Cell wall synthesizing complexes in Mycobacteriales.

Members of the order Mycobacteriales are distinguished by a characteristic diderm cell envelope, setting them apart from other Actinobacteria species. In addition to the conventional peptidoglycan cell wall, these organisms feature an extra polysaccharide polymer composed of arabinose and galactose, termed arabinogalactan. The nonreducing ends of arabinose are covalently linked to mycolic acids (MAs), forming the immobile inner leaflet of the highly hydrophobic MA membrane. The contiguous outer leaflet of the MA membrane comprises trehalose mycolates and various lipid species. Similar to all actinobacteria, Mycobacteriales exhibit apical growth, facilitated by a polar localized elongasome complex. A septal cell envelope synthesis machinery, the divisome, builds instead of the cell wall structures during cytokinesis. In recent years, a growing body of knowledge has emerged regarding the cell wall synthesizing complexes of Mycobacteriales., focusing particularly on three model species: Corynebacterium glutamicum, Mycobacterium smegmatis, and Mycobacterium tuberculosis.

Recombinant production of the lantibiotic nisin using Corynebacterium glutamicum in a two-step process.

BACKGROUND: The bacteriocin nisin is naturally produced by Lactococcus lactis as an inactive prepeptide that is modified posttranslationally resulting in five (methyl-)lanthionine rings characteristic for class Ia bacteriocins. Export and proteolytic cleavage of the leader peptide results in release of active nisin. By targeting the universal peptidoglycan precursor lipid II, nisin has a broad target spectrum including important human pathogens such as Listeria monocytogenes and methicillin-resistant Staphylococcus aureus strains. Industrial nisin production is currently performed using natural producer strains resulting in rather low product purity and limiting its application to preservation of dairy food products. RESULTS: We established heterologous nisin production using the biotechnological workhorse organism Corynebacterium glutamicum in a two-step process. We demonstrate successful biosynthesis and export of fully modified prenisin and its activation to mature nisin by a purified, soluble variant of the nisin protease NisP (sNisP) produced in Escherichia coli. Active nisin was detected by a L. lactis sensor strain with strictly nisin-dependent expression of the fluorescent protein mCherry. Following activation by sNisP, supernatants of the recombinant C. glutamicum producer strain cultivated in standard batch fermentations contained at least 1.25 mg/l active nisin. CONCLUSIONS: We demonstrate successful implementation of a two-step process for recombinant production of active nisin with C. glutamicum. This extends the spectrum of bioactive compounds that may be produced using C. glutamicum to a bacteriocin harboring complex posttranslational modifications. Our results provide a basis for further studies to optimize product yields, transfer production to sustainable substrates and purification of pharmaceutical grade nisin.

Single-cell growth inference of Corynebacterium glutamicum reveals asymptotically linear growth.

Regulation of growth and cell size is crucial for the optimization of bacterial cellular function. So far, single bacterial cells have been found to grow predominantly exponentially, which implies the need for tight regulation to maintain cell size homeostasis. Here, we characterize the growth behavior of the apically growing bacterium Corynebacterium glutamicum using a novel broadly applicable inference method for single-cell growth dynamics. Using this approach, we find that C. glutamicum exhibits asymptotically linear single-cell growth. To explain this growth mode, we model elongation as being rate-limited by the apical growth mechanism. Our model accurately reproduces the inferred cell growth dynamics and is validated with elongation measurements on a transglycosylase deficient ΔrodA mutant. Finally, with simulations we show that the distribution of cell lengths is narrower for linear than exponential growth, suggesting that this asymptotically linear growth mode can act as a substitute for tight division length and division symmetry regulation.

L-valine production in Corynebacterium glutamicum based on systematic metabolic engineering: progress and prospects.

L-valine is an essential branched-chain amino acid that cannot be synthesized by the human body and has a wide range of applications in food, medicine and feed. Market demand has stimulated people's interest in the industrial production of L-valine. At present, the mutagenized or engineered Corynebacterium glutamicum is an effective microbial cell factory for producing L-valine. Because the biosynthetic pathway and metabolic network of L-valine are intricate and strictly regulated by a variety of key enzymes and genes, highly targeted metabolic engineering can no longer meet the demand for efficient biosynthesis of L-valine. In recent years, the development of omics technology has promoted the upgrading of traditional metabolic engineering to systematic metabolic engineering. This whole-cell-scale transformation strategy has become a productive method for developing L-valine producing strains. This review provides an overview of the biosynthesis and regulation mechanism of L-valine, and summarizes the current metabolic engineering techniques and strategies for constructing L-valine high-producing strains. Finally, the opinion of constructing a cell factory for efficiently biosynthesizing L-valine was proposed.

