Optimization of Indole-3-acetic acid production by Bacillus velezensis isolated from Pyrus rhizosphere and its effect on plant growth

Abstract

Indole-3-acetic acid (IAA) is an important plant growth promoting hormone produced as secondary metabolite by many microorganisms. The current study aims to optimize conditions for IAA production by a rhizobacterial isolate and evaluation of its effect on plant growth. Seven bacterial isolated were purified from the rhizosphere of pear-tree and screened for IAA production and optimum production medium. The most potent bacterial isolate (S5) was selected for further investigations and molecularly identified using (16S rRNA). The selected isolate was identified as Bacillus velezensis strain MOST-IAA and given the accession number (ON792392.1) in National Center for Biotechnology Information (NCBI). For maximum IAA productivity, twenty one nutritional factors were screened for their significance on IAA using Placket Burman design and the significant factors were used for statistical modeling of the production conditions using Box-Behnken design. The produced model and optimization resulted in maximum IAA (56.60 μg/ml) at: 4.41 g/l, D(+) mannose; 8.66 g/l, mannitol; 0.93 g/l, tryptophan; 5.88 g/l, potassium nitrate; 1.29 g/l, ammonium chloride; 28.5 °C, temperature and 7.69, initial pH with correlation of 94.76% to the theoretical results. The produced IAA has been extracted and used in irrigation of barley seed for 10 days. Data showed significant differences among the test and control barley, especially in the length of the produced roots. Bacillus velezensis can be used to increase the soil fertility or biotechnologically used for production of IAA to be applied for plant growth improvement.