Int.J.Curr.Microbiol.App.Sci (2014) 3(4): 876-886 876 Original Research Article Improved exopolysaccharide production by Bacillus licheniformis strain-QS5 and application of statistical experimental design Mahmoud M.Berekaa* 1,2 1 Environmental Health Department, College of Applied Medical Sciences, University of Dammam, Dammam 31441, Saudi Arabia 2 Environmental Sciences Department, Faculty of Science, Alexandria University, Alexandria 21511, Egypt *Corresponding author ABSTRACT Introduction Exopolysaccharides are naturally formed macromolecules during growth of many organisms. Recently, vast number of bacterial exopolysaccharides (EPS) attracted attention of many scientists, their composition, structure, biosynthesis and functional properties have been extensively studied (Isobe et al., 1992; Kumar et al., 2007; Donot et al., 2012). EPS have found diverse applications in food, pharmaceutical, medical and other biotechnological applications (Stewart et ISSN: 2319-7706 Volume 3 Number 4 (2014) pp. 876-886 http://www.ijcmas.com Keywords Exo- polysaccharide, Bacillus licheniformis, statistical experimental design, optimization Among a group of bacilli, Bacillus species strain-QS5 producing exopolysaccharide, locally isolated from Eastern Province in Saudi Arabia, was characterized and identified based on 16S rRNA sequencing. Phylogenetic analysis revealed its closeness to Bacillus licheniformis. The bacterium showed 1.9- and 2.8-folds increase in EPS production on basal salts medium containing glucose (M2) or sucrose (M3), respectively. Maximum yield of EPS by B. licheniformis strain-QS5 (3.78 g/g) obtained during growth on M3 medium supplemented with sucrose. While, slight decrease in biopolymer yield 3.64 and 3.5 (g/g) was recorded by the two other candidates Bacillus sp QC1 and Bacillus sp KSW21, respectively.Statistically based experiments were applied to detect the optimal medium composition for production of exopolysaccharide (EPS). The effect of four variables namely; sucrose, phosphate buffer and ammonium sulfate were examined for their significance on exopolysaccharide production using Box-Behnken design. Based on statistical analysis, maximal EPS production was reached under optimal conditions with approximately 4-folds increase in comparison with the amount produced on complex production medium M1 and the use of sucrose as carbon source was crucial (p-value 0.051). Verification experiment was carried out to examine model validation and revealed more than 78% validity.