Abstract
An industrial clavulanic acid (CA) overproducer Streptomyces clavuligerus strain, namely DEPA, was engineered to further enhance its CA production. Single or multiple copies of ccaR, claR (pathway-specific activators), and cas2 (CA synthase) genes under the control of different promoters were introduced into this strain. CA titers of the resulting recombinants were analyzed by HPLC in a dynamic fashion and compared to the vector-only controls and a wild-type strain of S. clavuligerus while their growth was monitored throughout fermentation. The addition of an extra copy of ccaR, under control of its own promoter or constitutive ermE* promoter (PermE*), led to 7.6- and 2.3-fold increased volumetric levels of CA in respective recombinants, namely the AK9 and ID3 strains. Its highly stable multicopy expression by the glpF promoter (PglpF) provided up to 25.9-fold enhanced volumetric CA titers in the respective recombinant, IDG3. claR expression controlled with its own promoter or ermE* and glpF-mediated amplification in an industrial strain brought about only about 1.2-fold increase in the volumetric CA titers. An extra copy of cas2 integration with PermE* into the S. clavuligerus DEPA genome led to 3.8-fold higher volumetric CA production by GV61. Conclusively, multicopy expression of ccaR under PglpF can result in significantly improved industrial high-titer CA producers.
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