Polar Growth in Corynebacterium glutamicum Has a Flexible Cell Wall Synthase Requirement.

Members of the Corynebacterineae suborder of bacteria, including major pathogens such as Mycobacterium tuberculosis, grow via the insertion of new cell wall peptidoglycan (PG) material at their poles. This mode of elongation differs from that used by Escherichia coli and other more well-studied model organisms that grow by inserting new PG at dispersed sites along their cell body. Dispersed cell elongation is known to strictly require the SEDS-type PG synthase called RodA, whereas the other major class of PG synthases called class A penicillin-binding proteins (aPBPs) are not required for this mode of growth. Instead, they are thought to be important for maintaining the integrity of the PG matrix in organisms growing by dispersed elongation. In contrast, based on prior genetic studies in M. tuberculosis and related members of the Corynebacterineae suborder, the aPBPs are widely believed to be essential for polar growth, with RodA being dispensable. However, polar growth has not been directly assessed in mycobacterial or corynebacterial mutants lacking aPBP-type PG synthases. We therefore investigated the relative roles of aPBPs and RodA in polar growth using Corynebacterium glutamicum as a model member of Corynebacterineae. Notably, we discovered that the aPBPs are dispensable for polar growth and that this growth mode can be mediated by either an aPBP-type or a SEDS-type enzyme functioning as the sole elongation PG synthase. Thus, our results reveal that the mechanism of polar elongation is fundamentally flexible and, unlike dispersed elongation, can be effectively mediated in C. glutamicum by either a SEDS-bPBP or an aPBP-type synthase. IMPORTANCE The Corynebacterineae suborder includes a number of major bacterial pathogens. These organisms grow by polar extension unlike most well-studied model bacteria, which grow by inserting wall material at dispersed sites along their length. A better understanding of polar growth promises to uncover new avenues for targeting mycobacterial and corynebacterial infections. Here, we investigated the roles of the different classes of cell wall synthases for polar growth using Corynebacterium glutamicum as a model. We discovered that the polar growth mechanism is surprisingly flexible in this organism and, unlike dispersed synthesis, can function using either of the two known types of cell wall synthase enzymes.

Characterization of the Uncommon Lipid Families in Corynebacterium glutamicum by Mass Spectrometry.

This book chapter provides readers the step-by-step instruction for cell growth, lipid isolation, and lipid analysis to obtain the lipidome of Corynebacterium glutamicum (C. glutamicum) in the genus Corynebacterium, a biotechnologically important bacterium. We separate the lipid families by preparative HPLC with an analytical C-8 column, followed by linear ion-trap multiple stage mass spectrometry (LIT MSn) with high-resolution mass measurement to define the structures of cytidine diphosphate diacylglycerol (CDP-DAG), glucuronosyl diacylglycerol (GlcA-DAG), α-D-mannopyranosyl-(1 â†’ 4)-α-D-glucuronyl diacylglycerol (Man-GlcA-DAG), 1-mycolyl-2-acyl-phosphatidylglycerol (MA-PG), and acyl trehalose monomycolate (acyl-TMM) whose structures have been previously mis-assigned or not defined by mass spectrometric means. We also define the structures of mycolic acid, phosphatidylglycerol, phosphatidylinositol, cardiolipin, trehalose dimycolate lipids in the cell wall. The similarity of the lipidome to that in the Mycobacterium genera is consistent with the notion that Corynebacterium and Mycobacterium are gram-positive bacteria belonging to the suborder Corynebacterineae.

Adaptive laboratory evolution accelerated glutarate production by Corynebacterium glutamicum.

