Title: Improved pEKEx2-derived expression vectors for tightly controlled production of recombinant proteins in Corynebacterium glutamicum Bakkes PJ, Ramp P, Bida A, Dohmen-Olma D, Bott M, Freudl R Ref: Plasmid, 112:102540, 2020 : PubMed
The Escherichia coli/Corynebacterium glutamicum shuttle vector pEKEx2 is an IPTG-inducible expression vector that has been used successfully for the synthesis of numerous proteins in C. glutamicum. We discovered that the leaky gene expression observed for pEKEx2-derived plasmids relates to reduced functionality of the plasmid-encoded repressor LacI carrying a modified C-terminus, while duplicate DNA sequences in the pEKEx2 backbone contribute to plasmid instability. We constructed the pEKEx2-derivatives pPBEx2 and pPREx2, which harbor a restored lacI gene and which lack the unnecessary duplicate DNA sequences. pPREx2 in addition enables fusion of target genes to a C-terminal Strep-tag II coding region for easy protein detection and purification. In the absence of inducer, the novel vectors exhibit tight gene repression in C. glutamicum, as shown for the secretory production of Fusarium solani pisi cutinase and the cytosolic production of green fluorescent protein and C. glutamicum myo-inositol dehydrogenase. Undesired heterogeneity amongst clones expressing cutinase from pEKEx2 was attributed to the loss of a vector fragment containing the cutinase gene, which likely occurred via homologous recombination of the identical flanking DNA sequences. Such loss was not observed for pPBEx2. Using pPREx2, IolG-Strep was successfully produced and purified to homogeneity by Strep-Tactin affinity chromatography, obtaining 1.5 mg IolG with a specific activity of 27 mumol.min(-1).(mg protein)(-1) from 100 mL culture. The tight gene repression in the absence of inducer and the improved plasmid stability make expression vectors pPBEx2/pPREx2 attractive alternatives to the available molecular tools for genetic manipulation and high-level production of recombinant proteins in C. glutamicum.
The activity of bacteriophages and phage-related mobile elements is a major source for genome rearrangements and genetic instability of their bacterial hosts. The genome of the industrial amino acid producer Corynebacterium glutamicum ATCC 13032 contains three prophages (CGP1, CGP2, and CGP3) of so far unknown functionality. Several phage genes are regularly expressed, and the large prophage CGP3 ( approximately 190 kbp) has recently been shown to be induced under certain stress conditions. Here, we present the construction of MB001, a prophage-free variant of C. glutamicum ATCC 13032 with a 6% reduced genome. This strain does not show any unfavorable properties during extensive phenotypic characterization under various standard and stress conditions. As expected, we observed improved growth and fitness of MB001 under SOS-response-inducing conditions that trigger CGP3 induction in the wild-type strain. Further studies revealed that MB001 has a significantly increased transformation efficiency and produced about 30% more of the heterologous model protein enhanced yellow fluorescent protein (eYFP), presumably as a consequence of an increased plasmid copy number. These effects were attributed to the loss of the restriction-modification system (cg1996-cg1998) located within CGP3. The deletion of the prophages without any negative effect results in a novel platform strain for metabolic engineering and represents a useful step toward the construction of a C. glutamicum chassis genome of strain ATCC 13032 for biotechnological applications and synthetic biology.
We present a novel method for visualizing intracellular metabolite concentrations within single cells of Escherichia coli and Corynebacterium glutamicum that expedites the screening process of producers. It is based on transcription factors and we used it to isolate new L-lysine producing mutants of C. glutamicum from a large library of mutagenized cells using fluorescence-activated cell sorting (FACS). This high-throughput method fills the gap between existing high-throughput methods for mutant generation and genome analysis. The technology has diverse applications in the analysis of producer populations and screening of mutant libraries that carry mutations in plasmids or genomes.
The complete genomic sequence of Corynebacterium glutamicum ATCC 13032, well-known in industry for the production of amino acids, e.g. of L-glutamate and L-lysine was determined. The C. glutamicum genome was found to consist of a single circular chromosome comprising 3282708 base pairs. Several DNA regions of unusual composition were identified that were potentially acquired by horizontal gene transfer, e.g. a segment of DNA from C. diphtheriae and a prophage-containing region. After automated and manual annotation, 3002 protein-coding genes have been identified, and to 2489 of these, functions were assigned by homologies to known proteins. These analyses confirm the taxonomic position of C. glutamicum as related to Mycobacteria and show a broad metabolic diversity as expected for a bacterium living in the soil. As an example for biotechnological application the complete genome sequence was used to reconstruct the metabolic flow of carbon into a number of industrially important products derived from the amino acid L-aspartate.
