Enhanced tetracycline degradation through electron transfer activated by Bacillus cereus synthesized bio-FeS nanoparticles

The synthesis of bio-FeS nanoparticles (NPs) was generally using Gram-negative bacteria and mostly in anaerobic systems, thus limiting their application in the degradation of toxic wastewater. In this study, we successfully synthesized bio-FeS NPs for the first time using the resilient Gram-positive bacterium Bacillus cereus, with the objective of investigating the mechanism of promoting electron transfer in the aerobic/anaerobic degradation of tetracycline (TC). The degradation efficiency of TC was increased by 2.84 and 4.74 times, respectively, under aerobic and anaerobic conditions. Furthermore, the bio-FeS NPs were observed to significantly reduce the activation energy and Gibbs free energy, especially under aerobic conditions. It was found that bio-FeS NPs promoted intracellular electron transfer mainly through activating or replacing the Fe-S centers. The bio-FeS NPs significantly increased ETS activity and NADH levels, indicating that the dehydrogenase activity and intracellular electron transfer efficiency were increased. The bio-FeS NPs formed electron transfer channels inside and outside the cell, provided an effective way for the transfer of electron shuttles from intracellular to extracellular, and improved the extracellular redox activity. This study offered new insights and theories into the role of Gram-positive bacteria in the synthesis of bio-FeS NPs for the remediation of toxic wastewater.