In recent years, there has been significant progress in the biological synthesis of nanomaterials. However, the molecular mechanism of gold biomineralization in microorganisms of industrial relevance remains largely unexplored. Here we describe the biosynthesis mechanism of gold nanoparticles (AuNPs) in the fungus Rhizopus oryzae . Reduction of AuCl(4)(-) [Au(III)] to nanoparticulate Au(0) (AuNPs) occurs in both the cell wall and cytoplasmic region of R. oryzae . The average size of the as-synthesized AuNPs is ~15 nm. The biomineralization occurs through adsorption, initial reduction to Au(I), followed by complexation [Au(I) complexes], and final reduction to Au(0). Subtoxic concentrations (up to 130 μM) of AuCl(4)(-) in the growth medium increase growth of R. oryzae and induce two stress response proteins while simultaneously down-regulating two other proteins. The induction increases mycelial growth, protein yield, and AuNP biosynthesis. At higher Au(III) concentrations (>130 μM), both mycelial and protein yield decrease and damages to the cellular ultrastructure are observed, likely due to the toxic effect of Au(III). Protein profile analysis also confirms the gold toxicity on R. oryzae at high concentrations. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis shows that two proteins of 45 and 42 kDa participate in gold reduction, while an 80 kDa protein serves as a capping agent in AuNP biosynthesis.

Aquaculture sediments are a purported sizable pool of antibiotic resistance genes (ARGs). However, the pathways for transmission of ARGs from sediments to animals and humans remain unclear. We conducted an ARG survey in sediments from a bullfrog production facility located in Guangdong, China, and simulated zebrafish breeding systems were constructed, with or without biochar addition in sediments, to explore the effects of biochar on ARGs and their precursors of the sediment and zebrafish gut. After 60 days, 6 subtypes of ARGs and intI1 were detected, with sediments harboring more ARGs than zebrafish gut. The addition of biochar reduced the abundance of ARGs in the sediment and zebrafish gut, as well as suppressed the horizontal transmission of ARGs from sediment to zebrafish gut. Network analysis and partial least squares path modeling revealed that ARG enrichment was mainly affected by bacterial groups dominated by Nitrospirae, Gemmatimonades, Chloroflexi, and Cyanobacteria and intI1. Our findings provide insights into the transmission of ARGs from sediment to animals and highlight the efficacy of biochar amendments to aquaculture sediments to reduce the transmission of ARGs.

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Microplastics (MPs) and antibiotics are emerging pollutants in aquatic environments. MPs can absorb antibiotics in the environment, resulting in compound pollution. The relationship between the physicochemical properties of aged microplastics and the adsorption of CIP was investigated to assess the control on the fate and transport of CIP in the environment. The adsorption capacity decreased in the following sequence: aged PLA > PLA > aged PE > PE. The experiment data matched the pseudo-secondary dynamics and the Langmuir isotherm model well, implying that adsorption was primarily governed by monolayer chemisorption. When the solution's pH was close to the dissociation constant (pKa) of CIP, the sorption capacity of MPs increased. The greater the concentration of Na+ and fulvic acid, the stronger the inhibition of adsorption. The adsorption effect of microplastics on CIP was more strongly inhibited by norfloxacin (NOR) at lower concentrations (CNOR＜CCIP). Based on the adsorption data, FTIR, and XPS spectra, we demonstrated that the adsorption process was a non-spontaneous heat absorption reaction, with chemical and physical mechanisms including hydrogen bonding, π-π conjugation, ion exchange, and electrostatic interactions controlling it. This study's discovery of the mechanism of interaction between MPs and CIP serves as a foundation for assessing the environmental risk of MPs and antibiotic complex contamination.