Salmonella methylglyoxal detoxification by STM3117-encoded lactoylglutathione lyase affects virulence in coordination with Salmonella pathogenicity island 2 and phagosomal acidification

Abstract

Intracellular pathogens such as Salmonella enterica serovar Typhimurium (S. Typhimurium) manipulate their host cells through the interplay of various virulence factors. A multitude of such virulence factors are encoded on the genome of S. Typhimurium and are usually organized in pathogenicity islands. The virulence-associated genomic stretch of STM3117–3120 has structural features of pathogenicity islands and is present exclusively in non-typhoidal serovars of Salmonella. It encodes metabolic enzymes predicted to be involved in methylglyoxal metabolism. STM3117-encoded lactoylglutathione lyase significantly impacts the proliferation of intracellular Salmonella. The deletion mutant of STM3117 (Δlgl) fails to grow in epithelial cells but hyper-replicates in macrophages. This difference in proliferation outcome was the consequence of failure to detoxify methylglyoxal by Δlgl, which was also reflected in the form of oxidative DNA damage and upregulation of kefB in the mutant. Within macrophages, the toxicity of methylglyoxal adducts elicits the potassium efflux channel (KefB) in the mutant which subsequently modulates the acidification of mutant-containing vacuoles (MCVs). The perturbation in the pH of the MCV milieu and bacterial cytosol enhances the Salmonella pathogenicity island 2 translocation in Δlgl, increasing its net growth within macrophages. In epithelial cells, however, the maturation of Δlgl-containing vacuoles were affected as these non-phagocytic cells maintain less acidic vacuoles compared to those in macrophages. Remarkably, ectopic expression of Toll-like receptors 2 and 4 on epithelial cells partially restored the survival of Δlgl. This study identified a novel metabolic enzyme in S. Typhimurium whose activity during intracellular infection within a given host cell type differentially affected the virulence of the bacteria.

Cells producing their own nemesis: Understanding methylglyoxal metabolism

“…Later on, bacterial production of methylglyoxal from aminoacetone was also observed in other bacterial species like Arthrobacter and Bacillus subtilis which degraded threonine and NAD or glycine and acetyl CoA to aminoacetone . Salmonella Typhimurium is also predicted to produce methylglyoxal via aminoacetone in LB medium . The genome encodes a putative monoamine oxidase and a noncanonical lactoylglutathione lyase (GlxI).…”

“…The genome encodes a putative monoamine oxidase and a noncanonical lactoylglutathione lyase (GlxI). The lactoylglutathione lyase mutant rapidly loses viability due to uncontrolled methylglyoxal production, and this could be in part due to monoamine oxidase‐mediated methylglyoxal production , as it has been known that bacteria grown in complex nutrient media dissimilate threonine into aminoacetone and hence to methylglyoxal .…”

“…. Lactoylglutathione lyase, the enzyme for relieving methylglyoxal toxicity, has also been implicated to enhance virulence of certain intracellular bacterial pathogens . Brucella abortus and Salmonella Typhimurium induce the expression of their respective lactoylglutathione lyase genes to aid in macrophage persistence.…”

“…; refs. and . As overproduction of lactoylglutathione lyase (GlxI) confers tolerance to methylglyoxal, it may be used by the intracellular bacteria to survive and proliferate in macrophages.…”

Antigens of Aeromonas salmonicida subsp. salmonicida specifically induced in vivo in Oncorhynchus mykiss

“…It has also been shown to play an important role in the intracellular invasiveness of Salmonella as well as in the translocation of effectors encoded on the Salmonella pathogenicity island 2, and mutants deficient in this enzyme display a reduced invasiveness into epithelial cells (Chakraborty et al . ).…”