Genome-Centric Metagenomics and Metaproteomics Profiled the Shared and Unique Taxa in Isomeric Fatty Acid-Differentiated Anaerobic Co-Digestion of Food Waste and Sludge

Fatty acids (FAs)-involving structures, widely occurring in production and life, have been increasingly considered as major feedstocks and potential platforms for renewable energy generation. However, the role of isomeric FAs (particularly trans-FAs) in high-concerned energy-reserving technology represented by anaerobic digestion (AD) remains unclear. This study displayed that trans-oleic acid (TOA, 10 mg/L) significantly increased methane production by 56% during the codigestion of food waste and sludge, whereas the same concentration of cis-oleic acid (COA) led to a slight 20% increase. Genome-centric meta-omics and biochemical tests indicated that acidogenic taxa that harbor and express distinct functions in the cell envelopes were primarily responsible for TOA/COA-differentiated AD. Four shared taxa, including three monodermal acidogens and one hydrogenotrophic methanogen, were common drivers of both TOA- and COA-enhanced AD, resulting in stronger acidification and hydrogenotrophic methanogenesis than in the control bioreactor without oleic acid. In addition to four shared species, two unique didermal acidogens were specific drivers of TOA-enhanced AD, demonstrating more robust acidification compared to that of COA-enhanced AD. This study profiled the geometry-dependent effects of isomeric FAs on AD, providing new insights into targeted regulation for energy conservation and decarbonization of FAs-involving feedstocks.