Identification of a Stress-Induced Factor ofCorynebacterineaeThat Is Involved in the Regulation of the Outer Membrane Lipid Composition

Abstract

Corynebacterineae are gram-positive bacteria that possess a true outer membrane composed of mycolic acids and other lipids. Little is known concerning the modulation of mycolic acid composition and content in response to changes in the bacterial environment, especially temperature variations. To address this question, we investigated the function of the Rv3802c gene, a gene conserved in Corynebacterineae and located within a gene cluster involved in mycolic acid biosynthesis. We showed that the Rv3802 ortholog is essential in Mycobacterium smegmatis, while its Corynebacterium glutamicum ortholog, NCgl2775, is not. We provided evidence that the NCgl2775 gene is transcriptionally induced under heat stress conditions, and while the corresponding protein has no detectable activity under normal growth conditions, the increase in its expression triggers an increase in mycolic acid biosynthesis concomitant with a decrease in phospholipid content. We demonstrated that these lipid modifications are part of a larger outer membrane remodeling that occurs in response to exposure to a moderately elevated temperature (42°C). In addition to showing an increase in the ratio of saturated corynomycolates to unsaturated corynomycolates, our results strongly suggested that the balance between mycolic acids and phospholipids is modified inside the outer membrane following a heat challenge. Furthermore, we showed that these lipid modifications help the bacteria to protect against heat damage. The NCgl2775 protein and its orthologs thus appear to be a protein family that plays a role in the regulation of the outer membrane lipid composition of Corynebacterineae under stress conditions. We therefore propose to name this protein family the envelope lipids regulation factor (ElrF) family.

Tetrahydrolipstatin Inhibition, Functional Analyses, and Three-dimensional Structure of a Lipase Essential for Mycobacterial Viability

“…A recent study has suggested a role for Rv3802c and its orthologs in regulating outer membrane lipid composition under stress conditions (15). The authors found that the C. glutamicum ortholog NCgl2775 could be disrupted to give a viable mutant with no obvious alteration in cell wall composition, and we have confirmed these findings as our own mutant of C. glutamicum NCgl2775 was viable (data not shown).…”

“…The authors found that the C. glutamicum ortholog NCgl2775 could be disrupted to give a viable mutant with no obvious alteration in cell wall composition, and we have confirmed these findings as our own mutant of C. glutamicum NCgl2775 was viable (data not shown). This study provided evidence of transcriptional induction of NCgl2775 during heat stress leading to an increase in mycolic acid biosynthesis and a decrease in phospholipid content (15). However, this finding does not account for the essential nature of MSMEG_6394 and Rv3802c in M. smegmatis and M. tuberculosis, respectively, under normal growth conditions.…”

“…Previous studies have shown it to have phospholipase A and thioesterase activities (12), consistent with a role in mycolic acid biosynthesis, and significant lipase activity completely dependent on its Ser-Asp-His catalytic triad (14). A very recent study has suggested a role for Rv3802c in regulation of outer lipid composition in response to stress because the induction of the Corynebacterium glutamicum ortholog triggered an increase in mycolic acid biosynthesis as part of an outer membrane remodeling response to heat stress (15).…”

Mycoloyltransferases: A large and major family of enzymes shaping the cell envelope of Corynebacteriales

“…In C. glutamicum, studies using fusion between cmytA promoter region and the -galactosidase gene showed that cmytA is up-regulated in heat-stress conditions (42°C and 50°C versus 30°C), but not in other stress conditions. In particular, and in contrast to the reported regulation of M. tuberculosis Fbps in starvation conditions, cMytA level in C. glutamicum is unaffected by short time carbon starvation (45). C. glutamicum has been widely studied in osmotic stress conditions and Franzel et al (46) reported that cmytA and cmytB genes are down-regulated at the protein level in hyper-osmotic conditions (750 mM NaCl), whereas cmyt gene transcription is not affected as reported previously by Meniche et al (45).…”

Characterization of the Vibrio cholerae VolA Surface-Exposed Lipoprotein Lysophospholipase

“…It is likely that the lysophospholipase activity of VolA is coupled to the uptake of LPC-derived LCFAs, which can then be incorporated into the bacterial membrane. Bacteria have been shown to use membrane remodeling as a survival adaptation, making it likely that VolA plays a similar role during infection of the host (23,24). We observed that VolA is well conserved across many Vibrio species, prompting us to further characterize this intriguing protein.…”