The Function of MgDVP in a Chlorophyll d-Containing Organism

Abstract

The cyanobacterium Acaryochloris marina is an exceptional organism utilising chlorophyll d (Chl d) as its major photosynthetic pigment. Acaryochloris cells contain 90--99% Chl d with minor amounts of chlorophyll a and a chlorophyll c-like pigment. These unusual characteristics make it an excellent candidate to study various aspects of photosynthesis driven by Chl d. However, little is known about the pathway of Chl d biosynthesis. We specifically designed HPLC methods to analyse pigment compositions of Acaryochloris. This enabled us to detect intermediate products of the chlorophyll biosynthesis. We identified Mg-Protoporphyrin IX monomethyl ester (MgPMe) and Mg-2,4-divinyl pheoporphyrin (MgDVP) and the environmental factors influencing their concentration levels. HPLC-facilitated analysis of pigments from Acaryochloris cells cultured under various light quantities was performed; light stress conditions induced an increase in the ratio of MgDVP to Chl d. Pigment analysis of Acaryochloris cells grown under oxygen-stressed conditions demonstrated a decrease in MgDVP levels. We propose that the Chl d biosynthesis pathway favours an aerobic environment despite the fact that Acaryochloris cells can survive under anaerobic conditions.