Enterobacter sp. A11 and Comamonas sp. A23 were isolated and identified. Coculturing these two strains with Cd­(II) led to the production of biofilm, H2S, and succinic acid (SA), and Cd­(II) was adsorbed by cells and formed CdS precipitates. After centrifugation, 97% Cd­(II) was removed from the coculture. Proteomic and metabolomic analyses of the cocultured bacteria revealed that H2S and SA production pathways, metal transportation, and TCA cycle were active under Cd­(II) stress. In vitro addition of SA enhanced the production of H2S and biofilm formation and Cd­(II) adsorption. Two-season greenhouse pot experiments with Brassica rapa L. were performed with and without the coculture bacteria. Compared with the control, the average Cd amounts of the two-season pot experiments of the aboveground plants were decreased by 71.3%, 62.8%, and 38.6%, and the nonbioavailable and immobilized Cd in the soils were increased by 211.8%, 213.4%, and 116.7%, for low-, medium-, and high- Cd-spiked soils, respectively. The two strains survived well in soil during plant growth using plate counting, quantitative real-time PCR, and metagenomics analysis. Our results indicate that the combination of Enterobacter and Comamonas strains with the production of H2S and biofilm are important effectors for the highly efficient immobilization of Cd.

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The accumulation of cadmium (Cd) in plants is strongly impacted by soil microbes, but its mechanism remains poorly understood. Here, we report the mechanism of reduced Cd accumulation in rice by coculture of Enterobacter and Comamonas. In pot experiments, inoculation with the coculture decreased Cd content in rice grain and increased non-bioavailable Cd amount in Cd-spiked soils. Fluorescence in situ hybridization (FISH) and scanning electron microscopy (SEM) detection showed that the coculture colonized in the rhizosphere and rice roots’ vascular tissue and intercellular space. Soil metagenomics data showed that the coculture increased the abundance of sulfate reduction and biofilm formation genes and related bacterial species. Moreover, the coculture increased the content of organic matter, available nitrogen, and potassium, and increased the activities of arylsulfatase, β-galactosidase, phenoloxidase, arylamidase, urease, dehydrogenase, and peroxidase in soils. In subsequent rice transcriptomics assays, we found that the inoculation with coculture activated hypersensitive response, defense-related induction, and MAPK signaling pathway in rice. Heterologous protein expression in yeast confirmed the function of four Cd binding proteins (HIP28–1, HIP28–4, BCP2, and CID8), a Cd efflux protein (BCP1), and three Cd uptake proteins (COPT4, NRAM5, and HKT6) in rice. Succinic acid and phenylalanine were subsequently proved to inhibit rice Cd(II) uptake and activate Cd(II) efflux in rice roots. Thus, we propose a model that the coculture protects rice against Cd stress via Cd immobilization in soils and reducing Cd uptake in rice.

Novel biodegradable films were prepared via blending of poly (vinyl alcohol) and waste mycelium from sauce residue and citric acid fermentation residue, respectively. The performance of these two types of films when used as alternative covers for pak-choi growth under semiarid climatic conditions was evaluated via field test towards their abilities for water retention and biodegradation, together with the impact on the yield and nutritional quality of pak-choi. Experimental results showed that the use of these films could result in 50% higher water retention than a blank control film after 96-h treatment at 40°C. Films were biodegraded within 14 weeks under natural conditions, leading to a significant mineralization, progressively releasing over 56% of K ? , NO 3 -, Mg 2? and organics, beneficial for plant growth as fertilizer. The yield of pakchoi was increased by 80% in weight when using these films compared with the unmulched control. Compared to those treated with traditional LDPE mulching film, the average contents of chlorophyll, crude protein and soluble sugar in pak-choi were increased by 52.9, 7.2, 80.7% (blends of sauce residue) and 26.7, 11.4, 10.8% (blends of citric acid fermentation residue), respectively.

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