Studies on sulfate-reducing bacteria which degrade fatty acids and on an obligately anaerobic agarolytic bacterium

Abstract

Five methods were used to isolate sulfate-reducing bacteria using palmitate as the enrichment substrate. (1) Standard enrichment procedures gave rise to pure cultures of Desulfovibrio sapovorans. (2) In enrichments which involved the continual transfer of sediment throughout the isolation, two rod-shaped strains were isolated in pure culture and designated strains HoPal and AmPal. These latter strains had a number of characteristics similar to D. sapovorans, but also varied from the general description by a number of characteristics. Determination of their DNA base composition is required for confirmation of their identification. (3) When pasteurized sediment was used in the enrichments with palmitate as the electron donor, a strain of Desulfotomaculum sapomendens was isolated. (4) When enrichments were carried out at 13°C, a sulfate-reducing bacterium was enriched and purified. This bacterium was identified as Desulfobacterium species. (5) A series of enrichments were carried out whereby an increasing dilution of mud was used as the source material. Tubes with mud from the lower dilutions gave rise to typical Desulfovibrio sapovorans. However, mud used at higher dilutions gave rise to Desulfobacterium species, suggesting that these organisms may be present in higher numbers. Enrichments were carried out using branched-chain fatty acids as the electron donor. Freshwater enrichments with isobutyrate and 2-methyl butyrate gave rise to Desulfotomaculum acetoxidans and Desulfovibrio sapovorans, designated Amib and Am2mb respectively. Estuarine enrichments with isobutyrate and 2-methylbutyrate gave rise to Desulfobacterium vacuolatum, designated Okib and a Desulfosarcina species designated Ok2mb. Enrichments from both freshwater and estuarine sources using isovalerate grew very slowly and were not purified in this study. Studies on the physiology of strain Okib showed it was able to oxidize a range of amino acids and keto acids including proline, branched-chain amino acids, 5-aminovalerate and keto isocaproate. It neither fermented amino acids nor carried out Stickland reactions with pairs of amino acids. During the course of isolating the sulfate-reducing bacteria in this study, an obligately anaerobic agarolytic bacterium was enriched in association with a Desulfovibrio species. The agarolytic bacterium was obtained in pure culture and designated 16AV. This is the first account of the degradation of agar by an obligate anaerobe. Strain 16AV grew only on agar, agarose, galactose and cellobiose producing ethanol, acetate, H₂ and CO₂. Strain 16AV probably represents a new species of the genus Acetivibrio.