Romanian Biotechnological Letter Vol. 17, No. 2, 2012 Copyright © 2012 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER Romanian Biotechnological Letters, Vol. 17, No. 2, 2012 6862 Plackett-Burman Design to Optimize Biosurfactant Production by Marine Bacillus subtilis N10 Received for publication, June 15, 2011 Accepted, January 20, 2012 NERMEEN A. EL-SERSY National Institute of Oceanography and Fisheries, Microbiology Lab. Marine Environmental Division, Alexandria, Egypt Abstract Surfactants are amphipathic molecules which reduce surface tension and are widely used in pharmaceutical, cosmetic and food industries. In the present study, the production of biosurfactant by Marine Bacillus subtilis N10 was studied. B. subtilis was grown in Laury broth (LB) medium and biosurfactant production was evaluated by measuring the biodegradation of Paraffin oil, haemolytic activity, drop collapsing test, oil displacement test, surface tension and emulsification index (E24) each 24 h. Plackett-Burman experimental design was used to maximize biosurfactant production. Emulsification index (E24) (80%) was elevated up to 1.14 fold increase when compared to its production under the basal conditions. Using the predicted optimal medium, effect of physical parameters revealed that, optimum temperature was 35 o C with pH of 6, and after 24h of incubation, will give rise to a highest Emulsification index (86%). Moreover, the stability of the produced biosurfactant was tested which showed that, biosurfactant produced was stable to high temperature (100 C), neutral to alkaline pH (6-12) and high concentration of electrolyte (up to 20%). Key words: Biosurfactant - Plackett-Burman – Optimization - Marine - Bacillus subtilis Introduction Microbial compounds that exhibit pronounced surface and emulsifying activities are classified as biosurfactants. They have primarily been used for environmental applications because of their diversity, environment-friendly nature, suitability for large-scale production and selectivity [9]. There are many advantages of the biosurfactants as compared to their chemically synthesized counterpart. Unlike synthetic surfactants, microbially produced compounds are easily biodegradable and thus particularly suited for environmental applications such as bioremediation and dispersion of oil spills [23]. Surfactin is one of the most powerful lipopeptide biosurfactants produced by various strains of Bacillus subtilis. [18,28]. They have many properties: it was found to exhibit effective characteristics like antibacterial, antiviral, antifungal, antimycoplasma and hemolytic activities [26]. Addition of a non-sterile biosurfactant obtained from B. subtilis O9 could enhance biodegradation of aliphatic hydrocarbons from 20.9% to 35.5% and of aromatic hydrocarbon from nil to 41% [22]. The polycyclic aromatic hydrocarbons (PAHs) pose potential problem for bioremediation of contaminated sites because of their low water solubility. The surface-active agents increase the surface area of hydrophobic water insoluble substrates and increase their bioavailability [30]. Successful bioprocessing will occur only when all the essential factors are brought together. To understand and control a fermentation process, it is necessary to know how the organism responds to a set of measurable environmental conditions. Medium development 7049 Romanian Biotechnological Letters, Vol. 17, No. 2, 2012