An improved protocol for electrotransformation of Corynebacterium pseudotuberculosis

The MprF homolog LysX synthesizes lysyl-diacylglycerol contributing to antibiotic resistance and virulence

Lysyl-diacylglycerol (Lys-DAG) was identified three decades ago in Mycobacterium phlei, but the biosynthetic pathway and function of this aminoacylated lipid have since remained uncharacterized. Combining genetic methods, mass spectrometry, and biochemical approaches, we show that the multiple peptide resistance factor (MprF) homolog LysX from Corynebacterium pseudotuberculosis and two mycobacterial species is responsible for Lys-DAG synthesis. LysX is conserved in most Actinobacteria and was previously implicated in the synthesis of another modified lipid, lysyl-phosphatidylglycerol (Lys-PG), in Mycobacterium tuberculosis. Although we detected low levels of Lys-PG in the membrane of C. pseudotuberculosis, our data suggest that Lys-PG is not directly synthesized by LysX and may require an additional downstream pathway, which is as yet undefined. Our results show that LysX in C. pseudotuberculosis is a major factor of resistance against a variety of positively charged antibacterial agents, including cationic antimicrobial peptides (e.g., human peptide LL-37 and polymyxin B) and aminoglycosides (e.g., gentamycin and apramycin). Deletion of lysX caused an increase in cellular membrane permeability without dissipation of the membrane potential, suggesting that loss of the protein does not result in mechanical damage to the cell membrane. Furthermore, lysX-deficient cells exhibited an attenuated virulence phenotype in a Galleria mellonella infection model, supporting a role for LysX during infection. Altogether, Lys-DAG represents a novel molecular determinant for antimicrobial resistance and virulence that may be widespread in Actinobacteria and points to a richer landscape than previously realized of lipid components contributing to overall membrane physiology in this important bacterial phylum. IMPORTANCE In the past two decades, tRNA-dependent modification of membrane phosphatidylglycerol has been implicated in altering the biochemical properties of the cell surface, thereby enhancing the antimicrobial resistance and virulence of various bacterial pathogens. Here, we show that in several Actinobacteria, the multifunctional protein LysX attaches lysine to diacylglycerol instead of phosphatidylglycerol. We found that lysyl-diacylglycerol (Lys-DAG) confers high levels of resistance against various cationic antimicrobial peptides and aminoglycosides and also enhances virulence. Our data show that Lys-DAG is a lipid commonly found in important actinobacterial pathogens, including Mycobacterium and Corynebacterium species.

Insights of OxyR role in mechanisms of host-pathogen interaction of Corynebacterium diphtheriae

Corynebacterium diphtheriae, the leading causing agent of diphtheria, has been increasingly related to invasive diseases, including sepsis, endocarditis, pneumonia, and osteomyelitis. Oxidative stress defense is required not only for successful growth and survival under environmental conditions but also in the regulation of virulence mechanisms of human pathogenic species, by promoting mucosal colonization, survival, dissemination, and defense against the innate immune system. OxyR, functioning as a negative and/or positive transcriptional regulator, has been included among the major bacterial coordinators of antioxidant response. OxyR was first reported as a repressor of catalase expression in C. diphtheriae. However, the involvement of OxyR in C. diphtheriae pathogenesis remains unclear. Accordingly, this work aimed to investigate the role of OxyR in mechanisms of host-pathogen interaction of C. diphtheriae through the disruption of the OxyR of the diphtheria toxin (DT)-producing C. diphtheriae CDC-E8392 strain. The effects of OxyR gene disruption were analyzed through interaction assays with human epithelial cell lines (HEp-2 and pneumocytes A549) and by the induction of experimental infections in Caenorhabditis elegans nematodes and Swiss Webster mice. The OxyR disruption exerted influence on NO production and mechanism accountable for the expression of the aggregative-adherence pattern (AA) expressed by CDC-E8392 strain on human epithelial HEp-2 cells. Moreover, invasive potential and intracytoplasmic survival within HEp-2 cells, as well as the arthritogenic potential in mice, were found affected by the OxyR disruption. In conclusion, data suggest that OxyR is implicated in mechanisms of host-pathogen interaction of C. diphtheriae.

