RNA-SEQ Reveals Changes in the Staphylococcus aureus Transcriptome following blue light illumination

Purpose: In an effort to better understand the mechanism of blue light inhibition in Staphylococcus aureus, a whole transcriptome analysis of S. aureus isolate BUSA2288 was performed using RNA-seq to analyze the differential gene expression in response to blue light exposure. Methods: RNA was extracted from S. aureus cultures pooled from 24 one ml well samples illuminated with a dose of 250 J/cm2 of 465 nm blue light, and from control cultures grown in the dark. Complementary DNA (cDNA) were generated from the RNA samples and then sequenced using the Illumina MiSeq Next Generation Sequencer. The combined results of 2 independent experiments were analyzed using the Pairwise Analysis tools in GeneSifter®. The genes were normalized by Mapped Reads using EdgeR statistics including a Benjamini and Hochberg false discovery rate correction. Quality was set at a minimum number of 10 reads and a p value of 0.05. The lower threshold for change was 5 fold. Results: Transcriptomic comparisons using a cutoff of 5 fold identified a total of 28 down-regulated genes and 6 up-regulated genes in the samples that were exposed to blue light. All but 6 of the differentially regulated genes fall into 8 functional categories: amino acid biosynthesis, cell envelope components, cellular processes, central intermediary metabolism, energy metabolism, protein synthesis, regulatory function, and transport and binding proteins. Five genes encode conserved proteins of unknown function. Conclusions: Blue light has been shown to be bactericidal against S. aureus and is a potential alternative therapy for antibiotic resistant organisms. The mechanism for the inactivation of bacteria is hypothesized to involve ROS. We have found evidence that supports this hypothesis that involves multiple pathways including essential metabolic pathways and known virulence pathways. Overall design: S. aureus mRNA profiles were produced from 24 pooled samples of S. aureus cultures exposed to blue light (BL) and compared to parallel samples grown in the dark (NL). Two independent experiments were performed.