[Objective] To study the mechanism of plant growth-promoting rhizobacterium (PGPR) in the rhizosphere of sea rice and the effects of PGPR on the growth of terrestrial crops under salt stress. [Methods] The salt tolerance, alkali-reducing ability, and plant growth-promoting effect were determined for 15 bacterial strains isolated from the rhizosphere soil of sea rice. Highly active strains were selected for species identification and construction of a consortium. The effect of the consortium on the seed germination of mung bean was verified. [Results] The 15 strains of PGPR were moderately halophilic and strain SL-1 was an extreme halophile among them. Four halophilic strains had alkali tolerance and alkali-degrading effect, among which strain SH-3 had the highest alkali-degrading effect (16.83%). These four strains demonstrated different plant growth-promoting effects. All the strains could produce extracellular polymers (EPS), and strain SH-3 had the highest EPS production (0.47 g/g). The strains were capable of producing indole-3-acetic acid (IAA), with the yields between 0.70 mg/L and 1.48 mg/L. Three highly active strains SL-1, SM-1 and SH-3 belonging to Bacillus and Enterobacter were used to construct a consortium. Seed germination experiments showed that PGPR and the consortium promoted the seed germination of mung bean under salt stress. Moreover, the consortium showcased stronger promoting effect on seed germination than single PGPR. Compared with the control group, the consortium was more effective at the salt concentration of 15 g/L. Specifically, it improved the root length, germination rate, and simplified vitality index, while decreasing the relative salt injure rate from 80.53% to 18.95% and increasing the salt tolerance threshold of mung bean seeds from 10 g/L to 15 g/L. The data indicated that strains of the consortium coordinated to promote the seed germination of mung bean. The correlation analysis showed a strong positive correlation between EPS and IAA, both of which promoted the seed germination, growth, and development of mung bean under salt stress. [Conclusion] Strains SL-1, SM-1 and SH-3 had strong halophilicity, alkali tolerance, and abilities of degrading alkali, producing EPS and IAA, and promoting plant growth. The findings provide a scientific basis for the rational development and utilization of soil microbial resources and the improvement of saline-alkali soil environment.

[Objective] To explore the differences and potential associations of endophytic microbial communities in different niches of chili pepper and provide a theoretical basis for the exploration and application of endophytic microbial resources in chili pepper. [Methods] The 16S rRNA and internal transcribed spacer (ITS) genes sequencing were employed to study the community structure characteristics of endophytic bacteria and fungi in different ecological niches (roots, stems, leaves, and fruits) of 91 pepper germplasm accessions, along with functional annotations. Additionally, co-occurrence network analysis and traceability analysis were performed on the endophytic bacterial communities. [Results] The operational taxonomic unit (OTU) of endophytic microbial communities were highly common among the four ecological niches, including 46.36% common bacterial OTUs and 29.66% common fungal OTUs. The diversity of endophytic bacterial and fungal communities in chili pepper exhibited variations across different ecological niches, with the endophytic communities in roots being distinctly separated from those in the other three niches (P<0.05). The Shannon index of endophytic bacteria varied significantly among niches, whereas that of endophytic fungi remained relatively stable. The dominant endophytic bacteria in chili pepper were Proteobacteria, Firmicutes, and Bacteroidota, with Proteobacteria being enriched in the roots and Firmicutes and Bacteroidetes being predominant in the fruits. Ascomycota and Basidiomycota, the dominant endophytic fungal phyla, exhibited minimal differences in relative abundance across the four ecological niches. Functional annotation results indicated that chili pepper harbored various endophytic bacteria capable of synthesizing secondary metabolites and antibiotics. Within the fungal community, pathogenic fungi were found to have the highest relative abundance. Additionally, more than 80.0% of the endophytic bacteria in chili pepper originated from their directly associated morphologically lower niches, exhibiting complex interaction networks, strong community stability, and a modular structure. [Conclusion] Compared with the endophytic fungal community, the endophytic bacterial community in chili pepper is sensitive to changes in ecological niches, while the niche specificity of the fungi is comparatively weak. The endophytic bacteria associated with each niche of chili pepper primarily originate from the niche located beneath, exhibiting significant niche enrichment, where the roots serving as a crucial source in shaping the endophytic bacterial community.

