Objective To screen the microbial strains producing volatile organic compounds (VOCs) with both broad-spectrum antagonistic activity and postharvest fruit preservation potential. Methods Endophytic bacterial strains were isolated and purified by the dilution plating method from the roots and branches of wild tea plants in Guangxi, China. Candidate strains were initially selected based on the number of functional traits via six types of functional media: cellulase, amylase, siderophore, organic phosphorus, inorganic phosphorus, and nitrogen-fixing media. The antagonistic activity of the strains against seven common plant pathogenic fungi was determined by the dual-culture assay, and thus the broad-spectrum antagonistic strains were screened out. Strains with superior overall performance were further selected to evaluate their antagonistic activity against the postharvest anthracnose pathogens—Colletotrichum fructicola and Colletotrichum musae—of mangoes and bananas. An in vitro banana preservation assay was conducted with the chemical preservative prochloraz as a positive control. Results Functional screening on selective media yielded 98 strains that simultaneously possessed four or more plant growth-promoting or stress-tolerance traits, including nitrogen fixation, phosphate solubilization, and siderophore production. In dual-culture assays against seven common plant pathogenic fungi, 18 broad-spectrum antagonistic strains significantly inhibiting at least five pathogens were screened out, among which four strains exhibited stable and strong antagonistic activity against all the seven pathogens. On this basis, two key indicators, number of functional traits and broad-spectrum inhibition rate, were comprehensively evaluated, and five strains with the best overall performance were finally selected for subsequent specific antagonism assays against the pathogens causing mango and banana anthracnose and for validation of their postharvest fruit preservation effects. In dual-culture assays, the inhibition rates of the tested strains against the two anthracnose pathogens ranged from 43.36% to 83.50%. In plate-on-plate assays, the VOCs produced by these strains exhibited inhibition rates of 56.80%-99.25% against C. fructicola and 54.50%-99.85% against C. musae, with several strains showing nearly 100.00% inhibitory activity against both pathogens. In vitro fruit preservation tests demonstrated that VOCs produced by the antagonistic strains delayed the postharvest decay of mangoes and bananas to varying degrees. Strain T-1-6 showed the most pronounced effect, extending the onset of visible banana decay to 21 days (the final decay grade was grade 0), and its preservation effect was comparable to that of the chemical preservative prochloraz, achieving approximately 50% control efficacy against surface molds on mangoes. Analysis of 16S rRNA gene and gyrB sequences revealed that all the five dominant antagonistic strains belonged to the genus Bacillus, including B. amyloliquefaciens, B. thuringiensis, B. cereus, and B. subtilis. Conclusion The VOCs-producing endophytic Bacillus strains from tea plants possess multiple functional traits and broad-spectrum antagonistic activity. This study provides promising candidate strains and a theoretical basis for the green disease control and biopreservation of postharvest tropical fruits such as mangoes and bananas.

Soil nutrient deficiency is a major limiting factor affecting crop yields. Excessive use of chemical fertilizers can lead to soil compaction, environmental pollution, and decreased crop yields and quality. Microalgae-based fertilizer, functioning as a novel green bio-fertilizer, not only effectively promotes crop growth but also enhances soil fertility under various adverse soil conditions. Objectives This study investigated the effects of different fertilizer treatments on the growth of foxtail millet (Setaria italica L.) and the physicochemical properties, enzymes activities, and microbial communities of infertile soil, aiming to provide theoretical support for the application of microalgae-based fertilizer in chemical fertilizer reduction and green sustainable agricultural production. Methods The foxtail millet cultivar ‘Jingu 21’ was cultivated in this study under five fertilizer treatments: full chemical fertilizer (T1), chemical-microalgae integrated fertilizer (T2: 80% chemical fertilizer+20% microalgae-based fertilizer; T3: 60% chemical fertilizer+40% microalgae-based fertilizer; T4: 40% chemical fertilizer+60% microalgae-based fertilizer), and full microalgae-based fertilizer (T5). The growth indexes, biomass, and pigment content of foxtail millet in each treatment were determined, and the physicochemical properties, enzyme activities, and bacterial community characteristics of the infertile soil were measured, after 90 days of cultivation. Results Among the five fertilizer treatments, T4 had the most significant effect of promoting the seedling growth of foxtail millet in the infertile soil. Compared with T1, T4 increased the seedling height, the aboveground dry weight, and the content of chlorophyll a, chlorophyll b, and carotenoids by 26.41%, 126.47%, 17.1%, 24.5%, and 28.0%, respectively. In addition, T5, T2, T3, and T4 increased the content of total nitrogen, available phosphorus, and organic matter and the activities of sucrase, nitrate reductase, peroxidase, and phosphatase in the soil, compared with T1, and T4 had the most significant soil improvement effect. The 16S rRNA gene amplicon sequencing results showed that compared with T1 and T5, T4 increased the diversity of soil microorganisms, in which the relative abundance of Acidobacteriota and Chloroflexi was significantly increased. The correlation analysis showed that the composition of soil microbial diversity was significantly and positively correlated with urease, and the soil microbial community composition had significantly positive correlations with available phosphorus, sucrase, peroxidase, and urease. Redundancy analysis showed that urease and available phosphorus were the main environmental factors affecting the soil bacterial community structure. The relative abundance of Chloroflexi had significantly positive correlations with the urease activity and the available phosphorus content. Conclusion The combined application of microalgae-based fertilizer with reduced chemical fertilizer not only effectively improves the nutrient content and enzyme activities but also enhances the microbial diversity and community structure in the soil, thereby promoting the growth of foxtail millet seedlings in infertile soil.

