Chitin is a polysaccharide that is polymerized by N-acetylglucosamine through β-1, 4 glycosidic linkages and ubiquitous in the global terrestrial and aquatic ecosystems. Chitin is one of the most abundant organic macromolecular polymers on earth. Chitinases are a class of enzymes that catalyze the degradation of chitin. Chitinases are not only the focus of basic research but also have shown broad application potential in a variety of fields such as agriculture, medicine, and environmental science. This paper systematically reviewed the research progress in fungal chitinases in terms of the classification, distribution characteristics in different fungal taxa, biological functions in yeasts and filamentous fungi, enzymatic characteristics, and applications in agricultural pest and disease control, disease treatment, and production of chitooligosaccharides. Furthermore, we discussed the future research directions of fungal chitinases. This paper provides new perspectives for the study of fungal chitinases.

[Objective] To study the therapeutic effect of Bifidobacterium adolescentis strains with strong antioxidant capacity on a mouse model of ulcerative colitis (UC). [Methods] The B. adolescentis strains with strong antioxidant capacity were screened based on 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging rate, reducing capacity, and hydrogen peroxide tolerance. Subsequently, we established a mouse model of dextran sulfate sodium (DSS)-induced colitis to investigate the alleviating effects of the B. adolescentis strains with strong antioxidant capacity on UC. [Results] Among the 26 strains of B. adolescentis, TH02767, TH03658, and TH03664 demonstrated strong antioxidant capacity. Only TH02767 showed an alleviating effect on UC in terms of disease activity index and spleen index in the mouse model (P < 0.05). Moreover, the intervention with TH02767 lowered the levels of tumor necrosis factor-α, interleukin-6, interleukin-1β, and myeloperoxidase (P < 0.05), while enhancing the production of interleukin-10 (P < 0.05) in the colon. In addition, TH02767 modulated gut microbiota in the mice by reducing the relative abundance of Deferribacterota and increasing the relative abundance of Bacteroidetes. At the genus level, it increased the relative abundance of Muribaculum and Muribaculaceae (P < 0.05). [Conclusion] B. adolescentis TH02767 screened out in this study for its robust antioxidant capacity not only ameliorates the clinical symptoms associated with DSS-induced colitis in mice but also significantly reduces the levels of pro-inflammatory cytokines and modulates the gut microbiota.

[Objective] To reveal the dynamics of bacterial communities in surface water and groundwater in the densely populated area of the Jianghan Plain across seasons and explore the underlying factors causing the temporal variations. [Methods] Water samples were collected from both surface water and groundwater in the densely populated area of the Jianghan Plain, and metagenomic sequencing was employed to investigate the seasonal variations of bacterial communities. The variations in environmental factors, bacterial community structure, and bacterial community assembly processes in the surface water and groundwater were compared considering rainy and dry seasons. [Results] For the surface water, the salinity (P < 0.01) and conductivity (P < 0.01) during the rainy season were lower than those during the dry season, while no significant seasonal variation was observed in turbidity. For the groundwater, the turbidity was higher in the rainy season than in the dry season (P < 0.05), while neither salinity nor conductivity showcased seasonal variations. The Shannon index of bacteria in the surface water in the rainy season was higher than that in the dry season (P < 0.01), whereas that in the groundwater presented no significant seasonal difference. The principal coordinates analysis and permutational multivariate analysis of variance (P=0.001) revealed significant seasonal variations in bacterial communities between surface water and groundwater. The Mantel test showed no significant correlations between the bacterial community in the groundwater and environmental factors during the dry season, while other communities were significantly correlated with at least one environmental factor. The neutral community model, modified stochasticity ratio (MST), and β nearest taxon index all indicated that stochastic processes exerted stronger effects on the bacterial community in the surface water during the rainy season than during the dry season, and the trend was similar but not significant for the bacterial community in the groundwater. The migration rate of surface water was higher during the rainy season than during the dry season, whereas that of groundwater showed an opposite trend. (5) The seasonal variations in the diversity of antibiotic resistance genes exhibited a negative correlation with MST (ρ=−0.164, P=4.942E−2) in the surface water, whereas the correlation was positive in the groundwater (ρ=0.393, P=1.452E−6). [Conclusion] The temporal dynamics of bacterial communities in surface water and groundwater in the densely populated area of the Jianghan Plain showed notable differences. These differences can potentially be attributed to distinct basic properties between surface water and groundwater, frequent environmental disturbances during the rainy season, and water exchange processes between surface water and groundwater.