Optimization and Comparison of Different Methods and Factors for Efficient Transformation of Brucella abortus RB51strain

Background:

The development of protective vaccines for Brucella spp. has been hampered by the difficulty in transformation of Brucella cells with foreign DNA for genetic manipulation. It seems that the formation of Brucella spheroplasts would increase the efficiency of transformation. The aim of this study was to devise an efficient method for the transformation of Brucella spp.

Materials and Methods:

At first, spheroplast of Brucella was prepared by glycine and ampicillin induction and transformed using optimized protocols of CaCl₂, electroporation, and lipofection methods. Then, the efficacy of transformation was compared between the three-mentioned methods.

Results:

Ampicillin-induced spheroplasts from early-log phase culture of brucella when incubated in a medium-containing 0.2 M sucrose during cell recovery had higher transformation efficiency in three different methods. Comparison of the transformation efficiency of Brucella abortus RB51 using the CaCl₂, lipofection, and electroporation methods revealed that the transformation efficiency with the lipofection method was significantly higher than with other two methods (P < 0.05).

Conclusions:

Lipofection method by lipofectamine 2000 on ampicillin-induced spheroplasts can be a suitable approach for Brucella transformation.

Evaluation of Parameters for High Efficiency Transformation of Acinetobacter baumannii

Acinetobacter baumannii is an emerging, nosocomial pathogen that is poorly characterized due to a paucity of genetic tools and methods. While whole genome sequence data from several epidemic and environmental strains have recently become available, the functional characterization of genes is significantly lagging. Efficient transformation is one of the first steps to develop molecular tools that can be used to address these shortcomings. Here we report parameters allowing high efficiency transformation of A. baumannii. Using a multi-factorial experimental design we found that growth phase, voltage, and resistance all significantly contribute to transformation efficiency. The highest efficiency (4.3 × 10(8) Transformants/μg DNA) was obtained at the stationary growth phase of the bacterium (OD 6.0) using 25 ng of plasmid DNA under 100 Ohms resistance and 1.7 kV/cm voltage. The optimized electroporation parameters reported here provide a useful tool for genetic manipulation of A. baumannii.

Corynebacterium diphtheriae putative tellurite-resistance protein (CDCE8392_0813) contributes to the intracellular survival in human epithelial cells and lethality of Caenorhabditis elegans

Corynebacterium diphtheriae, the aetiologic agent of diphtheria, also represents a global medical challenge because of the existence of invasive strains as causative agents of systemic infections. Although tellurite (TeO3^2-) is toxic to most microorganisms, TeO3^2--resistant bacteria, including C. diphtheriae, exist in nature. The presence of TeO3^2--resistance (Te^R) determinants in pathogenic bacteria might provide selective advantages in the natural environment. In the present study, we investigated the role of the putative Te^R determinant (CDCE8392_813gene) in the virulence attributes of diphtheria bacilli. The disruption of CDCE8392_0813 gene expression in the LDCIC-L1 mutant increased susceptibility to TeO3^2- and reactive oxygen species (hydrogen peroxide), but not to other antimicrobial agents. The LDCIC-L1 mutant also showed a decrease in both the lethality of Caenorhabditis elegans and the survival inside of human epithelial cells compared to wild-type strain. Conversely, the haemagglutinating activity and adherence to and formation of biofilms on different abiotic surfaces were not regulated through the CDCE8392_0813 gene. In conclusion, the CDCE8392_813 gene contributes to the Te^R and pathogenic potential of C. diphtheriae.

C. pseudotuberculosis Phop confers virulence and may be targeted by natural compounds

The bacterial two-component system (TCS) regulates genes that are crucial for virulence in several pathogens. One of such TCS, the PhoPR system, consisting of a transmembrane sensory histidine kinase protein (PhoR) and an intracellular response regulator protein (PhoP), has been reported to have a major role in mycobacterial pathogenesis. We knocked out the phoP in C. pseudotuberculosis, the causal organism of caseous lymphadenitis (CLA), and using a combination of in vitro and in vivo mouse system, we showed for the first time, that the PhoP of C. pseudotuberculosis plays an important role in the virulence and pathogenicity of this bacterium. Furthermore, we modeled the PhoP of C. pseudotuberculosis and our docking results showed that several natural compounds including Rhein, an anthraquinone from Rheum undulatum, and some drug-like molecules may target PhoP to inhibit the TCS of C. pseudotuberculosis, and therefore may facilitate a remarkable attenuation of bacterial pathogenicity being the CLA. Experiments are currently underway to validate these in silico docking results.

