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 Emiliania huxleyi as a substrate for a mixed bacterial community by incubation in a sediment slurry under sulphate reducing conditions. This resulted in the formation of pyrophaeophytin a after 77 days, along with smaller amounts of phaeophorbide a, pyrophaeophorbide a and mesopyrophaeophorbide a, from an original pigment distribution comprising mainly phaeophytin a, with a lower abundance of chlorophyll a. Mesopyrophaeophorbide a has not been reported previously as a product of any chlorophyll a defunctionalization study. Its formation under the conditions used suggests that the reduction of the C-3 vinyl substituent, required for transformation of chlorophyll a to a number of sedimentary porphyrins and chlorins, is a process which involves anaerobic bacterial communities.