Transcriptome studies on Streptococcus pneumoniae, illustration of early response genes to THP-1 human macrophages

Pathogen-host interaction plays an essential role in pathogenicity. In this study, we investigated transcriptomes of one Streptococcus pneumoniae TIGR4-derived unencapsulated strain upon exposure to THP-1 human macrophage-like cells for 0.5 h, 1 h and 3 h, respectively. Expression of most genes was up-regulated and the changes of selected genes were validated by qRT-PCR. To characterize the functions of the identified genes, one locus of genes (SP1057-SP1063) was deleted in TIGR4 by insertion replacement mutagenesis. Compared to the wild-type strain, the constructed mutant exhibited lower binding and internalization activities to the THP-1 macrophages at early incubation time periods (0.5 h and/or 1 h) but not at 3 h. However, no change was observed in the intracellular survival assays. These data indicate that the SP1057-SP1063 locus is involved in the early stage of interaction with host macrophages. Further sequence and PCR analyses suggest that the SP1057-SP1063 locus was acquired by lateral transfer.