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Physiological ecology of Methanobrevibacter cuticularis sp. nov. and Methanobrevibacter curvatus sp. nov., isolated from the hindgut of the termite Reticulitermes flavipes

Leadbetter, Jared R. and Breznak, John A. (1996) Physiological ecology of Methanobrevibacter cuticularis sp. nov. and Methanobrevibacter curvatus sp. nov., isolated from the hindgut of the termite Reticulitermes flavipes. Applied and Environmental Microbiology, 62 (10). pp. 3620-3631. ISSN 0099-2240. PMCID PMC168169.

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Two morphologically distinct, H2- and CO2-utilizing methanogens were isolated from gut homogenates of the subterranean termite, Reticulitermes-flavipes (Kollar) (Rhinotermitidae). Strain RFM-1 was a short straight rod (0.4 by 1.2 micron), whereas strain RFM-2 was a slightly curved rod (0.34 by 1.6 microns) that possessed polar fibers. Their morphology, gram-positive staining reaction, resistance to cell lysis by chemical agents, and narrow range of utilizable substracts were typical of species belonging to the family Methanobacteriaceae. Analysis of the nearly complete sequences of the small-subunit rRNA- encoding genes confirmed this affiliation and supported their recognition as new species of Methanobrevibacter: M. cuticularis (RFM- 1) and M. curvatus (RFM-2). The per cell rates of methanogenesis by strains RFM-1 and RFM-2 in vitro, taken together with their in situ population densities (ca. 10(6) cells.gut-1; equivalent to 10(9) cells . ml of gut fluid-1), could fully account for the rate of methane emission by the live termites. UV epifluorescence and electron microscopy confirmed that RFM-1- and RFM-2-type cells were the dominant methanogens in R.flavipes collected in Michigan (but were not the only methanogens associated with this species) and that they colonized the peripheral, microoxic region of the hindgut, i.e., residing on or near the hindgut epithelium and also attached to filamentous prokaryotes associated with the gut wall. An examination of their oxygen tolerance revealed that both strains possessed catalase-like activity. Moreover, when dispersed in tubes or agar medium under H2-CO2-O2 (75: 18.8:6.2, vol/vol/vol), both strains grew to form a thin plate about 6 mm below the meniscus, just beneath the oxic-anoxic interface. Such growth plates were capable of mediating a net consumption of O2 that otherwise penetrated much deeper into uninoculated control tubes. Similar results were obtained with an authentic strain of Methanobrevibacter arboriphilicus. This is the first detailed description of an important and often cited but poorly understood component of the termite gut microbiota.

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Leadbetter, Jared R.0000-0002-7033-0844
Additional Information:© 1996, American Society for Microbiology Received 11 January 1996/Accepted 15 July 1996 This research was funded by National Science Foundation grants IBN91-06636 (to J.A.B.) and BIR91-20006 (to the Center for Microbial Ecology). Some of the electron micrographs (Fig. 7A and B) were part of an unpublished collection obtained during an earlier study (9). Thin sections and negative stains of pure cultures for electron microscopy were prepared by the Electron Microscopy Laboratory of the MSU Pesticide Research Center. Frozen thin sections were prepared at the Histotechnology Laboratory of the MSU Department of Pathology. We are extremely grateful to Tom Schmidt and Randall Hicks for help and advice on aspects dealing with molecular phylogeny and to David Emerson for his gift of oxygen microelectrodes and for his many helpful discussions. We thank David Stahl for kindly providing the unpublished SSU rRNA sequence of M. smithii, a result of work supported by NSF grant DEB-9408243. We also thank Andreas Brune for helpful discussions and criticisms.
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Issue or Number:10
PubMed Central ID:PMC168169
Record Number:CaltechAUTHORS:LEAaem96
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ID Code:1576
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Deposited On:31 Jan 2006
Last Modified:02 Oct 2019 22:44

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