Catalyzes the phosphatidyl group transfer from one phosphatidylglycerol molecule to another to form cardiolipin (CL) (diphosphatidylglycerol) and glycerol. Can also catalyze phosphatidyl group transfer to water to form phosphatidate. 2 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol) = a cardiolipin + glycerol Activated by phosphate. Inhibited by cardiolipin and phosphatidate. Triple deletion of clsA, clsB and clsC results in a complete lack of cardiolipin, regardless of growth phase or growth conditions. All three cardiolipin synthases (ClsA, ClsB and ClsC) contribute to CL synthesis in stationary phase. Only ClsA contributes to synthesis during logarithmic growth phase. Belongs to the phospholipase D family. Cardiolipin synthase subfamily. ClsB sub-subfamily.