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New insights into indole‐3‐acetic acid metabolism in Azospirillum brasilense
Author(s) -
Rivera D.,
Mora V.,
Lopez G.,
Rosas S.,
Spaepen S.,
Vanderleyden J.,
Cassan F.
Publication year - 2018
Publication title -
journal of applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 1364-5072
DOI - 10.1111/jam.14080
Subject(s) - azospirillum brasilense , biosynthesis , auxin , biochemistry , catabolism , indole 3 acetic acid , metabolism , hydrolysis , bacteria , biology , microbial inoculant , chemistry , enzyme , gene , genetics
Aims The aim of this research was to analyse the global indole‐3‐acetic acid ( IAA ) metabolism in three commercially used strains of Azospirillum brasilense . Methods and Results Azospirillum brasilense Sp245, Az39 and Cd, containing a plasmid with the ipd C‐ gus A fusion ( pFAJ 64), were cultured in minimal medium MMAB with or without 10 mg l −1 of l ‐trp till exponential or stationary growth phase. The cultures were then split into 10 ml tubes and individually treated with 10 mg ml −1 IAA , IBA or NAA (auxin catabolism and homeostasis); IAP he, IAL eu, IAA ‐ala, IAA ‐glucose ( IAA conjugate hydrolysis); or l ‐lys, 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, l‐ thr and l‐ trp (regulation of IAA biosynthesis and IAA conjugation). Bacterial growth, IAA production and ipd C expression were evaluated. None of the A. brasilense strains were able to hydrolyse IAA conjugates, catabolize auxins, or conjugate IAA with amino acids or glucose. l‐ amino acids l‐ met, l‐ val, l‐ cys and l‐ ser inhibited bacterial growth and decreased IAA biosynthesis. The expression of ipd C and IAA biosynthesis but not bacterial growth was affected by l‐ leu, l‐ phe, l‐ ala, l‐ ile, l‐ pro. l‐ arg, l‐ glu, l‐ his, l‐ lys, l‐ asp and l‐ thr did not affect any of the measured parameters. Conclusions In this paper, we confirmed that A. brasilense produces IAA only in presence of l‐ trp is not able to degrade auxins, conjugate IAA with sugars and/or l‐ amino acids, or hydrolyse such conjugates to release free IAA . Finally, we found that bacterial growth and/or IAA biosynthesis were inhibited by the presence of several l‐ amino acids probably by diversion of the cellular metabolism. Significance and Impact of the Study We propose a renewed model to explain IAA metabolism in A. brasilense , one of the most studied phytostimulatory bacteria.