Biotransformation pathways of phytol in recent anoxic sediments

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-tet ramethylhexadeca-1,3(4)-diene) as the major identifiable products, with phy ta-1,3(17)-diene (3,7,11,15-tetramethylhexadeca-1,3(17)-diene; neophytadien e) and isomeric phytenes (3,7,11,15-tetramethylhexadecene) as minor product s. Neither phytane (3,7,11,15-tetramethylhexadecane) nor compounds usually considered as anoxic biotransformation products of phytol, such as dihydrop hytol (3,7,11,15-tetramethylhexadecan-1-ol) or phytanic acid (3,7,11,15-tet ramethylhexadecanoic acid), were produced in the slurries. A similar anaero bic biodegradation of synthetic phytadienes showed the formation of the sam e isomeric phytenes as the major identifiable metabolites. Potentially comp etitive sulfurisation processes expected in these experiments were investig ated. The formation of a dimeric isoprenoid polysulfide (accounting for les s than 2% of the degradation products) from phytadienes was observed. The a nalysis of free C-20 isoprenoid compounds present in the anoxic part of a f resh sediment core collected at the same site as the sediments used for the in vitro incubations indicated that: (i) the transformation of phytol to p hytenes via phytadiene intermediates may represent an important pathway dur ing the anaerobic degradation of phytol in bacterially active environments, (ii) the role, if any, of dihydrophytol in this biodegradation pathway rem ains unclear. (C) 1998 Elsevier Science Ltd. All rights reserved.