FORMATION OF MESOPYROPHAEOPHORBIDE A DURING ANAEROBIC BACTERIAL-DEGRADATION OF THE MARINE PRYMNESIOPHYTE EMILIANIA-HUXLEYI

The transformations undergone by chlorophyll a under anoxic conditions have been simulated by using the widespread marine prymnesiophyte Emi liania huxleyi as a substrate for a mixed bacterial community by incub ation in a sediment slurry under sulphate reducing conditions. This re sulted in the formation of pyrophaeophytin a after 77 days, along with smaller amounts of phaeophorbide a, pyrophaeophorbide a and mesopyrop haeophorbide a, from an original pigment distribution comprising mainl y phaeophytin a, with a lower abundance of chlorophyll a. Mesopyrophae ophorbide a has not been reported previously as a product of any chlor ophyll a defunctionalization study. Its formation under the conditions used suggests that the reduction of the C-3 vinyl substituent, requir ed for transformation of chlorophyll a to a number of sedimentary porp hyrins and chlorins, is a process which involves anaerobic bacterial c ommunities.