Secretory Production of Rahnella aquatilis ATCC 33071 Levansucrase Expressed in Escherichia coli

To investigate the production and characteristics of thermostable levansucrase from Rahnella aquatilis ATCC 33071, the levansucrase gene from R. aquatilis was cloned and expressed in Escherichia coli without induction system. Expression of levansucrase gene in E. coli had no notable or detrimental effect on the growth of host strain, and the recombinant levansucrase exhibited levan synthesis activity. Levansucrase was secreted to the periplasm in E. coli, and addition of 0.5% glycine yielded further secretion of levansucrase to the growth medium and resulted in an increase of total levansucrase activity. Furthermore, the cellular levansucrase was evaluated for the production of levan by using toluene-permeabilized whole-cells. The levansucrase was thermostable at 37°C. The molecular size of levan was 1×106 Da, as determined by HPLC, and the degree of polymerization of levan varied with incubation temperatures: Low incubation temperature was preferable for the production of high-molecular size levan. the present study demonstrated that the mass production of levan and levan oligosaccharides can be achieved by glycine supplementation to the growth medium or by toluene-permeabilized whole-cells.