New insights into auxin metabolism in Bradyrhizobium japonicum

TORRES, DANIELA; MONGIARDINI, ELIAS; VANDERLEYDEN, JOZEF; STRNAD, MIROSLAV; DONADIO, FLORENCIA; SPAEPEN, STIJN; NOVÁK, OND?EJ; CASSÁN, FABRICIO; BENAVIDEZ, ILIANA; ROSAS, SUSANA; P?N?ÍK, ALE?; FRÉBORTOVÁ, JITKA

RESEARCH IN MICROBIOLOGY

ELSEVIER SCIENCE BV

Año: 2018 vol. 169 p. 313 - 323

0923-2508

Bacterial metabolism of phytohormones includes several processes such as biosynthesis, catabolism, conjugation, hydrolysis and homeostatic regulation. However, only biosynthesis and occasionally catabolism are studied in depth in microorganisms. In this work, we evaluated and reconsidered IAA metabolism in Bradyrhizobium japonicum E109, one of the most widely used strains for soybean inoculation around the world. The genomic analysis of the strain showed the presence of several genes responsible for IAA biosynthesis, mainly via indole-3-acetonitrile (IAN), indole-3-acetamide (IAM) and tryptamine (TAM) pathways. However; in vitro experiments showed that IAA is not accumulated in the culture medium in significant amounts. On the contrary, a strong degradation activity was observed after exogenous addition of 0.1 mM of IAA, IBA or NAA to the medium. B. japonicum E109 was not able to grow in culture medium containing IAA as a sole carbon source. In YEM medium, the bacteria degraded IAA and hydrolyzed amino acid auxin conjugates with alanine (IAAla), phenylalanine (IAPhe), and leucine (IAPhe), releasing IAA which was quickly degraded. Finally, the presence of exogenous IAA induced physiological changes in the bacteria such as increased biomass and exopolysaccharide production, as well as infection effectiveness and symbiotic behavior in soybean plants.