Enhanced production of recombinant proteins in Escherichia coli by filamentation suppression

During growth of high-cell-density cultures of Escherichia coli, overproduction of recombinant proteins often results in increased stress response, cell filamentation, and growth cessation. Filamentation of cells consequently lowers final achievable cell concentration and productivity of the target protein. Reported here is a methodology that should prove useful for the enhancement of cell growth and protein productivity by the suppression of cell filamentation. By the coexpression of the E. coli ftsA and ftsZ genes, which encode key proteins in cell division, growth of recombinant strains as well as production of human leptin and human insulin-like growth factor I was improved. Observation of cell morphology revealed that the coexpression of the ftsA and ftsZ genes successfully suppressed filamentation caused by the accumulation of recombinant proteins.     

Identification, characterization, and chromosomal organization of the ftsZ gene from Brevibacterium lactofermentum

The ftsZ gene was cloned from the chromosomal DNA of Brevibacterium lactofermentum by the polymerase chain reaction (PCR) using two oligonucleotides designed from two conserved regions found in most of the previously cloned and sequenced ftsZ genes from other microorganisms. ftsZ is a single-copy gene in corynebacteria and is located downstream from ftsQ and murC, indicating linkage between genes involved in peptidoglycan synthesis (mur genes) and genes involved in cell division (fts genes). The organisation of the cluster is similar to that in Streptomyces and different from those of Escherichia coli or Bacillus subtilis because ftsA is not located upstream of ftsZ. The gene was expressed in E. coli using the T7 expression system; the calculated molecular weight of the expressed protein was 50?kDa. Expression of the B. lactofermentum ftsZ gene in E. coli inhibited cell division and led to filamentation. The ftsZ gene of this organism does not complement ftsZ mutations or deletions in E. coli, when cloned on low or high-copy-number vectors.     

Identification, characterization, and chromosomal organization of the ftsZ gene from Brevibacterium lactofermentum

The ftsZ gene was cloned from the chromosomal DNA of Brevibacterium lactofermentum by the polymerase chain reaction (PCR) using two oligonucleotides designed from two conserved regions found in most of the previously cloned and sequenced ftsZ genes from other microorganisms. ftsZ is a single-copy gene in corynebacteria and is located downstream from ftsQ and murC, indicating linkage between genes involved in peptidoglycan synthesis (mur genes) and genes involved in cell division (fts genes). The organisation of the cluster is similar to that in Streptomyces and different from those of Escherichia coli or Bacillus subtilis because ftsA is not located upstream of ftsZ. The gene was expressed in E. coli using the T7 expression system; the calculated molecular weight of the expressed protein was 50 kDa. Expression of the B. lactofermentum ftsZ gene in E. coli inhibited cell division and led to filamentation. The ftsZ gene of this organism does not complement ftsZ mutations or deletions in E. coli, when cloned on low or high-copy-number vectors. Received: 14 January 1998 / Accepted: 31 March 1998     

FtsI and FtsW Are Localized to the Septum in Escherichia coli

The localization of FtsI (PBP3), a penicillin-binding protein specifically required for cell division in Escherichia coli, was investigated by immunofluorescence microscopy and found to localize to the septum. The localization of FtsI was not observed in ftsZ or ftsA mutants, indicating that it was dependent on the prior localization of these proteins. Addition of furazlocillin, a specific inhibitor of FtsI, prevented localization of FtsI even though FtsZ and FtsA localization occurred. Interestingly, the localization of FtsN was also prevented by furazlocillin. FtsZ displayed limited localization in furazlocillin-treated cells, whereas it was efficiently localized in FtsI-depleted cells. FtsW, another essential cell division protein, was also localized to the septum.     

Engineering Escherichia coli for Increased Productivity of Serine-Rich Proteins Based on Proteome Profiling

Variations in proteome profiles of Escherichia coli in response to the overproduction of human leptin, a serine-rich (11.6% of total amino acids) protein, were examined by two-dimensional gel electrophoresis. The levels of heat shock proteins increased, while those of protein elongation factors, 30S ribosomal protein, and some enzymes involved in amino acid biosynthesis decreased, after leptin overproduction. Most notably, the levels of enzymes involved in the biosynthesis of serine family amino acids significantly decreased. Based on this information, we designed a strategy to enhance the leptin productivity by manipulating the cysK gene, encoding cysteine synthase A. By coexpression of the cysK gene, we were able to increase the cell growth rate by approximately twofold. Also, the specific leptin productivity could be increased by fourfold. In addition, we found that cysK coexpression can improve the production of another serine-rich protein, interleukin-12 β chain, suggesting that this strategy may be useful for the production of other serine-rich proteins as well. The approach taken in this study should be useful in designing a strategy for improving recombinant protein production.     