BACKGROUND: The demand for biobased polymers is increasing steadily worldwide. Microbial hosts for production of their monomeric precursors such as glutarate are developed. To meet the market demand, production hosts have to be improved constantly with respect to product titers and yields, but also shortening bioprocess duration is important. RESULTS: In this study, adaptive laboratory evolution was used to improve a C. glutamicum strain engineered for production of the C5-dicarboxylic acid glutarate by flux enforcement. Deletion of the L-glutamic acid dehydrogenase gene gdh coupled growth to glutarate production since two transaminases in the glutarate pathway are crucial for nitrogen assimilation. The hypothesis that strains selected for faster glutarate-coupled growth by adaptive laboratory evolution show improved glutarate production was tested. A serial dilution growth experiment allowed isolating faster growing mutants with growth rates increasing from 0.10 h-1 by the parental strain to 0.17 h-1 by the fastest mutant. Indeed, the fastest growing mutant produced glutarate with a twofold higher volumetric productivity of 0.18 g L-1 h-1 than the parental strain. Genome sequencing of the evolved strain revealed candidate mutations for improved production. Reverse genetic engineering revealed that an amino acid exchange in the large subunit of L-glutamic acid-2-oxoglutarate aminotransferase was causal for accelerated glutarate production and its beneficial effect was dependent on flux enforcement due to deletion of gdh. Performance of the evolved mutant was stable at the 2 L bioreactor-scale operated in batch and fed-batch mode in a mineral salts medium and reached a titer of 22.7 g L-1, a yield of 0.23 g g-1 and a volumetric productivity of 0.35 g L-1 h-1. Reactive extraction of glutarate directly from the fermentation broth was optimized leading to yields of 58% and 99% in the reactive extraction and reactive re-extraction step, respectively. The fermentation medium was adapted according to the downstream processing results. CONCLUSION: Flux enforcement to couple growth to operation of a product biosynthesis pathway provides a basis to select strains growing and producing faster by adaptive laboratory evolution. After identifying candidate mutations by genome sequencing causal mutations can be identified by reverse genetics. As exemplified here for glutarate production by C. glutamicum, this approach allowed deducing rational metabolic engineering strategies.

Robotic integration enables autonomous operation of laboratory scale stirred tank bioreactors with model-driven process analysis.

Given its geometric similarity to large-scale production plants and the excellent possibilities for precise process control and monitoring, the classic stirred tank bioreactor (STR) still represents the gold standard for bioprocess development at a laboratory scale. However, compared to microbioreactor technologies, bioreactors often suffer from a low degree of process automation and deriving key performance indicators (KPIs) such as specific rates or yields often requires manual sampling and sample processing. A widely used parallelized STR setup was automated by connecting it to a liquid handling system and controlling it with a custom-made process control system. This allowed for the setup of a flexible modular platform enabling autonomous operation of the bioreactors without any operator present. Multiple unit operations like automated inoculation, sampling, sample processing and analysis, and decision making, for example for automated induction of protein production were implemented to achieve such functionality. The data gained during application studies was used for fitting of bioprocess models to derive relevant KPIs being in good agreement with literature. By combining the capabilities of STRs with the flexibility of liquid handling systems, this platform technology can be applied to a multitude of different bioprocess development pipelines at laboratory scale.

Elongation factor P is required for EIIGlc translation in Corynebacterium glutamicum due to an essential polyproline motif.

Translating ribosomes require elongation factor P (EF-P) to incorporate consecutive prolines (XPPX) into nascent peptide chains. The proteome of Corynebacterium glutamicum ATCC 13032 contains a total of 1,468 XPPX motifs, many of which are found in proteins involved in primary and secondary metabolism. We show here that synthesis of EIIGlc , the glucose-specific permease of the phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS) encoded by ptsG, is strongly dependent on EF-P, as an efp deletion mutant grows poorly on glucose as sole carbon source. The amount of EIIGlc is strongly reduced in this mutant, which consequently results in a lower rate of glucose uptake. Strikingly, the XPPX motif is essential for the activity of EIIGlc , and substitution of the prolines leads to inactivation of the protein. Finally, translation of GntR2, a transcriptional activator of ptsG, is also dependent on EF-P. However, its reduced amount in the efp mutant can be compensated for by other regulators. These results reveal for the first time a translational bottleneck involving production of the major glucose transporter EIIGlc , which has implications for future strain engineering strategies.

