Lsr2, a novel cyclic di-GMP receptor, regulate the synthesis of keto-mycolic acid and control biofilm formation in mycobacteria

Cyclic di-GMP (c-di-GMP) is a well-known second messenger that plays a key role in many physiological processes in bacteria. The synthesis of lipids is essential for bacterial biofilm formation. However, whether c-di-GMP signaling modulates the synthesis of lipid and further regulates biofilm formation in mycobacteria is unclear, and the c-di-GMP receptor involved remains unknown. In this study, we characterized the nucleoid-associated protein (NAP) Lsr2 as a novel c-di-GMP receptor in mycobacteria. c-di-GMP specifically binds to Lsr2 at a ratio of 1:1. We showed that c-di-GMP promotes mycobacterial biofilm formation in a manner dependent on Lsr2. Furthermore, Lsr2 mediates the synthesis of keto-mycolic acid, the lipid component of the mycobacterial cell wall, by positively regulating the expression of HadD, a (3R)-hydroxyacyl-ACP dehydratase, thus, Lsr2 ultimately controls biofilm formation. Finally, c-di-GMP promotes the positive regulation of HadD by Lsr2 and mycobacterial biofilm formation. Thus, we report a novel c-di-GMP receptor that links the second messenger’s function to lipid synthesis and biofilm formation in mycobacteria.