Global Transcriptional Analysis ofclpPMutations of Type 2Streptococcus pneumoniaeand Their Effects on Physiology and Virulence

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Abstract
Streptococcus pneumoniae is an important human pathogen that contains single copies of genes encoding the ClpP and FtsH ATP-dependent proteases but lacks the Lon and HslV proteases. We constructed and characterized the phenotypes of clpP, clpC, and clpX deletion replacement mutants, which lack the ClpP protease subunit or the putative ClpC or ClpX ATPase specificity factor. A ΔclpP mutant, but not a ΔclpC or ΔclpX mutant, of the virulent D39 type 2 strain of S. pneumoniae grew poorly at 30°C and failed to grow at 40°C. Despite this temperature sensitivity, transcription of the heat shock regulon determined by microarray analysis was induced in a ΔclpP mutant, which was also more sensitive to oxidative stress by H2O2 and to puromycin than its clpP+ parent strain. A ΔclpP mutant, but not a ΔclpC mutant, was strongly attenuated for virulence in the murine lung and sepsis infection models. All of these phenotypes were complemented in a ΔclpP/clpP+ merodiploid strain. Consistent with these complementation patterns, clpP was found to be in a monocistronic operon, whose transcription was induced about fivefold by heat shock in S. pneumoniae as determined by Northern and real-time reverse transcription-PCR analyses. Besides clpP, transcription of clpC, clpE, and clpL, but not clpX or ftsH, was induced by heat shock or entry into late exponential growth phase. Microarray analysis of ΔclpP mutants showed a limited change in transcription pattern (≈80 genes) consistent with these phenotypes, including repression of genes involved in oxidative stress, metal ion transport, and virulence. In addition, transcription of the early and late competence regulon was induced in the ΔclpP mutant, and competence gene expression and DNA uptake seemed to be constitutively induced throughout growth. Together, these results indicate that ClpP-mediated proteolysis plays a complex and central role in numerous pneumococcal stress responses, development of competence, and virulence.