Background: Heavy metal pollution has become a major source of environmental pollution because of increasing industrialization. Microbial remediation is a promising approach to remediate lead-contaminated environments owing to its cost-effective, environment-friendly, ecologically sustainable, and highly efficient properties. In this study, the growth-promoting functions and lead-adsorption ability of Bacillus cereus SEM-15 were examined, and the functional mechanism of the strain was preliminarily identified using scanning electron microscopy, energy spectrum, infrared spectrum, and genome analyses, providing theoretical support for utilization of B. cereus SEM-15 in heavy metals remediation. Results: B. cereus SEM-15 showed strong ability to dissolve inorganic phosphorus and secrete indole-3-acetic acid. The lead adsorption efficiency of the strain at lead ion concentration of 150 mg/L was more than 93%. Single factor analysis revealed the optimal conditions for heavy metal adsorption by B. cereus SEM-15 (adsorption time, initial lead ion concentration, pH, and inoculum amount were 10 min, 50–150 mg/L, 6–7, and 5 g/L, respectively) in nutrient-free environment, with the lead adsorption rate reaching 96.58%. Scanning electron microscopy of B. cereus SEM-15 cells before and after lead adsorption showed adherence of a large number of granular precipitates to the cell surface after lead adsorption. X-Ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results indicated the characteristic peaks of Pb–O, Pb–O-R (R = functional group), and Pb–S bonds after lead adsorption, and a shift in the characteristic peaks of bonds and groups related to C, N, and O. Genome annotation results showed the presence of genes related to heavy metals tolerance and plant growth promotion in B. cereus SEM-15, providing a molecular basis for the strain’s heavy metals tolerance and plant growth promotion functions. Conclusions: This study analyzed the lead adsorption characteristics of B. cereus SEM-15 and the associated influencing factors, and discussed the adsorption mechanism and related functional genes, providing a basis for clarifying the underlying molecular mechanism and offering a reference for further research on plant-microorganisms combined remediation of heavy metals polluted environments.

Plant nonspecific lipid transfer proteins (nsLTPs) are involved in a number of biological processes including root nodule symbiosis. However, the role of nsLTPs in legume-rhizobium symbiosis remains poorly understood, and no rhizobia proteins that interact with nsLTPs have been reported to date. In this study, we used a bacteria two-hybrid system and identified the high temperature protein G (HtpG) from Mesorhizobium huakuii that interacts with the nsLTP AsE246. The interaction between HtpG and AsE246 was confirmed by far-Western blotting and bimolecular fluorescence complementation. Our results indicated that the heat shock protein 90 (HSP90) domain of HtpG mediates the HtpG-AsE246 interaction. Immunofluorescence assay showed that HtpG was colocalized with AsE246 in infected nodule cells and symbiosome membranes. Expression of the htpG gene was relatively higher in young nodules and was highly expressed in the infection zones. Further investigation showed that htpG expression affects lipid abundance and profiles in root nodules and plays an essential role in nodule development and nitrogen fixation. Our findings provide further insights into the functional mechanisms behind the transport of symbiosome lipids via nsLTPs in root nodules.

Rhizobia are rod-shaped bacteria that form nitrogen-fixing root nodules on leguminous plants; however, they don’t carry MreB, a key determinant of rod-like cell shape. Here, we introduced an actin-like mreB homolog from a pseudomonad into Mesorhizobium huakuii 7653R (a microsymbiont of Astragalus sinicus L.) and examined the molecular, cellular, and symbiotic phenotypes of the resultant mutant. Exogenous mreB caused an enlarged cell size and slower growth in laboratory medium. However, the mutant formed small, ineffective nodules on A. sinicus (Nod⁺ Fix⁻), and rhizobial cells in the infection zone were unable to differentiate into bacteroids. RNA sequencing analysis also revealed minor effects of mreB on global gene expression in free-living cells but larger effects for cells grown in planta. Differentially expressed nodule-specific genes include cell cycle regulators such as the tubulin-like ftsZ₁ and ftsZ₂. Unlike the ubiquitous FtsZ₁, an FtsZ₂ homolog was commonly found in Rhizobium, Sinorhizobium, and Mesorhizobium spp. but not in closely related nonsymbiotic species. Bacterial two-hybrid analysis revealed that MreB interacts with FtsZ₁ and FtsZ₂, which are targeted by the host-derived nodule-specific cysteine-rich peptides. Significantly, MreB mutation D283A disrupted the protein–protein interactions and restored the aforementioned phenotypic defects caused by MreB in M. huakuii. Together, our data indicate that MreB is detrimental for modern rhizobia and its interaction with FtsZ₁ and FtsZ₂ causes the symbiotic process to cease at the late stage of bacteroid differentiation. These findings led to a hypothesis that loss of mreB in the common ancestor of members of Rhizobiales and subsequent acquisition of ftsZ₂ are critical evolutionary steps leading to legume-rhizobial symbiosis. [ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Background: The hypoglycemic activity of mulberry leaf polyphenols has been widely studied, while its mechanism of action needs further elucidation. Methods: The inhibitory activity mechanism of astragalin on α-glucosidase was investigated with a combination of multispectroscopic techniques and molecular docking. The hypoglycemic pathway was further revealed with a high-glucose human hepatocellular carcinomas (HepG2) cell model. Results: The results indicated that astragalin inhibited α-glucosidase with IC₅₀ of 154.5 µM, which was the highest in potency among the main polyphenols from mulberry leaves. Astragalin could bind to α-glucosidase with a single inhibition site and quench its endofluorescence with a static quenching mechanism. Astragalin changed the secondary structure of α-glucosidase, and the decreased α-helix content, representing the un-folding conformation, resulted in the decreased activity. The molecular docking further indicated that two sustainable hydrogen bonds were generated between astragalin and α-glucosidase residue Ser-88 and Tyr-133. The main driving forces to form the astragalin-α-glucosidase complex were the van der Waals force and hydrogen bond. Astragalin at a concentration of 80 µg/mL obtained the best hypoglycemic effect by activating the Adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway. Conclusions: This study provides new insights into the potential utilization of astragalin-rich foods in the improvement of diabetes mellitus.

