Genomic and Phenotypic Insights Into the Potential of Rock Phosphate Solubilizing Bacteria to Promote Millet Growth in vivo

Abstract

Rock phosphate (RP) is a natural source of phosphorus for agriculture, with the advantage of lower cost and less impact on the environment when compared to synthetic fertilizers. However, the release of phosphorus (P) from RP occurs slowly, which may limit its short-term availability to crops. Hence, the use of P-solubilizing microorganisms to improve the availability of P from this P source is an interesting approach, as microorganisms often perform other functions that assist plant growth, besides solubilizing P. Here, we describe the characterization of 101 bacterial isolates obtained from the rhizosphere and endosphere of maize plants for their P solubilizing activity in vitro, their growth-promoting activity on millet plants cultivated in soil amended with RP, and their gene content especially associated with phosphate solubilization. For the in vitro solubilization assays, two mineral P sources were used: rock phosphate from Araxá (Brazil) mine (AP) and iron phosphate (Fe-P). The amounts of P released from Fe–P in the solubilization assays were lower than those released from AP, and the endophytic bacteria outperformed the rhizospheric ones in the solubilization of both P sources. Six selected strains were evaluated for their ability to promote the growth of millet in soil fertilized with a commercial rock phosphate (cRP). Two of them, namely Bacillus megaterium UFMG50 and Ochrobactrum pseudogrignonense CNPMS2088, performed better than the others in the cRP assays, improving at least six physiological traits of millet or P content in the soil. Genomic analysis of these bacteria revealed the presence of genes related to P uptake and metabolism, and to organic acid synthesis. Using this approach, we identified six potential candidates as bioinoculants, which are promising for use under field conditions, as they have both the genetic potential and the experimentally demonstrated in vivo ability to improve rock phosphate solubilization and promote plant growth.

Innovative Rhizosphere-Based Enrichment under P-Limitation Selects for Bacterial Isolates with High-Performance P-Solubilizing Traits

“…For several characteristics, isolates originating from the B-V3 consortium scored generally better (i.e., more isolates with P-solubilizing traits or a higher efficiency in the particular traits) than isolates from other consortia (B-V1, B-V2 and B-V4). In this research, bacterial Psolubilization in liquid medium reached high rates compared to data described in the existing literature, especially for iron phosphate solubilization (42,43). One possible reason for these low P-solubilizing rates in literature is that the majority of research focuses on the solubilization of TCP as an insoluble P-source.…”

Comparative Genome Analysis Reveals Phylogenetic Identity of Bacillus velezensis HNA3 and Genomic Insights into Its Plant Growth Promotion and Biocontrol Effects

“…HNA3 has 19 phosphatase genes involved in phosphorus solubilization, including a phytase . Stimulating plant development rhizobacteria aids plant growth directly by increasing the resource acquisition, one of which is phosphorus ( 13 ) that increases soil fertility and, hence, increases crop yield ( 81 ).…”

Serratia plymuthica MBSA-MJ1 Increases Shoot Growth and Tissue Nutrient Concentration in Containerized Ornamentals Grown Under Low-Nutrient Conditions

“…Similarly, S. plymuthica BMA1 is an efficient phosphate solubilizer that increased plant growth of Vicia faba ( Borgi et al, 2020 ). The pH reduction observed in the in vitro phosphate solubilization assay ( Table 1 ), coupled with the identification of multiple genes involved in gluconic acid synthesis ( Silva et al, 2021 ), indicates that MBSA-MJ1 could be producing organic acids as a mechanism to solubilize phosphate ( Rodríguez et al, 2006 ). This mechanism for phosphate solubilization has been previously reported in Serratia marcescens strains ( Chen et al, 2006 ; Selvakumar et al, 2008 ; Ben Farhat et al, 2009 ).…”