Bacillus species consortium with tryptophan-dependent and -independent pathways mediated production of IAA and its derivatives modulates soil biological properties, growth and yield of wheat

Operation of both tryptophan-dependent and -independent pathways leading to higher indole-3-acetic acid (IAA) production by certain bacteria is known to beneficially influence plant growth and development. This study aimed to detect the operation of different pathways in bacteria for production of IAA and its derivatives, and evaluate the plant growth promoting potential of such promising bacteria in wheat crop.

The bacteria of chickpea origin were screened for IAA production through tryptophan-dependent and independent pathways. The prominent IAA producing bacteria were identified by 16S rRNA gene sequencing and evaluated for their growth promoting, soil and plant nutrient enriching potential in wheat crop (cv. Sujata).

Out of the 80 bacteria, three isolates KS-14, BEMS-9–1 and BS-2 were found to produce high levels of IAA and its derivatives by differentially operating both the pathways. These isolates were identified as Brevibacillus formosus, Bacillus paramycoides and Bacillus tequilensis, respectively. Evaluation of various combinations of these promising bacteria showed that the consortium of Br. formosus KS-14 and B. paramycoides BEMS-9–1 along with a 50% recommended dose of fertilizer not only significantly improved the morphological and physiological traits of wheat, but also yield and grain micronutrient loading, mediated through enhanced soil biological activities. This is the first report of the occurrence of tryptophan–independent pathway for IAA production in the three bacilli.

This study is a novel approach towards utilizing the bacteria producing IAA and its derivatives through tryptophan-dependent and -independent pathways for their promise as biostimulants in wheat.