Streptomyces are deeply studied and applied in the biocontrol of plant diseases. Streptomyces are widely distributed in soil, ocean and plant tissue. Streptomyces and the bioactive metabolites produced by Streptomyces exhibited antifungal, antibacterial, antivirus, nematicidal, pesticidal and herbicidal effects. The biocontrol mechanisms of Streptomyces against plant diseases, including antifungal activity, mycoparasitism, inducing resistance, enhancing plant growth, producing volatile organic compounds were summarized. The commercialized biocontrol agents developed based on Streptomyces were introduced. The research on Streptomyces-based biocontrol agents is limited in China, and the development and promotion of such agents could decrease the use of chemical fungicides and promote the environmental-friendly sustainable development of agriculture.

Non-alcoholic fatty liver disease (NAFLD) is a common chronic liver disease around the world, and it has a complex disease progression. Recent studies have demonstrated that gut microbiota (GM) plays a crucial role in the pathogenesis of NAFLD. The theory of gut-liver axis provides a theoretical basis for understanding the relationship between GM and the liver. Dysbiosis of GM leads to immune dysfunction, inflammatory responses, damaged gut barrier, and insulin resistance, all of which promote the development and progression of NAFLD. Furthermore, GM can participate in the development and progression of NAFLD through endotoxemia and abnormal metabolism of short chain fatty acids, bile acids, and choline. How to mitigate NAFLD by modifying GM has become the focus of current research, and the measures include fecal microbiota transplantation, probiotics, prebiotics, Chinese herbal medicines, and lifestyle interventions. The review focuses on the impact of the pathological state of GM on NAFLD and discusses the research progress in GM-targeted therapy for NAFLD. It is expected to provide new strategies and targets for the prevention and treatment of NAFLD.

[Objective] To study the effect of ferulic acid on the laccase activity of Dichomitus squalens and its molecular mechanism, providing a theoretical basis for microbial degradation of aromatic compounds. [Methods] Ferulic acid was added to the synthetic medium at different concentrations to investigate its effects on the growth of D. squalens and laccase activity. Transcriptomic and proteomic analyses were performed to examine the changes in laccase transcription and protein expression levels induced by ferulic acid. The lcc3 gene was knocked down using RNAi technology, and the impact on laccase activity and the ability to degrade various aromatic compounds was assessed. A self-constructed dual-luciferase system based on Gaussia luciferase and Nano luciferase was employed to identify the core promoter region of the lcc3 gene. [Results] An appropriate concentration of ferulic acid can significantly enhance laccase activity in D. squalens. Transcriptomic and proteomic analyses revealed that the transcription and expression levels of the lcc3 gene were markedly up-regulated under ferulic acid induction. In the lcc3-gene-knocked-down strain, both laccase activity and the ability to degrade various aromatic compounds decreased significantly, confirming that lcc3 is a key gene for laccase-related activities in degrading aromatic compounds in D. squalens. Moreover, the dual-luciferase system successfully identified the core promoter region of the lcc3 gene. [Conclusion] This study first revealed that ferulic acid can induce D. squalens laccase activity and clarified the molecular mechanism. It was also proved that lcc3 is a key gene for ferulic acid-induced laccase activity and degradation of aromatic compounds in D. squalens. Identifying the core promoter region of lcc3 lays a foundation for gene expression regulation research, and these findings offer theoretical support for using microbial laccases to degrade aromatic compounds.

