IAA biosynthesis in Azospirillum brasilense is regulated by amino acids.

CASSÁN, FABRICIO; FREDERIK DAS; SPAEPEN, STIJN; VANDERLEYDEN, JOS

Perth

Congreso; Rhizosphere 3 International Conference; 2011

Rhizosphere

Indole-3-acetic acid (IAA) is one of the most important molecules produced by Azospirillum sp. during plant-bacteria interaction. Our hypothesis states that both growth and IAA biosynthesis could be regulated by several amino acids. A. brasilense Sp245, Az39 and Cd pFAJ64 were pre-incubated in MMAB medium with or without 10 mg.l-1 L-tryptophane or 10 μg.ml-1 IAA until exponential or stationary growth phase, then fractionated in 10 ml tubes and individually supplemented with 10 mg.ml-1 of L-lys, L- trp, L-leu, L-ileu, L-phe, L-ala, L-val, L-arg, L-glu, L-his, L-met, L-asp, L-cys, L-ser, L-pro or L-treo. After further incubation for 30, 120 and 240 minutes, the following parameters were evaluated: biomass production (OD595); cellular viability (CFU.ml-1); IAA production (μg.ml-1) and ipdC gene expression (Miller Units). Our results show that L-val, L-ser and L-ileu inhibiting growth of the bacteria and as a consequence affected the IAA biosynthesis, while L-leu, L-phe and L-ala were inhibitory on the IAA biosynthesis process itself. The ipdc gene expression decreased in the presence of these amino acids, but increased by the addition of L-phe. Our results allow us to speculate about a new regulation mechanism for bacterial IAA biosynthesis in the rhizosphere due to the presence of specific amino acids in root exudates.