Alkaline environments benefit microbial K-strategists to efficiently utilize protein substrate and promote valorization of protein waste into short-chain fatty acids

Anaerobic bioconversion of protein into short-chain fatty acids (SCFAs) can help reduce the vast quantities of protein waste generated currently and provide precursors for biorefineries of value-added, renewable chemicals or fuels. However, low yields of SCFAs during this process have limited its application, since the underlying mechanism is not fully understood. Herein, we investigated the chemical and microbiological mechanisms of a combined heat-alkaline pretreatment and anaerobic alkaline fermentation scheme for protein conversion to SCFAs. A series of chemical analyses indicated that heat-alkaline pretreatment fragmented native proteins and induced protein unfolding, thus increasing the amount of readily biodegradable proteins. Further, microbial characterization, using the r-K life history theory, indicated that microbial K-strategists, such as Proteobacteria, have adapted to the alkaline fermentation environment and enriched the process of converting protein substrates, which corresponded to an improved acetate production. We also evaluated the technological and economic feasibility of utilizing Proteiniphilum acetatigenes to augment the process of SCFA generation from sewage sludge (a protein-rich waste). Our findings demonstrated the influence of chemical and biological process manipulations on microbial assembly structures and ecological strategies, supporting the further development of waste-to-profit technologies.