Synergistic biocontrol of Bacillus subtilis and Pseudomonas fluorescens against early blight disease in tomato.

Early blight of tomato caused by Alternaria solani results in significant crop losses. In this study, Bacillus subtilis J3 and Pseudomonas fluorescens J8 were co-cultured as a synthetic microbial community (BCA) for synergistic biocontrol of A. solani, and the inhibition mechanism was investigated. BCA presented an inhibition ration against A. solani at 94.91%, which lowered the disease incidence by 38.26-42.87%; reduced peroxidase, catalase, superoxide dismutase activity of tomatoes by 73.11-90.22%; and promoted the biomass by 66.91-489.21%. With BCA protection, the relative expression of tomato resistance genes (including gPAL2, SWRKY, PR-10, and CHI) in roots and leaves was 12.83-90.70% lower than without protection. BCA also significantly altered the rhizosphere and phyllosphere microbial community. The abundance of potentially beneficial bacteria, including Bacillus, Pseudomonas, Arthrobacter, Lysobacter, and Rhizobium, elevated by 6.58-192.77%. They were negatively correlated with resistance gene expression, indicating their vital involvement in disease control. These results provided essential information on the synergistic biocontrol mechanism of bacteria against pathogens, which could contribute to developing novel biocontrol strategies. KEY POINTS: • Bacillus and Pseudomonas present a synergistic biocontrol effect against A. solani. • Biocontrol prevents pathogen damage and improves tomato growth and systemic resistance. • Beneficial bacteria thrive in the rhizosphere is the key to microbial regulation.

Effect and mechanism of simultaneous cadmium-tetracycline removal by a self-assembled microbial-photocatalytic coupling system.

Electrochemical bacteria Shewanella oneidensis MR-4 (MR-4) was used to biologically generate cadmium sulfide (bio-CdS) nanocrystals and construct a self-assembled intimately coupled photocatalysis-biodegradation system (SA-ICPB) to remove cadmium (Cd) and tetracycline hydrochloride (TCH) from wastewater. The characterization using EDS, TEM, XRD, XPS, and UV-vis confirmed the successful CdS bio-synthesis and its visible-light response capacity (520 nm). 98.4% of Cd2+ (2 mM) was removed during bio-CdS generation within 30 min. The electrochemical analysis confirmed the photoelectric response capability of the bio-CdS as well as its photocatalytic efficiency. Under visible light, SA-ICPB entirely eliminated TCH (30 mg/L). In 2 h, 87.2% and 43.0% of TCH were removed separately with and without oxygen. 55.7% more chemical oxygen demand (COD) was removed with oxygen participation, indicating the degradation intermediates elimination by SA-ICPB required oxygen participation. Biodegradation dominated the process under aerobic circumstances. Electron paramagnetic resonance analysis indicated that h+ and ·O2- played a decisive role in photocatalytic degradation. Mass spectrometry analysis proved that TCH was dehydrated, dealkylated, and ring-opened before mineralizing. In conclusion, MR-4 can spontaneously generate SA-ICPB and rapidly-deeply eliminate antibiotics by coupling photocatalytic and microbial degradation. Such an approach was efficient for the deep degradation of persistent organic pollutants with antimicrobial properties.

Effect of bioaugmentation on tetracyclines influenced chicken manure composting and antibiotics resistance.

Antibiotic residue in husbandry waste has become a serious concern. In this study, contaminated chicken manure composting was conducted to reveal the bioaugmentation effect on tetracyclines residue and antibiotics resistance genes (ARGs). The bioaugmented composting removed most of the antibiotics in 7 days. Under bioaugmentation, 96.88 % of tetracycline and 92.31 % of oxytetracycline were removed, 6.32 % and 20.93 % higher than the control (P < 0.05). The high-temperature period was the most effective phase for eliminating antibiotics. The treatment showed a long high-temperature period (7 days), while no high-temperature period was in control. After composting, the treatment showed 13.87 % higher TN (26.51 g/kg) and 13.42 % higher NO3--N (2.45 g/kg) than control (23.28 and 2.16 g/kg, respectively) but 12.72 % lower C/N, indicating fast decomposition and less nutrient loss. Exogenous microorganisms from bioaugmentation significantly reshaped the microbial community structure and facilitated the enrichment of genera such as Truepera and Fermentimonas, whose abundance increased by 71.10 % and 75.37 % than the control, respectively. Remarkably, ARGs, including tetC, tetG, and tetW, were enhanced by 198.77 %, 846.77 %, and 62.63 % compared with the control, while the integron gene (intl1) was elevated by 700.26 %, indicating horizontal gene transfer of ARGs. Eventually, bioaugmentation was efficient in regulating microbial metabolism, relieving antibiotic stress, and eliminating antibiotics in composting. However, the ability to remove ARGs should be further investigated. Such an approach should be further considered for treating pollutants-influenced organic waste to eliminate environmental concerns.

Responsive change of crop-specific soil bacterial community to cadmium in farmlands surrounding mine area of Southeast China.

In arable soils co-influenced by mining and farming, soil bacteria significantly affect metal (Cadmium, Cd) bioavailability and accumulation. To reveal the soil microecology response under this co-influence, three intersection areas (cornfield, vegetable field, and paddy field) were investigated. With a similar nutrient condition, the soils showed varied Cd levels (0.31-7.70 mg/kg), which was negatively related to the distance from mining water flow. Different soils showed varied microbial community structures, which were dominated by Chloroflexi (19.64-24.82%), Actinobacteria (15.49-31.96%), Acidobacteriota (9.46-20.31%), and Proteobacteria (11.88-14.57%) phyla. A strong correlation was observed between functional microbial taxon (e. g. Acidobacteriota), soil physicochemical properties, and Cd contents. The relative abundance of tolerant bacteria including Vicinamibacteraceae, Knoellia, Ardenticatenales, Lysobacter, etc. elevated with the increase of Cd, which contributed to the enrichment of heavy metal resistance genes (HRGs) and integration genes (intlI), thus enhancing the resistance to heavy metal pollution. Cd content rather than crop species was identified as the dominant factor that influenced the bacterial community. Nevertheless, the peculiar agrotype of the paddy field contributed to its higher HRGs and intlI abundance. These results provided fundamental information about the crop-specific physiochemical-bacterial interaction, which was helpful to evaluate agricultural environmental risk around the intersection of farmland and pollution sources.