Abstract
Sulfoquinovosyl diacylglycerol (SQDG) is one of ubiquitous lipids that construct thylakoid membranes in oxygenic photosynthetic organisms, and is present also in several species of anoxygenic photosynthetic and root nodule bacteria. Photosystems are stabilized in thylakoid membranes by SQDG whereas intracellular sulfur (S)-source for protein synthesis is ensured by degradation of SQDG in green algae starved for S. In oxygenic photosynthetic organisms, SQDG is synthesized by sequential action of UDP-sulfoquinovose and SQDG synthases that are encoded by sqdB and sqdX genes, respectively (type I system of SQDG synthesis). Meanwhile, an anoxygenic photosynthetic bacterium, Rhodobacter sphaeroides, utilizes the sqdB gene and three unique genes, sqdA, sqdC, and sqdD (type II). In this study, we searched available genomic nucleotide sequences for the genes for types I and II. Besides oxygenic photosynthetic organisms, homologs of the genes for type I were scattered in several phyla of bacteria whereas those for type II were confined within species of Proteobacteria. We will also show lipid patterns of some bacteria including one that was newly suggested to possess the type I system.
