Acyl-AcpB, a FabT corepressor in Streptococcus pyogenes

Membranes are a universal barrier to all cells. Phospholipids, essential bacterial membrane components, are composed of a polar head and apolar fatty acid (FA) chains. Most bacterial FA are synthesized by the FA synthesis pathway (FASII). In streptococcaceae, enterococci and Lactococcus lactis, a unique feedback mechanism controls the FASII gene expression. FabT, encoded in the FASII main locus, is the repressor and it is activated by acyl-ACP. Many Streptococci, Enterococcus faecalis, but not L. lactis, possess two ACPS. AcpA encoding gene is within the FASII locus and is, to a certain extent, coregulated with the FASII genes. Acyl-AcpA is the end product of FASII. AcpB encoding gene is in operon with plsX. The role of AcpB as FabT corepressor is controversial. Streptococcus pyogenes, which causes a wide variety of diseases ranging from mild non-invasive to severe invasive infections, possesses AcpB. In this study, we show by comparing gene repression of FASII genes in wild-type, fabT mutant and acpB mutant strains grown in the presence and the absence of exogenous FAs, that AcpB is S. pyogenes FabT main co-repressor. Also, acpB deletion impacts the membrane FA composition and adhesion to eucaryotic cells, highlighting the role of AcpB.