Effects of food availability on the trade-off between growth and antioxidant responses in Caenorhabditis elegans exposed to sulfonamide antibiotics

Adverse effects of sulfonamide antibiotics (SAs) include growth inhibition and antioxidant activation which showed trade-off effects. Yet, the influence of food availability on such effects have not been thoroughly investigated. Caenorhabditis elegans were exposed to four SAs at high and low food availabilities which were represented by the optical densities of bacteria at 600 nm. The nematode feeding, growth and antioxidants including superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) were determined. Results showed that the control nematodes at low food availability had less growth and greater antioxidant responses than the nematodes at high food availability. In SA exposure, the nematode growth in the presence of food (at both high and low food availability) was less than that in its absence, supporting the role of food as an exposure pathway. The nematode growth at low food availability showed significantly greater inhibition than at high food availability (p < 0.05). The nematode antioxidants showed stimulations, and CAT had the greatest stimulation. Moreover, the stimulation on CAT at low food availability were significantly higher than those at high food availability (p < 0.05). That is to say, SA exposure at low food availability further biased the trade-off effects towards more energy investment in antioxidant with less in growth. Further studies on the expression levels of CAT encoding genes demonstrated that cells in intestines were the main antioxidant response sites, which further supported the contributions of food to the observed toxicities.