Quinoprotein glucose dehydrogenase (GDH) is the most important enzyme of inorganic phosphorus-dissolving metabolism, catalyzing the oxidation of glucose to gluconic acid. The insoluble phosphate in the sediment is converted into soluble phosphate, facilitating mass reproduction of algae. Therefore, studying the diversity of gcd genes which encode GDH is beneficial to reveal the microbial group that has a significant influence on the eutrophication of water. Taking the eutrophic Sancha Lake sediments as the research object, we acquired samples from six sites in the spring and autumn. A total of 219,778 high-quality sequences were obtained by DNA extraction of microbial groups in sediments, PCR amplification of the gcd gene, and high-throughput sequencing. Six phyla, nine classes, 15 orders, 29 families, 46 genera, and 610 operational taxonomic units (OTUs) were determined, suggesting the high genetic diversity of gcd. Gcd genes came mainly from the genera of Rhizobium (1.63–77.99%), Ensifer (0.13–56.95%), Shinella (0.32–25.49%), and Sinorhizobium (0.16–11.88%) in the phylum of Proteobacteria (25.10–98.85%). The abundance of these dominant gcd-harboring bacteria was higher in the spring than in autumn, suggesting that they have an important effect on the eutrophication of the Sancha Lake. The alpha and beta diversity of gcd genes presented spatial and temporal differences due to different sampling site types and sampling seasons. Pearson correlation analysis and canonical correlation analysis (CCA) showed that the diversity and abundance of gcd genes were significantly correlated with environmental factors such as dissolved oxygen (DO), phosphorus hydrochloride (HCl–P), and dissolved total phosphorus (DTP). OTU composition was significantly correlated with DO, total organic carbon (TOC), and DTP. GDH encoded by gcd genes transformed insoluble phosphate into dissolved phosphate, resulting in the eutrophication of Sancha Lake. The results suggest that gcd genes encoding GDH may play an important role in lake eutrophication.

Inorganic phosphate-solubilizing bacteria (IPB) are an important component of microbial populations in lake sediments. The phosphate that they decompose and release becomes an important source of phosphorus for eutrophic algae. The IPB strains were screened and isolated from the sediments of Sancha Lake using National Botanical Research Institute’s phosphate (NBRIP) plates. Their taxonomy was further determined by the 16S rDNA technique. The tricalcium phosphate-solubilizing ability of obtained IPB strains was evaluated using NBRIP- bromophenol blue (BPB) plates and Pikovskaya (PVK) liquid medium. Then, the ability of IPB strains to release phosphorus from the sediments were investigated by mimicking the lake environment. In this study, a total of 43 IPB strains were screened and isolated from the sediments of Sancha Lake, belonging to three phyla, eight families, and ten genera. Among them, two potentially new strains, SWSI1728 and SWSI1734, belonged to genus Bacillus, and a potentially new strain, SWSI1719, belonged to family Micromonosporaceae. Overall, the IBP strains were highly diverse and Bacillus and Paenibacillus were the dominant genera. In the tricalcium phosphate-solubilizing experiment, only 30 of the 43 IPB strains exhibited clear halo zones on plates, while in the liquid culture experiment, all strains were able to dissolve tricalcium phosphate. The phosphate-solubilizing abilities of the strains varied significantly, and the strain SWSI1725 of the Bacillus genus showed the strongest ability with a phosphate-solubilizing content of 103.57 mg/L. The sterilized systems demonstrated significantly elevated phosphorus hydrochloride (HCl–P) decomposition and release from the sediments after the inoculation of IPB strains, whereas no significant effect was demonstrated on the phosphonium hydroxide (NaOH-P). Thus, the IPB strains in the sediments of Sancha Lake possessed rich diversity and the ability to release phosphorus in sediments.

Biochar was prepared from rabbit faeces at 400°C, 500°C, 600°C, and 700°C, respectively (labelled RFB₄₀₀, RFB₅₀₀, RFB₆₀₀, and RFB₇₀₀, respectively), and was characterized by elemental analysis, BET, SEM and FTIR. The adsorption factors, kinetics, isothermal adsorption and thermodynamics of the adsorption properties were investigated in batch experiments. The results showed that RFB possessed a large specific surface area and was rich in pore structure, and the aromaticity and stability increased with the pyrolysis temperature of the biochar. When the solution pH was 11, adsorption achieved equilibrium at approximately 180 min. The kinetic data were well-represented by the pseudo-second-order model, indicating that the adsorption rate was jointly controlled by liquid film diffusion, surface adsorption and intra-particle diffusion. The results of isothermal adsorption and thermodynamics showed that the adsorption behaviour of CIP (ciprofloxacin) onto RFB was better fitted with the Langmuir model, and the adsorption process was spontaneous and endothermic. FTIR studies showed that RFB was rich in oxygen-containing functional groups and that hydrogen bonds and π-π bonds were closely related to the adsorption process. This work showed that the rabbit faeces-derived biochar has promise as an effective adsorbent to remove ciprofloxacin from wastewater.

A phosphate-solubilizing bacterium, designated CPCC 100624T, was isolated from a freshwater reservoir in south-west China. The 16S rRNA gene sequence comparison of strain CPCC 100624T with the available sequences in the GenBank database showed that the isolate was closely related to members of the genus Spirosoma . In the phylogenetic tree based on 16S rRNA gene sequences, strain CPCC 100624T formed a stable phylogenetic subclade with Spirosoma soli MIMBbqt12T within the genus Spirosoma , which indicated that strain CPCC 100624T could be identified as a member of the genus Spirosoma . The strain grew at 10–40 °C (optimum 30 °C), at pH 6.5–8.0 (optimum pH 7.0–7.5) and in the presence of 0–5 % (w/v) NaCl (optimum 0–1 %). MK-7 was detected as the main menaquinone, with a minor amount of MK-7(H6) in its menaquinone system. Cells contained summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), C16 : 1ω5c and iso-C15 : 0 as the major fatty acids. The polar lipids of strain CPCC 100624T contained phosphatidylethanolamine, one unidentified aminolipid, two aminophospholipids and three unidentified lipids. The genomic DNA G+C content was 49.3 mol%. On the basis of the above taxonomic data and differences in physiological characteristics from the closely related type strains, strain CPCC 100624T represents a novel species of the genus Spirosoma , for which the name Spirosoma lacussanchae sp. nov. is proposed. The type strain is CPCC 100624T (=NBRC 111852T=DSM 101771T).

Biochar was prepared from rabbit faeces (RFB₅₅₀) at 550 °C through pyrolysis and was characterized by performing an Elemental analysis, Scanning Electron Microscope, Brunauer-Emmett-Teller and Fourier Transform Infrared Spectroscopy. The related factors, kinetics, isothermal curves and thermodynamics of the adsorption behaviours were investigated by conducting batch experiments. The results revealed the adsorption equilibrium of Rhodamine B (RhB) and Congo red (CR) onto RFB₅₅₀ with initial concentrations of 30 mg · L⁻¹ at 25 °C and 210 min, and the best adsorption was observed when the pH of the RhB and CR solutions was 3 and 5, respectively. Pseudo-second-order kinetics was the most suitable model for describing the adsorption of RhB and CR onto RFB₅₅₀, indicating that the rate-limiting step was mainly chemical adsorption. The isotherm data were best described by the Freundlich model, and the adsorption process was multi-molecular layer adsorption. Thermodynamic parameters revealed the spontaneous adsorption of RhB and CR onto RFB₅₅₀. According to the results of the FTIR analysis, the oxygen-containing functional groups and aromatic structures on the surface of RFB₅₅₀ provided abundant adsorption sites for RhB and CR, and the adsorption mechanism was potentially related to the hydrogen bonds and π-π bonds.