Bacteria isolated from soils of the western Amazon and from rehabilitated bauxite-mining areas have potential as plant growth promoters

Abstract

Several processes that promote plant growth were investigated in endophytic and symbiotic bacteria isolated from cowpea and siratro nodules and also in bacterial strains recommended for the inoculation of cowpea beans. The processes verified in 31 strains were: antagonism against phytopathogenic fungi, free-living biological nitrogen fixation, solubilization of insoluble phosphates and indole acetic acid (IAA) production. The resistance to antibiotics was also assessed. Sequencing of the partial 16S rRNA gene was performed and the strains were identified as belonging to different genera. Eight strains, including some identified as Burkholderia fungorum, fixed nitrogen in the free-living state. Eighteen strains exhibited potential to solubilize calcium phosphate, and 13 strains could solubilize aluminum phosphate. High levels of IAA production were recorded with L-tryptophan addition for the strain UFLA04-321 (42.3 μg mL⁻¹). Strains highly efficient in symbiosis with cowpea bean, including strains already approved as inoculants showed the ability to perform other processes that promote plant growth. Besides, these strains exhibited resistance to several antibiotics. The ability of the nitrogen-fixing bacteria to perform other processes and their adaptation to environmental conditions add value to these strains, which could lead to improved inoculants for plant growth and environmental quality.

Bacterial strains from floodplain soils perform different plant-growth promoting processes and enhance cowpea growth

“…No strain was able to solubilize Fe phosphate. These results corroborate findings reported in the scientific literature for bacteria isolated from cowpea nodules (Marra et al, 2012;Oliveira-Longatti et al (2014). Marra et al (2012) tested the ability of symbiotic and non-symbiotic strains in GELP to solubilize inorganic phosphates in solid medium.…”

“…However, the quantity of synthesized IAA is highly variable among and within genera and species . Additionally, various factors, including presence and/or concentration of tryptophan, temperature, pH, concentration and source of C and/or other nutrients, can interfere both in the ability to synthesize IAA and in the quantity produced in culture medium (Ona et al, 2005;Patil et al, 2011;Oliveira-Longatti et al, 2014). In this study, for most strains evaluated, IAA synthesis was obtained when the culture media (DYGS and 79) were supplemented with amino acid tryptophan (Table 3).…”

“…exhibited the highest indices of Ca phosphate solubilization in vitro (3.54 and 2.32, respectively) ( Table 2) and are indicated for future experiments in vivo to evaluate their contribution relative to P availability in the soil. Oliveira-Longatti et al (2014) also reported Ca phosphate solubilization by strains of Enterobacter sp. and Pseudomonas sp.…”

“…These non-symbiotic endophytic nodule bacteria, similar to some LN-NFB, can act on plant nutrition and growth by different mechanisms, such as siderophore production, free-living N 2 fixation, phytohormone synthesis and solubilization of inorganic phosphates (Carson et al, 1992;Li et al, 2008;Marra et al, 2012;Oliveira-Longatti et al, 2014). Besides, these bacteria can be considered plant growthpromoting rhizobacteria (PGPR).…”

Nursery growth and rhizobia symbiosis of scandent Leguminosae species native to the Amazon region

“…Burkholderia fungorum strains showed efficiency in nitrogen fixation in free-living conditions, and calcium phosphate and aluminum solubilization (OliveiraLongatti et al 2013;2014) and also were proved to present nodulation ability in Phaseolus vulgaris . The symbiosis of Burkholderia fungorum with Dalbergia inundata found in this work expands the knowledge on the capacity of beta-rhizobia to nodulate legumes from the subfamily Papilionoideae…”