[Objective] To explore the effects of strain CDWB36 and its metabolite pyrroloquinoline quinone (PQQ) on the drought resistance and growth of pepper, so as to provide efficient strain resources for the development and utilization of multifunctional microbial agents. [Methods] A strain CDWB36 was identified based on the morphological characteristics and the 16S rRNA gene-based phylogenetic tree. HPLC and spectroscopy were employed to detect PQQ. The fermentation conditions were optimized by single factor tests with PQQ production as the indicator. The effects of the PQQ-containing microbial agent on the growth, physio-biochemical characteristics, soil nutrients, and rhizosphere microbial community structure of pepper under drought stress were determined by pot experiments. [Results] Strain CDWB36 was identified as Acinetobacter calcoaceticus and it had the ability to produce PQQ. The optimum conditions of strain CDWB36 for producing PQQ were 10 g/L yeast powder, 4 g/L mixed nitrogen sources (ammonium sulfate: glutamic acid: tyrosine=2:1:1), 1.0 g/L MgSO₄, 0.40 g/L CaCl₂, 0.5% inoculum amount, 28 ℃, and pH 6.5. The PQQ production of the strain in shake flasks after 7 days of fermentation at the optimized conditions reached 61.48 mg/L, which increased by 3.3 times compared with that before optimization. Compared with CK, the PQQ-containing microbial agent increased the plant height, stem diameter, aboveground fresh weight, and belowground fresh weight of pepper by 35.05%, 8.22%, 14.41%, and 51.70%, respectively, demonstrating better plant growth-promoting effect than the PQQ solution. Moreover, the PQQ-containing microbial agent significantly improved the activities of antioxidant enzymes and the content of osmoregulatory substances (soluble sugar, soluble protein, and proline) in leaves, while increasing the soil nutrient content. The PQQ-containing microbial agent significantly changed the relative abundance of bacteria and fungi in the rhizosphere soil of pepper, increasing the relative abundance of Bacillus, Aspergillus, and Streptococcus by 1.99 times, 1.38 times, and 8.75 times, respectively, compared with CK. [Conclusion] A. calcoaceticus CDWB36 has the ability to produce PQQ. Optimizing the fermentation conditions can effectively enhance the PQQ production. The fermentation broth of CDWB36 significantly promotes pepper growth under drought stress, and PQQ is a key substance in the broth for promoting pepper growth. Therefore, the strain has broad application prospects in enhancing the stress resistance and promoting the growth of plants.

