Figure 4.

Transcriptional analysis of selected genes from the Staphylococcus aureus white variant after co-culture with Pseudomonas aeruginosa. Several genes involved in pigment production were analyzed by qRT-PCR after co-culture with P. aeruginosa 6611. These genes included crtM, which is directly involved in staphyloxanthin synthesis. Transcriptional factors SigB and Sara control the expression of the crtOPQMN operon, and product of the hfq gene may be involved in post-transcriptional control of the operon. FPP-synthase gene is involved in the synthesis of farnesyl-diphosphate which is the substrate for the crtOPQMN operon. The results indicate no significant changes in expression of these genes through the first 7 hours of co-culture. In the later time intervals of 24 hours and 48 hours, these genes (with the exception of sarA which was slightly downregulated) were significantly downregulated. The agrA gene could be involved in the downregulation of staphyloxanthin. The expression of the katA gene may be correlated to the production of staphyloxanthin since both confer resistance to H₂O₂. The transcription of agrA is downregulated after 7 hours and into the later time intervals. In contrast, katA gene is significantly upregulated after 8 hours and reached its peak (more than 3-fold) at 24 hours.

Notes: The columns represent fold change in gene expression of co-cultured S. aureus white variant as compared to the white variant that was not co-cultured. Time points represent data gathered after 1, 7, 24, and 48 hours after the start of co-culture with P. aeruginosa 6611.

Abbreviations: qRT-PCR, quantitative reverse transcription polymerase chain reaction; crtM, carotenoid biosynthetic gene M; sigB, sigma B transcription factor gene; sarA, staphylococcal accessory regulator A gene; FPP synth, farnesyl pyrophosphate synthase gene; hfq, host factor gene for Q beta; katA, catalase gene A; agrA, accessory gene regulator A; crtOPQMN, carotenoid biosynthetic operon.