ISOLATION AND GENETIC COMPLEMENTATION OF A SULFOLIPID-DEFICIENT MUTANT OF RHODOBACTER-SPHAEROIDES

All photosynthetic organisms are thought to contain the sulfolipid 6-s ulfo-alpha-D-quinovosyl diacylglucerol. However, the pathway of sulfol ipid biosynthesis has not been elucidated, and the functional or struc tural significance of this lipid is not known. Mutants of Rhodobacter sphaeroides deficient in sulfolipid accumulation were isolated by dire ctly screening for altered sulfolipid content. The mutants had no appa rent phenotype except for the sulfolipid deficiency. A gene, designate d sqdA, which complemented one of the mutations was isolated and chara cterized. The putative sqdA gene product is a protein with a molecular mass of 33.6 kDa that has no sequence similarity to any enzyme of kno wn function.