[Objective] To observe the effects of supplementing compound probiotics on the structure of gut microbiota, content of short-chain fatty acids (SCFAs), and levels of inflammatory cytokines in Chinese wrestlers. [Methods] Eighteen non-sports undergraduates from Shandong Sport University were recruited as a control group, while 30 Chinese wrestlers served as the experimental group. Both groups received oral compound probiotics for 8 weeks. Venous blood and stool samples were collected before and after the intervention. Enzyme-linked immunosorbent assay (ELISA) was used to measure inflammatory cytokines levels in plasma. The structural characteristics of gut microbiota were analyzed using 16S rRNA gene sequencing of the V3−V4 region, and gas chromatography-mass spectrometry (GC-MS) was employed to determine SCFAs content in stool samples. [Results] Prior to the intervention, the experimental group exhibited lower levels of interleukin-1 (IL-1), interleukin-6 (IL-6), and C reactive protein (CRP) (P < 0.001, P < 0.01, P < 0.01), and higher levels of interleukin-10 (IL-10) compared to the control group (P < 0.001). After 8 weeks of probiotic supplementation, plasma levels of IL-6 and CRP in the Chinese wrestlers further declined (P < 0.01, P < 0.05). Before the intervention, the abundance of Bifidobacterium adolescentis was higher in Chinese wrestlers than that in the control group (P < 0.01). Following 8 weeks of supplementation, Chinese wrestlers showed an increased abundance of Collinsella (P < 0.01), a decreased abundance of Faecalibacterium (P < 0.01), and reduced α-diversity in gut microbiota (P < 0.01). Prior to the intervention, there was no significant difference in SCFAs content between the two groups. After 8 weeks of intervention with compound probiotics, the content of acetic acid and butyric acid in the stool samples increased in both the control group (P < 0.01, P < 0.05) and the experimental group (P < 0.05). The correlation analysis results indicated a positive correlation between B. adolescentis abundance and plasma IL-10 level (r=0.233, P=0.037) and negative correlations of B. adolescentis and C. aerofaciens abundance with plasma IL-6 level (r=−0.499, P=0.000; r=−0.366, P=0.001) in Chinese wrestlers. Additionally, there was a positive correlation between C. aerofaciens abundance and the butyric acid content in stool samples of Chinese wrestlers (r=0.243, P=0.032). [Conclusion] The 8 weeks intervention with compound probiotics effectively reduced pro-inflammatory cytokine levels and increased anti-inflammatory cytokine levels in plasma. Furthermore, it enhanced the abundance of butyric acid-producing bacteria in the gut microbiota, promoting the production of SCFAs, and improving anti-inflammatory capacity.

[Objective] Streptococcus suis is a prevalent pathogen attacking pigs and a zoonotic agent. In 1998, an outbreak of S. suis infection in Jiangsu caused numerous pig deaths and 14 human deaths. Therefore, investigating S. suis infections in healthy pigs from slaughterhouses in Jiangsu is crucial for public health. [Methods] Tonsils were collected from healthy pigs in slaughterhouses of Jiangsu in 2023, and S. suis was isolated, identified, and serotyped. The pathogenicity of S. suis isolates to zebrafish and mouse models was examined. Furthermore, the antibiotic resistance characteristics and genes and the antimicrobial susceptibility of the isolates were identified and evaluated. [Results] The positive rate of S. suis in the samples collected from Kunshan in July 2023 was 50.85% (30/59). A total of 62 strains were isolated from the samples collected from Kunshan, and serotype 31 (12.90%, 8/62) had the highest isolation rate, followed by serotype 19 (11.29%, 7/62) and serotype NCL2 (8.06%, 5/62). In the samples collected from Danyang in July and November 2023, the positive rate of S. suis was 60.71% (34/56), and 77 strains were isolated. Serotype 16 had the highest isolation rate of 11.69% (9/77), followed by serotype 9 (10.39%, 8/77), serotype 21 (10.39%, 8/77), and serotype 31 (10.39%, 8/77). The isolates from both regions exhibited high resistance to lincosamides (98.56%, 137/139), macrolides (95.68%, 133/139), and tetracyclines (96.40%, 134/139). Furthermore, 97.84% (136/139) of strains were multi-drug resistant. All the strains were sensitive to cefotaxime and vancomycin. According to the sources and serotypes, we selected 42 representative strains (18 from Kunshan and 24 from Danyang) to perform zebrafish infection experiments. At a dose of 3×10⁶ CFU/fish, seven strains exhibited high pathogenicity to zebrafish, causing the mortality rates ≥80.00%. Three strains (serotypes 1, 3, and 23) causing mortality rates ≥80.00% in zebrafish and comparable to the virulent strain SC070731 were selected for mouse infection experiments. All the three strains led to the mortality rates ≥80.00% in mice. [Conclusion] The healthy pigs in Jiangsu have a high carrying rate of S. suis (55.65%, 64/115), and 97.84% (136/139) of the isolates are multi-drug resistant. Strains of serotypes 1, 3, and 23 exhibited strong pathogenicity.

