Mechanistic insight into enhancement of undissolved rice husk biochar on Tetracycline biodegradation by strain Serratia marcescens basing on electron transfer response

Undissolved biochar (UBC) plays a key role in persistently affecting bacterial characteristics after loss of dissolved biochar. However, its potential role as electron shuttle mediating tetracycline (TC) removal by bacteria is less understood. Result demonstrated UBC (700°C) coupled strain MSM2304 resulted in 72.19% of TC biodegradation (37.76% in free cells). UBC improved nutrients usage of TOC and TN to enhance cells proliferation, and facilitated biofilms formation and secretion of redox-active-related extracellular polymeric substances (EPS) including protein (40% higher) and humus (30% higher). Moreover, UBC optimized cells oxidative stress indicators including reactive oxygen species (40% lower), total antioxidant capacity (30% higher), superoxide dismutase (35% higher), and catalase (30% higher) during TC exposure. Importantly, UBC not only accelerated electron transfer from intracellular into extracellular by stimulating cytochrome C reductase activity and cytochrome C development, also decreased extracellular electron transfer resistance between MSM2304 and TC from 231.7 to 109.5 Ω, proved by cyclic voltammetry and electrochemical impedance spectra of EPS, and helped quinone moieties formation on UBC through C=O and C=C or C=O production determined by FTIR and XPS. These findings indicate UBC could be as electron shuttle and contribute to provide a better understanding of interactions between biochar and microorganism.