[Objective] This study investigates the effects of various diets on the structure and diversity of the fungal community in the tobacco beetle Lasioderma serricorne, aiming to provide a theoretical basis for developing green control strategies for stored-product pests through microbial regulation. [Methods] The PacBio SMRT platform was used for full-length internal transcribed spacer (ITS) amplicon sequencing, on the basis of which the community structure characteristics of fungi in L. serricorne were compared among three groups: artificial feed (SL), tobacco domestication (YC), and wild environment (WF). Additionally, culturable fungi were isolated via the culture method, and the tissue expression pattern of the core symbiotic fungus Symbiotaphrina kochii was localized by RT-qPCR. [Results] SL, YC, and WF groups contained 35, 32, and 15 operational taxonomic units (OTUs), respectively. The core OTUs shared by the three groups accounted for 31.43%, 34.38%, and 73.33% in SL, YC, and WF groups, respectively. The Sobs index of the SL group was 29.00±1.13, which was higher than those of the YC group (16.17±2.30) and WF group (12.33±1.33) (P<0.001). Symbiotaphrina was the core functional group shared by the three groups, and its relative abundance was more than 81.000 0% in all the three groups. Aspergillus and Xeromyces were the characteristic genera of the SL and YC groups, while Symbiotaphrinabuchneri and Symbiotaphrina microtheca formed the evolutionary clades specific to the YC and WF groups. Eight Ascomycota strains were isolated via the culture method, belonging to three genus: Symbiotaphrina (three strains), Talaromyces (three strains), and Penicillium (two strains). Tissue-specific expression analysis confirmed the higher expression level of S. kochii in mycetocytes (10.42±1.03) than in the fat body (0.74±0.08) and midgut (0.31±0.01) (P<0.001), validating its intracellular colonization. [Conclusion] This study for the first time reveals that diets regulate the fungal community assembly in L. serricorne through a “nutrient-microbiota” interaction network and demonstrates the pivotal role of Symbiotaphrina in adaptive evolution of the host. These findings establish a theoretical foundation and provide critical targets for developing precision pest control technologies based on targeted modulation of microbial interaction networks.

[Objective] To screen and identify an endophytic bacterial strain with plant growth-promoting effects on rice from the stem of rice grown in the soda saline-alkaline soil in Daqing City, Heilongjiang Province and explore its plant growth-promoting effects and related genes, with a view to enriching and utilizing the endophytic microbial resources of rice. [Methods] An endophytic bacterial strain was isolated from rice stems via the dilution coating method, and the strain was identified by morphological observation, physiological and biochemical tests, and 16S rRNA gene sequencing. The mechanisms underlying the plant growth-promoting effects of the strain were deciphered by Illumina sequencing of the whole genome. antiSMASH was used to predict the synthetic gene clusters of secondary metabolites. The plant growth-promoting performance of the strain was evaluated by promotion performance, rice seed germination, and seedling cultivation tests. [Results] An isolated endophytic bacterial strain of rice was designated as J-7, and the strain was identified as Acinetobacter baumannii by whole genome sequencing and ANI analysis. The strain was a mesophilic bacterium with an OD₆₀₀ value of 0.679 at pH 10.5, showcasing alkaline tolerance. The strain had an OD₆₀₀ value of 0.293 in the presence of 1.0 mol/L NaCl, exhibiting salt tolerance. The strain had the ability to solubilize inorganic and organic phosphorus, with the amounts of inorganic and organic phosphorus solubilized being (179.54±1.21) mg/L and (65.57±1.07) mg/L, respectively. In addition, the strain had the ability to produce siderophores and utilize ferric ammonium salts. The strain genome (national microbiology data center accession number: NMDC60154488) was 3 666 630 bp in length, with the G+C content of 39% and a total of 3 432 genes (including 8 potential synthetic gene clusters of secondary metabolites). The rice seed germination test results showed that the application of 1×10⁷ CFU/mL suspension of the strain significantly increased the radicle length and stem base width by 13.02% and 17.68%, respectively, compared with the control group. The rice seedling cultivation test results showed that the application of 2×10⁹ CFU/mL suspension of the strain significantly increased the plant height and root length by 32.69% and 36.55%, respectively, compared with the control group. [Conclusion] Strain J-7 has a good growth-promoting effect on rice, showing application potential in agriculture as a microbial strain resource. Whole genome sequencing provides a theoretical basis for in-depth study of the plant growth-promoting mechanism of A. baumannii.