[Objective] To elucidate the structural and functional characteristics of the gut microbiota of Trypoxylus dichotomus larvae and isolate cellulose-degrading bacteria. [Methods] Metagenomic sequencing was employed to analyze the structure and functions of the gut microbiota. Cellulose-degrading bacteria were isolated and screened from the larval gut with carboxymethyl cellulose (CMC) as the sole carbon source. The strains were identified based on morphological characteristics and molecular evidence. [Results] The gut microbiota was dominated by bacteria, which accounted for 81.3%. At the phylum level, Firmicutes (45.8%) and Bacteroidota (20.3%) were the dominant phyla. The top three abundant genera were Clostridium (3.90%), Bacteroidia (3.52%), and Dysgonomonas (2.41%). The functional analysis of metagenome data revealed that the genes of the gut microbiota were mainly associated with carbohydrate, amino acid, and energy metabolism. The annotation in the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed that the genes related to carbohydrate metabolism were predominant. The annotation in the carbohydrate-active enzyme database (CAZy) indicated that 48 856 (7.43%) genes were successfully annotated to 344 carbohydrate metabolism enzyme families, with glycoside hydrolase (GH, 48.67%) being the most dominant enzyme family in the gut bacteria. Among the top ten functionally abundant enzymes, six belonged to the GH family. Additionally, three strains of cellulose-degrading bacteria, TRC-3 (Bacillus subtilis), TRC-5 (B. subtilis), and TRC-6 (B. safensis), were isolated from the gut. TRC-3 exhibited stronger activities of filter paper enzyme, endoglucanase, exoglucanase, and β-glucosidase. [Conclusion] The gut microbiota of Trypoxylus dichotomus larvae exhibits high diversity and complexity, carrying a large number of genes encoding carbohydrate-active enzymes and harboring rich cellulose-degrading bacteria.

[Objective] To studyhydroxyl radical the differentially expressed genes (DEGs) in Halomonas campaniensis XH26 after co-culture with Fe₃O₄ nanoparticles (NPs), and clarify the molecular mechanism of Fe₃O₄ NPs in increasing the ectoine accumulation in strain XH26. [Methods] Strain XH26 was co-cultured with low-, medium-, and high-concentration (0.01, 0.10, and 0.50 g/L respectively in L, M, and H groups) Fe₃O₄ NPs, and the strain cultured without Fe₃O₄ NPs (0 g/L) was taken as the control group (C). Transcriptome sequencing was performed by Illumina HiSeq 300PE. The DEGs between different groups were mined, and key genes were screened for RT-qPCR verification. [Results] Compared with group C, group M showed an increase of 55.67% (708.87 mg/L) in ectoine accumulation, and groups M and H showed increased ferrous ions and antioxidant capacity. The hydroxyl radical content in group H was higher than that in group M. The transcriptomics analysis showed that the DEGs between groups M and C were enriched in arginine/proline metabolism (13), nitrogen metabolism (11), and sulfur metabolism (10) pathways. They were mainly related to the ectoine synthesis pathways (11), electron transport pathways (7), and antioxidant enzyme systems (5). RT-qPCR was employed to verify the expression of lysC, asd, and ectABC involved in ectoine synthesis, astA/B/D/E in arginine metabolic pathway, and argE/H in urea cycle, which showed the results consistent with the results of RNA-seq. [Conclusion] Ectoine is an important stable protective agent for bacterial cells and biomacromolecules. Strain XH26 exposed to the stress of Fe₃O₄ NPs showed increased intracellular reactive oxygen species and altered amino acid/nitrogen metabolism processes. Strain XH26 increased the accumulation of ectoine to cope with the stress of Fe₃O₄ NPs by improving the antioxidant capacity.

[Objective] Based on the critical role of type Ⅰ signal peptidase in the secretion system, this study explores the interaction between signal peptidase and signal peptides to guide the optimization of aminopeptidase secretion expression in Bacillus amyloliquefaciens. [Methods] The endogenous signal peptidase and signal peptide of Bacillus amyloliquefaciens TCCC 19030 were examined using relative fluorescence intensity and enzyme activity for analysis, and molecular docking to study their interaction. [Results] The signal peptide YolC fused with aminopeptidase exhibited the highest extracellular enzyme activity, reaching 11 847.67 U/mL. Overexpression of the signal peptidase SipW increased aminopeptidase activity to 16 261 U/mL. Molecular docking results also showed that YolC had the lowest binding free energy with SipW, at −4.4 kcal/mol. [Conclusion] Optimization of signal peptides and overexpression of signal peptidase can effectively enhance the secretion of aminopeptidase. The binding energy between signal peptidase and signal peptide is a key factor influencing the secretion levels of the target protein.

