Brucella synthesizes phosphatidylcholine from choline provided by the host.

COMERCI, D; ALTABE, SILVIA GRACIELA; DE MENDOZA, D; UGALDE, R

Merida, Yucatan, México

Congreso; 58th Brucellosis Research Conference; 2005

Phosphatidylcholine (PC) is one of the major structural constituents of the eukaryotic membranes and the principal source of lipid second messenger involved in signal transduction pathways. PC is also found in an increasing number of prokaryotes, mainly in symbionts, pathogens and photosynthetic bacteria. Besides the currently known methylation pathway for PC formation, a novel pathway was described in the legume symbiont Sinorhizobium meliloti in which choline is directly condensed with CDP-DAG by the action the enzyme phosphatidylcholine synthase (Pcs). The Brucella cell envelope has unique characteristics such as a low endotoxic LPS, several porins and OMPs covalently bound to the peptidoglycan layer and the presence of PC as one of the main phospholipids. Until now, the metabolic pathway for PC formation in Brucella and the enzymes involved were completely unknown, although pmta and pcs genes were detected in the three Brucella sequenced genomes. We cloned the pmta and pcs genes from B. abortus S2308 and characterized mutants defective in PC synthesis. Phospholipid composition of pmtA and pcs mutants indicated that PC synthesis occurs exclusively via the phosphatidylcholine synthase pathway.Transformation of E. coli with an expression vector containing the B. abortus pcs homologue was sufficient for PC synthesis upon induction with IPTG, while no PC formation was detected when bacteria were transformed with a vector containing pmtA. These findings imply that Brucella depends on choline provided by the host cell to form PC. Although the ability of the mutant to invade and sustain intracellular replication was not affected, a reproducible virulence defect in mice was observed,which suggests that PC is necessary to maintain a chronic infection process. A possible role for PC as a modulator of the inflammatory response generated during infection is discussed