Development of an efficient electroporation method for iturin A-producing Bacillus subtilis ZK

In order to efficiently introduce DNA into B. subtilis ZK, which produces iturin A at a high level, we optimized seven electroporation conditions and explored an efficient electroporation method. Using the optimal conditions, the electroporation efficiency was improved to 1.03 × 10⁷ transformants/μg of DNA, an approximately 10,000-fold increase in electroporation efficiency. This efficiency is the highest electroporation efficiency for B. subtilis and enables the construction of a directed evolution library or the knockout of a gene in B. subtilis ZK for molecular genetics studies. In the optimization process, the combined effects of three types of wall-weakening agents were evaluated using a response surface methodology (RSM) design, which led to a two orders of magnitude increase in electroporation efficiency. To the best of our limited knowledge, this study provides the first demonstration of using an RSM design for optimization of the electroporation conditions for B. subtilis. To validate the electroporation efficiency, a case study was performed and a gene (rapC) was inactivated in B. subtilis ZK using a suicide plasmid pMUTIN4. Moreover, we found that the rapC mutants exhibited a marked decrease in iturin A production, suggesting that the rapC gene was closely related to the iturin A production.

Enhancing DNA electro-transformation efficiency on a clinical Staphylococcus capitis isolate

Clinical staphylococcus isolates possess a stronger restriction-modification (RM) barrier than laboratory strains. Clinical isolates are therefore more resistant to acceptance of foreign genetic material than laboratory strains, as their restriction systems more readily recognize and destroy foreign DNA. This stronger barrier consequently restricts genetic studies to a small number of domestic strains that are capable of accepting foreign DNA. In this study, an isolate of Staphylococcus capitis, obtained from the blood of a very low birth-weight baby, was transformed with a shuttle vector, pBT2. Optimal conditions for electro-transformation were as follows: cells were harvested at mid-log phase, electro-competent cells were prepared; cells were pre-treated at 55°C for 1min; 3μg of plasmid DNA was mixed with 70-80μL of competent cells (3-4×10(10)cells/mL) at 20°C in 0.5M sucrose, 10% glycerol; and electroporation was conducted using 2.1kV/cm field strength with a 0.1cm gap. Compared to the conventional method, which involves DNA electroporation of Staphylococcus aureus RN4220 as an intermediate strain to overcome the restriction barrier, our proposed approach exhibits a higher level (3 log10 units) of transformation efficiency. Heat treatment was used to temporarily inactivate the recipient RM barrier. Other important parameters contributing to improved electro-transformation efficiency were growth stage for cell harvesting, the quantity of DNA, the transformation temperature and field strength. The approach described here may facilitate genetic manipulations of this opportunistic pathogen.

Characterization of the Opp peptide transporter of Corynebacterium pseudotuberculosis and its role in virulence and pathogenicity

Despite the economic importance of caseous lymphadenitis (CLA), a chronic disease caused by Corynebacterium pseudotuberculosis, few genes related to the virulence of its etiologic agent have been characterized. The oligopeptide permease (Opp) transporters are located in the plasma membrane and have functions generally related to the uptake of peptides from the extracellular environment. These peptide transporters, in addition to having an important role in cell nutrition, also participate in the regulation of various processes involving intercellular signaling, including the control of the expression of virulence genes in pathogenic bacteria. To study the role of Opp in C. pseudotuberculosis, an OppD deficient strain was constructed via simple crossover with a nonreplicative plasmid carrying part of the oppD gene sequence. As occurred to the wild-type, the ΔoppD strain showed impaired growth when exposed to the toxic glutathione peptide (GSH), indicating two possible scenarios: (i) that this component can be internalized by the bacterium through an Opp-independent pathway or (ii) that there is toxicity while the peptide is extracellular. Additionally, the ΔoppD mutant presented a reduced ability to adhere to and infect macrophages compared to the wild-type, although both strains exhibit the same potential to colonize spleens and cause injury and death to infected mice.

