Putrescine or a combination of methionine and arginine restores virulence gene expression in a tRNA modification‐deficient mutant of Shigella flexneri: a possible role in adaptation of virulence

Abstract

SummaryThe wild-type strain YSH6000 of Shigella flexneri growing in minimal medium contains the modified nucleoside epoxy-Q (oQ) in a subset of tRNAs. This nucleoside is lacking in tRNA from a tgt mutant of this bacterium. When these bacteria are growing in minimal medium, the expression of virulence genes is 10-fold lower in the tgt mutant than in the wild type, although only a twofold reduction in the expression of these virulence factors is observed in broth. Such a strong media-dependant expression of virulence genes was not observed in the wild type. Accordingly, the level of the positive regulator of virulence, VirF, is much lower in the mutant than in the wild type. However, the transcription of the virF gene in minimal medium is the same in the wild type and in the tgt mutant. As the undermodification of tRNA is not affected by the quality of the growth medium, we conclude that such an environmental change in growth conditions partly restores virulence gene expression by counteracting poor translation of the virF mRNA mediated by an oQ-deficient tRNA. Virulence gene expression is partly restored in the tgt mutant by the addition of a mixture of arginine and methionine. Addition of the polyamine putrescine, synthesis of which is metabolically related to that of arginine and methionine, has a comparable stimulatory effect on virulence gene expression. These results not only suggest a role for amino acids and polyamines in the environmental regulation of virulence gene expression in S. flexneri , but also demonstrate a strong and specific involvement of tRNA modifications, and especially oQ, in the adaptation of virulence gene expression to the nutritional quality of the growth medium.

Involvement of potD in Streptococcus pneumoniae Polyamine Transport and Pathogenesis

“…In order to determine how both potD inactivation and de novo polyamine synthesis inhibition would effect the growth of WU2⌬potD, the two polyamine synthesis inhibitors MGBG and DFMO were added to either THY or CDM containing 1 mg/ml choline. For the experiment, 10 5 CFU of either wild-type WU2 or WU2⌬potD were grown in THY alone or in the presence of both MGBG and DFMO (Fig. 4A).…”

“…The concentrations of intracellular polyamines have been shown to influence the efficiency and fidelity of translation and to stabilize DNA, RNA, and various enzymes involved in both transcription and translation as well as to modulate the synthesis of various proteins at the translational level (31). The polyamine putrescine has been shown to restore virulence gene expression in the pathogen Shigella flexneri (10), to influence the formation of filaments in Candida albicans that are necessary for virulence in mouse models (16), and to be involved in host cell adherence by Trichomonas vaginalis (11). The data presented here show that the polyamine transport system encoded by potABCD influences the overall pathogenesis of Streptococcus pneumoniae within the murine host.…”

“…Many clinically relative bacterial species contain genes associated with a superfamily of amino acid-polyamine-organocation transporters as determined on the basis of sequence analysis (22), but almost nothing is known about their function during in vitro growth or in a human host. Shigella flexneri mutants unable to synthesize modified nucleosides necessary for tRNA synthesis can utilize supplemental putrescine to restore virulence gene expression (10). Enterococcus faecalis can use agmatine as another energy source and takes up this polyamine by an agmatine-putrescine antiporter (8).…”

Mapping of a YscY Binding Domain within the LcrH Chaperone That Is Required for Regulation of Yersinia Type III Secretion

“…From our work with the chaperone hybrids, however, the cause of low PcrH expression must reside in the extreme N terminus, since Hyb9, which essentially contained all of PcrH except for the first 17 LcrH amino acids, was expressed at roughly LcrH-like levels in Yersinia. It has been established that the 5Ј end of many E. coli genes is responsible for control of translation efficiency (12) as well as a wide variety of virulence determinants produced by numerous bacterial pathogens (17,19,20,50,57,61). Therefore, minor codons in the extreme N terminus of LcrH might have evolved to control the translation efficiency of this important regulatory molecule, a concept we are currently exploring.…”

The truA gene of Pseudomonas aeruginosa is required for the expression of type III secretory genes

“…Recently, a strong and specific involvement of tRNA modifications in the adaptation of virulence gene expression to the nutritional quality of the growth medium has been reported (Durand & Bjork, 2003;Urbonavicius et al, 2002). The presence of modified nucleosides in tRNA was also shown to be important for virulence of Shigella (Durant & Davis, 1997), Agrobacterium tumefaciens (Gray et al, 1992), Pseudomonas aeruginosa (Sage et al, 1997;Urbonavicius et al, 2002) and Pseudomonas syringae (Kinscherf & Willis, 2002).…”