Bacillus subtilis A-5 has the capabilities of high-molecular-weight γ-PGA production, antagonism to plant pathogenic fungi, and salt/alkaline tolerance. This multifunctional bacterium has great potential for enhancing soil fertility and plant security in agricultural ecosystem. The genome size of B. subtilis A-5 was 4,190,775 bp, containing 1 Chr and 2 plasmids (pA and pB) with 43.37% guanine-cytosine content and 4605 coding sequences. The γ-PGA synthase gene cluster was predicted to consist of pgsBCA and factor (pgsE). The γ-PGA-degrading enzymes were mainly pgdS, GGT, and cwlO. Nine gene clusters producing secondary metabolite substances, namely, four unknown function gene clusters and five antibiotic synthesis gene clusters (surfactin, fengycin, bacillibactin, subtilosin_A, and bacilysin), were predicted in the genome of B. subtilis A-5 using antiSMASH. In addition, B. subtilis A-5 contained genes related to carbohydrate and protein decomposition, proline synthesis, pyruvate kinase, and stress-resistant proteins. This affords significant insights into the survival and application of B. subtilis A-5 in adverse agricultural environmental conditions.

This study investigated the effects of bio-organic fertilizer (BF) containing plant growth-promoting bacterium Bacillus velezensis SS-20 on soil properties, microbial community structure, and C/N cycle functional genes. The results showed that compared with chemical fertilizer (CF) and deactivated bio-organic fertilizer (BFD) treatments, BF significantly improved soil physicochemical properties. Soil pH, organic matter, total nitrogen, total potassium, and total phosphorus content under BF treatment were increased by 14.8%, 56.5%, 48.2%, 38.8%, and 58.4%, respectively, compared to the control; soil urease and sucrase activities increased by 3.5 and 2.4 times those of CF treatment, respectively. Meanwhile, BF increased pakchoi yield by 11.2% (vs. CF). BF treatment enhanced the relative abundance of beneficial bacteria Actinomycetota by 28.4% compared with the BFD treatment and raised that of fungi Ascomycota to 1.9 times that of the control. At the genus level, BF significantly enriched biocontrol-relevant genus Pseudogymnoascus, whose abundance reached three times that of CF treatment, while the abundance of potentially harmful genus Penicillium decreased by 82%. BF also led to a high degree of synergy in carbon and nitrogen cycles. Functional gene analysis indicated that BF down-regulated multiple carbon-degrading genes, increased organic nitrogen metabolism genes by 5.3%, and reduced denitrification genes by 13.3%. Overall, bio-organic fertilizer optimized the soil microenvironment, regulated the microbial community structure, and improved C/N use efficiency and plant growth by introducing functional microorganisms and organic matter.

The current fertilizer recommendations for melon plantation have many limitations and exhibit deficiencies regarding future development. Therefore, in this study, the optimal quantities of fertilizer, in terms of the effects of single factors and interaction effects, are studied. There were significant interaction effects between N and P, N and K, P and K; the contents of soluble protein, vitamin C (Vc), and soluble sugar in melon could be improved using the optimal fertilization ratios. The optimal ratio of N:P:K was 2.33:1:3.85, with the amounts of N, P₂O₅, and K₂O, respectively, being 157.5, 67.58, and 260.38 kg/hm², yielding 8.73 g/kg of soluble protein in melon. The optimal ratio of N:P:K was 2.03:1:3.36, with amounts of N, P₂O₅, and K₂O being 157.50, 77.40, and 260.38 kg/hm², respectively, yielding 25.32 g/kg Vc content in melon. Finally, the optimal ratio of N:P:K was 1.53:1:3.36, with the amounts of N, P₂O₅, and K₂O being 118.07, 77.40, respectively, and 260.38 kg/hm², yielding 13.34% soluble sugar content in melon.

(1) Background: A vegetable eel co-culture system is an economically efficient way of agricultural cultivation, which can have an impact on the soil microbial environment and play a pivotal role in the soil nutrient cycle, but there is little research on its impact on soil ammonia-oxidizing microorganisms. (2) Methods: NovaSeq platform sequencing was employed to investigate the richness, structure, and diversity of soil ammonia-oxidizing microbial communities, exploring the effects of a vegetable eel co-culture system on soil nitrogen cycling. Four different planting treatments were set up: unfertilized without vegetable eel (CCK), fertilized without vegetable eel (CRT), unfertilized with vegetable eel (ICK), and fertilized with vegetable eel (IRT). (3) Results: A vegetable eel co-culture system significantly increased soil pH and decreased bulk density under fertilization conditions. The soil nitrification potential rate was enhanced by a vegetable eel co-culture system to an average of 26.3%. A vegetable eel co-culture system significantly altered the community structure of all ammonia-oxidizing microorganisms, with a significant increase in the richness and diversity of ammonia-oxidizing bacteria (AOB) and comammox clade-A, while fertilization significantly increased the diversity of all ammonia-oxidizing microbial communities. Structural equation modeling (SEM) analysis showed that the main environmental factors affecting the structure of the ammonia-oxidizing microbial community were nitrate and total nitrogen. The number of amoA genes in AOB and comammox clade-B was significantly positively correlated with the soil potential N nitrification rate (PNR), which played a leading role in the nitrification of alkaline vegetable soil. The network analysis revealed that a vegetable eel co-culture system improved the modularity of AOB and comammox clade-B by 13.14% and 5.66%. (4) Conclusions: This study showed that the vegetable eel co-culture system stimulated the evolution of ammonia-oxidizing microbial communities by changing the physicochemical properties, which in turn promoted the soil nitrification reaction.

Removal of lake sediment has been shown to be an effective method for lake restoration. High phosphorus (P) content makes it possible for lake sediment to provide fertility for agricultural production. However, little research has focused on the responses of the soil-phosphorus-related microbial community to the sediment-derived fertilizer enriched in phosphorus content. The phoD-harboring gene, important to the global phosphorus cycle, encodes alkaline phosphatase hydrolyzing organic P in soil. Accordingly, a plot experiment was performed to compare the effects of four different fertilization treatments—no-fertilizer control (CK), 50% chemical fertilization with compressed sediment (CS), 50% chemical fertilization with original lake sediment (S), and conventional chemical fertilization treatment (CT)—on the phoD gene community using QPCR and high-throughput sequencing analysis. Relationships among soil physicochemical properties, phoD-harboring microbial community abundance and composition were also evaluated. Results showed that compared to CT, CS significantly increased soil organic matter (SOM) content by 20.29%, and S enhanced the humus content by 20.75% (p < 0.05). There was no significant influence on phoD gene microbial community richness (Chao1 and Sobs indexes) and diversity (Shannon index) between all treatments. The CS treatment significantly altered the phoD community structure and enhanced the Chinese cabbage yield by 40.19% (p < 0.05). Pearson analysis showed that phoD gene abundance (copy number) had significant and negative relationships with SOM, total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), and the Chao1 index. Redundancy analysis showed that shifts in the phoD community structure were related to soil physicochemical properties (SOM, TN, TP, AN, AP, and humus) rather than soil pH. In conclusion, the compressed sediment can be used in farmland since it optimizes the phoD-harboring microbial community abundance, composition, and structure, and thus significantly increases the Chinese cabbage yield.