Biodegradation of free phytol by bacterial communities isolated from marine sediments under aerobic and denitrifying conditions

Biodegradation of (E)-phytol [3,7,11,15-tetramethylhexadec-2(E)-en-1-ol] by two bacterial communities isolated from recent marine sediments under aero bic and denitrifying conditions was studied at 20 degrees C. This isoprenoi d alcohol is metabolized efficiently by these two bacterial communities via 6,10,14-trimethylpentadecan-2-one and (E)-phytenic acid. The first step in both aerobic and anaerobic bacterial degradation of (E)-phytol involves th e transient production of (E)-phytenal, which in turn can be abiotically co nverted to 6,10,14-trimethylpentadecan-2-one. Most of the isoprenoid metabo lites identified in vitro could be detected in a fresh sediment core collec ted at the same site as the sediments used for the incubations. Since (E)-p hytenal is less sensitive to abiotic degradation at the temperature of the sediments (15 degrees C), the major part of (E)-phytol appeared to be biode graded in situ via (E)-phytenic acid, (Z)- and (E)-phytenic acids are prese nt in particularly large quantities in the upper section of the core, and t heir concentrations quickly decrease with depth in the core. This degradati on (which takes place without significant production of phytanic acid) is a ttributed to the involvement of alternating beta-decarboxymethylation and b eta-oxidation reaction sequences induced by denitrifiers. Despite the low n itrate concentration of marine sediments, denitrifying bacteria seem to pla y a significant role in the mineralization of (E)-phytol.