Investigating TprA/PhrA mediated regulation in Streptococcus pneumoniae

Streptococcus pneumoniae is one of the leading causes of death amongst children and elderly. Its ability to detect and adapt to the changing environmental stimuli is important for pathogenicity. Several transcriptional regulatory pathways have crucial roles on pneumococcal adaptation to environmental changes. TprA/PhrA quorum sensing (QS) system is one of a new family of regulatory systems shown to be involved in virulence, galactose utilisation, and neuraminidase production, and its potential utility as an anti-infective target had been demonstrated previously. However, it is not known in detail how TprA/PhrA contributes to the pneumococcal virulence, therefore, the goal of this study was to reveal the mechanism of TprA/PhrA mediated virulence in S. pneumoniae.

The results showed that spd1517 and spd1947 regulated by TprA/PhrA quorum sensing system, are required for galactose and mucin utilisation in S. pneumoniae. Loss of spd1517 or spd1947 decreased the neuraminidase activity. SPD1517 has an impact on capsule biosynthesis and cell morphology as its deletion resulted in enlarged and elongated cells. I demonstrated that the pneumococcal galactose catabolic pathways are differentially expressed under different galactose and oxygen concentrations, and temperature ranges. Transcriptional reporter assays revealed that TprA and SPD1947 are activators of pneumococcal tagatose pathway, but these regulators have no significant effect on expression of galK, a key gene of the Leloir pathway. Putative binding motif sequences for TprA were identified in the pneumococcal genome. Two of the genes were identified as potentially regulated by TprA/PhrA through in silico analysis: spd1255 codes for an ABC transporter and spd0559, a galactose transporter. These were tested for interaction with TprA. It was found that spd1255 plays a role in import of PhrA peptide, and TprA interacts with the putative promoter region of spd0559, providing evidence that the TprA regulon may be wider than it was previously reported.