Genetic evidence for inhibition of bacterial division protein FtsZ by berberine

Background

Berberine is a plant alkaloid that is widely used as an anti-infective in traditional medicine. Escherichia coli exposed to berberine form filaments, suggesting an antibacterial mechanism that involves inhibition of cell division. Berberine is a DNA ligand and may induce filamentation through induction of the SOS response. Also, there is biochemical evidence for berberine inhibition of the cell division protein FtsZ. Here we aimed to assess possible berberine mechanism(s) of action in growing bacteria using genetics tools.

Methodology/Principal Findings

First, we tested whether berberine inhibits bacterial growth through DNA damage and induction of the SOS response. The SOS response induced by berberine was much lower compared to that induced by mitomycin C in an SOS response reporter strain. Also, cell filamentation was observed in an SOS-negative E. coli strain. To test whether berberine inhibits FtsZ, we assessed its effects on formation of the cell division Z-rings, and observed a dramatic reduction in Z-rings in the presence of berberine. We next used two different strategies for RNA silencing of ftsZ and both resulted in sensitisation of bacteria to berberine, visible as a drop in the Minimum Inhibitory Concentration (MIC). Furthermore, Fractional Inhibitory Concentration Indices (FICIs) showed a high level of synergy between ftsZ silencing and berberine treatment (FICI values of 0.23 and 0.25 for peptide nucleic acid- and expressed antisense RNA-based silencing of ftsZ, respectively). Finally, over-expression of ftsZ led to a mild rescue effect in berberine-treated cells.

Conclusions

The results argue against DNA binding as the primary mechanism of action of berberine and support the hypothesis that its antibacterial properties are due to inhibition of the cell division protein FtsZ. In addition, the genetic approach used here provides a means to rapidly test the activity of other putative FtsZ inhibitors.     

CRISPRi engineering E. coli for morphology diversification

Microbial morphology engineering has recently become interesting for biotechnology. Genes ftsZ and mreB encoding proteins of bacterial fission ring and skeletons, respectively, are essential for cell growth, they both are the most important genes keeping the bacterial shapes including the cell length and width, respectively. Clustered regularly interspaced short palindromic repeats interference, abbreviated as CRISPRi, was for the first time used in this study to regulate expression intensities of ftsZ or/and mreB in E. coli. Five sgRNAs associated with CRISPRi were designed and synthesized, respectively, to target five various locations on genes ftsZ or mreB encoded in the E. coli chromosome, resulting in various reduced expression levels of ftsZ or/and mreB, respectively, forming elongated or/and fatter cells. Repressions on gene expressions of ftsZ or/and mreB could be further intensified by combining various sgRNAs together. It was found that the stronger the repression on genes ftsZ or/and mreB, the longer the E. coli fibers, and the larger the E. coli cells. Combined repressions on expressions of ftsZ and mreB generated long and larger E. coli with diverse morphologies including various sizes of gourds, bars, coccus, spindles, multi-angles and ellipsoids. In all cases, accumulations of intracellular biopolyester polyhydroxybutyrate (PHB) were in direct proportional to the intracellular volumes, ranging from 40% to 80% PHB in bacterial cell dry weights, depending on the cell volumes increases by the above CRISPRi applications.     

Improvement of productivity of active form of glutamate racemase in Escherichia coli by coexpression of folding accessory proteins

Since two classes of folding accessory proteins, molecular chaperones and foldases, prevent the misfolding of newly synthesized polypeptides in the cell, their coexpression could be expected to improve the productivity of soluble and active recombinant proteins. Escherichia coli cytoplasmic glutamate racemase (GluR), which has five cysteine thiol groups and no disulfide bond, was selected as a model enzyme and overexpressed in E. coli. The effects of coexpressing a series of folding accessory proteins (DnaK, DnaJ, GrpE, GroEL/ES, trigger factor (TF), DsbA, DsbB, DsbC, DsbD, and thioredoxin (Trx)) on the productivity of active GluR in E. coli were examined. A relatively large amount of active GluR produced by mild induction with 10 μM isopropyl-β-d-thiogalactopyranoside (IPTG). Active GluR productivity was further increased 2.2–2.3-fold by coexpression of GroEL/ES, Trx, or DsbB–DsbD (DsbBD), while it was decreased by coexpression of DnaK–DnaJ–GrpE and TF. These results demonstrate that coexpression of appropriate folding accessory proteins could significantly improve the productivity of active form of proteins in E. coli.     

