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

Abstract

The degradation of vitamin E by aerobic bacterial communities, isolated from marine sediment and microbial mat samples, was investigated. Polymerase chain reaction-denaturing gradient gel electrophoresis (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 the pattern obtained from the second sediment subculture. Biodegradation appeared to involve an initial ω-oxidation of the isoprenoid side chain and subsequent β-oxidation, affording 2,5,7,8-tetramethyl-2(2′-carboxyethyl)-6-hydroxychroman (α-CEHC). This compound was not accumulated at the end of growth, showing that the bacterial degradation of vitamin E is not limited to the isoprenoid side chain. In cultures still containing residual sediment, the presence of metabolites with a shortened side chain and opened chroman ring (e.g., α-tocopheronolactone and α-tocopherylhydroquinonolactone) attested to the simultaneous involvement of biodegradation and autoxidation. The induction of autoxidation during these incubations was attributed to some of the sediment components, which could act as catalysts for free radical reactions. In oxic environments, the combination of free radical oxidation and aerobic biodegradation should result in very rapid degradation of vitamin E. Different pathways are proposed to explain the formation of the different compounds resulting from these interactions.