Abstract
BackgroundThe production of indole-3-acetic acid (IAA) is an essential tool for rhizobacteria to stimulate and facilitate plant growth. For this, eighty rhizobial bacteria isolated from root nodules of Acacia cyanophylla grown in different regions of Morocco were firstly screened for their ability to produce IAA. Then, IAA production by a combination of isolates and the inoculation effect on the germination of Acacia cyanophylla seeds was studied using the best performing isolates in terms of IAA production. The best IAA producer bacterial isolate (I69) was selected to optimize IAA production using response surface methodology based on the central composite design. ResultsResults showed that the majority of tested isolates were able to produce IAA with a relatively higher concentration of 135 μg/ml for the isolate I69, followed by isolates I22 and I75 with respective concentrations of 116 μg/ml and 105 μg/ml IAA. The IAA production and the seed germination rate were relatively increased by the synergistic effect of I69 and I22. Later, response surface methodology was used to determine optimal operating conditions leading to IAA production optimization. Thus, an incubation temperature of 36 °C, a pH of 6.5, an incubation time of 1 day, and respective tryptophan and NaCl concentrations of 1 g/l and 0.1 g/l were optimal parameters leading to 166 μg/ml IAA which was the maximal produced concentration. ConclusionThe present study highlighted that IAA-producing rhizobacteria could be harnessed to improve plant growth. Furthermore, their production can be easily controlled using response surface methodology, which represents a very useful tool for optimization.
Highlights
The production of indole-3-acetic acid (IAA) is an essential tool for rhizobacteria to stimulate and facilitate plant growth
This study aimed to perform a screening of rhizobacteria that produce IAA and to optimize factors leading to the highest IAA concentration using experimental designs methodology
Screening of isolates for IAA production The colorimetric assay showed that 96% of the eighty tested isolates were able to produce IAA on YMB medium at varying concentrations depending on their efficiency and their enzymatic potency
Summary
The production of indole-3-acetic acid (IAA) is an essential tool for rhizobacteria to stimulate and facilitate plant growth. Indole-3-Acetic Acid (IAA) is one of the most important and physiologically active phytohormones [1, 2] It is a secondary metabolite of L-tryptophan that acts as a regulator of many biological processes for plant development while acting on organogenesis, trophic responses, and cellular responses such as cell expansion, division, differentiation, and regulation of genes [3, 4]. IAA synthesized by rhizobacteria affects mostly the root system by increasing its size, weight, lateral roots number, and the area of contact with the soil This mechanism contributes to increase nutrient research and acquisition in soil, which improves plant development and yield [15, 16]. It has been shown that nodulated roots contain more IAA than non-nodulated roots [19, 20], and auxins could be essential for maintaining a root nodule functional [21]
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