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A gram-negative, rod- to oval-shaped, aerotolerant anaerobic bacterium was isolated from an anaerobic enrichment inoculated with sediment taken from below the cyanobacterial mat of a high-salinity pond near Bratina Island on the McMurdo Ice Shelf, Antarctica. The organism was positive for terminal oxidase and catalase and was motile by means of a polar flagellum. Optimal growth of anaerobic cultures occurred at 12 degrees C, at pH 6.5, and at an NaCl concentration of 3% (w/v). Of a variety of polysaccharides tested, only starch and glycogen supported growth. No growth was observed on cellulosic substrates and xylan, and the organism was unable to attack esculin. Monosaccharides and disaccharides, including the cyanobacterial cell-wall constituent N-acetyl glucosamine, were fermented. Per 100 mol of hexose, the following products (in mol) were formed: acetate, 60; formate, 130; ethanol, 56; lactate, 73; CO2, 15; and butyrate, 2. Propionate, ethanol, n-propanol, n-butanol and succinate were not detectable in the culture medium (< 1 mol per 100 mol of monomer). Hydrogen was not detected in the head space (detection limit < 10(-5) atm). Growth yields in aerobic static liquid cultures were slightly higher than those in anaerobic culture, and fermentation favoured acetate at the expense of electron sink products. Growth was inhibited in aerobic shaking cultures, and the organism did not utilize nitrate or sulfate as electron acceptors. The G+C content of the DNA from the bacterium was 42.8 mol%. A phylogenetic analysis indicated that the organism is a member of the gamma-subgroup of Proteobacteria, but that it is distinct from other members of this group based on the sequence of its 16S rRNA gene, mol% G+C, morphology, and physiological and biochemical characteristics. It is designated as a new genus and species; the type strain is star-1 (DSM 10704).

A gram-positive, motile, rod-shaped, strictly anaerobic bacterium was isolated from an enrichment initiated with sediment taken from below the cyanobacterial mat of a low-salinity pond on the McMurdo Ice Shelf, Antarctica. The organism grew optimally at 12 degrees C, at pH 6.5, and at an NaCl concentration of0.5% (w/v). It survived freeze-thawing at low salt concentrations,but not exposure to temperatures over 25 degrees C for more than 20 h or short-term exposure to temperatures50 degrees C. Out of a variety of polysaccharides tested as growth substrates, only xylan supported growth. The organism also grew on a variety of mono- and disaccharides including the cyanobacterial cell wall constituent, N-acetyl glucosamine. Fermentation products on a mol product per 100 mol of hexose monomer fermented basis were: acetate, 72; formate, 72; butyrate, 55; hydrogen, 114; and CO2, 100. Not detectable in the culture medium(2 mol per 100 mol of monomer) were lactate, propionate, ethanol,n-propanol, n-butanol, and succinate. The G+C content of the DNA from the bacterium was 33 mol%, and a phylogenetic analysis indicated that it grouped closely with members of the RNA-DNA homology group 1 of the genus Clostridium. It differed from other species of this genus with regard to growth temperature optimum, substrate range, and fermentation pattern, and is therefore designated as a new species of Clostridium for which the name Clostridium vincentii is proposed. The type strain is lac-1 (DSM 10228).

Characteristics of dissimilatory nitrate reduction by Propionibacterium acidi-propionici, P. freudenreichii, P. jensenii, P. shermanii and P. thoenii were studied. All strains reduced nitrate to nitrite and further to N2O. Recovery of added nitrite-N as N2O-N approached 100%, so that no other end product existed in a significant quantity. Specific rates of N2O production were 3 to 6 orders of magnitude lower than specific rates of N2 production by common denitrifiers. Oxygen but not acetylene inhibited N2O production in P. acidi-propionici and P. thoenii. Nitrite reduction rates were generally higher than nitrate reduction rates. The enzymes involved in nitrate and nitrite reduction were either constitutive or derepressed by anacrobiosis. Nitrate stimulated synthesis of nitrate reductase in P. acidi-propionici. Specific growth rates and growth yields were increased by nitrate. At 10 mM, nitrite was toxic to all strains, and at 1 mM its effect ranged from none to total inhibition. No distinction was obvious between incomplete forms of denitrification and dissimilatory nitrate reduction to ammonia. N2O production from nitrite by propionibacteria may represent a detoxication mechanism rather than a part of an energy transformation system.

Methanogenesis by a Syntrophomonas wolfei/ Methanospirillum hungatei coculture was inhibited in presence of ethylene and the hydrogenation catalyst Pd-BaSO4. However, butyrate oxidation by S. wolfei continued and ethylene was reduced to ethane. Per mol of butyrate oxidized, 2.4 mol acetate was produced and 0.8 mol ethylene was reduced. Acetylene, propylene and butene were less effective as H2 acceptors than ethylene, and addition of bromoethanesulfonic acid was necessary to inhibit methanogenesis in the presence of the two longer-chain olefins. Other hydrogenation catalysts were less effective in the order Pd-charcoal < PE-asbestos < Pd-PEI beads < Pt-Al2O3, Pd-CaCO3. Optimal ethylene hydrogenation was achieved with still incubation in presence of 7.2 mg Pd-BaSO4 and 0.7 g sand per ml medium. The higher catabolic rate of S. wolfei in presence of the methanogen indicated that the biological H2 removal mechanism was more efficient than the catalytic olefin reduction.