Adaptive laboratory evolution of Pseudomonas putida and Corynebacterium glutamicum to enhance anthranilate tolerance.

Microbial bioproduction of the aromatic acid anthranilate (ortho-aminobenzoate) has the potential to replace its current, environmentally demanding production process. The host organism employed for such a process needs to fulfil certain demands to achieve industrially relevant product levels. As anthranilate is toxic for microorganisms, the use of particularly robust production hosts can overcome issues from product inhibition. The microorganisms Corynebacterium glutamicum and Pseudomonas putida are known for high tolerance towards a variety of chemicals and could serve as promising platform strains. In this study, the resistance of both wild-type strains towards anthranilate was assessed. To further enhance their native tolerance, adaptive laboratory evolution (ALE) was applied. Sequential batch fermentation processes were developed, adapted to the cultivation demands for C. glutamicum and P. putida, to enable long-term cultivation in the presence of anthranilate. Isolation and analysis of single mutants revealed phenotypes with improved growth behaviour in the presence of anthranilate for both strains. The characterization and improvement of both potential hosts provide an important basis for further process optimization and will aid the establishment of an industrially competitive method for microbial synthesis of anthranilate.

Increasing L-lysine production in Corynebacterium glutamicum by engineering amino acid transporters.

Corynebacterium glutamicum has a long and successful history in the biotechnological production of L-lysine. Besides the adjustment of metabolic pathways, intracellular and extracellular transport systems are critical for the cellular metabolism of L-lysine or its by-products. Here, three amino acid transmembrane transporters, namely, GluE, BrnE/BrnF, and LysP, which are widely present in C. glutamicum strains, were each investigated by gene knockout. In comparison with that in the wild-type strain, the yield of L-lysine increased by 9.0%, 12.3%, and 10.0% after the deletion of the gluE, brnE/brnF, and lysP genes, respectively, in C. glutamicum 23,604. Moreover, the amount of by-product amino acids decreased significantly when the gluE and brnE/brnF genes were deleted. It was also demonstrated that there was no effect on the growth of the strain when the gluE or lysP gene was deleted, whereas the biomass of C. glutamicum WL1702 (ΔbrnE/ΔbrnF) in the fermentation medium was significantly reduced in comparison with that of the wild type. These results also provide useful information for enhancing the production of L-lysine or other amino acids by C. glutamicum.

Optimization of ribosomal binding site sequences for gene expression and 4-hydroxyisoleucine biosynthesis in recombinant corynebacterium glutamicum.

4-Hydroxyisoleucine (4-HIL) has potential value for treating diabetes. α-Ketoglutarate (α-KG)-dependent l-isoleucine dioxygenase (IDO) can convert l-isoleucine (Ile) into 4-HIL. In our previous study, 4-HIL was de novo synthesized from glucose by expressing the ido gene in Corynebacterium glutamicum strain SN01, an Ile producer, and neither Ile nor α-KG was added. In this study, ribosomal binding site (RBS) engineering was applied for gene expression and 4-HIL biosynthesis in C. glutamicum. The 18 tested RBS sequences showed greatly differing strengths for expressing ido, and 8.10-104.22 mM 4-HIL was produced. To supply the cosubstrate α-KG at different levels, the odhI gene was then expressed using the RBS sequences of high, medium, and low strength in the above mentioned optimal strain SF01 carrying R8-ido. However, 4-HIL production decreased to varying amounts, and in some strains, the α-KG was redirected into l-glutamate synthesis. Next, the O2 supply was further enhanced in three ido-odhI coexpressing strains by overexpressing the vgb gene, and 4-HIL production changed dramatically. 4-HIL (up to 119.27 ± 5.03 mM) was produced in the best strain, SF08, suggesting that the synchronic supply of cosubstrates α-KG and O2 is critical for the high-yield production of 4-HIL. Finally, the avtA gene and the ldhA-pyk2 cluster were deleted separately in SF08 to reduce pyruvate-derived byproducts, and 4-HIL production increased to 122.16 ± 5.18 and 139.82 ± 1.56 mM, respectively, indicating that both strains were promising candidates for producing 4-HIL. Therefore, fine-tuning ido expression and the cosubstrates supply through RBS engineering is a useful strategy for improving 4-HIL biosynthesis in C. glutamicum.

Artificially designed routes for the conversion of starch to value-added mannosyl compounds through coupling in vitro and in vivo metabolic engineering strategies.

Starch/cellulose has become the major feedstock for manufacturing biofuels and biochemicals because of their abundance and sustainability. In this study, we presented an artificially designed "starch-mannose-fermentation" biotransformation process through coupling the advantages of in vivo and in vitro metabolic engineering strategies together. Starch was initially converted into mannose via an in vitro metabolic engineering biosystem, and then mannose was fermented by engineered microorganisms for biomanufacturing valuable mannosyl compounds. The in vitro metabolic engineering biosystem based on phosphorylation/dephosphorylation reactions was thermodynamically favorable and the conversion rate reached 81%. The mannose production using whole-cell biocatalysts reached 75.4 g/L in a 30-L reactor, indicating the potential industrial application. Furthermore, the produced mannose in the reactor was directly served as feedstock for the fermentation process to bottom-up produced 19.2 g/L mannosyl-oligosaccharides (MOS) and 7.2 g/L mannosylglycerate (MG) using recombinant Corynebacterium glutamicum strains. Notably, such a mannose fermentation process facilitated the synthesis of MOS, which has not been achieved under glucose fermentation and improved MG production by 2.6-fold than that using the same C-mole of glucose. This approach also allowed access to produce other kinds of mannosyl derivatives from starch.

Accelerated Growth of Corynebacterium glutamicum by Up-Regulating Stress- Responsive Genes Based on Transcriptome Analysis of a Fast-Doubling Evolved Strain.

Corynebacterium glutamicum, an important industrial strain, has a relatively slower reproduction rate. To acquire a growth-boosted C. glutamicum, a descendant strain was isolated from a continuous culture after 600 generations. The isolated descendant C. glutamicum, JH41 strain, was able to double 58% faster (td=1.15 h) than the parental type strain (PT, td=1.82 h). To understand the factors boosting reproduction, the transcriptomes of JH41 and PT strains were compared. The mRNAs involved in respiration and TCA cycle were upregulated. The intracellular ATP of the JH41 strain was 50% greater than the PT strain. The upregulation of NCgl1610 operon (a putative dyp-type heme peroxidase, a putative copper chaperone, and a putative copper importer) that presumed to role in the assembly and redox control of cytochrome c oxidase was found in the JH41 transcriptome. Plasmid-driven expression of the operon enabled the PT strain to double 19% faster (td=1.82 h) than its control (td=2.17 h) with 14% greater activity of cytochrome c oxidase and 27% greater intracellular ATP under the oxidative stress conditions. Upregulations of genes those might enhance translation fitness were also found in the JH41 transcriptome. Plasmid-driven expressions of NCgl0171 (encoding a cold-shock protein) and NCgl2435 (encoding a putative peptidyl-tRNA hydrolase) enabled the PT to double 22% and 32% faster than its control, respectively (empty vector: td=1.93 h, CspA: td=1.58 h, and Pth: td=1.44 h). Based on the results, the factors boosting growth rate in C. gluctamicum were further discussed in the viewpoints of cellular energy state, oxidative stress management, and translation.

Role of the unique, non-essential phosphatidylglycerol::prolipoprotein diacylglyceryl transferase (Lgt) in Corynebacterium glutamicum.

Bacterial lipoproteins are secreted proteins that are post-translationally lipidated. Following synthesis, preprolipoproteins are transported through the cytoplasmic membrane via the Sec or Tat translocon. As they exit the transport machinery, they are recognized by a phosphatidylglycerol::prolipoprotein diacylglyceryl transferase (Lgt), which converts them to prolipoproteins by adding a diacylglyceryl group to the sulfhydryl side chain of the invariant Cys+1 residue. Lipoprotein signal peptidase (LspA or signal peptidase II) subsequently cleaves the signal peptide, liberating the α-amino group of Cys+1, which can eventually be further modified. Here, we identified the lgt and lspA genes from Corynebacterium glutamicum and found that they are unique but not essential. We found that Lgt is necessary for the acylation and membrane anchoring of two model lipoproteins expressed in this species: MusE, a C. glutamicum maltose-binding lipoprotein, and LppX, a Mycobacterium tuberculosis lipoprotein. However, Lgt is not required for these proteins' signal peptide cleavage, or for LppX glycosylation. Taken together, these data show that in C. glutamicum the association of some lipoproteins with membranes through the covalent attachment of a lipid moiety is not essential for further post-translational modification.

CO2/HCO3- Accelerates Iron Reduction through Phenolic Compounds.

Iron is a vital mineral for almost all living organisms and has a pivotal role in central metabolism. Despite its great abundance on earth, the accessibility for microorganisms is often limited, because poorly soluble ferric iron (Fe3+) is the predominant oxidation state in an aerobic environment. Hence, the reduction of Fe3+ is of essential importance to meet the cellular demand of ferrous iron (Fe2+) but might become detrimental as excessive amounts of intracellular Fe2+ tend to undergo the cytotoxic Fenton reaction in the presence of hydrogen peroxide. We demonstrate that the complex formation rate of Fe3+ and phenolic compounds like protocatechuic acid was increased by 46% in the presence of HCO3- and thus accelerated the subsequent redox reaction, yielding reduced Fe2+ Consequently, elevated CO2/HCO3- levels increased the intracellular Fe2+ availability, which resulted in at least 50% higher biomass-specific fluorescence of a DtxR-based Corynebacterium glutamicum reporter strain, and stimulated growth. Since the increased Fe2+ availability was attributed to the interaction of HCO3- and chemical iron reduction, the abiotic effect postulated in this study is of general relevance in geochemical and biological environments.IMPORTANCE In an oxygenic environment, poorly soluble Fe3+ must be reduced to meet the cellular Fe2+ demand. This study demonstrates that elevated CO2/HCO3- levels accelerate chemical Fe3+ reduction through phenolic compounds, thus increasing intracellular Fe2+ availability. A number of biological environments are characterized by the presence of phenolic compounds and elevated HCO3- levels and include soil habitats and the human body. Fe2+ availability is of particular interest in the latter, as it controls the infectiousness of pathogens. Since the effect postulated here is abiotic, it generally affects the Fe2+ distribution in nature.

The Iron Deficiency Response of Corynebacterium glutamicum and a Link to Thiamine Biosynthesis.

The response to iron limitation of the Gram-positive soil bacterium Corynebacterium glutamicum was analyzed with respect to secreted metabolites, the transcriptome, and the proteome. During growth in glucose minimal medium, iron limitation caused a shift from lactate to pyruvate as the major secreted organic acid complemented by l-alanine and 2-oxoglutarate. Transcriptome and proteome analyses revealed that a pronounced iron starvation response governed by the transcriptional regulators DtxR and RipA was detectable in the late, but not in the early, exponential-growth phase. A link between iron starvation and thiamine pyrophosphate (TPP) biosynthesis was uncovered by the strong upregulation of thiC As phosphomethylpyrimidine synthase (ThiC) contains an iron-sulfur cluster, limiting activities of the TPP-dependent pyruvate-2-oxoglutarate dehydrogenase supercomplex probably cause the excretion of pyruvate and 2-oxoglutarate. In line with this explanation, thiamine supplementation could strongly diminish the secretion of these acids. The upregulation of thiC and other genes involved in thiamine biosynthesis and transport is presumably due to TPP riboswitches present at the 5' end of the corresponding operons. The results obtained in this study provide new insights into iron homeostasis in C. glutamicum and demonstrate that the metabolic consequences of iron limitation can be due to the iron dependency of coenzyme biosynthesis.IMPORTANCE Iron is an essential element for most organisms but causes problems due to poor solubility under oxic conditions and due to toxicity by catalyzing the formation of reactive oxygen species (ROS). Therefore, bacteria have evolved complex regulatory networks for iron homeostasis aiming at a sufficient iron supply while minimizing ROS formation. In our study, the responses of the actinobacterium Corynebacterium glutamicum to iron limitation were analyzed, resulting in a detailed view on the processes involved in iron homeostasis in this model organism. In particular, we provide evidence that iron limitation causes TPP deficiency, presumably due to insufficient activity of the iron-dependent phosphomethylpyrimidine synthase (ThiC). TPP deficiency was deduced from the upregulation of genes controlled by a TPP riboswitch and secretion of metabolites caused by insufficient activity of the TPP-dependent enzymes pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase. To our knowledge, the link between iron starvation and thiamine synthesis has not been elaborated previously.

Metabolic engineering of carbohydrate metabolism systems in Corynebacterium glutamicum for improving the efficiency of L-lysine production from mixed sugar.

The efficiency of industrial fermentation process mainly depends on carbon yield, final titer and productivity. To improve the efficiency of L-lysine production from mixed sugar, we engineered carbohydrate metabolism systems to enhance the effective use of sugar in this study. A functional metabolic pathway of sucrose and fructose was engineered through introduction of fructokinase from Clostridium acetobutylicum. L-lysine production was further increased through replacement of phosphoenolpyruvate-dependent glucose and fructose uptake system (PTSGlc and PTSFru) by inositol permeases (IolT1 and IolT2) and ATP-dependent glucokinase (ATP-GlK). However, the shortage of intracellular ATP has a significantly negative impact on sugar consumption rate, cell growth and L-lysine production. To overcome this defect, the recombinant strain was modified to co-express bifunctional ADP-dependent glucokinase (ADP-GlK/PFK) and NADH dehydrogenase (NDH-2) as well as to inactivate SigmaH factor (SigH), thus reducing the consumption of ATP and increasing ATP regeneration. Combination of these genetic modifications resulted in an engineered C. glutamicum strain K-8 capable of producing 221.3 ± 17.6 g/L L-lysine with productivity of 5.53 g/L/h and carbon yield of 0.71 g/g glucose in fed-batch fermentation. As far as we know, this is the best efficiency of L-lysine production from mixed sugar. This is also the first report for improving the efficiency of L-lysine production by systematic modification of carbohydrate metabolism systems.

Growth promotion in Corynebacterium glutamicum by overexpression of the NCgl2986 gene encoding a protein homologous to peptidoglycan amidases.

We previously reported the extracellular production of antibody fragment Fab by Corynebacterium glutamicum. In the course of searching for genes which improve the secretion efficiency of Fab, we coincidentally found that the final growth increased significantly when the NCgl2986 gene encoding an amidase-like protein was overexpressed. This effect was observed when cells were grown on the production medium MMTG, which contains high concentrations of glucose and neutralizing agent CaCO3, but not on MMTG without CaCO3 or Lennox medium. Not only turbidity but also dry cell weight was increased by NCgl2986 overexpression, although the growth rate was not affected. It was recently reported that the Mycobacterium tuberculosis homolog Rv3915 functions as an activator of MurA protein, which catalyzes the initial step of peptidoglycan synthesis. Growth promotion was also observed when the MurA protein was overproduced. His-tagged NCgl2986 protein was purified, but its peptidoglycan hydrolyzing activity could not be detected. These results suggest that NCgl2986 promotes cell growth by activating the peptidoglycan synthetic pathway.

A novel expression vector for Corynebacterium glutamicum with an auxotrophy complementation system.

Corynebacterium glutamicum is an important industrial strain used for the production of amino acids and vitamins. Most tools developed for overexpression of genes in C. glutamicum are based on the inducible promoter regulated by the lacIq gene or contain an antibiotic resistance gene as a selection marker. These vectors are essential for rapid identification of recombinant strains and detailed study of gene functions, but, as a considerable disadvantage, these vectors are not suitable for large-scale industrial production due to the need for the addition of isopropyl-ß-D-thiogalactopyranoside (IPTG) and antibiotics. In this study, the novel Escherichia coli-C. glutamicum shuttle expression vector pLY-4, derived from the expression vector pXMJ19, was constructed. The constitutive vector pLY-4 contains a large multiple cloning site, the strong promoter tacM and two selective markers: the original chloramphenicol resistance gene cat is used for molecular cloning operations, and the auxotrophy complementation marker alr, which can be stably replicated in the auxotrophic host strain without antibiotic selection pressure, is used for industrial fermentation. Heterologous expression of the gapC gene using the vector pLY-4 in C. glutamicum for L-methionine production indicated the potential application of pLY-4 in the development of C. glutamicum strain engineering and industrial fermentation.