Controlling cell volume for efficient PHB production by Halomonas

Bacterial morphology is decided by cytoskeleton protein MreB and cell division protein FtsZ encoded by essential genes mreB and ftsZ, respectively. Inactivating mreB and ftsZ lead to increasing cell sizes and cell lengths, respectively, yet seriously reduce cell growth ability. Here we develop a temperature-responsible plasmid expression system for compensated expression of relevant gene(s) in mreB or ftsZ disrupted recombinants H. campaniensis LS21, allowing mreB or ftsZ disrupted recombinants to grow normally at 30 °C in a bioreactor for 12 h so that a certain cell density can be reached, followed by 36 h cell size expansions or cell shape elongations at elevated 37 °C at which the mreB and ftsZ encoded plasmid pTKmf failed to replicate in the recombinants and thus lost themselves. Finally, 80% PHB yield increase was achieved via controllable morphology manipulated H. campaniensis LS21. It is concluded that controllable expanding cell volumes (widths or lengths) provides more spaces for accumulating more inclusion body polyhydroxybutyrate (PHB) and the resulting cell gravity precipitation benefits the final separation of cells and product during downstream.     

The effects of ftsZ mutation on the production of recombinant protein in Bacillus subtilis

In this paper, the possibility of using a mutation of ftsZ as a pseudo-spore mutant is investigated. ftsZ, which is essential for cell division and sporulation of Bacillus subtilis, was placed under the spac promoter, which is inducible with isopropyl thiogalactose (IPTG). Cell growth of the ftsZ mutant and its β-galactosidase activity under the aprE promoter were compared with the wild type. In the presence of 1 mM IPTG, cell growth of the ftsZ mutant was almost the same as that of the wild type and its sporulation frequency was slightly lower than that of the wild type. However, under uninduced conditions, cell growth of ftsZ mutant was severely impaired. When induced with 0.2 mM IPTG, the ftsZ mutant showed about 13 times higher β-galactosidase activity than the wild type. When the ftsZ mutant was used for secretory production of subtilisin, only three times higher extracellular subtilisin activity was measured, compared with the wild type. By real-time PCR investigation, it was revealed that the ftsZ mutant intracellular mRNA level for subtilisin was more than 16 times higher, compared with the wild type. However, it appears that the secretion pathway is somewhat damaged in the ftsZ mutant. These results suggest that the cell division mutant can also be used like a sporulation mutant to produce recombinant proteins, with a precise control of cell growth and induction.     

Cell Envelope Components Influencing Filament Length in the Heterocyst-Forming Cyanobacterium Anabaena sp. Strain PCC 7120

Heterocyst-forming cyanobacteria grow as chains of cells (known as trichomes or filaments) that can be hundreds of cells long. The filament consists of individual cells surrounded by a cytoplasmic membrane and peptidoglycan layers. The cells, however, share a continuous outer membrane, and septal proteins, such as SepJ, are important for cell-cell contact and filament formation. Here, we addressed a possible role of cell envelope components in filamentation, the process of producing and maintaining filaments, in the model cyanobacterium Anabaena sp. strain PCC 7120. We studied filament length and the response of the filaments to mechanical fragmentation in a number of strains with mutations in genes encoding cell envelope components. Previously published peptidoglycan- and outer membrane-related gene mutants and strains with mutations in two genes (all5045 and alr0718) encoding class B penicillin-binding proteins isolated in this work were used. Our results show that filament length is affected in most cell envelope mutants, but the filaments of alr5045 and alr2270 gene mutants were particularly fragmented. All5045 is a dd-transpeptidase involved in peptidoglycan elongation during cell growth, and Alr2270 is an enzyme involved in the biosynthesis of lipid A, a key component of lipopolysaccharide. These results indicate that both components of the cell envelope, the murein sacculus and the outer membrane, influence filamentation. As deduced from the filament fragmentation phenotypes of their mutants, however, none of these elements is as important for filamentation as the septal protein SepJ.     

