Synthesis of silver nanoparticles using living electroactive biofilm protected by polydopamine

Enhanced Stability and Detection Range of Microbial Electrochemical Biotoxicity Sensor by Polydopamine Encapsulation

With the rapid development of modern industry, it is urgently needed to measure the biotoxicity of complex chemicals. Microbial electrochemical biotoxicity sensors are an attractive technology; however, their application is usually limited by their stability and reusability after measurements. Here, we improve their performance by encapsulating the electroactive biofilm with polydopamine (PDA), and we evaluate the improvement by different concentrations of heavy metal ions (Cu2+, Ag+, and Fe3+) in terms of inhibition ratio (IR) and durability. Results indicate that the PDA-encapsulated sensor exhibits a more significant detection concentration than the control group, with a 3-fold increase for Cu2+ and a 1.5-fold increase for Ag+. Moreover, it achieves 15 more continuous toxicity tests than the control group, maintaining high electrochemical activity even after continuous toxicity impacts. Images from a confocal laser scanning microscope reveal that the PDA encapsulation protects the activity of the electroactive biofilm. The study, thus, demonstrates that PDA encapsulation is efficacious in improving the performance of microbial electrochemical biotoxicity sensors, which can extend its application to more complex media.

Biosynthesis of silver nanoparticles using Burkholderia contaminans ZCC and mechanistic analysis at the proteome level

The biogenic synthesis of silver nanoparticles (AgNPs) by microorganisms has been a subject of increasing attention. Despite extensive studies on this biosynthetic pathway, the mechanisms underlying the involvement of proteins and enzymes in AgNPs production have not been fully explored. Herein, we reported that Burkholderia contaminans ZCC was able to reduce Ag+ to AgNPs with a diameter of (10±5) nm inside the cell. Exposure of B. contaminans ZCC to Ag+ ions led to significant changes in the functional groups of cellular proteins, with approximately 5.72% of the (C-OH) bonds being converted to (C-C/C-H) (3.61%) and CO (2.11%) bonds, and 4.52% of the CO (carbonyl) bonds being converted to (C-OH) bonds. Furthermore, the presence of Ag+ and AgNPs induced the ability of extracellular electron transfer for ZCC cells via specific membrane proteins, but this did not occur in the absence of Ag+ ions. Proteomic analysis of the proteins and enzymes involved in heavy metal efflux systems, protein secretion system, oxidative phosphorylation, intracellular electron transfer chain, and glutathione metabolism suggests that glutathione S-transferase and ubiquinol-cytochrome c reductase iron-sulfur subunit play importance roles in the biosynthesis of AgNPs. These findings contribute to a deeper understanding of the functions exerted by glutathione S-transferase and ferredoxin-thioredoxin reductase iron-sulfur subunits in the biogenesis of AgNPs, thereby hold immense potential for optimizing biotechnological techniques aimed at enhancing the yield and purity of biosynthetic AgNPs.

Endogenous electric field accelerates phenol degradation in bioelectrochemical systems with reduced electrode spacing

Reducing the electrode spacing in bioelectrochemical systems (BESs) are widely reported to improve power output, which was mainly attributed to the decrease of ohmic resistance (R_ohm) for a long time. Here we found the change of endogenous electric field (EF) intensity was the key to improve electroactivity in response to a reduced electrode spacing, which also accelerated phenol biodegradation. Correlation and principal components analysis revealed that the microbial community of electroactive biofilm (EAB) was independent of R_ohm, while the EF intensity was found closely related to most of predominant genera. A strong EF selectively enriched phenol-degrading bacteria Comamonas in suspension and Geobacter in EAB, contributed to the improvement of degradation efficiency. EF also induced the secretion of extracellular polymeric substances, protected EAB from being inactivated by phenol. Our findings highlighted the importance of EF intensity on BESs performance, providing new insights into the design and application of BESs in wastewater treatment.