[Objective] To develop probiotics for gynecological inflammation, we isolated and screened out Lactobacillus with antimicrobial and probiotic properties from the vagina of healthy women. [Methods] The plate streaking method was employed to isolate the Lactobacillus strains from vaginal samples, and the isolates were then identified based on morphological and 16S rRNA gene sequencing evidence. The growth and adhesion of the five strains were characterized. The Oxford cup method with Escherichia coli and Staphylococcus aureus as indicator strains was employed to assess the antimicrobial activities of the strains. The microtiter plate method was used to measure the inhibitory effects of the strains on Candida albicans. The antimicrobial components were explored by organic acid elimination and hydrogen peroxide elimination methods. [Results] Five strains of Lactobacillus were isolated, including three strains (Q2.1, BHC04, and Q8.5) of Lactobacillus crispatus and two strains (Q6.3 and BHG05) of Lactobacillus gasseri. All the five strains of Lactobacillus had strong growth and high acid production. Strains Q2.1, BHC04, and BHG05 had a short delay period and reached a plateau growth stage after 20 h, and strains BHG05, Q6.3, and Q8.5 had high acid production, with the culture medium finally reaching pH 3.80–4.03. The adhesion capacity (hydrophobicity, self-agglutination rate, and co-agglutination rate with pathogens) of L. crispatus Q2.1, BHC04, and Q8.5 was significantly higher than that of the positive control strain, L. delbrueckii DM8909. The inhibitory effects of the five strains on E. coli, S. aureus, and C. albicans were stronger than those of the positive control (nisin). Strains BHC04, BHG05, and Q8.5 showcased stronger inhibitory effects on E. coli than DM8909. The inhibitory effect of BHG05 on C. albicans was significantly stronger than that of DM8909, with the inhibition rate reaching up to (73.14±0.14)%. The inhibitory effects of BHC04 and Q8.5 on C. albicans were not significantly different from that of DM8909, with the inhibition rates reaching up to (72.80±0.30)% and (72.93±0.10)%, respectively. According to the results above, we selected BHC04 and BHG05 as high quality strains with antimicrobial potential. The five strains produced organic acids and hydrogen peroxide to exert antimicrobial effects. [Conclusion] Two strains of Lactobacillus with antimicrobial effects and excellent probiotic properties were screened out. They can be used as candidate strains of antimicrobial probiotics for the prevention and treatment of gynecological inflammation caused by E. coli, S. aureus, and C. albicans.

[Objective] The Yellow River estuary located at the confluence of the Yellow River, land, and ocean is an area with mixed freshwater and seawater and a diverse and productive estuary ecosystem. This study aims to characterize the bacterial communities in freshwater and seawater of the Yellow River estuary. [Methods] High-throughput absolute abundance quantification was adopted to measure the absolute abundance of bacterial communities. The dominant taxa, α and β diversity, co-occurrence network, assembly mechanisms, and potential functions were compared between the bacterial communities in freshwater and seawater. The correlations between dominant taxa and environmental factors were explored. [Results] The absolute abundance of bacteria in freshwater was 2.61×10⁶ copies/mL, which was 1.8 times of that in seawater. The common dominant phyla in freshwater and seawater were Actinomycetota, Pseudomonadota, Cyanobacteriota, and Bacteroidota, with significant differences in absolute abundance. The abundance of Actinomycetota ranked first in freshwater, which was approximately equal to the sum of all dominant phyla in seawater. The abundance of Pseudomonadota was the highest in seawater. The alpha diversity of bacteria in freshwater was higher than that in seawater. There were significant differences in the bacterial community structure between freshwater and seawater, mainly due to the differences in the abundance of the dominant taxa. The bacterial co-occurrence network in freshwater was more complex and stable than that in seawater, and stochastic processes dominated the bacterial community assembly in both freshwater and seawater. The bacterial communities in freshwater and seawater presented different functions, while they shared some common functions. Metabolism was the most abundant function, with higher relative abundance in freshwater than in seawater. Five environmental factors ((pH, oxidation-reduction potential (ORP), electrical conductivity (EC), total organic carbon (TOC), and total nitrogen (TN)) correlated with the dominant bacterial taxa to different extent. There were collinear relationships among the four environmental factors except EC. The dominant genera showing positive correlations with pH, TOC and TN were all negatively correlated with ORP, and vice versa. Actinomycetota and Pseudomonadota were positively and negatively correlated with pH, respectively. [Conclusion] The bacterial communities showed great differences between freshwater and seawater in the Yellow River estuary. The differences were mainly reflected in the abundance, diversity, functional structure, and co-occurrence network. The bacterial communities in freshwater and seawater had similar dominant taxa and assembly mechanisms. The results provide data support for studying the microbial ecology and exploiting microbial resources in the Yellow River estuary.

[Objective] Riemerella anatipestifer (RA) is a Gram-negative bacterium that mainly infects domesticated birds such as ducks and geese. The clinical isolates of RA are multi-drug resistant and increasing year by year. However, the transmission ways of antibiotic resistance genes in RA have not been identified. This study aims to identify the transmission ways and distribution of antibiotic resistance genes in the clinical isolates of RA. [Methods] The drug resistance phenotypes of the reference strain RA ATCC 11845 and the clinical isolates RA CH-1 and RA CH-2 to 28 antibiotics belonging to 10 categories were determined. The antibiotic resistance genes were identified by genome analysis and construction of gene deletion strains. The transmission ways of antibiotic resistance genes were identified by natural transformation. The distribution of these resistance genes in different clinical isolates was detected by PCR. [Results] RA CH-1 and RA CH-2 were resistant to β-lactams, tetracyclines, macrolides, lincosamides, and amide alcohols, while RA ATCC 11845 was sensitive to the above antibiotics. The resistant strains became sensitive to the corresponding antibiotics after the deletion of 13 resistance genes, respectively, indicating that these genes were involved in antibiotic resistance. All the resistant genes can be transferred to the sensitive strain RA ATCC 11845 by natural transformation. The detection rates of resistance genes in 100 clinical isolates from 2017 to 2023 varied within the range of 3% to 89%. [Conclusion] Antibiotic resistance genes can be transmitted in RA through natural transformation, and different antibiotic resistance genes presented varied distribution in clinical isolates, among which tetX (B739_0030) and bla_OXA (G148_1768) were carried by the most and fewest strains, respectively.

