Enhancement of extracellular purine nucleoside accumulation by Bacillus strains through genetic modifications of genes involved in nucleoside export

Using a simple method to introduce genetic modifications into the chromosome of naturally nontransformable Bacillus, a set of marker-free inosine-producing and 5-aminoimidazole-4-carboxamide (AICA) ribonucleoside-producing Bacillus amyloliquefaciens strains has been constructed. These strains differ in expression levels of the genes responsible for nucleoside export. Overexpression of B. amyloliquefaciens pbuE and heterologous expression of Escherichia coli nepI, which encode nucleoside efflux transporters, each notably enhanced inosine production by a B. amyloliquefaciens nucleoside-producing strain. pbuE overexpression was found to increase AICA ribonucleoside accumulation, indicating that the substrate specificity of the PbuE pump extends to this nucleoside. These results demonstrate that identifying genes whose products facilitate transport of a desired nucleoside out of cells and enhancing their expression can improve the performance of strains used for industrial production.