Streptococcus suis is a major pathogen in pigs and also a zoonotic pathogen. This bacterium has numerous serotypes, among which S. suis serotype 4 (SS4) is known to infect humans and poses a threat to public health due to its potential high pathogenicity. [Objective] To develop a multiplex PCR method based on specific virulence-associated genes of SS4 virulent strains to achieve precise identification of such strains. [Methods] Based on previous research results, four target genes specific to SS4 virulent strains—sly, igdE, tran, and sao—were selected, and the SS4 serotype-specific gene wzy was used as an internal reference gene to design a pentaplex PCR method. After optimization of the multiplex PCR amplification system, specificity and sensitivity tests were conducted. This method was then employed to detect newly isolated SS4 strains. Additionally, zebrafish virulence assays were performed to validate the accuracy of this method. [Results] The multiplex PCR method specifically amplified the target genes, effectively distinguishing SS4 virulent strains from lowly virulent strains. The method exhibited high sensitivity, with a minimum detection limit of 4.1×10² CFU or 12.5 pg of genomic DNA. Specificity validation confirmed that this method accurately identified SS4 virulent strains. This method was then employed to examine six clinically isolated SS4 strains. Three strains were identified as virulent, showing high pathogenicity in zebrafish and causing a mortality rate of 60.00%-86.67%. The other three strains were identified as lowly virulent strains, exhibiting low pathogenicity in zebrafish and causing a mortality rate of 0-6.67%. [Conclusion] A multiplex PCR method based on virulence-associated genes of S. suis was successfully developed, enabling accurate and sensitive identification of SS4 virulent strains. This method provides technical support for the early diagnosis and effective prevention and control of S. suis infections.

Root-knot nematodes(Meloidogyne spp.) are widely distributed and highly destructive, causing substantial economic losses in agricultural production. Biocontrol has been considered as an effective measure for managing these pathogens. [Objective] To explore efficient and eco-friendly biocontrol resources for controlling root-knot nematodes. [Methods] Bacillus strains were isolated from soil via the serial dilution method. Strains with strong nematicidal activity against Meloidogyne incognita second-stage juveniles (J2) were screened by in vitro bioassays. The selected strains were identified based on morphological, physiological, and biochemical characteristics, as well as molecular biological evidence. The biocontrol potential of these strains was further evaluated by egg hatching inhibition assays, phosphorus/potassium solubilization tests, enzymatic activity profiling, and antagonistic spectrum analysis. Additionally, pot and greenhouse experiments were conducted to validate the biocontrol efficacy of strains. [Results] Among 189 bacterial strains isolated from 16 soil samples, strains Sneb2550 and Sneb2556 demonstrated strong nematicidal activity against M. incognita J2, inducing the corrected mortality rates of 95.64% and 95.36%, respectively, after 24 h. Based on morphological features, physiological and biochemical characteristics, and 16S rRNA gene and gyrB sequences, strains Sneb2550 and Sneb2556 were identified as Bacillus proteolyticus and B. amyloliquefaciens, respectively. Functional characterization showed that strain Sneb2550 produced protease and inhibited Fusarium asiaticum, Trichothecium roseum,and Alternaria solani. Strain Sneb2556 produced protease and amylase, solubilized phosphate, and suppressed F. asiaticum, Aternaria alternata, Botryosphaeria dothidea, T. roseum, Colletotrichum gloeosporioides, and A. solani. Moreover, both strains did not adversely affect cucumber seed germination and significantly promoted the radicle growth. Under pot conditions, Bacillus Sneb2550 and Sneb2556 significantly reduced root galls formation, with the reduction rates of 56.02% and 50.19%, respectively, while promoting plant growth. Field experiments showed that root irrigation with Bacillus Sneb2550 and Sneb2556 effectively controlled cucumber root-knot nematodes, with the control effects of 60.90% and 52.63%, respectively, while promoting plant growth. [Conclusion] Bacillus Sneb2550 and Sneb2556 effectively controlled cucumber root-knot nematodes and promoted plant growth, providing new potential resources for the biocontrol of root-knot nematodes.

