The degradation of lactic acid under anoxic conditions was studied in several strains of Lactobacillus buchneri and in close relatives such as Lactobacillus parabuchneri, Lactobacillus kefir, and Lactobacillus hilgardii. Of these lactobacilli, L. buchneri and L. parabuchneri were able to degrade lactic acid under anoxic conditions, without requiring an external electron acceptor. Each mole of lactic acid was converted into approximately 0.5 mol of acetic acid, 0.5 mol of 1,2-propanediol, and traces of ethanol. Based on stoichiometry studies and the high levels of NAD-linked 1, 2-propanediol-dependent oxidoreductase (530 to 790 nmol min(-1) mg of protein(-1)), a novel pathway for anaerobic lactic acid degradation is proposed. The anaerobic degradation of lactic acid by L. buchneri does not support cell growth and is pH dependent. Acidic conditions are needed to induce the lactic-acid-degrading capacity of the cells and to maintain the lactic-acid-degrading activity. At a pH above 5.8 hardly any lactic acid degradation was observed. The exact function of anaerobic lactic acid degradation by L. buchneri is not certain, but some results indicate that it plays a role in maintaining cell viability.

Although abundant geochemical data indicate that anaerobic methane oxidation occurs in marine sediments, the linkage to specific microorganisms remains unclear. In order to examine processes of methane consumption and oxidation, sediment samples from mud volcanoes at two distinct sites on the Mediterranean Ridge were collected via the submersible Nautile. Geochemical data strongly indicate that methane is oxidized under anaerobic conditions, and compound-specific carbon isotope analyses indicate that this reaction is facilitated by a consortium of archaea and bacteria. Specifically, these methane-rich sediments contain high abundances of methanogen-specific biomarkers that are significantly depleted in 13 C (␦ 13 C values are as low as ؊95‰). Biomarkers inferred to derive from sulfate-reducing bacteria and other heterotrophic bacteria are similarly depleted. Consistent with previous work, such depletion can be explained by consumption of 13 Cdepleted methane by methanogens operating in reverse and as part a consortium of organisms in which sulfate serves as the terminal electron acceptor. Moreover, our results indicate that this process is widespread in Mediterranean mud volcanoes and in some localized settings is the predominant microbiological process.Methane can have a stronger greenhouse effect than CO 2 , and recent work has highlighted its potential climatic impact on glacial timescales (24) and in relation to major geologic events (8,12). Consequently, controls on methane production and consumption are important concerns in the evaluation of past and future climate change. In marine sediments, anaerobic methane oxidation could be the dominant pathway for methane consumption (2,4,6,15,25,26), but the organisms involved have not been isolated and the mechanism remains controversial. Methanogenic archaea operating in reverse (9,11,14) or novel, previously uncharacterized archaea (13) have been proposed to play a vital role, but current evidence remains ambiguous.Methane tends to be highly depleted in 13 C, and organisms that consume methane either directly or indirectly via heterotrophic consumption of methanotroph biomass will be similarly depleted in 13 C. For this study, we determined distributions and carbon isotope abundances of organic components in methane-rich mud volcano sediments of the Eastern Mediterranean Ridge. In particular, we examined the ␦ 13 C values of compounds derived from specific organisms (i.e., biomarkers) presumed to play a major role in methane oxidation, including methanogens, aerobic methanotrophs, sulfate-reducing bacteria, and anaerobic heterotrophic bacteria. From these results, we evaluate the controls on and microorganisms responsible for methane oxidation in these sediments and the conditions under which methane oxidation occurs. MATERIALS AND METHODSSamples. Using a bordeaux core, samples were collected from surface sediments (upper 30 cm) of several mud volcano flows (mud breccias) in the Olimpi (Milano and Napoli mud volcanoes) and Anaximander (Amsterdam mud volcano) fi...

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A strictly anaerobic bacterium, strain PCE1, was isolated from a tetrachloroethene-dechlorinating enrichment culture. Cells of the bacterium were motile curved rods, with approximately four lateral flagella. They possessed a gram-positive type of cell wall and contained cytochrome c. Optimum growth occurred at pH 7.2-7.8 and 34-38 degrees C. The organism grew with L-lactate, pyruvate, butyrate, formate, succinate, or ethanol as electron donors, using either tetrachloroethene, 2-chlorophenol, 2,4,6-trichlorophenol, 3-chloro-4-hydroxy-phenylacetate, sulfite, thiosulfate, or fumarate as electron acceptors. Strain PCE1 also grew fermentatively with pyruvate as the sole substrate. L-Lactate and pyruvate were oxidized to acetate. Tetrachloroethene was reductively dechlorinated to trichloroethene and small amounts ( 5%) of cis-1,2-dichloroethene and trans-1,2-dichloroethene. Chlorinated phenolic compounds were dechlorinated specifically at the ortho-position. On the basis of 16S rRNA sequence analysis, the organism was identified as a species within the genus Desulfitobacterium, which until now only contained the chlorophenol-dechlorinating bacterium, Desulfitobacterium dehalogenans.

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