Heavy metal pollution has attracted increasing attention because of its toxicity, environmental persistence, bioaccumulation, and potential contribution to antibiotic resistance. The accurate, rapid, efficient, and sensitive detection of heavy metals in the environment is of great significance for environmental protection and human health. A whole-cell microbial biosensor (WCMB), integrating a biorecognition module and a signal processing module, provides a new strategy for heavy metal monitoring. Great progress has been achieved in the transcription factor-based WCMBs for the monitoring of heavy metals in recent years. This paper introduced the basic composition and design principles of WCMBs, summarized the construction and application of WCMBs for heavy metal detection that were developed in recent years, analyzed the optimization strategies of WCMBs by synthetic biology, and finally prospected the future research directions of WCMBs. This paper is expected to be an important reference for the effective prevention and control of heavy metal pollution in the environment.

[Objective] To study the probiotic properties and safety of Limosilactobacillus reuteri CHF7-2 isolated from Chahua chicken, providing a theoretical basis for the development of this strain as a microecological feed additive. [Methods] In vitro assays were conducted to evaluate the adhension, enzyme production, antibacterial activity, and antioxidant activity of strain CHF7-2. PacBio Sequel II and Illumina NovaSeq 6000 were used for whole genome sequencing of strain CHF7-2. Bioinformatics tools and databases were then used for genome annotation to explore the probiotic mechanisms and safety of this strain at the molecular level. [Results] Strain CHF7-2 possessed significant probiotic properties and safety. It exhibited high surface hydrophobicity, self-coagulation, and antioxidant activity. The strain inhibited the growth of Escherichia coli K88, Staphylococcus aureus ATCC 49521, Salmonella gallinarum CICC 21510, and Salmonella choleraesuis CVCC 3383. Strain CHF7-2 produced protease and lipase, and it was safe for use in feed since it did not exhibit hemolytic activity. Whole genome sequencing revealed that the genome size of CHF7-2 was 2 116 761 bp, with the G+C content of 38.8%, encoding 2 067 genes. Additionally, the genome carried the biosynthetic gene cluster of the class III bacteriocin EnlA and multiple genes involved in the acid tolerance, bile salt tolerance, heat stress tolerance, cold stress tolerance, adhesion, antioxidation, and organic acid synthesis, with no virulence or antibiotic resistance genes detected. [Conclusion] L. reuteri CHF7-2 is a potential probiotic strain and a promising candidate for use as a microecological feed additive.

[Objective] To develop a DNA vaccine by loading avian pathogenic Escherichia coli ghosts with the fimbrium gene flfA of Gallibacterium anatis and evaluate the immune effect of this vaccine in chickens. [Methods] Taking flfA of G. anatis as the target gene, we constructed the eukaryotic expression plasmid pCAGGS-flfA from the plasmid pCAGGS-HA carrying the chicken β-actin promoter, which enhanced the efficacy of vaccine. The temperature-sensitive plasmid PBV-E-SN was then constructed and transformed into the ampicillin-sensitive avian pathogenic E. coli isolate to prepare a bacterial ghost. Finally, pCAGGS-flfA was loaded into the bacterial ghost to prepare a bacterial ghost vaccine. Seven-day-old chickens were assigned into five groups: bacterial ghost loading pCAGGS-flfA, pCAGGS-flfA, empty bacterial ghost, PBS, and normal control. The primary vaccination was carried out for 7-day-old chickens, and the booster immunization was performed two weeks after the primary immunization. The chickens were challenged with G. anatis four weeks after the primary immunization, and the immune effect of the vaccine was evaluated. [Results] The eukaryotic expression plasmid pCAGGS-flfA was successfully expressed in cells in vitro. The lysis rate of the constructed avian pathogenic E. coli ghosts heated at 42 °C for 210 min reached 99.94%. The specific IgG antibody titer measured by ELISA, the number of shedding bacteria in chicken cloacal swabs and throat swabs, and the bacterial loads in tissue and organs of challenged chickens showed that the immune effects in the bacterial ghost loading pCAGGS-flfA group and the pCAGGS-flfA group were much higher than those in other groups. Moreover, the bacterial ghost loading pCAGGS-flfA showed stronger immune effect than pCAGGS-flfA. [Conclusion] Bacterial ghosts as the carriers of pCAGGS-flfA significantly enhanced the immune effect of the DNA vaccine.

