Staged microbial consortium valorizes cattle manure wastewater and promotes maize growth.

Aims: Ammonia-oxidizing bacteria play important roles in nitrogen transformation and agricultural-waste valorization; however, their large-scale application is often limited by high cultivation costs and insufficient functional stability. This study aimed to develop a low-cost and stable microbial consortium for converting cattle manure wastewater into a bioactive fermentation broth and to investigate its underlying mechanisms.

Methods and results: The heterotrophic ammonia-oxidizing bacterium Ensifer sp. S2-8-1 was used as the core strain, and Bacillus subtilis was employed as the auxiliary strain. Three cultivation systems were compared: S2-8-1 monoculture, simultaneous co-culture, and a staged consortium (SYC). Among them, SYC exhibited the best overall performance, maintaining the highest viable bacterial density and reaching 3.93 × 107 CFU ml-1 on day 12. In a soil-maize pot experiment, SYC significantly enhanced rhizosphere nitrification, increased NO3--N availability, and promoted maize growth, resulting in a 41.4% increase in whole-plant dry matter compared with the water control. The consortium also improved photosynthetic performance and cytokinin accumulation. Comparative metatranscriptomic analysis revealed significant upregulation of heterotrophic ammonia oxidation-related genes (CYP450) and cytokinin-related genes (miaA and LOG) in S2-8-1 under SYC conditions, suggesting coordinated activation of nitrogen transformation and plant growth-promoting signaling pathways.

Conclusions: The staged "pre-modification followed by synergy" consortium effectively converts cattle manure wastewater into a stable and bioactive fermentation broth, enhancing both microbial biomass production and plant growth-promoting activity. This strategy provides a scalable approach for livestock wastewater valorization and the development of compound microbial fertilizers.