Improvement of levan production in Zymomonas mobilis ATCC 31821 under osmotic pressure stress via Adaptive Laboratory Evolution (ALE)

Abstract The main idea of the current study was to increase the production of levan in Zymomonas mobilis ATCC 31821 using the Adaptive Laboratory Evolution (ALE) approach which benefits from the principles of Darwinian evolution. In this study, ALE was used to improve the production of levan in Z. mobilis through the serial passage by gradually increasing KCl concentration. The morphological changes were assessed by Scanning Electron Microscopy (SEM). Levan and ethanol production were evaluated using phenol-sulfuric acid and dichromate calorimetric methods, respectively. Production of levan in high osmotic pressure adapted strains was higher compared to the wild-type strain so levan production in the final evolved strain was 6 g l− 1 (10 times more than the ancestor strain). SEM images showed that adapted strains changed morphologically from rod to round shape. ALE had no adverse effect on ethanol production in evolved strains. These results suggested that ALE can play an essential role in the semi-rational metabolic engineering of industrial strains and compared to rational genetic engineering, provides broad insights into the genetic manipulation of microbial systems to improve the desired phenotype.