Traditional Chinese Baijiu products can be classified into multiple flavor types such as strong-flavor, light-flavor, soy sauce-flavor, and complex-flavor types. Due to differences in fermentation raw materials, starters, fermentation vessels, fermentation processes, and geographical environments, Baijiu products of different flavor types have unique and complex pit-mud microorganisms. As one of the core microbial groups in the complex microbial community of Baijiu, lactic acid bacteria, whose metabolites lactic acid and its derivatives are important flavor substances in strong-flavor Baijiu, play an important role in the flavor and taste of Baijiu. At present, the research on lactic acid bacteria in the brewing of strong-flavor Baijiu is scattered and not systematic enough. On the basis of our work, we review the research on the role of lactic acid bacteria in the brewing of strong-flavor Baijiu. This review encompasses the isolation and screening of lactic acid bacteria in the brewing of strong-flavor Baijiu by conventional microbiological methods and the in-depth understanding of the role of lactic acid bacteria in the brewing of strong-flavor Baijiu by modern microbiological research methods. Combining traditional with modern microbiological research methods to conduct systematic and in-depth research on lactic acid bacteria in strong-flavor Baijiu based on actual strains can provide references for deeply understanding the role of lactic acid bacteria in the brewing process and then strengthening or optimizing the brewing process.

[Objective] To evaluate the colonization ability and biocontrol effects of Streptomyces sp. ZH-356 with antagonistic effects on plant pathogenic fungi and reveal the biocontrol mechanism of Streptomyces sp. ZH-356 by omics analysis. [Methods] The colonization of Streptomyces sp. ZH-356 in plants was detected by the GFP fluorescent labeling method. The biocontrol effects and potential of Streptomyces sp. ZH-356 on plant fungal diseases were evaluated based on the biocontrol effects of the inoculant in different dosage forms (seed coating agent, wettable powder, gum inoculant, and bone glue inoculant). The whole genome information of Streptomyces sp. ZH-356 was analyzed by third-generation sequencing, and its gene functions were annotated. The comparative transcriptome analysis was performed to screen the differentially expressed genes during the antagonizing process of Streptomyces sp. ZH-356 against plant pathogenic fungi, and thus the genes involved in the synthesis of antagonistic substances were predicted. [Results] Streptomyces sp. ZH-356 stably colonized the roots and stems of tomato and wheat plants. Different dosage forms of inoculants prepared based on Streptomyces sp. ZH-356 demonstrated strong control effects on tomato early blight and apple valsa canker. Among them, the seed coating agent prepared with Streptomyces sp. ZH-356 did not affect the germination rate of tomato seeds after treatment while protecting tomato seedlings from the infection of Alternaria solani. The wettable powder prepared with Streptomyces sp. ZH-356 showed both prevention and treatment effects on tomato early blight, with the prevention effect stronger than the treatment effect. The liquid inoculants prepared from Streptomyces sp. ZH-356 had control effects on apple Valsa canker, regardless of whether the diseased bark was scraped or not, while the control effect was better when the diseased bark was scraped and better than that of thiophanate-methyl. The whole genome sequencing results showed that Streptomyces sp. ZH-356 contained only one linear chromosome with a size of 9 435 898 bp and the average G+C content of 70.82%. A total of 8 432 coding genes, 69 tRNA genes, and 18 rRNA genes were predicted. Species annotation results showed that Streptomyces sp. ZH-356 did not belong to any Streptomyces species whose genome has been sequenced. Genome-wide analysis showed that there were 32 biosynthetic gene clusters (BGCs) for secondary metabolites in ZH-356. Transcriptomic analysis showed that the expression of the NRPS/T1PKS gene cluster ZH_356_GM000343-ZH_356_GM000422 was significantly up-regulated in the process of antagonizing plant pathogenic fungi, suggesting that it may be a BGC mediating the biosynthesis of active substances against plant pathogenic fungi in Streptomyces sp. ZH-356. Moreover, ZH_356_GM000409 may be the core biosynthetic gene of the active substances. [Conclusion] Streptomyces sp. ZH-356 can colonize plants, and the biocontrol agents prepared based on this strain demonstrate good control effects on plant fungal diseases. The active substances for the antagonistic effects may be synthesized by the gene cluster ZH_356_GM000343-ZH_356_GM000422. The above work lays a foundation for the industrial application of strain ZH-356 and the research on the mechanism of antagonizing plant pathogenic fungi.

