termites, often surpasses the thermodynamically-favored, but nutritionally "empty", formation of methane from H2 and CO2, as in the rumen of cattle. We have also shown that these novel spirochetes contribute to termite nitrogen economy by fixing atmospheric N2 (yet another property previously unknown among spirochetes). Other bacteria contribute to termite nitrogen economy by recycling the N in uric acid (an insect excretory product) back to termites for biosynthesis. Such microbial activities are particularly important for termites, as their food resources (e.g. wood) are difficult to digest and are typically poor in nitrogen. Our experiments are done at various levels: from physiological measurements with the termites themselves or with their total gut microbiota, to studies of metabolism by pure and purposely-mixed cultures of termite gut microbes, to studies of cloned microbial genes and gene products. This multilevel approach adds to the excitement of the research, but also demands that we be versatile as experimentalists.

An additional area of interest is a recently-initiated, collaborative effort with Prof. Tom Schmidt to tap into the as-yet-untapped microbial diversity in soils. Of particular interest to us are novel bacteria whose presence and abundance has been inferred from 16S rDNA sequences retrieved from soil, but which themselves are not-yet-cultured or poorly represented in culture, e.g members of the "Verrucomicrobia", "Acidobacteria" and "Planctomyces" groups. Apparently, traditional cultivation techniques have been inadequate to isolate such organisms. Hence, we are using: (i) genomic approaches to give insight into their physiological capabilities; (ii) molecular probes to monitor their populations in soils and in laboratory microcosms before and after certain perturbations; and, based on the results of such efforts, (iii) novel approaches to the enrichment and isolation of such organisms in pure culture for detailed study. We anticipate that this work will help illuminate the role of such organisms in the C & N cycles of soils and their impact on soil fertility.

Publications

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