DAILY VARIATIONS IN ABIOTIC AND BIOTIC STRESS TOLERANCE IN C. elegans

Introduction: Circadian rhythms control several behaviors through neural networks, hormones and gene expression. One of these outputs in invertebrates, vertebrates and plants is the stress resistance behavior. Methods: We first studied the circadian variation in abiotic stress resistance of adult C. elegans cultured in liquid survival medium as well as the genetic mechanisms that underlie such behavior. Measuring the stress resistance by tap response behavior we found a rhythm in response to osmotic (NaCl LC50=340mM) and oxidative (H 2 O 2 LC50=50mM) shocks, with a minimum at ZT0 (i.e., lights off) and ZT12 (lights on), respectively. In addition, the expression of glutathione peroxidase ( C11E4.1 ) and glycerol-3- phosphate dehydrogenase ( gpdh-1 ) (genes related to the control of stress responses) also showed a circadian fluctuation in basal levels with a peak at night. Moreover, in the mutant osr-1 (AM1 strain), a negative regulator of the gpdh-1 pathway, the osmotic resistance rhythms were masked at 350mM but reappeared when the strain was treated with a higher NaCl concentration. We then studied the response to biotic stress. In order to do so we studied the response of C. elegans to a soil dwelling bacterium, P. fluorescens. These bacteria elicit at least two types of deleterious effects in C. elegans . Slow-killing depends on the GacS pathway. Fast-killing (similar to what has been described for P. aeruginosa ) depends strongly on hydrogen cyanide production. Results: The response observed in C. elegans nematodes to fast paralytic killing varies along the day and its sensitivity is higher during the night, at ZT12 (lights off). This behavior correlates well with HCN tolerance, which is higher during the day, at ZT0 (lights on). This innate immune response to P. fluorescens and P. aeruginosa might depend on the stress response pathway of C. elegans . Conclusion: This work demonstrates for the first time that in the adult nematode C. elegans stress responses vary throughout the day, and suggests an underlying rhythmic gene expression that governs these behaviours. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil