Project description:Corynebacterium glutamicum is able to grow with lactate as sole or combined carbon and energy source. Quinone-dependent L-lactate dehydrogenase LldD is known to be essential for utilization of L-lactate by C. glutamicum. D-lactate also serves as sole carbon source for C. glutamicum ATCC 13032. Here, the gene cg1027 was shown to encode the quinone-dependent D-lactate dehydrogenase (Dld) by enzymatic analysis of the protein purified from recombinant E. coli. The absorption spectrum of purified Dld indicated the presence of FAD as bound cofactor. Inactivation of dld resulted in the loss of the ability to grow with D-lactate, which could be restored by plasmid-borne expression of dld. Heterologous expression of dld from C. glutamicum ATCC 13032 in C. efficiens enabled this species to grow with D-lactate as sole carbon source. Homologs of dld of C. glutamicum ATCC 13032 are not encoded in the sequenced genomes of other corynebacteria and mycobacteria. However, the dld locus of C. glutamicum ATCC 13032 shares 2367 bp of 2372 bp identical nucleotides with the dld locus of Propionibacterium freudenreichii subsp. shermanii, a bacterium used in Swiss-type cheese making. Both loci are flanked by insertion sequences of the same family suggesting a possible event of horizontal gene transfer.
Project description:The demand for alternative sources of food proteins is increasing due to the limitations and challenges associated with conventional food production. Advances in biotechnology have enabled the production of proteins using microorganisms, thus prompting the exploration of attractive microbial hosts capable of producing functional proteins in high titers. Corynebacterium glutamicum is widely used in industry for the production of amino acids and has many advantages as a host organism for recombinant protein production. However, its performance in this area is limited by low yields of target proteins and high levels of native protein secretion. Despite representing a challenge for heterologous protein production, the C. glutamicum secretome has not been fully characterized. In this study, state-of-the-art mass spectrometry-based proteomics was used to identify and analyze the proteins secreted by C. glutamicum. Both the wild-type strain and a strain that produced and secreted a recombinant ß-lactoglobulin protein were analyzed. A total of 427 proteins were identified in the culture supernatants, with 148 predicted to possess a secretion signal peptide. The top 12 most abundant proteins accounted for almost 80% of the secretome. These are uncharacterized proteins of unknown function, resuscitation promoting factors, protein PS1, Porin B, ABC-type transporter protein and hypothetical membrane protein. The data from this study can provide valuable insight for researchers looking to improve protein secretion and optimize C. glutamicum as a host for secretory protein production.
Project description:To identify genes which are differentially expressed in Corynebacterium glutamicum in the cg2699 deletion strain, we performed DNA microarray analyses of C. glutamicum Δcg2699 compared to the WT.
Project description:To identify genes which are differentially expressed in Corynebacterium glutamicum in the cg2460 deletion strain, we performed DNA microarray analyses of C. glutamicum Δcg2460 compared to the WT.
Project description:Previous findings have demonstrated that the NADH/NAD+ ratio has a strong impact on the glycolytic flux in C. glutamicum under anaerobic conditions in the absence of external electron acceptors. During an attempt to rewire anaerobic metabolism to achieve high yield formation of ethanol, we inactivated the malate dehydrogenase and lactate dehydrogenase in a C. glutamicum strain expressing pyruvate decarboxylase and alcohol dehydrogenase, to eliminate formation of the by-products succinate and lactate, respectively. This modification increased the yield of ethanol but had a negative effect on glycolysis, which we found to correlate with an elevated NADH/NAD+ ratio. The pyruvate dehydrogenase (PDH) of C. glutamicum is active under anaerobic conditions, and can potentially exacerbate the negative effect on glycolysis, due to NADH formation. To reduce PDH activity under anaerobic conditions, we decided to replace the gene encoding the E3 subunit of PDH with its Escherichia coli counterpart, as E. coli PDH has been reported to be functional under aerobic conditions only. The resultant strain JS133 produced far less acetate with a further increased ethanol production, however, the glycolytic flux was still low. After observing differences in glycolytic flux for JS133 on glucose and fructose, we speculated that the pentose phosphate pathway (PPP) might be involved in the reduced flux on glucose. To prove this, we deleted the zwf gene, encoding glucose-6-phosphate dehydrogenase, which is the entry point into PPP, and immediately observed a stimulating effect on glycolysis. Subsequent characterization revealed a direct correlation between the intracellular NADH/NAD+ and NADPH/NADP+ ratios under anoxic conditions. Based on these findings we managed to re-channel the metabolism of C. glutamicum successfully towards either to ethanol or D-lactate with 92% and 98% of the theoretical yield respectively, which is the highest yields for D-lactate production thus far reported in the literature.