Metabolic cascade of complex organic wastes to medium-chain carboxylic acids: A review on the state-of-the-art multi-omics analysis for anaerobic chain elongation pathways

Abstract

Medium-chain carboxylic acid (MCCA) production from organic wastes has attracted much attention because of their higher energy contents and diverse applications. Anaerobic reactor microbiomes are stable and resilient and have resulted in efficient performance during many years of operation for thousands of full-scale anaerobic digesters worldwide. The method underlying how the relevant microbial pathways contribute to elongate carbon chains in reactor microbiomes is important. In particular, the reverse β-oxidation pathway genes are critical to upgrading short-chain fermentation products to MCCAs via a chain elongation (CE) process. Diverse genomics and metagenomics studies have been conducted in various fields, ranging from intracellular metabolic pathways to metabolic cascades between different strains. This review covers taxonomic approach to culture processes depending on types of organic wastes and the deeper understanding of genome and metagenome-scale CE pathway construction, and the co-culture and multi-omics technology that should be addressed in future research.