Investigation of low-cost media for Bacillus thuringiensis subspecies israelensis

Abstract

Bacillus thuringiensis subspecies israelensis (Bti) has been used as a mosquito control agent in agricultural field and residences. The production of Bti by conventional medium was expensive. The objective of this study was to investigate low-cost media for Bti’s production with a cost analysis of the medium formulated. Soybean Casein Digest Medium (TSB) was used as a conventional medium to compare with Saberi medium at room temperature (approximately 21.5˚C) on static and agitation (by obituary shaker at 100 rpm). Saberi medium was also modified to vary the percentage of nitrogen and carbon source to observe the growth rate and sporulation, compared to the Saberi medium. The growth of Bti in TSB with agitation for 24 hours yielded the highest growth rate. Sporulation of Bti in TSB with agitation at room temperature was 6 days which was faster than Bti in the Saberi medium. Modified Saberi nitrogen source and carbon source medium could not support the growth of Bti due to an imbalance in the percentage of nitrogen source and carbon source. Determination of sugar utilization showed sugar in the medium was utilized mostly in the exponential phase of Bti, from 3 hours to 6 hours. The price of TSB was 76.80 Thai baht per liter while Saberi medium’s cost was 20.43 Thai baht per liter. In this study, the Saberi medium may not be able to replace TSB in terms of growth rate and period of sporulation. Further study will be needed to optimize the media that use agro-industrial wastes as ingredients following the concept of circular economy and sustainability.