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PHYSIOLOGICAL ECOLOGY OF CLOSTRIDIUM GLYCOLICUM RD-1, AN AEROTOLERANT ACETOGEN ISOLATED FROM SEA GRASS ROOTS
Citation:
Devereux, R D., K. Kusel, T. Trinkwalter, G. Acker, H. L. Drake, AND A. Karnolz. PHYSIOLOGICAL ECOLOGY OF CLOSTRIDIUM GLYCOLICUM RD-1, AN AEROTOLERANT ACETOGEN ISOLATED FROM SEA GRASS ROOTS. APPLIED AND ENVIRONMENTAL MICROBIOLOGY 67(10):4734-4741, (2001).
Description:
An anaerobic, H2-utilizing bacterium, strain RD-1, was isolated from the highest growth-positive dilution series of a root homogenate prepared from the sea grass Halodule wrightii. Cells of RD-1 were gram-positive, spore-forming, motile rods that were linked by connecting filaments. Acetate was produced in stoichiometries indicative of an acetyl-CoA-pathway-dependent metabolism when RD-1 utilized H2-C02, formate, lactate, or pyruvate. Growth on sugars or ethylene glycol yielded acetate and ethanol as end products. RD-1 grew at the expense of glucose in the presence of low initial concentrations (up to 6% vol/vol) of O2 in the headspace of static, horizontally-incubated culture tubes; the concentration of O2 decreased during growth in such cultures. Peroxidase, NADH-oxidase, and superoxide dismutase activities were detected in the cytoplasmic fraction of cells grown in the prexence of O2. In comparison to cultures incubated under strictly anoxic conditions, acetate production decreased, higher amounts of ethanol were produced, and lactate and H2 became significant end products when RD-1 was grown on glucose in the presence of O2. Similarily, when RD-1 was grown on fructose in the presence of elevated salt concentrations, lower amounts of acetate and higher amounts of ethanol and H2 were produced. When the concentration of O2 in the headspace exceeded 1% (vol/vol), supplemental H2 was not utilized. The 16S rRNA gene of RD-1 had a 99.7% sequence similarity to that of Clostridium glycolicum DSM 1288T, an organism characterized as a fermentative anaerobe. Comparative experiments with C. glycolicum DSM 1288T demonstrated that it had negligible H2- and formate-utilizing capacities. However,
carbon monoxide dehydrogenase was detected in both RD-1 and C. glucolicum DSM 1288T. A 91.4% DNA-DNA hybridization between the genomic DNA of RD-1 and that of C. glycolicum DSM 1288T confirmed that RD-1 was a strain of C. glycolicum. These results indicate that (i) RD-1 metabolizes certain substrates via the acetyl-CoA pathway, (ii) RD-1 can tolerate and consume limited amounts of O2, (iii) oxic conditions favor the production of ethanol, lactate, and H2 by RD-1 and (iv) the ability of RD-1 to cope with limited amounts of O2 might contribute to its survival in a habitat subject to daily gradients of photosynthesis-derived O2.