Indoleacetic acid production by the rhizosphere bacterium Azospirillum brasilense Cd under in vitro conditions

Abstract

Factors influencing indoleacetic acid release from Azospirillum brasilense Cd (ATCC 29729) were investigated under batch culture conditions. In the presence of ammonium in the liquid culture solution, indoleacetic acid release from bacterial cells was considerably higher than in the corresponding N-free medium that was slightly solidified with agar to provide conditions for N2 fixation. In the solution culture, the concentration of indoleacetic acid was low during the logarithmic growth phase and increased rapidly with the beginning of the stationary phase. A similar time course was found for the indoleacetic acid content (dry weight basis) of the bacterial cells. Addition of tryptophan strongly stimulated the release of indoleacetic acid, which again showed a steep rise in the early stationary phase. The pH of the nutrient solution increased from 6.8 to 9.3 during incubation but this was not responsible for the steep rise in indoleacetic acid levels. The sole carbon source in the substrate (DL-malic acid) was identified as the limiting growth factor. This suggests that the high increase in indoleacetic acid production in the stationary phase is the expression of an overall change in cell metabolism when the carbon source is exhausted. At this developmental stage the high production of indoleacetic acid seems to have the character of a secondary product. Press sap from wheat roots did not promote indoleacetic acid production by bacterial cells.Key words: Azospirillum, indoleacetic acid, tryptophan, pH solution.

Azospirillum brasilense Produces the Auxin-Like Phenylacetic Acid by Using the Key Enzyme for Indole-3-Acetic Acid Biosynthesis

“…No significant differences in pH were found between cultures supplemented with IAA and those supplemented with PAA, indicating that the slightly higher expression of the ipdC gene in the presence of PAA can be intrinsically attributed to PAA itself and is not due to a pH effect. (30,41,10,58,43,57). Secondary metabolism is often brought on by exhaustion of a nutrient (suboptimal growth conditions), biosynthesis or addition of an inducer, or a growth rate decrease (16).…”

Respuesta de diferentes variedades de cereales a la inoculación con Bradyrhizobium sp.

“…These rhizobacteria, like those introduced in the present experiment are associated with the roots of the grass, due to the influence of organic compounds product of root exudates, such as carbohydrates, organic acids and microbial growth factors (Omay et al, 1993;Chelius and Triplett, 2000). However, by not using specific laboratory techniques in this field, the authors of this paper cannot issue a conclusion with respect to defining this outcome, nor to those shown in Table 3, which suggest the marked influence of native microorganisms in some variables.…”

“…Estas rizobacterias, al igual que las introducidas en el presente experimento, se asocian a las raíces de la gramínea, debido a la influencia de compuestos orgánicos producto de los exudados radicales, como: carbohidratos, ácidos orgánicos y factores de crecimiento microbiano (Omay et al, 1993;Chelius y Triplett, 2000). No obstante, al no utilizar las técnicas de laboratorio específicas en este campo, los autores del presente trabajo no pueden emitir una conclusión definitoria con respecto a este resultado, ni a los mostrados en el Cuadro 3, los cuales sugieren la influencia marcada de los microorganismos autóctonos en algunas variables evaluadas.…”

Characterization of Streptomyces spp. Producing Indole-3-acetic acid as Biostimulant Agent

“…Tryptophan on rhizosphere could be obtained from the degradation of root cell and microbial cell and root exudates. This showed that IAA was produced during the late exponential and stationer phases (Omay et al, 1993). Spaepen et al (2007) mentioned that the role of IAA to the bacteria has not clearly known yet.…”