[Objective] To investigate the effects of Weizmannia coagulans BC-G44 on the intestinal microbiota structure, barrier function, and inflammatory response in the colon of the rat model of antibiotic-associated diarrhea (AAD). [Methods] A total of 30 five-week-old Sprague-Dawley (SD) rats with similar body weights were randomized into five groups (n=6): control (Con), model (Mod), low-dose W. coagulans BC-G44 (LBC-G44), medium-dose W. coagulans BC-G44 (MBC-G44), and high-dose W. coagulans BC-G44 (HBC-G44). The experiment encompassed a modeling period (7 days) and a recovery period (12 days). During the modeling period, rats in the Con group were administrated with normal saline at 2 mL/d by gavage, while those in the Mod, LBC-G44, MBC-G44, and HBC-G44 groups were administrated with a mixture containing clindamycin, ampicillin, and streptomycin (2 mL/d) by gavage to induce AAD. During the recovery period, the Con and Mod groups continued to receive normal saline, while the LBC-G44, MBC-G44, and HBC-G44 groups received W. coagulans BC-G44 suspensions at 10⁷, 10⁸, and 10⁹ CFU/d, respectively. On day 19, colonic tissue samples were collected for histological examination, and the concentrations of cytokines, and the expression levels of barrier proteins and inflammation-related genes in the colonic mucosa were measured. Furthermore, the microbiota composition and metabolites in the colonic chyme were analyzed. [Results] On day 7 of modeling, rats in the Mod, LBC-G44, MBC-G44, and HBC-G44 groups exhibited diarrhea, weight losses, and reduced food intake compared with those in the Con group (P<0.05). On day 19, compared with the Mod group, the MBC-G44 and HBC-G44 groups showed increases in the colonic mucosa thickness and goblet cell number (P<0.05). The HBC-G44 group showed increased relative abundance of Bacteroides and concentrations of lactate in the colonic chyme (P<0.05), elevated levels of d-lactic acid (d-LA) and diamine oxidase (DAO) in the colonic mucosa, and up-regulated relative mRNA levels of Claudin-1, Occludin, and MUC2 in the colonic mucosa (P<0.05). Meanwhile, compared with the Mod group, the MBC-G44 and HBC-G44 groups showed down-regulated relative mRNA levels of Toll-like receptor 4 gene (TLR4) and nuclear factor-kappa B gene (NF-κB) (P<0.05), and reduced concentrations of tumor necrosis factor (TNF)-α and interleukin (IL)-1β (P<0.05) in the colonic mucosa. [Conclusion] W. coagulans BC-G44 can ameliorate antibiotic-induced colonic injury, regulate the colonic microbiota composition and metabolites, enhance intestinal barrier function, and reduce intestinal inflammatory responses in rats, thus alleviating the symptoms of AAD.

