A preliminary metatranscriptomic insight of eggshells conditioning on substrates metabolism during food wastes anaerobic fermentation

The anaerobic treatment of food wastes (FW) for resource recovery has been extensively studied. However, the information on the traits of functional genes and enzymes for substrates metabolisms and their associations with microbial community are little. In this study, the influences of eggshells conditioning on the substrates metabolism for volatile fatty acids production (VFAs) in the process of FW fermentation were investigated at genetic levels by using the metatranscriptomic approach. The obtained results suggested that the critical genes involved in the carbohydrate and protein metabolisms (i.e. pgmB, GPI, glsA, pyrB and etc.) were up-regulated in the eggshell-conditioned reactor, which were beneficial to the bioconversion of macromolecule organics during FW fermentation. Moreover, the functional genes related with the intermediate products metabolism (i.e. pyruvate acid, butanoate) also exhibited differential genetic expression levels, which resulted in the alteration of microbial metabolic pathways and contributed to the acetic and butyric acids accumulation. In addition, a preliminary association of microbial distribution and genetic expressions was analyzed. The distinct distribution of microbial community in different FW fermentation systems affected the corresponding microbial contribution to those genetic expression levels of metabolic enzymes involved in VFAs production. This study would provide new insights of the underlying mechanism of VFAs promotion in the eggshell-conditioned FW fermentation process from the perspectives of substrates metabolisms at genetic and functional traits.