Genome-centric metagenomics revealed the effect of pH on the microbiome involved in short-chain fatty acids and ethanol production

Added-value chemicals production via food waste (FWs) valorization using open-mixed cultures is an emerging approach to replace petrochemical-based compounds. Nevertheless, the effects of operational parameters on the product spectrum remain uncertain given the wide number of co-occurring species and metabolisms. In this study, the identification of 58 metagenome-assembled genomes and their investigation assessed the effect of slight pH variations on microbial dynamics and the corresponding functions when FWs were subjected to anaerobic fermentation (AF) in 1-L continuous stirred tank reactors at 25 °C. The initial pH of 6.5 promoted a microbial community involved in acetate, butyrate and ethanol production, mediated by Bifidobacterium subtile IE007 and Eubacteriaceae IE027 as main species. A slight pH decrease to 6.1 shaped microbial functions that resulted in caproate and H₂ production, increasing the relevance of Eubacteriaceae IE037 role. This study elucidated the strong pH effect on product outputs when minimal variations take place in AF.