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Applied and Environmental Microbiology, November 2007, p. 6829-6841, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.00787-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Physiological Ecology of Stenoxybacter acetivorans, an Obligate Microaerophile in Termite Guts

Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824-4320

Received 9 April 2007/ Accepted 25 August 2007

Stenoxybacter acetivorans is a newly described, obligately microaerophilic ß-proteobacterium that is abundant in the acetate-rich hindgut of Reticulitermes. Here we tested the hypotheses that cells are located in the hypoxic, peripheral region of Reticulitermes flavipes hindguts and use acetate to fuel their O₂-consuming respiratory activity in situ. Physical fractionation of R. flavipes guts, followed by limited-cycle PCR with S. acetivorans-specific 16S rRNA gene primers, indicated that cells of this organism were indeed located primarily among the microbiota colonizing the hindgut wall. Likewise, reverse transcriptase PCR of hindgut RNA revealed S. acetivorans-specific transcripts for acetate-activating enzymes that were also found in cell extracts (acetate kinase and phosphotransacetylase), as well as transcripts of ccoN, which encodes the O₂-reducing subunit of high-affinity cbb₃-type cytochrome oxidases. However, S. acetivorans strains did not possess typical enzymes of the glyoxylate cycle (isocitrate lyase and malate synthase A), suggesting that they may use an alternate pathway to replenish tricarboxylic acid cycle intermediates or they obtain such compounds (or their precursors) in situ. Respirometric measurements indicated that much of the O₂ consumption by R. flavipes worker larvae was attributable to their guts, and the potential contribution of S. acetivorans to O₂ consumption by extracted guts was about 0.2%, a value similar to that obtained for other hindgut bacteria examined. Similar measurements obtained with guts of larvae prefed diets to disrupt major members of the hindgut microbiota implied that most of the O₂ consumption observed with extracted guts was attributable to protozoans, a group of microbes long thought to be "strict anaerobes."

Published ahead of print on 7 September 2007.

This article has been cited by other articles:

• Wertz, J. T., Breznak, J. A. (2007). Stenoxybacter acetivorans gen. nov., sp. nov., an Acetate-Oxidizing Obligate Microaerophile among Diverse O2-Consuming Bacteria from Termite Guts. Appl. Environ. Microbiol. 73: 6819-6828 [Abstract] [Full Text]