Mechanistic insight into enhanced methyl orange degradation by Raoultella planticola/MoS2 biohybrid: implication for electron transfer and microbial metabolism

The biodecolorization of traditional azo dyes is typically hindered by low electron transfer rate, a challenge that can be addressed by incorporating nanoparticles with redox properties to establish a stable biohybrid system. Here, a surface precipitated R. planticola/MoS2 biohybrid characterized by excellent biocompatibility was developed. The findings revealed that hybrid molybdic sulfide (MoS2) at concentrations ranging from 0.1 to 0.7 mM facilitated the biodecolorization of methyl orange (MO), with the R. planticola/MoS2(0.5mM) exhibiting the highest decolorization efficiency. The levels of nicotinamide adenine dinucleotide (NADH), adenosine triphosphate (ATP) in the R. planticola/MoS2 biohybrid increased by 92.08%, 42.61%, respectively, indicating a significant enhancement in microbial metabolic activity. Moreover, the electron transfer system activity (ETSA) of the biohybrid increased by 85.89%, accompanied by a decrease in charge transfer resistance, while MoS2 may involved in and contributed to a notable improvement in the electron transfer capability of the system. Structural equation modeling analysis showed a significant correlation between the R.planticola/MoS2 with extracellular polymeric substances (EPS) and antioxidant stress capacity, with standardized path coefficients of 0.837 and 0.999, respectively, indicating enhanced environmental adaptability of R. planticola. Even after 4 cycles of decolorization, the efficiency remained above 90%, demonstrating good stability. This study comprehensively elucidated the synergistic promotion mechanism of the R. planticola/MoS2 in enhancing MO biodegradation through enhancements in microbial metabolic activity and electron transfer capacity. The findings present a novel strategy for accelerating the biodecolorization of azo dyes and deepening the understanding of the interactions between nanomaterials and microorganisms.