[Objective] To investigate the changes of microbial communities on loess slopes with different noise conditions under the influences of temperature and time. [Methods] Based on the changes in soil phosphate content, the noise was determined at 70, 90, and 110 dB. The microbial communities presented variations along the temperature gradients of −5, 15, and 35 ℃ and the noise duration of 2, 4, and 6 h. Subsequently, metagenomic sequencing was carried out for the soil microbial communities. [Results] At the phylum level, Actinobacteria, Mucoromycota, Thermoproteota, and Myxococcota showed differences in the relative abundance among groups (P < 0.05). At the genus level, Arthrobacter, Rhizophagus, Pseudarthrobacter, Actinomadura, Kocuria, Rubrobacter, and Corynebacterium demonstrated different relative abundance among groups (P < 0.05). At the species level, there were significant differences in the relative abundance of Rhizophagus irregularis, Actinomadura sp. WMMB 499, Rubrobacter tropicus, Arthrobacter sp. PGP41, Arthrobacter sp. 24S4 2, and Arthrobacter crystallopoietes among groups (P < 0.05). [Conclusion] Different noise environments have significant effects on the relative abundance of soil microorganisms at the phylum, genus, and species levels.

Bacterial biofilms are aggregates surrounded by extracellular polymeric substances produced by bacteria, exhibiting significant resistance to antimicrobials and host immune defense mechanisms. As a result, they become a crucial factor in the recalcitrance of bacterial infections. Phages, as a class of viruses capable of specifically infecting and lysing bacteria, have demonstrated immense potential in the prevention and treatment of biofilm-associated infections. This review summarizes the efficacy, in vitro and in vivo research methods, and mechanisms of phages, phage endolysins, and phage-antibiotic combinations in combating biofilm-associated infections. Furthermore, it discusses the prospects and potential obstacles of phages in this field, aiming to give insights into the development of more effective therapeutic agents.

[Objective] Keratinases, a class of serine proteases capable of degrading keratin, have important application potential and research value in the utilization of keratin resources. The efficient industrial production of keratinase is helpful to promoting its application in leather, textiles, feed, chemical fertilizers, daily chemicals, and medicine. In this study, we optimized the fermentation conditions of Bacillus subtilis WB600-pMA5-KerBv, a recombinant keratinase-producing strain constructed in our laboratory, to improve the enzyme production. Furthermore, we explored the potential application of keratinase in the degradation of fibrin. [Methods] First, the composition of the fermentation medium was determined by single factor experiments. Then, response surface methodology was employed to optimize the medium formula for producing keratinase, and the factors significantly affecting the growth and enzyme production of bacteria and the optimum concentrations were determined. Subsequently, the DoseResp model was adopted to predict the optimal growth point of the strain and thus guide the expansion of enzyme production in a 5 L fermenter. Finally, the blood clot and fibrinogen degradation experiments were carried out to evaluate the degradation performance of the keratinase. [Results] The formula of the fermentation medium for producing keratinase by the recombinant strain was optimized as follows (g/L): glucose 25.0, yeast powder 25.0, soybean meal 15.0, dipotassium phosphate 14.04, potassium dihydrogen phosphate 2.58, and magnesium chloride 0.3. The optimal growth point of the strain was predicted based on the DoseResp model to guide the expansion of production in a 5 L fermenter. Under the optimized conditions, the OD₆₀₀ (bacterial biomass) increased from 2.45 in a shake flask to 77.80, and the enzyme activity increased by about 4.76 times from 4 471 U/mL in a shake flask to 21 301.67 U/mL. In addition, the keratinase showcased remarkable degradation ability on fibrinogen and blood clots. [Conclusion] The systematic fermentation optimization and model-based prediction of enzyme production in fermenters improved the production of keratinase in Bacillus subtilis. The findings provided a research basis for the application of keratinase in thrombolysis.

Airborne microorganisms (AMs), including bacteria, fungi, and viruses, are ubiquitous. They are indispensable components of the atmospheric ecosystem, play an essential role in maintaining the stability and functions of the atmospheric ecosystem. AMs include not only beneficial microorganisms but also pathogenic microorganisms, which pose a threat to human health. Therefore, comprehensively revealing the distribution characteristics and succession patterns of AMs is of great significance for improving air quality, safeguarding human health, and ensuring national biosafety. This review systematically elucidates the sources, distribution characteristics, influencing factors, and categories of pathogenic microorganisms as well as the health risks associated with AMs. It contributes to the in-depth understanding of AMs pollution and its health risks, providing a scientific basis for preventing and controlling the pollution and protecting human health and eco-environment.