Abstract
Microbial culture conditions in the laboratory, which conventionally involve the cultivation of one strain in one culture vessel, are vastly different from natural microbial environments. Even though perfectly mimicking natural microbial interactions is virtually impossible, the cocultivation of multiple microbial strains is a reasonable strategy to induce the production of secondary metabolites, which enables the discovery of new bioactive natural products. Our coculture of marine Streptomyces and Bacillus strains isolated together from an intertidal mudflat led to discover a new metabolite, dentigerumycin E (1). Dentigerumycin E was determined to be a new cyclic hexapeptide incorporating three piperazic acids, N-OH-Thr, N-OH-Gly, β-OH-Leu, and a pyran-bearing polyketide acyl chain mainly by analysis of its NMR and MS spectroscopic data. The putative PKS-NRPS biosynthetic gene cluster for dentigerumycin E was found in the Streptomyces strain, providing clear evidence that this cyclic peptide is produced by the Streptomyces strain. The absolute configuration of dentigerumycin E was established based on the advanced Marfey's method, ROESY NMR correlations, and analysis of the amino acid sequence of the ketoreductase domain in the biosynthetic gene cluster. In biological evaluation of dentigerumycin E (1) and its chemical derivatives [2-N,16-N-deoxydenteigerumycin E (2) and dentigerumycin methyl ester (3)], only dentigerumycin E exhibited antiproliferative and antimetastatic activities against human cancer cells, indicating that N-OH and carboxylic acid functional groups are essential for the biological activity.
Highlights
Genomic analysis of microbes strongly suggests that microorganisms have more potential gene clusters that would allow them to produce more secondary metabolites than are currently known (Omura et al, 2001)
LC-MS analysis of the cocultures indicated that a 10:1 ratio of JB5/GN1 provides the best yield of dentigerumycin E (1)
Dentigerumycin E was determined to be a new member of the dentigerumycin nonribosomal peptide class with three piperazic acid units and an acyl chain of polyketide synthase (PKS) origin (Oh et al, 2009)
Summary
Genomic analysis of microbes strongly suggests that microorganisms have more potential gene clusters that would allow them to produce more secondary metabolites than are currently known (Omura et al, 2001). Coculturing has been shown to alter individual cellular physiology and induce the production of microbial secondary metabolites that are genetically encoded but not produced under conventional laboratory culture conditions (Ueda and Beppu, 2017) In this context, coculturing different microbes to elicit the production of bioactive microbial compounds not previously observed when microbes are cultured independently could be a promising strategy to access microbial. Chemical analysis of a coculture of two marine bacterial strains isolated together from an intertidal mudflat in Wando, Republic of Korea, showed the induction of the formation of a bacterial metabolite. This result prompted us to scale up the coculture and subsequently characterize the metabolite. We report the production, structure elucidation, putative biosynthetic gene cluster (BGC), and biological activity of the new bacterial metabolite, dentigerumycin E (1)
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