Abiotic Factors Influence on Bacillus subtilis IMV B-7023 Phytase Activity

Abstract

Bacteria of the Bacillus genus can synthesize specific phytase enzymes. This property is especially important for soil bacteria. It helps to mineralize phytin and phytates and to provide these bacteria and plants (in the root zone of which they live) with the available phosphorus. Our previous studies have demonstrated that the Bacillus subtilis IMV B-7023 strain exhibits a phytase activity and can use phytate as a nutrition source. It is a component of the «Azogran» complex bacterial preparation for crop production. As known, abiotic environmental factors can influence the phytase activity of bacteria. In particular, the phytase activity changes significantly under different pH and temperatures. Solid soil particles, including nanosized minerals, can also influence bacteria’s enzymatic activity. The influence of abiotic factors on Bacillus subtilis IMV B-7023 phytase activity has not previously been studied, so this was the aim of our research. Methods. The phytase activity of bacteria was studied by measuring the amount of phosphate released from sodium phytate during the enzymatic reaction, and the nanomaterials’ influence on growth — by cultivation methods. Results. The highest B. subtilis IMV B-7023 phytase activity was observed at 28°C. Also, there was no B. subtilis IMV B-7023 phytase activity at pH 4—6. However, this activity increased at pH 7 and did not change significantly with increasing the buffer system pH to 12. Silicon dioxide influence on the B. subtilis IMV B-7023 growth activity during cultivation in a media with phytate as a phosphorus source depended on the nanomaterial concentration. Thus, at 0.05 and 0.5 g/L of silicon dioxide in the medium, this strain growth activity increased by 8—18%, and at 5.0 g/L of these nanoparticles, bacteria growth inhibition by 19% was observed. At the same time, clay mineral bentonite did not affect the B. subtilis IMV B-7023 growth under the studied cultivation conditions. In addition, silicon dioxide and bentonite stimulated B. subtilis IMV B-7023 phytase activity at all studied concentrations. So, phytase activity increased by 1.82—3.34 times upon adding silicon dioxide and by 2.54—5.83 times upon adding bentonite into the medium. Since the optimal values for phytase activity of most genus Bacillus bacteria are within neutral pH values and temperatures within 50—55°C, a property of B. subtilis IMV B-7023 to show maximum phytase activity at alkaline pH and lower temperatures (28°C) and also stimulation of this activity by soil minerals increases competitiveness of this strain as a component of a bacterial preparation for crop production. Conclusions. Abiotic environmental factors influence the B. subtilis IMV B-7023 supernagrowth and phytase activity. Optimal physicochemical factors for the phytase activity of these bacteria are temperature 28°C and pH 7—12. The concentrations 0.05, 0.5, and 5.0 g/L of silicon dioxide and bentonite increase B. subtilis IMV B-7023 phytase activity. The effect of these nanoscale minerals on the B. subtilis IMV B-7023 growth depends on their type and concentration during cultivation in the medium with phytate as a phosphorus source. The obtained results indicate the potential ability of the B. subtilis IMV B-7023 strain to effectively assimilate phytates in neutral and alkaline soils, especially due to the interaction of these bacteria with bentonite and silicon dioxide nanoparticles. This expands the possibility of using B. subtilis IMV B-7023 in agricultural technologies.