Horizontal Transfer of Iturin A Operon, itu , to Bacillus subtilis 168 and Conversion into an Iturin A Producer

Abstract

ABSTRACT Iturin A and its derivatives are lipopeptide antibiotics produced by Bacillus subtilis and several closely related bacteria. Three iturin group operons (i.e., iturin A, mycosubtilin, and bacillomycin D) of those antibiotic-producing strains have been cloned and sequenced thus far, strongly implying the horizontal transfer of these operons. To examine the nature of such horizontal transfer in terms of antibiotic production, a 42-kb region of the B. subtilis RB14 genome, which contains a complete 38-kb iturin A operon, was transferred via competent cell transformation to the genome of a non-iturin A producer, B. subtilis 168, using a method based on double-crossover homologous recombination with two short landing pad sequences (LPSs) in the genome. The recombinant was positively selected by confirming the elimination of the c I repressor gene, which was localized between the two LPSs and substituted by the transferred segment. The iturin A operon-transferred strain 168 was then converted into an iturin A producer by the introduction of an sfp gene, which encodes 4′-phosphopantetheinyl transferase and is mutated in strain 168. By inserting the pleiotropic regulator degQ , the productivity of iturin A increased sevenfold and was restored to about half that of the donor strain RB14, without the transfer of additional genes, such as regulatory or self-resistance genes.