Streptococcal viability and diminished stress tolerance in mutants lacking the signal recognition particle pathway or YidC2

Abstract

The signal recognition particle (SRP)-translocation pathway is conserved in all three domains of life and delivers membrane and secretory proteins to the cytoplasmic membrane or endoplasmic reticulum. We determined the requirement in the cariogenic oral pathogen Streptocococcus mutans of the three universally conserved elements of the SRP pathway: Ffh͞SRP54, scRNA, and FtsY͞SR␣. Previously, we reported that insertional interruption of S. mutans ffh was not lethal, but resulted in acid sensitivity. To test whether S. mutans could survive extensive disruption of the SRP pathway, single and double deletions of genes encoding Ffh, scRNA, and FtsY were generated. Without environmental stressors, all mutant strains were viable, but unlike the wild-type, none could initiate growth at pH 5.0 or in 3.5% NaCl. Survival of challenge with 0.3 mM H2O2 was also diminished without ffh. Members of the YidC͞Oxa1͞Alb3 family are also ubiquitous, involved in the translocation and assembly of membrane proteins, and have been identified in prokaryotes͞mitochondria͞chloroplasts. Two genes encoding YidC homologs, YidC1 and YidC2, are present in streptococcal genomes with both expressed in S. mutans. Deletion of YidC1 demonstrated no obvious phenotype. Elimination of YidC2 resulted in a stress-sensitive phenotype similar to SRP pathway mutants. Mutants lacking both YidC2 and SRP components were severely impaired and barely able to grow, even in the absence of environmental stress. Here, we report the dispensability of the cotranslational SRP protein translocation system in a bacterium. In S. mutans, this pathway contributes to protection against rapid environmental challenge and may overlap functionally with YidC2.protein translocation ͉ streptococcus ͉ Ffh ͉ FtsY ͉ membrane biogenesis

The 4.5S RNA component of the signal recognition particle is required for group A Streptococcus virulence

“…Similar to most Gram-positive bacteria, GAS encode two YidC proteins, YidC1 and YidC2. While not studied in GAS, YidC1 and YidC2 have been studied in S. mutans, where deletion of yidC1 caused only a minor growth phenotype while deletion of yidC2 resulted in a major stress phenotype similar to an SRP mutant strain (Hasona et al, 2005). Disruption of both yidC2 and components of the SRP pathway gave S. mutans strains that were severely impaired in growth and stress tolerance.…”

“…While isogenic 4.5S RNA, ffh and ftsY mutant strains of the cariogenic oral pathogen Streptococcus mutans are viable, they have diminished tolerance to several stresses, including low pH and high salt (Hasona et al, 2005;Kremer et al, 2001). In the absence of stress, growth yield was similar between the parental and SRP mutant S. mutans strains, although the doubling time increased.…”

Streptococcus mutans: a new Gram-positive paradigm?

“…The bacterial SRP translocation pathway was previously studied in E. coli and B. subtilis and in both cases was found to be essential for cell viability (Keenan et al, 2001;Phillips & Silhavy, 1992). However, proteins of the SRP pathways were unexpectedly shown to be dispensable in S. mutans (Hasona et al, 2005). Further studies revealed that overlapping and compensatory pathways exist in S. mutans and allow the organism to adapt and maintain membrane function in the absence of the SRP (Funes et al, 2009).…”

Cofactor Engineering Enhances the Physiological Function of an Industrial Strain

“…In turn, some signaling pathways could also affect ATP synthesis under stress. In Streptococcus, mutants deficient in the minimally conserved bacterial signal recognition particle (SRP) elements remain viable but are more sensitive to environmental stress because the SRP deficiency decreases ATPase activity and limits the ATP supply [40,41] . It was found that industrial strain grown on high environmental stress have a high ATP demand [42] and increase ATP supply [43] could well facilitate the resistance to stress.…”