Aerobic metabolism of vitamin E by marine bacteria : interaction with free radical oxidation (autoxidation) processes

The degradation of vitamin E by aerobic bacterial communities, isolated from marine sediment and microbial mat samples, was investigated. PCR-DGGE profiles and cloning/sequencing experiments revealed that biodegradation of vitamin E in sediments is mainly carried out by strains belonging to the genera Idiomarina and Bacillus for which the DGGE pattern matched with the pattern obtained from the second sediment subculture. Biodegradation processes appeared to involve an initial ω-oxidation of the isoprenoid side chain and subsequent β-oxidation sequences affording 2,5,7,8-tetramethyl–2(2’-carboxyethyl)-6-hydroxychroman (α-CEHC). This compound was not accumulated at the end of the growth, showing that the bacterial degradation of vitamin E is not limited to its isoprenoid side chain. In cultures still containing residual sediment, the presence of metabolites with a shortened side chain and an opened chroman ring (e.g., α-tocopheronolactone and α-tocopherylhydroquinonolactone) attested to the simultaneous involvement of biodegradation and autoxidation processes. The induction of autoxidation during these incubations was attributed to some of the sediment components, which could act as catalysts of free radical reactions. In oxic environments, the combination of free radical oxidation and aerobic biodegradation processes should result in a very fast degradation of vitamin E. Different pathways are proposed to explain the formation of the different compounds resulting from these interactions.