Genome-wide gene expression changes in an industrial clavulanic acid overproduction strain of Streptomyces clavuligerus.
Bottom Line: To increase production of the important pharmaceutical compound clavulanic acid, a β-lactamase inhibitor, both random mutagenesis approaches and rational engineering of Streptomyces clavuligerus strains have been extensively applied.A few additional transcriptional changes in primary metabolism at key points seem to divert metabolic fluxes to the biosynthetic precursors for clavulanic acid.In general, the observed changes largely coincide with genes that have been targeted by rational engineering in recent years, yet the presence of a number of previously unexplored genes clearly demonstrates that functional genomic analysis can provide new leads for strain improvement in biotechnology.
Affiliation: Department of Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.Show MeSH
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Mentions: Indeed, glycerol uptake and metabolism (SCLAV_0631‐0632 and SCLAV_0877‐0879) is clearly upregulated over twofold in DS48802, indicating an improved utilization of glycerol as a carbon source as well as increased production of the clavulanic acid precursor G3P (Fig. 2). Moreover, the aconitase and citrate synthase from the citric acid cycle appear to be downregulated. A likely explanation for this is that the carbon flux from G3P in this direction is reduced and is partly redirected to clavulanic acid biosynthesis. This situation is remarkably similar to the result of the rationally constructed gap1 deletion that blocked G3P conversion into 1,3‐bisphosphoglycerate, thus improving clavulanic acid biosynthesis by increasing the intracellular G3P pool (Li and Townsend, 2006). However, an advantage of the situation in DS48802, which seems to have an incomplete downregulation of the flux, could be that a considerable pool of acetyl‐CoA is maintained, e.g. for the biosynthesis of ornithine from glutamate. DS48802 also seems to avoid the potential negative effects of a complete deletion of the aconitase and citrate synthase genes: a complete absence of these enzyme activities could lead to acidogenesis with negative consequences for secondary metabolite production as shown by Viollier and colleagues (2001a,b). Moreover, DS48802 still seems to be able to synthesize α‐ketoglutarate (a co‐substrate required for clavaminic acid biosynthesis; Salowe et al., 1990), while achieving the benefits of higher acetyl‐CoA and/or G3P pools that have made these genes attractive targets for rational engineering to improve antibiotic production (Viollier et al., 2001a). A potentially important observation that we cannot explain yet from the current data are the differential transcript level changes of the two pyruvate kinase isoenzyme genes, one being downregulated (SCLAV_4329) and the other being upregulated (SCLAV_1203).
Affiliation: Department of Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.