Microbiome dynamics during anaerobic digestion of food waste and the genetic potential for poly (lactic acid) co-digestion

Anaerobic digestion of food waste (FW) and potential co-digestion with biodegradable packaging material (i.e., bioplastics) have been promising resource recovery strategies. Unveiling the microbiome dynamics involved in the digestion process and exploring the genetic potential for poly (lactic acid) hydrolysis therein provide the fundamental basis for further process control and optimization. The current study has shown that the FW-digesting microbiome changed in both composition and activity-dormancy status while consuming available substrates. The microbiome assembly was mainly driven by homogeneous selection (36.7% on average) and drift (59.5% on average), and the homogeneous selection effect scaled with the availability of substrates. Based on the ratio between the relative activity and abundance, the microbiome was clustered into four groups. The Group 1 microbes, including Bacterioidetes_vadinHA17 and Syntrophomonadaceae, accumulated high relative abundance during the early stage of the digestion process but entered dormancy after the preferred substrate was consumed. Other members, i.e., the Group 4 Syntrophobacteraceae and Pseudomonadaceae, showed low abundance but disproportional activity during the later stage of the digestion process. The genome-centric metagenomics revealed that inherent AD microbes, especially the Group 1 microbes, harbored robust hydrolase genes, facilitating the PLA degradation. In fact, PLA addition to FW digestor led to significant methane production enhancement (14%) but negligible changes in microbiome composition. The outcome of this study provided the theoretical basis for developing microbiome management and engineering strategies that prospect efficient FW and PLA co-digestion processes.