446 - Light- and Temperature-Controlled Redox Cycling in Pseudomonas Aeruginosa Biofilms

Abstract

Many organisms are subject to earth’s 24h day-night cycle and have evolved a biological clock in anticipation of daily changes in light and temperature. This biological clock is mechanistically linked to redox cycling, which is a conserved phenomenon, whereby cells undergo 24h cycles of the redox state. Redox cycling was shown to exist in heterotrophic eukaryotes and archaea, thus, our objective was to test if this kind of redox cycling also exists in heterotrophic bacteria, like the pathogen Pseudomonas aeruginosa. We observed the redox state of growing biofilms, exposed to 12h cycles of light & dark and temperature variation. Using the redox indicator triphenyl tetrazolium chloride, which is reduced by the electron transport chain, we visualized oscillations in respiration levels (or metabolic activity) over the course of biofilm development. When reducing the cycle length to 6h, respiratory cycling adjusted accordingly. Interestingly, when extending periods to 24h of light and dark, we observed redox cycling patterns that followed 12h cycles, hinting at internal timekeeping within the biofilm. Further investigation of this phenomenon by RNAseq revealed that regulation of components of the electron transport chain (ETC), as well as peroxiredoxins, oxidative phosphorylation and glutathione metabolism are subject to light/dark and temperature cycling. Finally, a sensor for this regulation was found to be a PAS (Per-ARNT-Sim) domain-containing histidine kinase that might be responsible for adjusting metabolic rates according to light and temperature changes. P. aeruginosa might sense such cues when it is in a host. Since immune activity is regulated by the host’s biological clock, redox cycling in P. aeruginosa might have evolved to anticipate host immune activity. Thus, this phenomenon might ultimately be an adaptation to host-associated lifestyle.