Legionella pneumophila couples fatty acid flux to microbial differentiation and virulence

Abstract

SummaryDuring its life cycle, Legionella pneumophila alternates between at least two phenotypes: a resilient, infectious form equipped for transmission and a replicative cell type that grows in amoebae and macrophages. Considering its versatility, we postulated that multiple cues regulate L. pneumophila differentiation. Beginning with a Biolog Phenotype MicroArray screen, we demonstrate that excess short-chain fatty acids (SCFAs) trigger replicative cells to cease growth and activate their panel of transmissive traits. To co-ordinate their response to SCFAs, L. pneumophila utilizes the LetA/LetS twocomponent system, but not phosphotransacetylase or acetyl kinase, two enzymes that generate highenergy phosphate intermediates. Instead, the stringent response enzyme SpoT appears to monitor fatty acid biosynthesis to govern transmission trait expression, as an altered distribution of acylated acyl carrier proteins correlated with the SpoT-dependent differentiation of cells treated with either excess SCFAs or the fatty acid biosynthesis inhibitors cerulenin and 5-(tetradecyloxy)-2-furoic acid. We postulate that, by exploiting the stringent response pathway to couple cellular differentiation to its metabolic state, L. pneumophila swiftly acclimates to stresses encountered in its host or the environment, thereby enhancing its overall fitness.

Growth-related Metabolism of the Carbon Storage Poly-3-hydroxybutyrate in Legionella pneumophila

“…Notably, this phenotype was observed for two independently generated ⌬lpp0931-33 mutant strains, and it therefore appears less probable that second site mutations caused this effect. Indeed, the reduced growth might be explained by a ⌬Lpp0931-33-dependent decrease in the concentrations of acylated acyl carrier proteins, which are measured by the stringent response enzyme SpoT in L. pneumophila and could lead to a change in the expression of the transmissive phenotype (cell cycle) as reported earlier (46). Conversely, this phenotype could be suppressed by the additional inactivation of the ketothiolase in the ⌬keto/ ⌬lpp0931-33 double mutant by blocking the conversion of AcCoA into acetoacetyl-CoA, thereby also influencing (i.e.…”

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…seems to be tied to carbon metabolism intermediates, including short-chain fatty acids such as acetate or intermediates of the tricarboxylic acid cycle (67,173). Likewise, L. pneumophila requires its LetS/LetA TCS to induce transmission traits in response to SCFAs, as well as to other metabolic stresses and ppGpp (199,200). However, a direct stimulatory factor has never been definitively demonstrated in this or any other bacterium.…”

“…The leading hypothesis to explain these findings is that nutrient depletion perturbs fatty acid biosynthesis, which in turn stimulates production of ppGpp by SpoT. When ppGpp levels are high, both the stationary-phase sigma factor RpoS and the LetS/ LetA TCS cooperate to induce the expression of transmission genes (197)(198)(199)(200).…”

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

“…It is believed that LetA/LetS responds to the alarmone (p)ppGpp and the intracellular concentration of (p)ppGpp is regulated by RelA and SpoT (Dalebroux et al 2010a;Edwards et al 2009;Dalebroux et al 2009;Hammer and Swanson 1999;Hammer et al 2002;Zusman et al 2002). LetA seems to be involved in the expression of two small regulatory RNAs (RsmY and RsmZ) that are substrates for the RNA-binding protein CsrA.…”