Optimization of biosurfactant production by Streptomyces isolated from Egyptian arid soil using Plackett–Burman design

Surfactants are amphipathic molecules which reduce surface tension, widely used in pharmaceutical, cosmetic and food industries. The current study aimed to isolate Streptomyces species from Egyptian arid soil, efficient in biosurfactant production. Fifty isolates of Streptomyces were obtained from arid soil in Egypt. Primary screening, using lipase, drop collapse, parafilm M and haemolysis tests, showed 37 isolates (74%) having biosurfactant activity. Secondary screening resulted in 17 isolates based on their activities using emulsification index method. Isolate 5S was selected as the most efficient in biosurfactant production, having emulsification index equal to 31.74%. Plackett–Burman design was adopted to evaluate the factors affecting biosurfactant production. Among the tested nine variables of starch nitrate medium, treated molasses, peptone, Tween 80, incubation period and inoculum size were identified as significant factors affecting biosurfactant production. Cultivation of isolate 5S in the optimized medium elevated biosurfactant production to 42.68% (according to emulsification index) from 31.74%, obtained in un-optimized medium.