Branched-Chain Fatty Acids Promote Listeria monocytogenes Intracellular Infection and Virulence

Abstract

Anteiso-branched-chain fatty acids (BCFA) represent the dominant group of membrane fatty acids and have been established as crucial determinants in resistance against environmental stresses in Listeria monocytogenes, a facultative intracellular pathogen. Here, we investigate the role of anteiso-BCFA in L. monocytogenes virulence by using mutants deficient in branched-chain alpha-keto acid dehydrogenase (BKD), an enzyme complex involved in the synthesis of BCFA. In tissue culture models of infection, anteiso-BCFA contributed to intracellular growth and survival in macrophages and significantly enhanced plaque formation upon prolonged infection in L2 fibroblasts. The intracellular defects observed could be attributed partially to insufficient listeriolysin O (LLO) production, indicating a requirement for anteiso-BCFA in regulating virulence factor production. In a murine model of infection, the BKD-deficient mutant was highly attenuated, further emphasizing the importance of BKD-mediated metabolism in L. monocytogenes virulence. This study demonstrates an underappreciated role for BCFA in bacterial pathogenesis, which may provide insight into the development and application of antimicrobial agents.

Role of Serine/Threonine Phosphatase (SP-STP) in Streptococcus pyogenes Physiology and Virulence

“…Interestingly, the absence of C15:0 anteiso branched chain fatty acid in the M1⌬STP mutant (Table 1) is attributed to the 4 -10-fold down-regulation of the fabH gene (SPy1754), which is involved in the branched chain fatty acid synthesis (44). The down-regulation of the fabH/ SPy1754 in M1⌬STP and corresponding absence of the C15:0 anteiso branched chain fatty acid (44) corroborate with the attenuation of virulence, as was also observed in S. aureus (45) and L. monocytogenes (40). Further, the undetected C17:0 cyclopropane fatty acid, which is responsible for conferring acid tolerance to bacteria by altering the membrane rigidity and fluidity (46), may play an indirect role in reduced survival of the M1⌬STP mutant within the host, especially while encountering an unfavorable intracellular environment.…”

“…The role of lipid biosynthesis in virulence regulation has been studied for S. pneumoniae (38), S. aureus (39), and L. monocytogenes (40) but not for GAS. Like S. pneumoniae, the FAS-II operon in the M1SF370 GAS strain is constituted by SPy1743 to SPy1755.…”

Fatty Acids Regulate Stress Resistance and Virulence Factor Production for Listeria monocytogenes

“…In the present study, we demonstrate that genetic disruption or exposure to FA precursors that lead to alterations in FA composition significantly compromise stress resistance and intracellular fitness. Disruption of the synthesis of BCFAs, the dominant class of membrane FA, through genetic mutation, causes decreases in membrane fluidity (14,27), in vitro growth defects at low temperature and low pH (22,62), and reduced intracellular growth and infection in vivo (50). Here, we establish a specific requirement for BCFAs in resistance against surface stresses and phagosomal killing.…”

“…Second, we assayed for LLO production using bacteria grown with both butyrate and 2MB supplementation to test a potential signaling role for butyrate. Supplementation with 2MB (5 mM) by itself causes no changes in LLO production in WT bacteria (50). Supplementation with 25 mM 2MB in HEPES-buffered BHI completely restored anteiso-BCFA content in bacteria grown with 250 mM butyrate (Fig.…”

“…However, after transducing the insertion into a clean isogenic wild-type background, we demonstrated with two independent transductants that deficiency in BKD resulted in strong attenuation in both tissue culture and mouse infection models. The BKD insertion mutants also exhibited a significant defect in production of listeriolysin O, the cytolysin required for phagosomal escape (50).…”