Abstract:A high levan-producing strain of Bacillus licheniformis FRI MY-55 was isolated from a brackish water fish pond. The effects of carbon and nitrogen sources, initial pH of the medium, sucrose concentration, and temperature on levan production by this strain; effects of sucrose concentration and temperature on the molecular weight of levan; and prebiotic effect of levan were investigated. The maximum levan yield was obtained in the presence of sucrose and soytone at an initial pH of 7.0. B. licheniformis FRI MY-55 produced a remarkable level of 145.94 g/L of levan in 50% sucrose-containing medium. The maximum levan production rate was 3.92 g/L/h, which is the highest rate reported for any strain till date. The molecular weight of levan decreased with increasing temperature or sucrose concentration and ranged from 13.45 to 2.96 kDa. The produced levan had prebiotic effect.