Pigment Analysis of Gloeobacter violaceus PCC7421

Abstract

Precise pigment analyses of a cyanobacterium Gloeobacter violaceus PCC 7421 were performed. Phe a and Chl a' were found to be present as minor pigments like other cyanobacteria, suggesting the photosystems of this cyanobacterium are similar to other cyanobacteria. Menaquinone-4 (MQ-4) was detected in the PS I particles of G. violaceus, but phylloquinone was absent. MQ-4 should be the secondary electron acceptor of PS I in G. violaceus. The stoichiometry of MQ-4/Chl a' was estimated to be two, indicating that two molecules of MQ-4 were present in PS I. The genome sequences of G. violaceus showed the absence of genes homologous to the phylloquinone biosynthesis enzyme, thus an unknown pathway of the MQ-4 biosynthesis would be present in this cyanobacterium.