Project description:Streptomyces sp. are a rich source for natural products with recognized industrial value, explaining the high interest to improve and streamline production in these microbes. Here, we studied the production of pamamycins, macrodiolide homologues with a high activity against multi-resistant pathogenic microbes, using recombinant S. albus J1074/R2. Talc particles of micrometer size added to submerged cultures of the recombinant strain tripled pamamycin production up to 50 mg L-1. Furthermore, they strongly affected morphology, reduced the size of cell pellets, formed by the filamentous microbe during the process, up to six-fold, and shifted the pamamycin spectrum to larger derivatives. Integrated analysis of transcriptome and metabolome of particle-enhanced and control cultures provided detailed insights into the underlying molecular changes. The microparticles affected the expression of 3341 genes (56%), revealing a global and fundamental impact on metabolism. Morphology-associated genes, encoding major regulators such as SsgA, RelA, EshA, Factor C, as well as chaplins and rodlins, were found massively upregulated, indicating that the particles caused a substantially accelerated morphogenesis. In line, the pamamycin cluster was strongly upregulated (up to log2 10-fold). Furthermore, the microparticles perturbed genes encoding for central catabolism and CoA-ester metabolism, which were mainly activated. The altered expression resulted in changes in the availability of intracellular CoA-esters, the building blocks of pamamycin. Notably, the ratio between methylmalonyl CoA and malonyl-CoA was increased four-fold. Both metabolites compete for incorporation into pamamycin so that the altered availability explained the pronounced preference for larger derivatives in the microparticle-enhanced process. Our findings are straightforward to further develop pamamycins into antituberculosis leads. The novel insights into the behavior of S. albus in response to talc appears of general relevance to further explore and upgrade the concept of microparticle enhanced cultivation, widely used for filamentous microbes.

Project description:Background: Pamamycins macrodiolides of polyketide origin which form a family of differently large homologues with molecular weights between 579 and 663. They offer promising biological activity against pathogenic fungi and gram-positive bacteria. Admittedly, production titers are still low and pamamycins are typically formed as crude mixture which mainly contains smaller derivatives. Therefore, strategies that enable a more efficient production of pamamycins with increased fractions of the rare large derivatives are highly desired. Here we took a systems biology approach, integrating transcription profiling by RNA sequencing and intracellular metabolite analysis to enhance pamamycin production in the heterologous host S. albus J1074/R2. Results: Supplemented with L-valine, the recombinant pamamycin producer revealed a threefold increased pamamycin titer of about 3.5 mg L-1 and elevated fractions of larger derivatives: Pam 649 was strongly increased, and Pam 663 was newly formed. These beneficial effects were driven by increased availability of intracellular CoA esters, the building blocks for the polyketide, resulting from L-valine catabolism. Unfavorably, the presence of L-valine impaired growth of the strain, repressed genes of mannitol uptake and glycolysis, and suppressed pamamycin formation, despite the biosynthetic gene cluster was activated, restricting production to the post L-valine phase. A null mutant of the transcriptional regulator bkdR, controlling a branched-chain amino acid dehydrogenase complex, revealed decoupled pamamycin biosynthesis and accumulated the polyketide independent of the nutrient status. Supplemented with L-valine, the regulator mutant enabled the biosynthesis of pamamycin mixtures with up to 55% of the heavy derivatives Pam 635, Pam 649, and Pam 663, almost 20-fold more than the wild type. Conclusions: Our findings open the door to provide rare heavy pamamycins at markedly increased efficiency and facilitate studies to assess their specific biological activities and explore this important polyketide further.

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Streptomyces albus

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