The transcriptional changes of LrgA discriminates the responsiveness of Staphylococcus aureus towards blue light from that of photodynamic inactivation

Antimicrobial blue light (aBL) is utilized as a new approach to inhibit the growth of Staphylococcus aureus (S. aureus). Mediated by the endogenous chromophore, aBL possesses the similar photokilling property with aPDI (antimicrobial photodynamic inactivation), however, their mechanistic discrepancies in triggering the death of staphylococcal cells are not yet understood. Here, we describe the use of a 460-nm-LED to curb the viability of S. aureus. According to the results, the bacterial survival was sharply decreased when blue light was applied, reaching a maximum of 4.11 ± 0.04 log10 units. Moreover, the membrane integrity was damaged by aBL, causing the leakage of intracellular DNA. Transcriptomic analysis indicates the divergent gene expression upon either aBL or aPDI, with pathways such as transport, DNA repair, expression regulation and porphyrin massively affected by aBL. Among the commonly regulated genes, LrgA was underpinned on account of its involvement with biofilm formation and protein transport. By comparing the wildtype with the LrgA-overexpressing (LrgA+) strain, the survival rate, membrane penetration, surface structure and biofilm formation were, to a varying degree, improved for LrgA+, which may suggest that LrgA plays essential roles in modulating the responsiveness of S. aureus. Besides, LrgA may function through regulating the expression of autolysis-related systems. Finally, LrgA overexpression did not attenuate but aggravate the impairment induced by aPDI, showcasing a distinct responsive strategy from aBL. Taken together, this study unveils a unique molecular alteration for the aBL-mediated inactivation, providing the basis of utilizing blue light to reduce the harm brought by S. aureus.