Levan Production using Pseudomonas Brassicacearum Isolated from Rhizosphere Soil of Cowpea Farm in Iraq


The present investigation, was designed in order to isolate bacteria from rhizosphere soil of Cowpea farm in Iraq which is capable of levan production. The selected levan producing bacterium was identified as Pseudomonas brassicacearum based on the phenotypic identification by Bergey’s Manual of Systematic Bacteriology and confirmed with the 16S rRNA gene sequencing. Acid hydrolyzed levan sample was subjected to TLC technique which revealed that, levan is composed of only one sugar which is fructose. Rf values of levan produced by P. brassicacearum was 0.42 which is identical or close to Rf values of fructose of 0.42. The effect of some factors on levan production by P. brassicacearum was investigated. The results showed that the best carbon source for levan production was sucrose 7.77 g/l, and casein was the best nitrogen source for levan production which gave 8.56 g/l, followed by ammonium sulfate and corn steep liquor which they gave 8.52, 8.09 g/l respectively. The highest levan yield was at the sucrose concentration of 300 g/l which gave 7.95 g/l. At initial pH of 7.8, P. brassicacearum gave their highest levan production that was 7.77 g/l. Levan production by P. brassicacearum continued increasing until it reached its maximum production at 40ºC which was 8.24 g/l. The optimal incubation period for levan production, was estimated at 8.70 g/l after 72 h of incubation.