Aurachin SS, a new antibiotic from Streptomyces sp. NA04227

Strain NA04227 was isolated from an earwig (Forficula auricularia) collected in Qixia Mountain, Nanjing, China. This strain grows and sporulates well on CPA agar medium, and was identified as a Streptomyces sp. on the basis of its 16 s ribosomal RNA gene sequence (accession number: KY465886). The preliminary antibacterial assay of the crude extract from NA04227 in YEME medium showed strong antibacterial activity. To isolate and identify the bioactive components, we did a large-scale fermentation, and subjected the extract to a combination of chromatographic methods including normal phase, C-18 silica gel and Sephadex LH-20, leading to isolation and characterizations of a new compound, named as aurachin SS (1), together with two known compounds, aurachin C (2)¹² and aurachin D (3)¹² (Figure 1). Herein, we report the isolation, structure elucidation, biological activity and biosynthesis of these aurachins.

On the basis of the genetic organization and sequence identities, a biosynthetic pathway was proposed for biosynthesis of aurachins in NA04227 (Figure 3b). Anthranilic acid is activated by SauE,¹⁴ followed by extension of 5 with two malonyl-CoA units catalyzed by minimal PKS to form 6.¹ Prenylation with farnesyl diphosphate catalyzed by SauA would yield aurachin D (3),¹⁷ and then hydroxylation presumably by SauPI or SauPII led to afford aurachin C (2). However, the substrate flexibility of SauA might also accept geranyl pyrophosphate instead of farnesyl pyrophosphate as substrate to produce 7. Finally, one unidentified methyltransferase will recognize the geranyl pyrophosphate attached product (8) as substrate to generate auracin SS (1).

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD