Physiological ecology of termite gut spirochetes
Treponema sp. strains ZAS-1 and ZAS-2 were the first spirochetes to be isolated from termite hindguts and are also the first known spirochetal H2/CO2-acetogens. The ZAS strains were examined for nutritional and physiological properties relevant to in situ growth and survival. In addition to using H2...
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| Format: | Dissertation |
| Language: | English |
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ProQuest Dissertations & Theses
01-01-2003
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| Online Access: | Get full text |
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| Summary: | Treponema sp. strains ZAS-1 and ZAS-2 were the first spirochetes to be isolated from termite hindguts and are also the first known spirochetal H2/CO2-acetogens. The ZAS strains were examined for nutritional and physiological properties relevant to in situ growth and survival. In addition to using H2+CO2 as growth substrates, both strains grew on a variety of organic compounds and were capable of mixotrophic growth (i.e. the simultaneous use of both H 2 and organic substrates). Enzyme activities of the Wood/Ljungdahl pathway of acetogenesis were detected in both strains, whose H2 thresholds were within the range typical of acetogens (650 and 490 ppmv, respectively). Both strains were able to maintain growth in the presence of small amounts of O2 (0.5%, vol/vol) and possessed enzyme activities which could mediate protection from O2. These results demonstrate that Treponema strains ZAS-1 and ZAS-2 are nutritionally versatile, perform acetogenesis by the Wood/Ljungdahl pathway, and are likely able to tolerate oxidative stress in the partially hypoxic hindgut environment. Treponema strain ZAS-9, an additional spirochete from Z. angusticollis hindguts, was not a homoacetogen, and in fact produced H2 as a major product during sugar fermentation. This strain also differed from ZAS-1 and ZAS-2 in a variety of other properties, suggesting that strains ZAS-1 and ZAS-2 be assigned to a single new species of Treponema, whereas ZAS-9 should be considered a separate new Treponema species. Strains ZAS-1 and ZAS-2 had requirements for folate, and important cofactor in acetogenesis. On the notion that other termite gut microbes must supply folate in situ, heterotrophic organisms were isolated from the guts of the termite Zootermopsis angusticollis and screened for folate secretion. Two folate-secreting isolates (Serratia strain ZFX-1 and Lactococcus strain ZFX-2) were identified; both strains produced a compound that could replace the folate requirements of ZAS-1 and ZAS-2. The folate produced by both ZFX strains was identified as folinate. These results suggest that strains ZFX-1 and ZFX-2 are capable of supplying folinate to acetogenic spirochetes in the termite gut, and may also be important in providing folates to other members of the gut microbiota, as well as to the termite host. Despite the fact that methanogenesis is the more energetically favorable process, H2/CO2-homoacetogens are the primary H 2-consumers in the guts of wood-feeding termites. To explain this observation, I hypothesized that gut methanogens are inhibited by pteridine compounds. (Abstract shortened by UMI.) |
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| ISBN: | 0496480189 9780496480180 |