Influence of some environmental and nutritional conditions on biofilm formation of probiotic Bacillus subtilis strains

Biofilm formation in bacteria is an important survival strategy. Biofilm of probiotic Bacillus subtilis consist of long chains of cells that are covered by a polymeric matrix of exopolysaccharides. This bacterium is known as one of the most effective biocontrol agents against plant pathogens and has a high ability in biofilm formation. This study was aimed to investigate the effect of some environmental conditions including temperature, pH and osmotic pressure; nutritional elements such as sugars and amino acids secreted from wheat root and important soil elements like Ca2, Mn2, Mg2, Fe 2, Zn2, Mo6, Co2, B3 and Cu2 on biofilm formation of mentioned bacterium using polystyrene plate. Results of this study indicated that the most amount of biofilm in three studied strains produced at 30°C, pH 7 and the osmotic pressure using concentration of 75% sucrose. Cations of magnesium, calcium, zinc, iron, manganese and copper increased but cations of molybdenum, cobalt and boron decreased biofilm formation. All sugars and amino acids secreted from wheat root increased biofilm formation of studied strains. Among sugars, arabinose and glucose; and among amino acids, lysine and asparagine showed the greatest increasing effect on biofilm formation. According to our results, environmental conditions and the content of nutrient can influence on biofilm formation and consequently, the survival and establishment of probiotic bacteria in their environments, host colonization and biological control against plant pathogens.