Earthworm gut bacteria facilitate cadmium immobilization through the formation of CdS nanoparticles.

Gut bacteria of earthworm Amynthas hupeiensis exhibit significant potential for the in-situ remediation of cadmium (Cd)-contaminated soil. However, the mechanisms by which these gut bacteria immobilize and tolerate Cd remain elusive. The composition of the gut bacterial community was characterized by high-throughput sequencing. Cd-tolerant bacteria were isolated from the gut, and their roles in Cd immobilization, as well as their tolerance mechanisms, were explored through chemical characterization and transcriptome analysis. The predominant taxa in the gut bacterial community included unclassified Enterobacteriaceae, Citrobacter, and Bacillus, which were distinctly different from those in the surrounding soil. Notably, the most Cd-tolerant gut bacterium, Citrobacter freundii DS strain, immobilized 63.61% of Cd2+ within 96 h through extracellular biosorption and intracellular bioaccumulation of biosynthetic CdS nanoparticles, and modulation of solution pH and NH4+ concentration. Moreover, the characteristic signals of CdS were also observed in the gut content of A. hupeiensis when the sterilized Cd-contaminated soil was inoculated with C. freundii. The primary pathways involved in the response of C. freundii to Cd stress included the regulation of ABC transporters, bacterial chemotaxis, cell motility, oxidative phosphorylation, and two-component system. In conclusion, C. freundii facilitates Cd immobilization both in vitro and in vivo, thereby enhancing the host earthworm's adaptation to Cd-contaminated soil.

The toxicity of polystyrene micro- and nano-plastics on rare minnow (Gobiocypris rarus) varies with the particle size and concentration.

How the particle size and concentration of microplastics impact their toxicity is largely unknown. Herein, the effects of polystyrene microplastics (1 µm, MPs) and nanoplastics (100 nm, NPs) exposed at 1 mg/L (L) and 10 mg/L (H), respectively, on the growth, histopathology, oxidative stress, gut microbiome, and metabolism of rare minnow (Gobiocypris rarus) were investigated by chemical analysis and multi-omics. MPs and NPs inhibited the growth, induced histopathological injury and aggravated oxidative stress markedly with contrasting significance of particle size and concentration. The composition of core gut microbiota changed dramatically especially for the MPs-H. Similarly, gut bacterial communities were reshaped by the MPs and NPs but only NPs-H decreased both richness and Shannon indexes significantly. Co-occurrence network analysis revealed that the potential keystone genera underwent great changes in exposed groups compared to the control. MPs-H increased the network complexity and the frequency of positive interactions which was opposite to other exposed groups. Moreover, the metabolomic profiles associated with amino acid, lipid, unsaturated fatty acid and hormone metabolism were disturbed significantly especially for MPs-H and NPs-H. In conclusion, the toxicity of MPs depends on both the particle size and concentration, and varies with the specific indicators as well.