Correlation-guided discovery of non-canonical succinate producers from mixed culture fermentation

In microbial communities, the taxa responsible for producing specific metabolites are often unknown, even when those metabolites accumulate consistently, and the community members that support or compete with this process remain poorly understood. This study aimed to identify taxa associated with succinate accumulation in mixed culture fermentation by correlating succinate concentrations with full-length rRNA operon amplicon profiles of microbial communities from bioreactors fed the organic fraction of municipal solid waste. The four OTUs associated with succinate were affiliated with Clostridium butyricum, Lactiplantibacillus plantarum, Leuconostoc gelidum, and Dysosmobacter welbionis. All tested strains produced succinate in axenic cultures, suggesting the corresponding taxa plausibly contributed to the original community, although their activity in mixed culture and its modulation by community interactions remain to be determined. L. plantarum demonstrated the highest succinate-producing capacity, reaching 1.27 ± 0.01 mM in modified MRS medium, supplemented with NaHCO₃ (2 g/L). L. gelidum and D. welbionis produced up to 0.90 ± 0.00 and 0.82 ± 0.06 mM of succinate in MRS medium, followed by C. butyricum at 0.16 ± 0.02 mM in mineral medium supplemented with organic waste fraction. This approach enabled the identification of taxa not previously associated with succinate production, and provides a route to prioritise candidate producers in undefined mixed cultures for isolation, co-culture and synthetic community studies.