Engineering an Ag₂Se@PANi core-shell nanozymes - Klebsiella pasteurii hybrid system with enhanced ammonia synthesis

Microbially mediated nitrogen fixation offers a sustainable and eco-friendly alternative to the energy-intensive Haber-Bosch reaction for ammonia production. However, the efficient conversion of atmospheric nitrogen into ammonia via microorganism remains a notable challenge. In this work, we successfully enhanced ammonia production in Klebsiella pasteurii Sb-24 by integrating polyaniline (PANi) coated Ag₂Se core-shell nanozymes through a self-assembly process and revealed the underlying mechanisms. The results of this investigation revealed that Ag₂Se@PANi nanozymes expedited the logarithmic growth phase of K. pasteurii Sb-24 cells, enhanced nitrogen fixation activity, and effectively reduced reactive oxygen species levels in Sb-24 cells, with more pronounced enhancements observed at 38 °C compared to 28 °C. Upon optimization, the biohybrid system achieved a maximum NH₄⁺ production of 0.48 ± 0.05 μg·mL^-1 at 38 °C, surpassing the output of pure bacterium by 333 %. Further exploration into interfacial electron transfer mechanisms uncovered that Ag₂Se@PANi nanozymes efficiently facilitated electron transfer into K. pasteurii Sb-24 cells at 38 °C. These findings were corroborated by the upregulation of proteins involved in nitrogen fixation (i.e. Mo-Fe protein) and electron transfer as identified in the proteomic analysis. This study presents an effective strategy to enhancing ammonia production using PANi-based thermoelectric composites and lays a solid foundation for future research into the biomanufacturing using hybrid systems.