Glutamate Dehydrogenase (GdhA) of Streptococcus pneumoniae Is Required for High Temperature Adaptation

Abstract

During its progression from the nasopharynx to other sterile and non-sterile niches of its human host, Streptococcus pneumoniae must cope with changes in temperature. We hypothesised that the temperature adaptation is an important facet of pneumococcal survival in the host. Here, we evaluated the effect of temperature on pneumococcus and studied the role of glutamate dehydrogenase (GdhA) in thermal adaptation associated with virulence and survival. Microarray analysis revealed a significant transcriptional response to changes in temperature, affecting the expression of 252 genes in total at 34°C and 40°C relative to at 37°C. One of the differentially regulated genes was gdhA, which is upregulated at 40°C and downregulated at 34°C relative to 37°C. Deletion of gdhA attenuated the growth, cell size, biofilm formation, pH survival, and biosynthesis of proteins associated with virulence in a temperature-dependent manner. Moreover, deletion of gdhA stimulated formate production irrespective of temperature fluctuation. Finally, Δ gdhA grown at 40°C was less virulent compare to other temperatures or than the wild type at the same temperature in a Galleria mellonella infection model, suggesting that GdhA is required for pneumococcal virulence at elevated temperature.

The involvement of CiaR and the CiaR-regulated serine protease HtrA in thermal adaptation of Streptococcus pneumoniae

“…StkP is a conserved Ser/Thr kinase in pneumococcus and is involved in the localization of cell division apparatus, cell elongation and phosphorylation of cell division protein FtsZ [43], which is mainly regulated by CiaR [43–45]. However, the changes in the transcript level of stkP (SPD_1542), ftsZ (SPD_1479), or ftsW (SPD_0952) were not significant in our previous study [13]. The results also showed that overexpressing htrA has no impact on cell size at any temperature.…”

“…Our previous data showed that the pneumococcus responds to thermal fluctuations using a highly complex genetic network [13]. Using microarray analysis, we showed massive alterations in the pneumococcal transcriptome at 34 and 40 °C relative to 37 °C, affecting 252 genes [13]. To further our understanding of pneumococcal thermal adaptation, we focused on the two-component regulatory system CiaR because of its temperature-associated differential expression [upregulated at 34 °C (2.1-fold) and downregulated at 40 °C (2.6-fold), relative to 37 °C].…”

“…However, none of these genes are found to be regulated by CiaR in S. pneumoniae (Table S1a), and nor was their expression affected by temperature [13]. One possibility for decreased biofilm formation in the ciaR mutant could be related to impaired competence, as the addition of exogenous CSP (competence-stimulating peptide encoded by comC ) increased the biomass of biofilm during late-exponential growth [40].…”

“… Streptococcus pneumoniae is exposed to different temperatures among different niches of the human host during colonization and invasive disease [3]. Our previous data showed that the pneumococcus responds to thermal fluctuations using a highly complex genetic network [13]. Using microarray analysis, we showed massive alterations in the pneumococcal transcriptome at 34 and 40 °C relative to 37 °C, affecting 252 genes [13].…”

“…The reason we focused on HtrA-like serine protease was that it was shown that HtrA plays an important role in stress response, including oxidative and antimicrobial stresses [18,[27][28][29]. This serine protease is upregulated at 34 °C (6.4-fold) and downregulated at 40 °C (3.7-fold) [13]. Although HtrA is known as a heat shock serine protease that participates in degradation of misfolded proteins at high-temperature stress, it was reported that the HtrA homologue DegP in Escherichia coli acts as a protease and a chaperone to protect cells at both low and high temperatures [30].…”