Biotransformation pathways of phytol in recent anoxic sediments

Abstract

E-Phytol (3,7,11,15-tetramethylhexadec-2(E)-en-1-ol) incubated in anaerobic sediment slurries was rapidly biodegraded (98% after 6 months) by a mixed bacterial community to Z and E isomers of phyta-1,3(4)-diene (3,7,11,15-tetramethylhexadeca-1,3(4)-diene) as the major identifiable products, with phyta-1,3(17)-diene (3,7,11,15-tetramethylhexadeca-1,3(17)-diene; neophytadiene) and isomeric phytenes (3,7,11,15-tetramethylhexadecene) as minor products. Neither phytane (3,7,11,15-tetramethylhexadecane) nor compounds usually considered as anoxic biotransformation products of phytol, such as dihydrophytol (3,7,11,15-tetramethylhexadecan-1-ol) or phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), were produced in the slurries. A similar anaerobic biodegradation of synthetic phytadienes showed the formation of the same isomeric phytenes as the major identifiable metabolites. Potentially competitive sulfurisation processes expected in these experiments were investigated. The formation of a dimeric isoprenoid polysulfide (accounting for less than 2% of the degradation products) from phytadienes was observed. The analysis of free C 20 isoprenoid compounds present in the anoxic part of a fresh sediment core collected at the same site as the sediments used for the in vitro incubations indicated that: (i) the transformation of phytol to phytenes via phytadiene intermediates may represent an important pathway during the anaerobic degradation of phytol in bacterially active environments, (ii) the role, if any, of dihydrophytol in this biodegradation pathway remains unclear.