Nutritional factors affecting levan production by Bacillus sp.V8 strain isolated from rhizosphere bean (Vicea faba) plant

Abstract

This investigation was designed to study the production of levan by fermentation; a number of 37 bacterial isolates were obtained from rhizosphere of different plants in Egypt and tested for levan production. Only one isolate (V8) was selected as a high efficiency levan producing bacterium and identified as Bacillus lentus V8 based on phenotypic identification by Bergey's Manual of Systematic Bacteriology and confirmed with 16S rRNA gene sequencing. The specific growth rate (μ) and doubling time (td) were calculated at the log phase of growth curves being 0.097h-1 and 7.15 h, respectively. Levan concentration was increased after 96 h (stationary phase). The effect of some nutritional factors on growth and levan production by Bacillus sp.V8 was investigated. 25% sucrose was the best carbon source for levan production followed by 25% black strap sugar cane molasses. Addition of fructose to the fermentation medium considerably reduced the levan production due to the inhibition of levansucrase activity. 1.5 gl-1 ammonium phosphates was most effective as nitrogen sources. 7.2 gl-1 K2HPO4 found to be optimal for levan production, which gave 39.97 [or] 36.60 gl-1 of levan dry weight on modified productive medium supplemented with sucrose [or] black strap sugar cane molasses using shake flasks as a batch culture, respectively.