Production and Optimization of Exopolysaccharide from Thermophilic Bacteria

Abstract

Exopolysaccharides (EPS) are the large molecular weight carbohydrate polymers extracted from higher plants, algae, fungi and bacteria. The thermophilic Bacillus zhangzhounesis 2CA and Bacillus licheniformis 2CS used in the present study were isolated from Çermik hot springs. The growth conditions of the strains designated as 2CA and 2CS in different basal media (M1, M2 and M3), different carbon sources and different concentrations of yeast extract (%w v-1: 0.05, 0.1, 0.15 and 0.2) and the amount of EPS produced were investigated. In addition, the phenol-sulfuric acid method and the Lowry method were used to determine the amount of carbohydrates and proteins within the EPS produced by the bacteria, respectively. The highest total EPS dry weight for B. licheniformis 2ÇS was obtained as 121 mg in M3 medium (0.2% yeast extract + 1% sucrose), carbohydrate content in EPS was 333.28 µg mL-1 and protein content was 0.19 µg mL-1. When these two bacteria were compared in terms of the amount of carbohydrates in the EPS produced, the highest amount of carbohydrates was found in EPS of B. zhangzhounesis 2CA (1087.03 µg mL-1). The antibacterial effects of EPS were investigated against pathogenic microorganisms (E. coli, S. aureus, K. pneumoniae and P. aeruginosa). It was determined that the highest antibacterial activity against E. coli (with 16 mm zone diameter) was obtained with EPS produced by B. licheniformis 2ÇS bacteria in M3 medium (0.2% yeast extract + 1% sucrose).