In Pseudomonas putida A ATCC 12633 cells grown with tetradecyltrimethylammonium bromide and exposed to Al(3)Cl, phosphatidylcholine (PC) levels increased, which alleviated stress caused by the Al(3+). Here we cloned and sequenced a gene from this strain that encodes a phosphatidylcholine synthase (PCS) and characterized a pcs-deficient mutant. In the pcs-deficient mutant, PC could not be detected, whereas the mutant could be successfully complemented and expressed the enzyme, indicating that PC synthesis occurs exclusively via the PCS pathway in this organism. Although under non-stressing growth conditions the pcs-deficient mutant showed growth like that of the wild-type strain, the mutant was much more sensitive when challenged with Al(3+), which strongly supports the supposition that PC is involved in the response of P. putida to Al(3+) and acts as a temporary reservoir of available ions through the formation of Al(3+) : PC complexes.