title: Growth, natural relationships, cellular fatty acids and metabolic adaptation of sulfate-reducing bacteria that utilize long-chain alkanes under anoxic conditions.
abstract: Natural relationships, improvement of anaerobic growth on hydrocarbons, and properties that may provide clues to an understanding of oxygen-independent alkane metabolism were studied with two mesophilic sulfate-reducing bacteria, strains Hxd3 and Pnd3. Strain Hxd3 had been formerly isolated from an oil tank; strain Pnd3 was isolated from marine sediment. Strains Hxd3 and Pnd3 grew under strictly anoxic conditions on n-alkanes in the range of C12-C20 and C14-C17, respectively, reducing sulfate to sulfide. Both strains shared 90% 16 S rRNA sequence similarity and clustered with classified species of completely oxidizing, sulfate-reducing bacteria within the delta-subclass of Proteobacteria. Anaerobic growth on alkanes was stimulated by alpha-cyclodextrin, which served as a non-degradable carrier for the hydrophobic substrate. Cells of strain Hxd3 grown on hydrocarbons and alpha-cyclodextrin were used to study the composition of cellular fatty acids and in vivo activities. When strain Hxd3 was grown on hexadecane (C16H34), cellular fatty acids with C-odd chains were dominant. Vice versa, cultures grown on heptadecane (C17H36) contained mainly fatty acids with C-even chains. In contrast, during growth on 1-alkenes or fatty acids, a C-even substrate yielded C-even fatty acids, and a C-odd substrate yielded C-odd fatty acids. These results suggest that anaerobic degradation of alkanes by strain Hxd3 does not occur via a desaturation to the corresponding 1-alkenes, a hypothetical reaction formerly discussed in the literature. Rather an alteration of the carbon chain by a C-odd carbon unit is likely to occur during activation; one hypothetical reaction is a terminal addition of a C1 unit. In contrast, fatty acid analyses of strain Pnd3 after growth on alkanes did not indicate an alteration of the carbon chain by a C-odd carbon unit, suggesting that the initial reaction differed from that in strain Hxd3. When hexadecane-grown cells of strain Hxd3 were resuspended in medium with 1-hexadecene, an adaptation period of 2 days was observed. Also this result is not in favor of an anaerobic alkane degradation via the corresponding 1-alkene.
authors.affiliation: Max-Planck-Institut für Marine Mikrobiologie, Bremen, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Aeckersberg
authors.forename: F A
authors.initials: FA
authors.lastname: Rainey
authors.forename: F
authors.initials: F
authors.lastname: Widdel
mesh_terms: D000222:Adaptation, Physiological; D000473:Alkanes / Q000378:metabolism; D000475:Alkenes / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000737:chemistry / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D001483:Base Sequence; D002849:Chromatography, Gas; D003505:Cyclodextrins / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis; D019015:Geologic Sediments / Q000382:microbiology; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D013431:Sulfates / Q000378:metabolism; D013440:Sulfides / Q000032:analysis; D016999:Sulfur-Reducing Bacteria / Q000737:chemistry / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D013997:Time Factors; D014871:Water Microbiology
chemical_list: D000473:Alkanes; D000475:Alkenes; D003505:Cyclodextrins; D005227:Fatty Acids; D013431:Sulfates; D013440:Sulfides; C007932:n-hexadecane; C016486:heptadecane