Objective To investigate the growth-promoting properties and mechanisms of Bacillus amyloliquefaciens DGL1 isolated from arid sandy soils of the Qinghai-Xizang Plateau on oat plants under drought stress, thus providing a high-quality microbial resource and a theoretical basis for developing microbial fertilizers suitable for arid regions. Methods The growth-promoting effects of strain DGL1 on oat root length, plant height, and fresh weight under drought stress were determined. The degree of cell membrane lipid peroxidation and the activities of antioxidant enzymes in oat plants under drought stress were measured. The genome and transcriptome of strain DGL1 were sequenced via high-throughput technology. Results Strain DGL1 significantly increased the root length, plant height, and fresh weight of oat plants under drought stress. It markedly elevated the activities of antioxidant enzymes [(superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)] while reducing the content of malondialdehyde and H₂O₂. Genomic analysis revealed that DGL1 carried the genes related to oxidative stress (gpx encoding glutathione peroxidase, opuD encoding glycine-betaine transporter, and ahpF encoding alkyl hydroperoxide reductase), synthesis of the IAA precursor l-tryptophan (trpA, trpB, and trpC), and flagellar biosynthesis (FliP, FliQ, and FliR). Transcriptome sequencing further revealed that genes associated with biofilm formation, nitrogen and phosphorus uptake, material and energy metabolism, and auxin precursor synthesis—all crucial for root colonization—presented upregulated expression under drought stress. The strain might enhance plant drought tolerance via these pathways. Conclusion Strain DGL1 can enhance the drought tolerance of oat plants and has great potential for application in developing bio-inoculants for arid land agriculture.

As a pioneer species in desert areas and the main host of Cistanche deserticola, Atriplex canescens is widely planted in the Ulan Buh Desert in Inner Mongolia. Rhizosphere and endophytic microorganisms play a significant role in the growth and stress resistance of plants. However, few studies have been conducted on the growth-promoting functions of rhizosphere and endophytic bacteria on A. canescens in the Ulan Buh Desert. Objective We screened plant growth-promoting strains from the rhizosphere and endophytic bacteria of A. canescens, aiming to provide microbial resources for the sustainable breeding of A. canescens in this region. Methods Rhizosphere soil and plant samples of A. canescens were collected from the Ulan Buh Desert in Dengkou County, Inner Mongolia. Rhizosphere and endophytic bacteria were isolated and purified. The plant growth-promoting effects of these bacteria and the plant growth-promoting bacteria of Astragalus previously obtained by our research group on A. canescens seedlings were investigated. Molecular biological identification and functional analysis were conducted on the strains with significant plant growth-promoting effects. Then, these strains were combined and the growth-promoting effects of the strain combinations on A. canescens were evaluated. Results A total of 60 rhizosphere bacterial strains and 14 endophytic bacterial strains of A. canescens were isolated. Two endophytic bacterial strains significantly promoted the growth of A. canescens seedlings. Among the Astragalus growth-promoting bacteria tested, three strains had significant growth-promoting effects on A. canescens seedlings. The five plant growth-promoting strains were identified as four species belonging to three genera: Pseudomonas, Bacillus, and Acinetobacter. These strains had different levels of nitrogen fixation, inorganic and organic phosphorus solubilization, potassium feldspar and potassium aluminum silicate solubilization, and indole-3-acetic acid (IAA) and biofilm production. Most of the strains had the ability to produce siderophores. Multiple strain combinations promoted the growth of A. canescens. Combinations 2 (IH-2, IH-9, and TYA27), 3 (IH-2, IH-9, and PAS13-2) and 4 (IH-2, TYA39, and TYA27) demonstrated the best comprehensive plant growth-promoting effects, with Pseudomonas bijieensis IH-2 as the core strain. Conclusion The growth-promoting bacteria of A. canescens in the Ulan Buh Desert mainly include Pseudomonas and Bacillus. P. bijieensis plays a core role in the plant growth-promoting bacterial combinations.

