Relative weight of organic waste bacterial community taxa among composts and digestates through 16S rRNA gene profilings and taxonomic inferences

Organic waste (OW) recycling via anaerobic digestion (AD) and/or composting is considered to act as sanitary processes reducing health risks associated with an agricultural use. Even though these treatments are increasingly used, little is known about the impact of the OW origins on the microbiome profiles including pathogenic bacteria found in the end-products. In this study, nine plants were chosen to represent the most common origins of OW (agricultural, urban and central). At first, the impact of treatments was assessed by analyzing changes in OTU profiles inferred from V5-V6 16S rRNA gene sequences. While, digestates OTU profiles could not be differentiated into three categories but into two entities agri/central and urban, composting was found to drive bacterial community towards similar structures. Secondly, to better resolve the genetic structure changes, variations of reads allocated at the genus level are investigated using DESEQ2 analysis. With a significant change of about half of reads against their inferred state among OW, composting was found to drive more bacterial communities towards similar structures than AD treatment. In AD, about one third of the digestate microbiome was significantly affected in each category (agri/central and urban). Despite this similar effect, a remarkable difference depending on OW origins was highlighted. In digestate from urban origin, this microbial shaping was mostly presented in the form of enrichment while in the other one it was in the form of reduction. These results indicating that the OW origins in AD rather than in composting play a crucial role in shaping the microbial communities of end-product. It also highlights to what extent the cells arriving with the influent wastewater and activated sludge directly contributed to the observed diversity in the digestates, at the contrary in the case of OW of agricultural and central origins a lot of genera can' t adapt to the new environment. Finally, based on whole relative abundances of enriched genera covering a common functional trait predicted using MACADAM, enriched functional features were estimated in end-products. Interestingly, the distinctive enriched communities in both digestates (agri/central and urban) shared similar hierarchical functional traits (e.g. chemoheterotrophy, fermentation). In compost, others functional traits such as arsenate detoxification and oil bioremediation could be widely increased. Our findings provide new insights into our perception of the compositions, ecological roles and predicted functional profiles of the microbial community in compost and digestates.