Light/dark and temperature cycling modulate metabolic electron flow inPseudomonas aeruginosabiofilms

Abstract

Sunlight drives phototrophic metabolism, which affects redox conditions and produces substrates for non-phototrophs. These environmental parameters fluctuate daily due to Earth’s rotation, and non-phototrophic organisms can therefore benefit from the ability to respond to, or even anticipate, such changes. Circadian rhythms, such as diurnal changes in body temperature, in host organisms can also affect local conditions for colonizing bacteria. Here, we investigated the effects of light/dark and temperature cycling on biofilms of the opportunistic pathogen Pseudomonas aeruginosaPA14. We grew biofilms in the presence of a respiratory indicator dye and found that greater dye reduction occurred in biofilm zones that formed during dark intervals and at lower temperatures. This pattern formation occurred with cycling of blue, red, or far-red light, and a screen of mutants representing potential sensory proteins identified two with defects in pattern formation specifically under red light cycling. We also found that the physiological states of biofilm subzones formed under specific light and temperature conditions were retained during subsequent condition cycling. Light/dark and temperature cycling affected expression of genes involved in primary metabolic pathways and redox homeostasis, including those encoding electron transport chain components. Consistent with this, we found that cbb3-type oxidases contribute to dye reduction under light/dark cycling conditions. Together, our results indicate that cyclic changes in light exposure and temperature have lasting effects on redox metabolism in biofilms formed by a non-phototrophic, pathogenic bacterium.

Light-regulated gene expression in Bacteria: Fundamentals, advances, and perspectives

“…Early on, researchers realized that optogenetically controlled expression lends itself to the generation of spatial patterns within bacterial communities and lawns. In fact, certain bacteria naturally produce spatially ordered structures when exposed to alternating dark/light cycles e.g., (Kahl et al, 2022). As recently reviewed (Barbier et al, 2022), the patterning of microbial communities gains traction and appears suited for diverse applications in synthetic biology and biotechnology.…”