Objective To explore the nitrogen and phosphorus removal efficiency of different immobilization strategies and mineralization methods of Bacillus licheniformis ZXT for high nitrogen-phosphorus wastewater, clarify the optimal mineralization conditions and carrier mechanism of action, and provide technical support for the green treatment and recovery of complex high nitrogen-phosphorus wastewater resources such as swine manure wastewater. Methods Four systems—free bacteria, chemical precipitation, activated carbon fiber (ACF) immobilization, and polyvinyl alcohol-sodium alginate-carbon powder (PVA-SA-CP) immobilization—were compared for their mineralization effects under Mg:N:P molar ratios of 0.6:1:1, 1:1:1, and 1.4:1:1. Characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) were employed to analyze mineral properties. The application potential of the systems was verified with actual swine manure wastewater. Results The ACF immobilization system exhibited the optimal efficiency. Under the Mg:N:P ratio of 1:1:1, after seven days of cultivation, the final concentration of NH₄⁺ was only 0.59 mg/L (removal rate: 99.81%) and the final concentration of PO₄^3- was as low as 0.03 mg/L (removal rate: 99.99%), both meeting the national discharge standards (GB 8978—1996), with the formation of regular crystalline long plate-like struvite (i.e., magnesium ammonium phosphate, MAP). The PVA-SA-CP immobilization system showed significantly weaker removal effects under the same ratio, with final concentrations of NH₄⁺ and PO₄^3- being 5.07 mg/L and 0.45 mg/L, respectively. The chemical precipitation method failed to meet the standards, as the final concentration of NH₄⁺ ranged from 38.90 to 48.01 mg/L (removal rate: 84.70%-87.61%) within 24 h. Free bacteria achieved the removal rates of 99.97% for NH₄⁺ and 99.92% for PO₄^3- in actual swine manure wastewater after eight days of cultivation, with final NH₄⁺ and PO₄^3- concentrations of 0.15 mg/L and 0.05 mg/L, respectively, which complied with the discharge requirements. Conclusion Due to its developed microporous structure and good biocompatibility, ACF can efficiently enrich bacteria and promote the regular assembly of extracellular polymeric substances. The mineralization with ACF-immobilized B. licheniformis ZXT is the optimal choice, with Mg:N:P=1:1:1 as the best mineralization ratio. This technology can achieve efficient purification of high nitrogen-phosphorus wastewater and recovery of nitrogen and phosphorus resources, thus having important application value in actual wastewater treatment.

