Carbon source-dependent activation of herbicide-mixture degradation in a synthetic microbial community enriched from black soil

The extensive use of herbicides in agriculture has resulted in persistent soil contamination. Although microbial degradation of single herbicides has been extensively investigated, the responses and co-metabolism of microbial consortia to complex herbicide mixtures remain unclear. This study aimed to investigate the influence of a simple carbon source (glucose) on herbicide degradation by a natural microbial consortium (NMC) and identify key degraders for constructing an efficient synthetic microbial community (SynCom). An NMC enriched from herbicide-stressed agricultural black soil in Northeast China was inoculated into mineral salt media containing a mixture of herbicides (atrazine, nicosulfuron and mesotrione) as the sole carbon/nitrogen source, without (MSM) or with glucose supplementation (GSM). Significant herbicide degradation occurred only in the GSM system, with degradation rates of 97.27% for nicosulfuron, 68.00% for mesotrione, and 22.91% for atrazine after 8 days. Integrated 16S rRNA gene sequencing and metagenomic analysis linked the glucose amendment to a specific shift in the microbial community structure and activation of central carbon metabolism (tricarboxylic acid [TCA] and glycolytic), which enhanced cellular energy supply and environmental acidification for co-metabolic degradation of herbicides. In contrast, metabolism in the MSM system was biased toward biosynthesis. Combined random forest (RF) and co-occurrence network analyses identified the Burkholderia-Caballeronia-Paraburkholderia complex, Rhodanobacter , and Achromobacter as the keystone taxa. Metagenomic screening showed that these taxa were enriched for functional genes associated with herbicide degradation, including atzF (allophanate hydrolase) and gst (glutathione S-transferase). A simplified four-isolate SynCom, constructed based on these functional associations, degraded the herbicide mixtures more efficiently than either the individual isolates or the NMC in the GSM system. These findings elucidate the role of labile carbon in driving the co-metabolism of complex herbicides and provide direct candidate strains and a construction strategy, facilitating practical bioremediation applications.