The SaeRS system has been extensively and intensively studied for its involvement in the regulation of virulence factor expression and biofilm formation in the Gram-positive pathogen Staphylococcusaureus, mediating severe pathogenicity. The activation of the system depends on the recognition of external signals by the sensor histidine kinase SaeS and the phosphorylation status of the response regulator SaeR. With the help of auxiliary proteins SaeP and SaeQ, S. aureus is prompted to express a variety of virulence factors, coordinate its biofilm formation, and even evade the host immune response. In addition, other regulatory systems and modulators of S. aureus can synergize with the SaeRS system to participate in the regulation of virulence factor expression, enhancing bacterial pathogenicity. This paper reviews the SaeRS system and its interactions with other regulatory systems and factors to regulate the expression of virulence factors and biofilm formation. It summarizes targeted drugs against the SaeRS system and analyzes specific examples of anti-SaeRS system drugs to provide clues for the screening and design of new targeted drugs. This review is expected to provide a theoretical basis for the research on the specific regulatory mechanisms of the SaeRS system and the treatment of S. aureus-associated infections.

Honeybees (Apis mellifera) are important pollinators worldwide and models for the research on development and behaviors, showcasing great economic, environmental, and scientific benefits. As the symbiont of honeybees, the gut microbiota is transmitted through social behavioral interactions and plays a crucial role in the development and health of honeybees. It not only helps honeybees digest and absorb nutrients but also helps resist pathogen invasion and enhance immunity. Recently, honeybees have emerged as the models for studying gut microbiota. Researchers not only analyzed the composition and function of the gut microbiota in honeybees but also explored the diversity and functions of strains. This paper reviews the temporospatial dynamics of the gut microbiota in honeybees, the factors affecting the gut microbiota, the influences of the gut microbiota on the biological characteristics and health of honeybees, and the functional applications of the gut microbiota, providing references for the research and application of the gut microbiota in honeybees.

[Objective] To identify mazEF family type II toxin-antitoxin systems of Leuconostocpseudomesenteroides L64 and to elucidate the molecular roles of the mazEF systems in the host exposed to environmental acid stress. [Methods] Putative MazF toxins were induced alone or co-expressed with their cognate antitoxins in Escherichiacoli. The toxic effect of MazF on bacterial growth and the antitoxic effects of cognate antitoxins were examined. The lacZ reporter system and electrophoretic mobility shift assay (EMSA) were used to decipher the auto-regulation mechanism of the mazEF system invivo and invitro. The putative target genes regulated by MazE were predicted and validated through invivo and invitro experiments. [Results] Among the three putative mazEF systems in L. pseudomesenteroides L64, mazEF1-Leup (OYT_01690-OYT_01685) encoded a functional type II toxin-antitoxin system. MazE1-Leup (OYT_01685) inhibited mazEF1-Leup transcription by binding to the palindromic sequence (TAACAaaatgTGTTA) in the promoter. In addition, MazE1-Leup inhibited transcription of the dlt-acpS-alr operon by binding to the similar palindromic sequence (TAACAtattgaaatatatgTGTTA) in the promoter of dlt-acpS-alr. [Conclusion] mazEF1-Leup (OYT_01690-OYT_01685) encodes a functional mazEF family type II toxin-antitoxin system. Beyond regulating its own operon, MazE1-Leup regulates the transcription of dlt-acpS-alr and finally assists L. pseudomesenteroides L64 in response to low acid stress.

Interactions between microbial symbionts and insects are essential for the growth, development, and reproduction of insects. This review focuses on how microbial symbionts regulate lipid metabolism in insects via signaling pathways. Microbial symbionts affect lipid metabolism in insects through a variety of mechanisms. Microbial symbionts provide lipids or lipid precursors such as steroids to their insect hosts. Microbial symbionts can also modulate host insulin signaling pathway by producing short-chain fatty acids or activating immune signaling pathways, thereby changing the lipid content of insects. In addition, microbial symbionts can activate target of rapamycin and adipokinetic hormone signaling pathways to regulate lipid metabolism in insects. Further research in the similarities and differences of these signaling pathways in different insect species is of great significance for comprehension of insect ecological adaptability and reproductive strategies, and development of new pest management strategies.