Zinc solubilizing Bacillus strains that modulate growth, yield and zinc biofortification of soybean and wheat

Zinc (Zn), an essential micronutrient, is required for improving crop productivity, human and animal nutrition. To overcome zinc deficiency, use of zinc solubilizing bacteria has been a promising alternative for enhancing zinc availability in soil and thereby improving zinc assimilation in seeds while maintaining crop yield. The premise of this study is to isolate and identify predominant Bacillus isolates from Nimar region and their effect on yield enhancement, zinc -mobilization and -assimilation by soybean and wheat crops. In this study, we recovered a total of 115 predominant bacilli from rhizosphere of two soybean cultivars namely JS 93-05 and JS 335 cultivated at 17 different locations of Nimar region, Madhya Pradesh, India. Of the 115 isolates, 20 potential zinc solubilizing bacilli were selected. Isolates KMR-5, THB-2, BBU-5, DBU-5, DBU-1, KHKD-1, KKI-6 and BHKD-6 were found to be highly efficient in solubilizing insoluble zinc compounds both on solid plate and in liquid assay conditions. Twenty bacilli were identified as Bacillus cereus, B. anthracis, B. thuringiensis, B. tequilensis and B. subtilis subsp. Inaquosorum based on morphological, biochemical and cellular fatty acid profiling and further characterized through 16S rRNA gene sequences. On evaluation of these strains under microcosm conditions, inoculation of KMR-5 and KBY-1 strains of B. cereus significantly increased seed yield of soybean and wheat, but KMR-5, BHKD-6 and DBU-1 increased the Zn concentration in soybean and wheat seeds, when compared to other strains and un-inoculated control. Strain KMR-5 had increased both seed yield as well as zinc assimilation in soybean and wheat. Thus, this study selected three types of strains (1) yield enhancing strains, (2) Zn-enriching strains and (3) yield and zinc enrichment strain that could be utilized for improving seed yield and enrichment of zinc in seeds of soybean and wheat crops.