Lighting up the environment: bioluminescence hormesis under chemical contamination

In this Review, I assess bioluminescence hormetic response to chemicals, examining concentration-response relationships and predominantly focusing on stimulation by sub-toxic exposures of numerous chemicals applied individually or in mixtures at concentrations <1 ng L^-1 to ~43 g L^-1. Stimulation develops rapidly, becoming detectable in 15 min, but exhibits considerable temporal variation and may decrease or return to control levels after maximization within 2-3 d from exposure. This produces non-linear responses that take different forms over time and may alternate among S-shaped, J-shaped, and U-shaped curves. The bioluminescence hormetic response is determined by chemical interactions, e.g., through chemical binding with luciferase α and β subunits and adenylyl cyclase protein. LuxR mRNA expression is also promoted at low sub-toxic concentrations, while competing with N-acylhomoserine lactone at high concentrations, therefore generating hormesis. Autoinducers triggering pathways of quorum sensing, e.g., autoinducer-2, may also be involved in the stimulatory response of bioluminescence. Furthermore, biphasic relative expression of mRNAs involved in quorum system (e.g., luxR, litR and luxO), together with increased luciferase content at low sub-toxic concentrations, indicate an intricate relationship between bioluminescence and quorum sensing under contaminant-induced hormesis. Based on recent advances, I propose that bioluminescence stimulation may present a catabolic form of hormesis, highlighting the importance of integrating bioluminescence hormesis with anabolic and catabolic processes. I discuss these complex phenomena to explain the mechanisms regulating bioluminescence hormesis. These newly emerged insights reshape the traditional knowledge of bioluminescence response and organismal stress under chemical challenges. They also aid in closing a significant gap in chemical biology mechanisms, challenging chemical risk assessments and providing a perspective for protecting the environment and improving biotechnological application and environmental health.