Cloning, sequencing, and characterization of the genetic region relevant to biosynthesis of the lipopeptides iturin A and surfactin in Bacillus subtilis

Bacillus subtilis B3 was found to produce lipopeptides iturins and fengycin that have activity against several plant pathogens such as Fusarium graminearum, Rhizoctonia solani, Rhizoctonia cerealis, and Pyricularia grisea. A 3642-bp genomic region of B. subtilis B3 comprising srfDB3, aspB3, lpaB3, and yczEB3 genes that resulted in biosynthesis of surfactin in B. subtilis 168 was cloned, sequenced, and characterized. Among them, the srfDB3 gene encodes thioesterase, which is required for biosynthesis of surfactin in B. subtilis; the aspB3 gene encodes a putative aspartate aminotransferase-like protein; the lpaB3 encodes phosphopantetheinyl transferase, which shows high identity to the product of lpa-14 gene regulating the biosynthesis of iturin A and surfactin in B. subtilis RB14; the yczEB3 encodes a YczE-like protein with significant similarities in signal peptide and part of the ABC transport system. The genetic regions between the srfD gene and lpa gene from B. subtilis B3 and B. subtilis A13, which produces iturin A, contain an approximate 1-kb nucleotide fragment encoding an aspartate aminotransferase-like protein; however, the relevant regions from B. subtilis 168 and B. subtilis ATCC21332 producing surfactin comprise an approximately 4-kb nucleotide fragment encoding four unknown proteins. There is 73% identity between the Lpa family and the Sfp family, although both are highly conserved.