Objective The rhizosphere microbial community plays a critical role in plant growth, development, and quality formation. Therefore, this study systematically isolated plant growth-promoting microbial resources from the rhizosphere of Bupleurum chinense and evaluated their application potential, aiming to provide excellent strains for the development of microbial fertilizers to reduce the use of chemical fertilizers and pesticides. Methods Plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) were isolated and identified from the rhizosphere of B. chinense by the culture-dependent methods. Functional traits of PGPR strains were screened through in vitro assays, and the synergistic growth-promoting effects of PGPR and AMF were subsequently evaluated by a pot experiment. Results A total of 25 PGPR species and 2 AMF species (Funneliformis mosseae and Entrophospora etunicata) were isolated from the rhizosphere of B. chinense. Functional screening of PGPR revealed that Lysobacter antibioticus, Pseudomonas germanica, Rhodococcus corynebacterioides, and Methylobacterium marchantiae exhibited outstanding abilities in indole-3-acetic acid production, organic phosphorus solubilization, inorganic phosphorus solubilization, and nitrogen fixation, respectively. The pot experiment showed that co-inoculation with PGPR and AMF significantly enhanced the plant growth, biomass accumulation, and nutrient uptake of B. chinense, with plant growth-promoting effects markedly greater than single inoculation treatments. Conclusion This study isolated and identified some plant growth-promoting microorganisms from the rhizosphere of B. chinense and demonstrated the synergistic effects between PGPR and AMF, providing valuable microbial resources and theoretical bases for the sustainable cultivation of B. chinense.

Objective Sebum metabolism disorders are a key contributing factor to various dermatological conditions. As an emerging class of microbial agents, postbiotics show potential in regulating metabolic processes. This study aimed to investigate the efficacy and mechanisms of Lacticaseibacillus paracasei CCFM1224 postbiotics in alleviating sebum metabolism disorders and explore the active components responsible for the effects. Methods Using a mouse model of oleic acid-induced sebum metabolism disorders, we comprehensively evaluated the efficacy of CCFM1224 postbiotics in ameliorating sebum imbalance. This evaluation encompassed phenotypic measurements, hormonal parameters, and skin lipid content. Changes in the expression of genes related to skin lipid metabolism were measured via real-time quantitative PCR. Subsequently, a free fatty acid-induced lipid accumulation model in HepG2 cells was utilized to screen the active components of postbiotics. Results CCFM1224 postbiotics significantly ameliorated sebum metabolism disorders in mice. This was evidenced by mitigated abnormal weight gain, a reduced testicle index, alleviated histopathological skin damage, and decreased levels of inflammatory cytokines (IL-6, IL-1β, and TNF-α) as well as triglyceride (TG) and non-esterified fatty acid (NEFA) in the skin tissue. CCFM1224 postbiotics modulated sebum metabolism by downregulating the expression of lipogenesis-related genes (FASN, PPAR-γ, and SREBP-1c) and upregulating the expression of lipolysis-related genes (PPAR-α, HSL, and ATGL). Further cellular validation identified the inactivated bacterial cell component as the key functional fraction, which effectively alleviated intracellular lipid accumulation and associated damage, thereby clarifying the material basis for the effects of CCFM1224 postbiotics. Conclusion L. paracasei CCFM1224 ameliorate sebum metabolism disorders by modulating hormone secretion and lipid metabolic pathways. The key bioactive components were identified as the inactivated bacterial cells, rather than the fermentation supernatant. This finding provides a theoretical foundation for the application of postbiotics in regulating lipid metabolism disorders and establishes a basis for developing related functional microbial preparations.

Objective To obtain microbial communities capable of degrading polystyrene microplastics (PS) and polypropylene microplastics (PP) and analyze their degradation efficiency and synergistic mechanisms, thus providing resources and theoretical support for the in-situ bioremediation and enriching our understanding of the mechanisms underlying the synergistic degradation of complex pollutants by microbial communities. Methods The microbial communities capable of degrading PS and PP were enriched from plastic-contaminated activated sludge of enterprises. A 60-day degradation experiment was carried out to evaluate the degradation efficiency of the microbial communities on the two microplastics based on the weight loss rate. The surface structures, hydrophobicity, and molecular weight changes of microplastics were characterized by scanning electron microscopy (SEM), water contact angle (WCA), and gel permeation chromatography (GPC). Fourier transform infrared spectroscopy (FTIR) and GC-MS were employed to analyze the degradation products and metabolic pathways of microplastics. The dominant groups, core functional bacteria, and their encoded related enzymes in the microbial communities were clarified through metagenomic analysis, on the basis of which the synergistic degradation mechanisms of the microbial communities were explored. Results The enriched microbial communities were dominated by Bacillota and Pseudomonadota. Bacillus initiated the initial degradation and Achromobacter participated in the intermediate metabolism, forming an “initiation-metabolism” synergistic network. PS and PP could be degraded without pretreatment within 60 days, with weight loss rates of (13.4±2.3)% and (23.2±2.4)%, respectively. Characterization confirmed that the microplastics during degradation presented damaged surfaces, reduced hydrophobicity, and decreased molecular weights. FTIR and GC-MS revealed that PS generated phenols and aldehydes through benzene ring hydroxylation and other processes, and entered the tricarboxylic acid cycle through the aromatic degradation pathway; PP were metabolized through the fatty acid degradation pathway via the oxidation chain of hydroxylation→carbonylation→esterification. The functional annotation of metagenomic data revealed that the genes encoding primary degradative enzymes and metabolic enzymes from Bacillus and Achromobacter exhibited complementary functions, forming the molecular basis for efficient degradation. Conclusion The microbial communities identified in this study efficiently degrade PS and PP. It is hypothesized that their core functional bacteria, Bacillus and Achromobacter, achieve degradation of both microplastics through a synergistic “initiation-metabolism” network and functionally complementary enzyme systems. This provides insights for managing residual microplastics after source control and deepens our understanding of the mechanisms underlying microbial synergistic degradation of complex pollutants.

