Environmental pH changes, but not the LuxS signalling pathway, regulate SpeB expression in M1 group A streptococci

Abstract

The autoinducer-2/LuxS signalling pathway participates in quorum sensing in diverse bacterial species. In group A streptococci (GAS), LuxS has been shown to be involved in regulating the expression of several important virulence factors. Streptococcal pyrogenic exotoxin B (SpeB), a cysteine protease that has important roles in GAS pathogenesis, is positively regulated by LuxS in M3 and M5 strains. In the present study, it was found that the supernatant harvested from an overnight culture stimulated M1 strains to express speB. However, mutation of the luxS gene in M1 strains or treating M1 strains with luxS mutant culture supernatant did not affect speB expression, indicating that the LuxS pathway is not involved in regulation of speB expression in M1 strains. In addition, the acid property of culture broth was found to be able to stimulate M1 strains to express speB in the same LuxS-independent manner. These results indicate that speB expression in M1 strains is induced by environmental pH changes but is not regulated by the LuxS signalling pathway.

Repression of Rgg But Not Upregulation of LacD.1 in emm1-type covS Mutant Mediates the SpeB Repression in Group A Streptococcus

“…Primers used for real-time PCR analysis were designed by Primer3 1 (v.0.4.0) according to the MGAS5005 sequence (NCBI reference sequence: NC_007297.1) and are described in Table 2 . Southern blot and Northern blot analyses were performed as described previously (Chiang-Ni et al, 2012). Ten microgram of genomic DNAs extracted from GAS strains were digested by restriction enzymes for Southern blot analysis.…”

“…High-copy-number E. coli-Streptococcus shuttle vector pDL278 (Chiang-Ni et al, 2012) was employed to construct the rgg over-expression strain. The rgg gene with its native promoter was amplified by primers rgg-F-4 and rgg-R-3 (1958 bp) and ligated into pDL278 with the Bam HI site (designed as pCN138).…”

Establishment of Quantitative Real-Time PCR System for Analyzing Cas9 Gene Expression in Listeria innocua

“…Therefore, Cas9 also plays a crucial role in infection process of bacteria via regulating virulence factor. Chiang-Ni et al (2012) indicated that environmental pH changes regulate the expression of virulence factor SpeB in Streptococcus pyogenes. However, little is known about whether the expression of Cas9 is influenced by medium pH in gram-positive bacteria.…”

“…Bacteria culture: Neutral medium and acidic medium preparation were performed as described previously (Chiang-Ni et al, 2012). 100 mM HEPES and MES were used to adjust the fresh THY broth to pH = 7.5 (neutral medium) and pH = 6.0 (acidic medium) respectively.…”

“…Also, the published data indicated that Cas9 regulates the expression of virulence factor in transcriptional level in gram-negative bacteria . The environmental pH may influence the expression of virulence gene in gram-positive bacteria (Chiang-Ni et al, 2012). Up to now, the function of Cas9 in different medium pH in gram-positive bacteria is still unknown.…”