| Congresso Brasileiro de Microbiologia 2023 | Resumo: 9-1 | ||||
Resumo:Abiotic stresses have negative impact on the physiology and morphology of plants through by interfering in the genetic regulation of cellular pathways. Phytohormones play a vital role in the stimulation of plant defense response mechanisms against stresses. Indole-3-acetic acid (IAA) is an important auxin produced by plants and some rhizobacteria; exogenous IAA results in enhanced root length, surface area, and number of root tips, leading to improved uptake of nutrients, thereby enhancing plant health under drought environments. Nowadays, in the face of climate changes, the search for plant growth-promoting bacteria capable of growing under osmotic stress conditions is a relevant alternative to increase plant productivity. We aimed to evaluate the growth capacity and IAA production under PEG-mediated osmotic stress of bacteria isolated from the rhizosphere of maize (Zea Mays ), cultivated in three soils from different land use types: (1) Mixed Ombrophylous Forest; (2) a four-year restoration area, with long-standing record of use for agriculture; (3) agriculture. Soils were collected from 0–20 cm depth and maize seeds were planted in plastic pots with one of the soil samples. After 45 days of grown in a greenhouse, rhizospheric soils were used for serial dilution and inoculation onto Tryptone Soya Agar medium (TSA 10%) plus 28,5% (w/v) sorbitol. Eighteen rhizobacteria were selected for quantitative analysis to verify the ability of bacteria to grow and produce IAA in Tryptone Soya Broth (TSB) with L-tryptophan (100 µg.mL-1) and Polyethylene glycol (PEG) in different concentrations (0.15M; 0.49M and 0.73M). Sequencing analysis of the 16S rDNA allowed the identification of these strains as belonging to genera Pseudomonas, Enterobacter, Achromobacter, Priestia, Rhodococcus, Bacillus, Stutzerimonas, Burkholderia and Pantoea. All the selected strains could grow in the three PEG concentrations, and TSB + 0.49M and 0.73M affected the growth rate of all strains. For two strains, one Pseudomonas sp and one Priestia sp., PEG 0.15M didn’t affect their growth rate; moreover, for this Priestia sp. strain, even with a reduction of 40% of the growth rate in PEG 0.73M, the production of IAA was 24,3 ug.mL-1, significantly higher than the control condition (16,4 ug.mL-1) after 48h of incubation. The highest IAA production (97.77 ug.mL-1) was achieved by Pantoea sp. grown under PEG 0.73M, even with a 80% reduction of growth rate. Other studies with Azospirillum brasilense indicated that PEG was able to increase IAA biosynthesis, independent of bacterial growth. In our case, the IAA synthesis in response to PEG-mediated stress was divergent even between strains of the same genus, corroborating the statement that mechanisms that regulate bacterial IAA biosynthesis under stressful conditions are still largely unknown and complex, mostly because the interplay of enzymes that mediate multiple interconnected biosynthesis pathways. Palavras-chave: Plant growth promoting bacteria, drought stress, auxin Agência de fomento:CNPq; Fundação Araucária | |||||