Objective Chondroitinases are crucial enzymes for the preparation of low-molecular-weight chondroitin sulfate (CS), yet the existing enzymes are insufficient to meet the demands of diverse applications, highlighting the need to discover novel chondroitinases with enhanced properties. Methods A novel chondroitinase belonging to the polysaccharide lyase family 8 (PL8), designated SlChase, was discovered and identified from the model strain Streptomyces lividans TK24. Following heterologous expression in Escherichia coli and the subsequent purification, a soluble and highly active recombinant SlChase was successfully obtained. Results This enzyme exhibited substantial activity within the temperature range of 30-40 ℃ and pH range of 5.5-6.5, and demonstrated excellent long-term stability during storage at 4 ℃. Mg²⁺ and dithiothreitol (DTT) moderately enhanced its catalytic activity, whereas metal ions including Zn²⁺ and Fe³⁺ exerted inhibitory effects on its activity. Notably, SlChase displayed prominent activity towards unsulfated chondroitin (CS-0S), whereas its catalytic activity towards chondroitin sulfate A/C was drastically decreased. Conclusion The discovered SlChase not only expands the diversity of PL8 family enzymes but also affords a novel enzymatic tool for the specific degradation of unsulfated chondroitin, with promising applications in glycoscience research and related biocatalytic processes. Furthermore, this study provides a paradigm for the exploration and utilization of enzymatic resources derived from Streptomyces spp.

In recent decades, the extensive and inappropriate use of antibiotics has led to the emergence of antibiotic-resistant bacteria, posing a serious threat to human health. Phage therapy has emerged as a promising approach for preventing and treating infections caused by drug-resistant bacteria, garnering considerable research interest. However, the rapid development of phage-resistant bacterial strains complicates the effectiveness of phage therapy. The phage steering strategy holds promise for addressing this challenge. Objective To isolate virulent phages specific to Salmonella that are suitable for phage steering therapy. Methods Specific virulent phages for Salmonella S503 were isolated and purified from wastewater samples collected from a wet market via the double agar overlay method. Their fundamental biological characteristics, antibacterial efficacy, genomic information, and in vitro biological safety were analyzed. Phage-resistant strains were generated through co-culturing Salmonella S503 with the phages. Subsequently, growth curve analysis, bacterial virulence testing, and antibiotic sensitivity assays were employed to systematically compare the characteristics of the wild-type strain and its phage-resistant counterpart. Results The isolated Salmonella phage was designated HK-1. This phage exhibited strong antibacterial properties, high stability, and confirmed biological safety in vitro. Compared with the wild-type strain Salmonella S503, the phage-resistant strain Salmonella S503-R displayed slow growth, significantly reduced virulence, and increased susceptibility to 11 different antibiotics. Furthermore, phage HK-1 demonstrated synergistic bactericidal effects when being combined with rifampicin, ampicillin, fosfomycin, and gentamicin. Notably, the combinations of HK-1 with ampicillin, fosfomycin, and gentamicin effectively inhibited the growth of Salmonella S503 within 24 h. Conclusion We successfully isolated a virulent phage from wastewater samples. This phage is suitable for phage steering therapy and offers potential for the prevention and treatment of antibiotic-resistant Salmonella.