L-amino acids Inhibits Indole-3-acetic acid biosynthesis and growth of Azospirillum brasilense

RIVERA D.; CONIGLIO A.; OBANDO M.; CASSÁN F.

La Falda, Córdoba

Workshop; II LATIN AMERICAN PGPR WORKSHOP; 2014

UNRC, Universidad Nacional de Quilmes, Universidad de Antioquía

Indole-3-acetic acid (IAA) is one of the most important molecules produced by Azospirillum sp. and is considered to be an important mechanism by which these bacteria promote plant growth and the interaction. Genetic and biochemical analysis of the IAA biosynthesis in Azospirillum brasilense revealed multiple pathways for IAA synthesis with the indole-3-pyruvate pathway as the most significance. However, it has been explored very little about its ability to conjugate, hydrolyze or catabolize such molecules, which in together is defined as bacterial auxin metabolism. The aim of this study was to evaluate the IAA metabolism in A. brasilense Az39, but particularly the regulation of bacterial growth and IAA biosynthesis by several amino acids. Azospirillum brasilense Az39 was incubated in MMAB minimal medium a temperature of 37 °C to 180 rpm by 24 h. In exponential growth phase conditions was standardized, whereby the suspension centrifuged, washed twice with sterile saline (0.85%) leaving at a DO595: 0.5 and used as inoculum at 0.5% (v/v). Once done, the culture was fractionated with 5 mL in test tubes of 10 mL capacity and added 100 μg.mL-1 of the following L-amino acids: L-phe, L-ile, L-leu, L-val, L-ser, L-ala, L-asn, individually or combined with LTrp (regulation and conjugation); IAA-L-phe, IAA-L-ala; IAA-Lleu (hydrolysis) and IAA (catabolism) by triplicate. Three controls were performed by addition of distilled water. The reaction was incubated 120-240 min beforeevaluating: IAA concentration (μg.mL-1), biomass production (OD595) and cell viability (CFU.mL-1). An inhibitory effect on growth and IAA biosynthesis was observed by exposition of the bacterial culture to several amino acids. Our screening experiments showed that L-ile, L-leu, Lval,y L-ala impacted in a decrease in biomass production and significantly (P