Legumes in the inverted repeat-lacking clade (IRLC) each produce a unique set of nodule-specific cysteine-rich (NCR) peptides, which act in concert to determine the terminal differentiation of nitrogen-fixing bacteroid. IRLC legumes differ greatly in their numbers of NCR and sequence diversity. This raises the significant question how bacteroid differentiation is collectively controlled by the specific NCR repertoire of an IRLC legume. Astragalus sinicus is an IRLC legume that forms indeterminate nodules with its microsymbiont Mesorhizobium huakuii 7653R. Here, we performed transcriptome analysis of root and nodule samples at 3, 7, 14, 28 days postinoculation with M. huakuii 7653R and its isogenic ∆ bacA mutant. BacA is a broad-specificity peptide transporter required for the host-derived NCRs to target rhizobial cells. A total of 167 NCRs were identified in the RNA transcripts. Comparative sequence and electrochemical analysis revealed that A. sinicus NCRs (AsNCRs) are dominated by a unique cationic group (termed subgroup C), whose mature portion is relatively long (>60 amino acids) and phylogenetically distinct and possessing six highly conserved cysteine residues. Subsequent functional characterization showed that a 7653R variant harboring AsNCR083 (a representative of subgroup C AsNCR) displayed significant growth inhibition in laboratory media and formed ineffective white nodules on A. sinicus with irregular symbiosomes. Finally, bacterial two-hybrid analysis led to the identification of GroEL1 and GroEL3 as the molecular targets of AsNCR067 and AsNCR076. Together, our data contribute to a systematic understanding of the NCR repertoire associated with the A. sinicus and M. huakuii symbiosis. [ ] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

This study examined the effects of dietary silkworm pupae powder (SWP) supplementation on the growth performance, muscle fatty acid composition, and intestinal function in mandarin fish (Siniperca chuatsi) during a 60-day feeding trial. A total of 360 fish (initial body weight 52.44 ± 0.06 g) were distributed randomly into three groups with three replicates per group and 40 fish per replicate. The three groups were fed either the basal diet, supplementation with 1.0 % fermented SWP (T1), or supplementation with 1.0 % fermented induced SWP (T2, induced by Beauveria bassiana). Results showed that fish fed T1 had significantly higher (P < 0.05) condition factor, C16:0, C20:4n-6, C20:5 n3, C22:6n3 C22:5n6, C22:5n-3, and n-3/n-6 levels, but lower (P < 0.05) fat body ratio, C18:1, C18:2n-6 and crude lipid levels than those fish fed basal diet. All fish had similar (P > 0.05) weight gain rate, specific growth rate, feed conversion rate, feed intake, and hepatosomatic index. Fish fed T2 had higher (P < 0.05) trypsin activity than those fish fed basal diet. Compared with the basal diet, fish fed T1 or T2 had higher (P < 0.05) villus length, muscular layer thickness, glutathione peroxidase, alkaline phosphatase, and lysozyme activities, but lower (P < 0.05) triglyceride and total cholesterol levels. Comparative transcriptomic analysis indicated that T1 or T2 enhanced immunity and lipid metabolism ability, as manifested in the up-regulated expression of il12rb1, scdb, tlr2, and FABP7, and the down-regulated expression of EBP and hsd17b7. These findings suggest that dietary supplementation with fermented SWP could enhance the health and quality of mandarin fish, potentially offering a valuable strategy for improving aquaculture productivity.