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SUMMARY: Fourteen previously unstudied strains of the genus Desulfovibrio and eight thermophilic strains of the genus Desulfotomaculum were allotted to species on the results of physiological and biochemical tests. On DNA base composition the Desulfovibrio strains fell clearly into three groups, corresponding to Dv. salexigens, Dv. desulfuricans and Dv. vulgaris. NaCl-dependence appeared to be a constant and unique feature of Dv. salexigens strains, and ‘sulphate-free’ growth on pyruvate a constant characteristic of Dv. desulfuricans, although one strain of Dv. vulgaris also dismuted pyruvate. Fumarate dismutation showed no species correlation. ‘Sulphate-free’ growth on choline was often minimal and the test appeared to be of little value. A high degree of resistance to Hibitane was not a constant characteristic of Dv. salexigens. The thermophilic strains showed great uniformity in DNA base composition, Hibitane resistance and ‘sulphate-free’ growth, and were all classified as Desulfotomaculum nigrificans.

Fifty-six Australian soils were examined for their ability to produce sulphate from sulphur and sulphide from added sulphur, sulphate and cystine. Selective liquid media were used to obtain initial counts and progressive activities of some of the principal organisms involved. Attempts were made to correlate soil properties, initial microbial counts, classes of micro-organisms detected and metabolic activities. Almost half of the soils oxidized sulphur very slowly or not at all, most probably due to absence of thiobacilli, particularly Th. thiooxidans . Even soils which oxidized sulphur rapidly never gave initial counts greater than 10 4 cells/g. The majority of soils produced sulphide from sulphur, between one-half and two-thirds of them formed sulphide from cystine but sulphate reduction was very rare. Sulphide escaped more readily from aerobic than from waterlogged soils. Numerous genera were isolated including Desulfovibrio and Desulfatomaculum capable of reducing sulphur, both aerobically and anaerobically, particularly sporing and non-sporing mesophiles which were sometimes present at 10 6 cells/g of soil. Sulphate reduction by the genus Desulfovibrio was uncommon, and by the genus Desulfatomaculum extremely rare. Many genera of sporing and non-sporing mesophiles seemed capable of producing sulphide from cystine when first isolated, but they quickly lost this ability on subculturing. Initial counts of 10 6 cells/g of soil were occasionally found but usually much lower. No significant correlations, only trends, were found suggesting that any soil properties measured affected the occurrence or activities of organisms capable of producing sulphate or sulphide.

Determinative studies were carried out on an obligatory anaerobic, sulfate- reducing bacterium (strain No. 61) isolated from a pond water in Skarvs Nes district in the East Antarctica. This sulfate-reducing bacterium was nonsporulating, sigmoid or straight rods with a single polar flagellum, gram negative, and possessed cytochrome c3 and desulfoviridin, characteristic of the genus Desulfovibrio. It could grow with lactate, malate, pyruvate, or choline when sulfate was present in the culture medium and had a stable sodium chloride requirement. These observations dinicated that strain No. 61 closely resembled Desulfovibrio desulfuricans var. aestuarii.