Cell division in a minimal bacterium in the absence of ftsZ

Mycoplasma genomes exhibit an impressively low amount of genes involved in cell division and some species even lack the ftsZ gene, which is found widespread in the microbial world and is considered essential for cell division by binary fission. We constructed a Mycoplasma genitalium ftsZ null mutant by gene replacement to investigate the role of this gene and the presence of alternative cell division mechanisms in this minimal bacterium. Our results demonstrate that ftsZ is non‐essential for cell growth and reveal that, in the absence of the FtsZ protein, M. genitalium can manage feasible cell divisions and cytokinesis using the force generated by its motile machinery. This is an alternative mechanism, completely independent of the FtsZ protein, to perform cell division by binary fission in a microorganism. We also propose that the mycoplasma cytoskeleton, a complex network of proteins involved in many aspects of the biology of these microorganisms, may have taken over the function of many genes involved in cell division, allowing their loss in the regressive evolution of the streamlined mycoplasma genomes.     

Characterization of ftsZ, the Cell Division Gene of Buchnera aphidicola (Endosymbiont of Aphids) and Detection of the Product

Buchnera aphidicola, the endosymbiont of the aphid Schizaphis graminum, contains the gene ftsZ, which codes for a protein involved in the initiation of septum formation during cell division. With immunological techniques, this protein has been detected in cell-free extracts of the endosymbiont. Nucleotide sequence determination of a 6.4-kilobase B. aphidicola DNA fragment has indicated that, as in E. coli, ftsZ is adjacent to genes coding for other cell division proteins as well as genes involved in murein synthesis (murC–ddlB–ftsA–ftsZ). Although B. aphidicola ftsZ is expressed in E. coli, it cannot complement E. coli ftsZ mutants. High levels of B. aphidicola FtsZ results in the formation of long filamentous E. coli cells, suggesting that this protein interferes with cell division. The presence of FtsZ indicates that in this, as well as in many other previously described properties, B. aphidicola resembles free-living bacteria. Received: 22 July 1997 / Accepted: 28 July 1997     

Enhancement of Recombinant Hemoglobin Production in Escherichia coli BL21(DE3) Containing the Plesiomonas shigelloides Heme Transport System

To produce recombinant hemoglobin in Escherichia coli, sufficient intracellular heme must be present, or the protein folds improperly and is degraded. In this study, coexpression of human hemoglobin genes and Plesiomonas shigelloides heme transport genes enhanced recombinant hemoglobin production in E. coli BL21(DE3) grown in medium containing heme.     

Cloning and characterization of an ftsZ homologue from a bacterial symbiont of Drosophila melanogaster

A 1194 by open reading frame that codes for a 398 amino acid peptide was cloned from a λgt11 library of Drosophila melanogaster genomic DNA. The predicted peptide sequence is very similar to three previously characterized protein sequences that are encoded by the ftsZ genes in Escherichia coli, Bacillus subtilis and Rhizobium meliloti. The FtsZ protein has a major role in the initiation of cell division in prokaryotic cells. Using a tetracycline treatment that eradicates bacterial parasites from insects, the ftsZ homologue has been found to be derived from a bacterium that lives within the strain. However, polymerase chain reaction (PCR) amplification of the gene from treated embryos suggests that it is not derived from a gut bacterium. Nevertheless, by amplifying and characterizing part of the 16S rRNA from this bacterium we have been able to demonstrate that it is a member of the genus Wolbachia, a parasitic organism that infects, and disturbs the sexual cycle of various strains of Drosophila simulans. We suggest that this ftsZ homologue is implicated in the cell division of Wolbachia, an organism that fails to grow outside the host organism. Sequence and alignment analysis of this ftsZ homologue show the presence of a potential GTP-binding motif indicating that it may function as a GTPase. The consequences of this function particularly with respect to its role in cell division are discussed.     

Suppression of filamentation in recombinant Escherichia coli by amplified FtsZ activity

A stable plasmid pSYL107 containing the Alcaligenes eutrophus polyhydroxyalkanoate biosynthesis genes and the Escherichia coli ftsZ gene was constructed. Cell filamentation previously observed during the synthesis of poly(3-hydroxybutyric acid), PHB, could be suppressed by the amplified activity of FtsZ. In a defined medium XL1-Blue (pSYL107) accumulated twice as much PHB than XL1-Blue harboring pSYL105, which does not contain the ftsZ gene.