Anaerobic oxidation of n-alkenes by sulphate-reducing bacteria from the genus Desulfatiferula: n-ketones as potential metabolites.

Two alkene-degrading sulphate-reducing bacteria from the genus Desulfatiferula (Desulfatiferula olefinivorans strain LM2801(T) and Desulfatiferula sp. strain BE2801) were investigated for their 1-alkene metabolism. Their total cellular fatty acids were predominantly C-even when they were grown on C-even 1-alkene (1-hexadecene), whereas a mixture of fatty acids with C-odd or C-even carbon chains predominated when cells were grown on C-odd 1-alkene (1-pentadecene). This is consistent with the fatty acid composition of other sulphate-reducing strains previously reported to grow on n-alkenes. Linear and 3-OH-fatty acids appear to be the main fatty acids produced by the two Desulfatiferula strains. The analysis of their neutral lipids led to identifying several n-alkanols and n-ketones with the same number of carbon atoms as the alkene growth substrate and with functionality located between C-1 and C-5. Growth of strains LM2801(T) and BE2801 on (per) deuterated 1-alkenes provided direct evidence of their anaerobic transformation to corresponding 1-alkanols, n-ketones and linear (3-OH-) fatty acids. These results demonstrate that Desulfatiferula strains oxidize a 1-alkene by oxidation of the double bond at C-1, but also at C-2 to C-5 (after eventual isomerization of the double bond) yielding the corresponding C-2 to C-5 n-ketones (via the corresponding n-alkanols). The formation of specific 3-OH-fatty acids by elongation of shorter chain fatty acids was also demonstrated. Based on our observations, pathways for anaerobic 1-alkene metabolism in sulphate-reducing bacteria from the genus Desulfatiferula are proposed. They indicate that n-ketones can constitute new metabolites of the biodegradation of n-alkenes in anaerobic environments.