Exploring multifunctional Bacillus bacteria for enhanced legume crop growth and antifungal protection: a sustainable approach

LENCINA, N; GOTTIG, N.; JORGELINA OTTADO; GARAVAGLIA, B.S.

Congreso; XVIII Congreso Samige; 2023

Modern agriculture needs sustainable and efficient solutions to enhance productivity. In this context, the strategic application of bacteria has emerged as a promising ecological practice. Particularly, the genus Rhizobium, distinguished for its atmospheric nitrogen fixation capacity, establishes a beneficial symbiosis with leguminous plants by inducing root nodule formation. On the other hand, bacteria of the Bacillus genus have demonstrated multifunctionality, stimulating plant growth and countering pathogens.In our laboratory, we isolated several strains from industrial residues, and some of them were identified as Bacillus sp. Taking into account that some species of Bacillus genus are known to have plant growth promoting activity, we conducted a comprehensive analysis of these strains to evaluate relevant enzymatic activities. Moreover, considering that to enhance legume crops, a common practice is bacterial co-inoculation, this was evaluated together with Bradyrhyzobium japonicum E109.The results obtained demonstrated that all strains assayed exhibited a diverse enzymatic profile. We evaluated amylase, cellulase, phospholipase and protease activity, surfactant, siderophore and auxins production. These activities are essential for plant growth promotion and development. Additionally, we observed strong antifungal activity (40-86%) against Rhizoctonia solani, Macrophomina phaseolina, and Fusarium graminearum, among others. This finding has relevance because seeds are treated with antifungal chemical compounds that affect B. japonicum E109 viability.So, with the aim to take advantage of both bacterial genera, we conducted a co-culture test. We observed that Bacillus sp. I30 was compatible with B. japonicum E109. Therefore, it was used in a co-inoculation assay in soybean seeds (Glycine max). The results revealed a positive impact on plant nodulation with a significant increase in the number, fresh weight and dry weight of nodules.To accurately identify the strain I30, we sequenced its complete genome and confirmed its classification as Bacillus velezensis.In light of these results, we have successfully characterized bacteria isolated from industrial residues, presenting enzymatic activities of key importance for their utilization as inoculants. Furthermore, we have demonstrated that these strains possess a pronounced antifungal capacity against relevant agricultural fungi, and one of them, identified as Bacillus velezensis I-30 through genomic sequencing, was capable of coexisting through co-inoculation with B. japonicum E109, providing growth-promoting advantages in soybean plants. These findings reinforce the foundation for future research and application of these bacterial strains in sustainable and effective agricultural strategies