# Evaluating Soil Bacteria for the Development of New Biopreparations with Agricultural Applications
## 4 Discussion
Extensive studies have investigated the ability of various _Bacillus_ sp. strains to solubilize phosphorus under laboratory conditions, revealing significant potential for agricultural applications. For instance, _B. subtilis_ has shown promising results in solubilizing inorganic phosphorus. In a study involving Bacillus strains isolated from San Luis, Argentina, _B. subtilis_ SL-7 demonstrated a high solubilization index on [PERSON]'s agar, outperforming the recognized plant growth-promoting bacterium _B. velexensis_ FZB42 [63]. Additionally, _B. velexensis_ strain Ag75 has been identified as a potent phosphate solubilizer, significantly increasing biomass and shoot phosphorus content in maize, and enhancing yields in both maize and soybean by 17.8% and 26.5%, respectively, in field experiments [64]. _P. megaterium_ has also been highlighted for its phosphorus solubilization capabilities, particularly through the production of organic acids such as succinic acid, which is strongly correlated with increased soluble phosphorus concentration [65]. This species has been shown to be effective at solubilizing phosphorus from various sources, including poultry bones and fish bones [66; 67; 68]. Although _P. amylolyticus_, part of the _Paenibacillus_ genus, may utilize mechanisms including organic acid production to solubilize phosphorus from insoluble compounds, enhancing availability to plants, the literature on its specific phosphorus solubilization capabilities remains limited [69; 70]. The _P. amylolticus_ strains tested in this study possess the ability to solubilize phosphorus. Various methodologies have been employed to study nitrogen fixation, including culturing of diazotrophic bacteria in nitrogen-free media and measuring nitrogenase activity using spectrophotometry and reagents such as Nessler's reagent [71] or the acetylene reduction assay [72]. The use of 16S rRNA PCR and sequencing enables the identification and confirmation of nitrogen-fixing bacteria [73]. The fixation of atmospheric nitrogen by bacteria is a crucial component of sustainable agriculture, as it reduces reliance on synthetic fertilizers [74]. Four of the five strains tested in our study are capable of fixing atmospheric nitrogen. _Bacillus_ species are known for their plant growth-promoting traits. According to the literature, they are able to fix nitrogen, making it available to plants, produce growth hormones, and solubilize phosphate [75]. Studies have also shown that certain Bacillus strains, including _B. subtilis_ and _B. licheniformis_, as well as _P. megaterium_, exhibit high nitrogenase activity in the acetylene reduction assay [76]. _B. subtilis_ and _P. megaterium_ isolated from soils in Vietnam cultivated with cassava have been found to have nitrogen-fixing abilities. The authors highlighted the importance of optimizing cultivation conditions for the growth and metabolic activity of nitrogen-fixing organisms. One of the most critical parameters affecting their growth and activity is pH [77]. The _B. licheniformis_ tested in the present study did not exhibit growth on nitrogen-free medium. It is possible that the isolated strain does not possess the ability to fix nitrogen, or the growth conditions may have affected its activity. The nitrogen-fixation abilities of _P. amylolyticus_ have not been studied extensively, although other _Peanibacillus_ species have been shown to be capable of fixing nitrogen [78; 79]. _P. amylolitycus_ exhibited growth on the nitrogen-free medium, which suggest that it may be capable of nitrogen fixation. The results obtained in this study regarding the antimicrobial activity of the selected bacterial strains are consistent with findings reported in the literature. _B. subtilis_ is particularly well known for its strong antimicrobial properties against various phytopathogens. This is primarily attributed to its production of secondary metabolites, including nonribosomal peptides and other antimicrobial compounds, which endow it with robust biocontrol capabilities. In other studies, _B.