Catalyzes the reversible phosphatidyl group transfer from one phosphatidylglycerol molecule to another to form cardiolipin (CL) (diphosphatidylglycerol) and glycerol. 2 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol) = a cardiolipin + glycerol Optimum pH is 7.0. Seems to be post-translationally processed from a 53-55 kDa form to a 45-46 kDa form (PubMed:7665497 and PubMed:19341704). Mutants have increased sensitivity to novobiocin. 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. ClsA sub-subfamily.