Role of the Streptococcus agalactiae ClpP serine protease in heat-induced stress defence and growth arrest

Abstract

The main causes of microbial death after heat exposure are not well understood. Here, it is shown that the heat-shock protein ClpP plays a major role in heat-induced growth arrest in Streptococcus agalactiae. A mutant lacking the ClpP protease was more sensitive to the inhibitory effects of heat, salt and oxidative stress than the isogenic wild-type strain. During growth arrest, this mutant displayed important modifications of its total protein content, including a decreased level of essential metabolic enzymes such as the alcohol dehydrogenase. Analysis of protein carbonylation demonstrated that the ClpP protease plays a role in preventing accelerated protein oxidation. Higher levels of oxidized DnaK, a key modulator of the heat-shock regulon, were observed in the ClpP mutant and these were increased following heat shock. Accumulation of oxidized/inactivated DnaK might explain why the ClpP mutant was unable to properly synthesize DNA and proteins, and why it exhibited an aberrant cell morphology. Even though ClpP plays a minor role in the virulence of S. agalactiae in a murine infection model, the data presented here point to the importance of ClpP in oxidative stress defence in preventing heat-induced cell alterations.

Transcription of clpP Is Enhanced by a Unique Tandem Repeat Sequence in Streptococcus mutans

“…The cotranscription of clpP and upp was later confirmed by RT-PCR analysis. Previous studies on clpP gene expression in other gram-positive bacteria, including streptococci, have shown that clpP transcription is monocistronic and that the length of its product correlates with the length of the smaller transcript observed here (19,23,33,38,43,49). It is very surprising to see that the cotranscription of the clpP gene with upp is observed only in S. mutans, since the upp locus is topologically linked to the clpP locus in all streptococci.…”

“…In low-GϩC-content gram-positive bacteria, such as streptococci, the intracellular protease ClpP plays important roles in many cellular processes, including stress resistance, biofilm formation, and pathogenesis (12,18,31,33,38,43,49). Although, the importance of ClpP in various biological processes is well documented, regulation of its expression has not been thoroughly investigated.…”

“…In bacteria, production of clpP transcript is strongly induced after exposure to thermal or other stress conditions (18,19,23,43,49). Furthermore, in low-GϩC-content gram-positive bacteria, including S. mutans, regulation of the clpP expression is primarily controlled by the CtsR repressor, which binds to a heptanucleotide repeat, A/GGTCAAA/T (15,42).…”

“…In various microorganisms, targets for ClpP-mediated proteolysis include several global regulators, including the following: Spx, which is involved in oxidative stress (62); RsiW, which is required during alkaline stress (60); and several regulators involved in bacterial development, such as ComK (competence development) (29,41,56), Sda (sporulation) (53), and H alternate sigma factor (34,35,44). Since ClpP is involved in protein quality control, inactivation of clpP leads to various biological changes, such as stress sensitivity, aberrant cell morphology, developmental defects, and severely attenuated virulence (20,22,26,43). Thus, ClpP protease, along with the Clp ATPases, is central in the coordination of developmental decisions and stress response in prokaryotic microorganisms.…”

spr1630 Is Responsible for the Lethality ofclpXMutations inStreptococcus pneumoniae

“…While it thus might be expected that Clp protease mutations would usually be highly pleiotropic, the most prominent phenotype associated with loss of ClpP varies from one species to another. Thus, for example, clpP mutants of a number of low-GC gram-positive species have reduced thermo-tolerance (7,11,20,28,29,35). A loss of virulence is the most prominent phenotypic effect of mutation of ClpP in Staphylococcus aureus (8), while in Salmonella, altered expression of flagellar operons is a major effect (43).…”