Pseudomonas plecoglossicida is the pathogen of visceral white spot disease in large yellow croaker (Larimichthys crocea). At present, the pathogenic mechanism of P. plecoglossicida has been partially understood, and some effective vaccines have been screened, whereas no commercial vaccine has been developed. [Objective] To deepen the understanding about the pathogenic mechanism and develop efficient attenuated live vaccines of P. plecoglossicida. [Methods] We targeted luxR and the RNA polymerase σ factor gene rpoE associated with quorum sensing to construct deletion mutants of P. plecoglossicida NB2011 by double homologous recombination. In addition, the strain ΔT6SS1ΔluxR with deletion of both the type VI secretion system 1 (T6SS1) gene and luxR was constructed. The biological characteristics and virulence of the mutants were analyzed. The relative percent of survival of fish after vaccination with the double deletion mutant was investigated. [Results] We successfully constructedΔluxR, ΔT6SS1ΔluxR, and ΔrpoE. Compared with the wild type, none of the three mutants showed significant changes in the growth rate, swarming ability or swimming ability, while ΔluxR and ΔT6SS1ΔluxR showed significant decreases in biofilm formation. The internalization, adsorption, and intracellular proliferation of the mutants in mouse macrophages were observed. All the three mutants could survive in J774A.1 macrophages and showed lower proliferation capacities than the wild type. Compared with the wild type, the two single mutants showed significantly reduced virulence to goldfish (Carassius auratus) after intraperitoneal injection at a concentration of 1.0×10⁷ cells/mL. The double deletion mutant ΔT6SS1ΔluxR showed no virulence when challenging goldfish at the same dose, with the LD₅₀>10⁸ cells/mL. In the immune protection experiment, the goldfish was vaccinated with ΔT6SS1ΔluxR, and the fish was artificially challenged with the wild type 28 days later. The relative percent of survival reached 78.60%, which indicated effective protection. [Conclusion] In this study, three gene deletion mutants were successfully constructed, and the virulence of the mutants was significantly decreased. Among them, ΔT6SS1ΔluxR is expected to be a candidate strain for the development of the attenuated live vaccine against P. plecoglossicida infection.

Photobacterium damselae subsp. damselae (PDD), a pathogenic bacterium widely found in seawater, can infect a variety of economic fish and cause huge economic losses to the global aquaculture industry. The flagellar gene flgK encodes the flagellar hook protein FlgK, which is essential for the normal formation of bacterial flagella. [Objective] To systematically analyze the influencing mechanism of flgK on the virulence of PDD. [Methods] The flgK-deleted mutant of PDD (ΔflgK-PDD) was constructed by homologous recombination mediated by a high-efficiency suicide plasmid, and the mutation was confirmed by gene sequencing. The biological characteristics, virulence gene expression, and pathogenicity were compared between ΔflgK-PDD and the wild-type strain (WT-PDD). [Results] There was no significant difference in the growth ability, hemolytic activity or phospholipase activity between ΔflgK-PDD and WT-PDD. However, the motility and biofilm formation of ΔflgK-PDD were significantly lower than those of WT-PDD. Transmission electron microscopy showed that ΔflgK-PDD failed to form a flagellar structure. The artificial infection experiments showed that the LD₅₀ of ΔflgK-PDD in Sebastes schlegelii was 557% that of WT-PDD, and the pathogenicity was significantly reduced. Real-time quantitative PCR results showed that compared with WT-PDD, ΔflgK-PDD demonstrated significantly down-regulated expression of the flagellar-related genes fliK and flgL, the type II secretion system (T2SS)-related genes gspC and gspD, and the virulence gene hlyA_pl. The expression levels of flagellar-related gene fliH, T2SS-related gene gspE, outer membrane-related genes ompP, lapB, and flhB were significantly up-regulated, and those of the remaining genes did not change significantly. [Conclusion] The mutation of flgK can lead to the failure of ΔflgK-PDD to form a complete flagellar structure and significantly change the relative expression levels of flagellar-related genes, thereby reducing the motility and colonization ability and ultimately weakening the pathogenicity of PDD.

[Objective] Adipic acid is a key monomer for plastics such as nylon 66 and poly (butylene adipate-co-terephthalate) (PBAT), with a vast market potential. This study aims to explore the optimal expression levels of genes in the biosynthetic pathway of adipic acid. [Methods] We regulated the expression levels of genes in the adipic acid synthesis pathway by randomly combining gradient-strength constitutive promoters. The high-throughput screening based on an adipic acid biosensor was conducted to select the strain with the optimal combination. Subsequently, the fermentation media, carbon sources, metal ions, and precursor substance addition amounts were optimized. [Results] After screening, the optimal strain Escherichia coli MG1655 Δ8-D47 was obtained, with an adipic acid yield of 431.32 mg/L. After fermentation condition optimization, the yield of adipic acid in a shake flask reached 550.34 mg/L, which represented a 134% increase compared with that of the control strain Z1. [Conclusion] Metabolic pathway imbalance in microbial synthesis of adipic acid is the main factor limiting the increase in yield.