Bioencapsulation of Biosurfactant-Producing <i>Bacillus subtilis</i> (PTCC 1023) in Alginate Beads

Abstract

Background: Biosurfactants are amphipathic molecules that reduce surface tension. Cell encapsulation represents one of the current leading methodologies aimed at the delivery of the biological products. Alginate is one of the most frequently employed materials used for this purpose. Objectives: The aim of the present study was to evaluate the achievability of immobilizing Bacillus subtilis in calcium alginate beads to provide a concrete base for further process development of its biosurfactant production. Methods: Alginate and bacterial solutions were mixed by stirring to obtain a uniform mixture and added by drops into CaCl2 solution to form spherical beads. The spherical beads were agitated for two hours to harden. Equal numbers of beads were poured into 50 mL nutrient broth medium and incubated in the shaking incubator. Surface tension, emulsification activity, and foam production were measured every 24 hours. Results: B. subtilis showed hemolytic activity. Bead formation at concentrations of 3% and above showed the stability of the alginate solution, while in concentrations of 1% or less, it did not show proper stability. Ideal concentration of microbial suspension was achieved in 0.5 McFarland. Beads were the same size, spherical, and concurrent (3 - 4mm). Maximum foam stability, height, and bioemulsifier production were achieved at 24 hours’ incubation, while CMD values were minimal at this point. The growth of typical bacillial colonies was 250 - 300 CFU/bead. Conclusions: B. subtilis entrapped in beads was able to preserve its viability and produce biosurfactants as secondary metabolites. Therefore, this method could be applied as a continuous culture system of biosurfactant production.