Transfers a methylene group from S-adenosyl-L-methionine to the cis double bond of an unsaturated fatty acid chain resulting in the replacement of the double bond with a methylene bridge. 1-acyl-2-(9Z)-enoyl-sn-glycero-3-phospholipid + S-adenosyl-L-methionine = 1-acyl-2-(9-cyclopronane)-acyl-sn-glycero-3-phospholipid + H(+) + S-adenosyl-L-homocysteine Inhibited by sinefungin, A9145C and S-adenosyl-L-homocysteine. Lipid metabolism; fatty acid biosynthesis. Homodimer (PubMed:30057024). Homodimerization is required for catalysis (PubMed:30057024). One subunit probably binds to the lipid bilayer and positions the other subunit for catalysis (PubMed:30057024). Each of the subunit of the dimer contains a smaller N-domain that associates tightly with a larger catalytic C-domain. Belongs to the CFA/CMAS family.