Inoculation with Bacillus megaterium CNPMS B119 and Bacillus subtilis CNPMS B2084 improve P-acquisition and maize yield in Brazil

Phosphorus (P) is a critical nutrient for plant growth, yet its uptake is often hindered by soil factors like clay minerals and metal oxides such as aluminum (Al), iron (Fe), and calcium (Ca), which bind P and limit its availability. Phosphate-solubilizing bacteria (PSB) have the unique ability to convert insoluble P into a soluble form, thereby fostering plant growth. This study aimed to assess the efficacy of inoculation of Bacillus megaterium B119 (rhizospheric) and B. subtilis B2084 (endophytic) via seed treatment in enhancing maize yield, grain P content, and enzyme activities across two distinct soil types in field conditions. Additionally, we investigated various mechanisms contributing to plant growth promotion, compatibility with commercial inoculants, and the maize root adhesion profile of these strains. During five crop seasons in two experimental areas in Brazil, Sete Lagoas-MG and Santo Antônio de Goiás-GO, single inoculations with either B119 or B2084 were implemented in three seasons, while a co-inoculation with both strains was applied in two seasons. All treatments received P fertilizer according to plot recommendations, except for control. Both the Bacillus strains exhibited plant growth-promoting properties relevant to P dynamics, including phosphate solubilization and mineralization, production of indole-3-acetic acid (IAA)-like molecules, siderophores, exopolysaccharides (EPS), biofilms, and phosphatases, with no antagonism observed with Azospirillum and Bradyrizhobium. Strain B2084 displayed superior maize root adhesion compared to B119. In field trials, single inoculations with either B119 or B2084 resulted in increased maize grain yield, with relative average productivities of 22 and 16% in Sete Lagoas and 6 and 3% in Santo Antônio de Goiás, respectively. Co-inoculation proved more effective, with an average yield increase of 24% in Sete Lagoas and 11% in Santo Antônio de Goiás compared to the non-inoculated control. Across all seasons, accumulated grain P content correlated with yield, and soil P availability in the rhizosphere increased after co-inoculation in Santo Antônio de Goiás. These findings complement previous research efforts and have led to the validation and registration of the first Brazilian inoculant formulated with Bacillus strains for maize, effectively enhancing and P grain content.

Parameter evaluation for developing phosphate-solubilizing Bacillus inoculants

Bacterial inoculants have been used in agriculture to improve plant performance. However, laboratory and field requirements must be completed before a candidate can be employed as an inoculant. Therefore, this study aimed to evaluate the parameters for inoculant formulation and the potential of Bacillus subtilis (B70) and B. pumilus (B32) to improve phosphorus availability in maize (Zea mays L.) crops. In vitro experiments assessed the bacterial ability to solubilize and mineralize phosphate, their adherence to roots, and shelf life in cassava starch (CS), carboxymethyl cellulose (CMC), peat, and activated charcoal (AC) stored at 4 °C and room temperature for 6 months. A field experiment evaluated the effectiveness of strains to increase the P availability to plants growing with rock phosphate (RP) and a mixture of RP and triple superphosphate (TS) and their contribution to improving maize yield and P accumulation in grains. The B70 was outstanding in solubilizing RP and phytate mineralization and more stable in carriers and storage conditions than B32. However, root adherence was more noticeable in B32. Among carriers, AC was the most effective for preserving viable cell counts, closely similar to those of the initial inoculum of both strains. Maize productivity using the mixture RPTS was similar for B70 and B32. The best combination was B70 with RP, which improved the maize yield (6532 kg ha-1) and P accumulation in grains (15.95 kg ha-1). Our results indicated that the inoculant formulation with AC carrier and B70 is a feasible strategy for improving phosphorus mobilization in the soil and maize productivity.

Co-inoculation with tropical strains of Azospirillum and Bacillus is more efficient than single inoculation for improving plant growth and nutrient uptake in maize

Usage of Bacillus and Azospirillum as new eco-friendly microbial consortium inoculants is a promising strategy to increase plant growth and crop yield by improving nutrient availability in agricultural sustainable systems. In this study, we designed a multispecies inoculum containing B. thuringiensis (strain B116), B. subtillis (strain B2084) and Azospirillum sp. (strains A1626 and A2142) to investigate their individual or co-inoculated ability to solubilize and mineralize phosphate, produce indole acetic acid (IAA) and their effect on maize growth promotion in hydroponics and in a non-sterile soil. All strains showed significant IAA production, P mineralization (sodium phytate) and Ca-P, Fe-P (tricalcium phosphate and iron phosphate, respectively) solubilization. In hydroponics, co-inoculation with A1626 x A2142, B2084 x A2142, B2084 x A1626 resulted in higher root total length, total surface area, and surface area of roots with diameter between 0 and 1 mm than other treatments with single inoculant, except B2084. In a greenhouse experiment, maize inoculated with the two Azospirillum strains exhibited enhanced shoot dry weight, shoot P and K content, root dry weight, root N and K content and acid and alkaline phosphatase activities than the other treatments. There was a significant correlation between soil P and P shoot, alkaline phosphatase and P shoot and between acid phosphatase and root dry weight. It may be concluded that co-inoculations are most effective than single inoculants strains, mainly between two selected Azospirillum strains. Thus, they could have synergistic interactions during maize growth, and be useful in the formulation of new inoculants to improve the tropical cropping systems sustainability.

Research status of Bacillus phytase

Phytic acid is abundant in seeds, roots and stems of plants, it acts as an anti-nutrient in food and feed industry, since it affects the absorption of nutrients by humans and monogastric animals. Furthermore, phosphorus produced through its decomposition by microorganisms can cause environmental pollution. Phytase degrades phytic acid generating precursors of inositol that can be used in clinical practice; in addition, phytase treatment can minimize the anti-nutritional effect of phytic acid. The use of phytase synthesized from Bacillus is more advantageous due to its high activity. Additionally, its good heat resistance under neutral conditions greatly fills the gap of commercial utilization of acid phytase. In this review, we summarize the latest research results on Bacillus phytase, including its physiological and biochemical characteristics, molecular structure information, calcium effects on its catalytic activity and stability, its catalytic mechanism and molecular modification.

Crop type exerts greater influence upon rhizosphere phosphohydrolase gene abundance and phylogenetic diversity than phosphorus fertilization

Rock phosphate is an alternative form of phosphorus (P) fertilizer; however, there is no information regarding the influence of P fertilizer sources in Brazilian Cerrado soils upon microbial genes coding for phosphohydrolase enzymes in crop rhizospheres. Here, we analyze a field experiment comparing maize and sorghum grown under different P fertilization (rock phosphate and triple superphosphate) upon crop performance, phosphatase activity and rhizosphere microbiomes at three levels of diversity: small subunit rRNA marker genes of bacteria, archaea and fungi; a suite of alkaline and acid phosphatase and phytase genes; and ecotypes of individual genes. We found no significant difference in crop performance between the fertilizer sources, but the accumulation of fertilizer P into pools of organic soil P differed. Phosphatase activity was the only biological parameter influenced by P fertilization. Differences in rhizosphere microbiomes were observed at all levels of biodiversity due to crop type, but not fertilization. Inspection of phosphohydrolase gene ecotypes responsible for differences between the crops suggests a role for lateral genetic transfer in establishing ecotype distributions. Moreover, they were not reflected in microbial community composition, suggesting that they confer competitive advantage to individual cells rather than species in the sorghum rhizosphere.