[Objective] Preliminary studies have identified four protein elicitors from the whole genome of Saccharothrix yanglingensis Hhs.015 that can induce a hypersensitive response (HR) in Nicotiana benthamiana. This study investigated the two elicitors capable of triggering a strong HR and their associated immune mechanisms, aiming to provide a basis for probing into the molecular mechanisms by which Hhs.015 enhances the disease resistance of plants. [Methods] The protein elicitors capable of inducing the immune responses of plants were screened based on the HR and reactive oxygen species (ROS) levels. A prokaryotic expression system was used to purify the proteins. Furthermore, we verified the roles of the protein elicitors in inducing plant disease resistance by observing the disease spots, measuring the activities of defense-related enzymes, and analyzing the expression of defense genes. Additionally, we treated Arabidopsis thaliana seedlings with the protein elicitors to evaluate the plant growth-promoting effects of the elicitors. [Results] The protein elicitors HSyp1 and HSyp2 from Hhs.015 that could induce a HR, callose and ROS deposition, and upregulation of defense genes in N. benthamiana, were screened and found to be soluble. HSyp1 and HSyp2 enhanced the resistance of different plants to Sclerotinia sclerotiorum, Phytophthora capsica, and Valsa mali. Furthermore, HSyp1 and HSyp2 promoted the cotyledon and root development of A. thaliana seedlings, and HSyp2 exhibited stronger plant growth-promoting effect than HSyp1. [Conclusion] This study identified two protein elicitors HSyp1 and HSyp2 capable of triggering immune responses, enhance disease resistance, and promoting growth of plants. The findings provide a theoretical basis for the development of new biocontrol agents and offer experimental evidence for their future field application.

[Objective] The basic leucine zipper (bZIP) factors are a group of large and conserved transcription factors in eukaryotes, and they are involved in the growth, development, and infection of pathogenic fungi in plants. This study aims to identify the bZIP transcription factors in the whole genome of Setosphaeria turcica and explore their functions during HT-toxin induction. [Methods] The members of the bZIP family were screened and identified from the genome database of Setosphaeria turcica, and their physicochemical properties, conserved domains, subcellular localization, cis-acting elements, phylogenetic relationship, and protein-protein interaction network were analyzed. The RNA-seq database was used to analyze the expression of bZIP family members during pathogen infection and HT-toxin induction. [Results] Fourteen bZIP family members (StbZIP1–14) were screened from the genome of Setosphaeria turcica, with significant differences in physical and chemical properties. These factors had the lengths of 226–613 aa, relative molecular weights of 25.24–66.30 kDa, isoelectric points of 4.66–10.36, and the subcellular localization in the nucleus. These factors carried 660 cis-acting elements involved in abiotic stress, hormone induction, cell cycle regulation, enhancers, and core promoters. The phylogenetic analysis with 11 other major pathogenic fungi in plants indicated that StbZIPs were clustered into 10 groups and had a clear co-linear relationship with AabZIPs of Alternaria alternata. The expression levels of StbZIP1, StbZIP5, StbZIP7, StbZIP10, and StbZIP11 were significantly correlated with HT-toxin induction, among which StbZIP5 had the highest expression level and demonstrated upregulated expression after 21 days and 28 days of HT-toxin induction. The protein-protein interaction network of StbZIPs predicted three StbZIPs interaction pathways centered on StbZIP5. [Conclusion] The members of the bZIP family of Setosphaeria turcica have significant physicochemical and structural differences, extensive genetic diversity, and significant functional differentiation, playing an important role in transcriptional regulation during HT-toxin induction.