Bacillus subtilis, a bacterial inhabitant in calcareous soil and its ability to demineralize fixed Fe and Zn salt in its habitat

Calcareous soils are unproductive for agriculture. World over 30 percent of soils are calcareous soils limiting crop cultivation and productivity. In calcareous soils, most of the plant nutrients and micronutrients are not freely available to the crop plants as these often lie in fixed or bonded form. Therefore, these nutrients have to be released from their bonded form into freely available form in such soils to make them available for crop plant growth. The application of microbial species native to such calcareous soils and having the ability and capacity to release such bonded nutrients into freely available form is a need of the day to convert these unproductive soils into productive ones.

In the present investigation, we studied the presence of microbial flora particularly the bacterial species in the calcareous soil in western Maharashtra, India, and their role in the release of the bonded Fe and Zn micronutrients into a freely available form, from such soil to make these available for the kidney-bean plant growth.

Six bacterial isolates of distinct colony morphology were isolated from the calcareous soil as the calcareous soil- inhabiting bacterial species, on a specialized enriched media. Their ability as Fe and Zn salt-releasing/de-mineralizing bacterial species was assessed. The release of Fe and Zn from their fixed form by these bacterial species was 0.80 and 1.80 µg/g of calcareous soil respectively. The release of Fe and Zn in calcareous soil was found to play a role in the growth and yield-attributing parameters of kidney-bean plants in calcareous soil. These morphologically distinct bacterial cultures were identified as Bacillus subtilis and Bacillus sp by using the MALDI Bio Typer classification protocol. These calcareous soils inhabiting bacterial species can be applied as bio-inoculants to the calcareous soil regularly to make them crop productive as well as for the reclamation of such calcareous soils.