SIN-3 coregulator maintains adaptive capacity to different diets in <i>Caenorhabditis elegans</i> through vitamin B12

Diet has profound effects on metabolism and health, requiring animals to adapt their physiology to varying food sources. Here we show that the conserved SIN3 transcriptional coregulator is required in Caehnorhabditis elegans for animals to adapt to different bacterial diets. Shifting sin-3 mutant animals from the commonly used E. coli OP50 strain to the E. coli HT115 strain used for RNAi knockdown experiments has a dramatic impact on survival, leading to the lethality of mutant animals at the young adult stage. A major difference between OP50 and HT115 is vitamin B12 content, which is lower in OP50 than HT115. Feeding sin-3 mutant animals on OP50 bacteria supplemented with vitamin B12 reproduced the lethality observed on HT115. Vitamin B12 functions in two metabolic pathways: the canonical propionate breakdown pathway and the methionine/S-adenosylmethionine (met/SAM) cycle. Loss of metr-1, encoding the methionine synthase enzyme that requires vitamin B12 as a cofactor in the met/SAM cycle repressed lethality on HT115. Conversely, complementation with metabolites of the met/SAM cycle enhanced lethality on OP50. These results show that SIN-3 is required for animals to adapt to dietary changes through B12-dependent metabolic pathways.