Investigating molecular pathways and identifying genes and microbes that promote heat stress resistance and healthy ageing

Several studies have linked stress resistance to lifespan extension, and ageing has been associated with dysbiosis. With C. elegans longevity correlating with severe heat resistance and the recent recognition of a key role for the gut microbiota in defining worm healthspan, I looked at how C. elegans gut microbes found in its natural environment may interact with the worm physiology to mediate stress resistance and healthy ageing. I exposed young adult C. elegans to their natural gut microbiota and assayed for heat (42°C) and oxidative stress (7% tertbutyl hydroperoxide) resistance using LFASS (Label-Free Automated Survival Scoring) assays. To determine if microbial effects on stress resistance involve known gut-brain axis pathways, I conducted LFASS assays on Insulin/IGF-1 Signalling (IIS) and Kynurenine Pathway (KP) C. elegans mutants. My results showed that both the KP and IIS pathways are involved in severe stress resistance, with bacterial strains modulating the KP differentially and the gut microbiota influencing stress responses through both IIS-dependent and independent mechanisms. I then conducted health-span (movement, brood size) experiments and lifespan assays to determine whether enhanced stress resistance translates into healthier ageing and longevity. MYb71 (Ochrobactrum vermis), MYb330 (Pseudomonas), BIGb170 (Sphingobacterium multivorum), MYb396(a) (Comamonas), and MYb21 (Comamonas), were found to be beneficial, as they improved stress resistance without negatively impacting reproduction. Enhanced stress resistance did not lead to increased lifespan, suggesting that stress resistance and longevity are physiologically distinct. To identify new host genetic pathways potentially mediating gut microbiotas effects on severe stress resistance and healthy ageing, I conducted a genome-wide RNAi screen on young adult C. elegans exposed to severe heat stress. I found known thermoprotective genes, F44E5.5, sip-1, and dnj-5, and thermosensitising gene skn-1. I also identified some new thermoprotective candidate genes, such as clec-20, F20G2.5, pals-30 (immunity) and R08F11.1, fat-7 (fat metabolism). The genes from the RNAi screen will be used in conjunction with the beneficial microbial isolates to determine whether they produce a synergistic response.