Effects of SCR-3 on the immunosuppression accompanied with the systemic inflammatory response syndrome

Steroid receptor coactivator-3 (SRC-3) is a multifunctional protein that plays an important role in mammary gland growth, development, and tumorigenesis. In this study, SCR-3 gene knockout mice were used to study the effects of SCR-3 on the immunosuppression accompanied with systemic inflammatory response syndrome (SIRS). Bacterial clearance assay was performed by blood culture and frozen sections, and the results showed that the absence of SCR-3 protein serious damaged the innate immune system and the body's ability to inactivate or phagocytosis of bacteria was significantly decreased, and the absence of SCR-3 protein also weakened phagocytes' ability to degrade bacteria and their metabolites. Furthermore, animal model of inflammatory reaction was established and the immune function was determined, and the results revealed that SRC-3 protein may play an important role in maintenance of T-cells' immune function, and severe T-cell immune function disorder would be resulted once SRC-3 protein is missing. In addition, the results of our study showed the steady-state of lymphocyte subsets was destroyed after SIRS, leading the suppression of cellular immune function, and the absence of SCR-3 protein may aggravate the suppression of T-lymphocyte function. Therefore, the present study demonstrated that the absence of SCR-3 protein would aggravate immunosuppression. In addition, SRC-3 protein is a significant regulator of infection and inflammation, and SRC-3 protein play an essential role in the development of immunosuppression accompanied with SIRS.

Exopolysaccharide production by a genetically engineered Enterobacter cloacae strain for microbial enhanced oil recovery

Microbial enhanced oil recovery (MEOR) is a petroleum biotechnology for manipulating function and/or structure of microbial environments existing in oil reservoirs for prolonged exploitation of the largest source of energy. In this study, an Enterobacter cloacae which is capable of producing water-insoluble biopolymers at 37°C and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at higher temperature. The resultant transformants, GW3-3.0, could produce exopolysaccharide up to 8.83 g l(-1) in molasses medium at 54°C. This elevated temperature was within the same temperature range as that for many oil reservoirs. The transformants had stable genetic phenotype which was genetically fingerprinted by RAPD analysis. Core flooding experiments were carried out to ensure effective controlled profile for the simulation of oil recovery. The results have demonstrated that this approach has a promising application potential in MEOR.

Optimization of electroporation conditions for Arthrobacter with plasmid PART2

A prerequisite for genetic studies of Arthrobacter is a high efficiency transformation system that allows for DNA transfer, transposon mutagenesis, and expression of specific genes. In this study, we develop a detailed electroporation method through a systematic examination of the factors involved in the entire electroporation process. Key features of this procedure, including the addition of penicillin to cells during the early log phase of growth and the presence of 0.5M sorbitol in the electroporation and recovery media, produced the greatest increases in transformation efficiency and consistency of results. The transformation rate also varied depending on the electrical parameters, DNA concentration, and recovery time period. Using optimum conditions, we generally achieved an efficiency of 6.8 × 10(7) transformants per microgram of PART2 for Arthrobacter sp. A3. This protocol was also successfully applied to other Arthrobacter species. Therefore, we conclude that the proposed method is rapid, simple and convenient, which allows a transformation trial to be accomplished in minutes.

Efficient electrotransformation of Bacteroides fragilis

This study describes refined electroporation parameters for efficient transformation of Bacteroides fragilis by plasmids prepared from laboratory strains of Escherichia coli. Development of the method used included determination of the optimal growth conditions for competent cell preparation, selectable antimicrobial resistance markers, electric field strength, and postpulse incubation time. Of the four E. coli-Bacteroides shuttle plasmids tested (pVAL-1, pVAL-2, pNLY1, and pLYL05), pLYL05 containing the cefoxitin resistance marker was found to be the most suitable for B. fragilis transformation, and it generated 2- to 900-fold more transformants (about 10(4) transformants per microg pLYL05 DNA) than the other plasmids. For the 72-h cultivation period tested, B. fragilis cells harvested at 48 h yielded the highest numbers of transformants. The transformation efficiency of pLYL05 increased linearly with the electric field strength over a range from 5.0 to 12.5 kV/cm. At least 3 h of postpulse incubation was required to maximize the transformation efficiency. For deletion of B. fragilis genes by homologous recombination, competent cells grown to early exponential phase and 12 h of postpulse incubation were required for efficient integration of the pLYL05-based suicide vector into the target site. The expected integration was obtained in B. fragilis strain NCTC9343 only when a homologously prepared (i.e., in vivo methylated) suicide vector was used. Spontaneous resolution of the diploid successfully deleted the expected genetic region. Our simple and efficient plasmid transfer method enabled disruption of a B. fragilis gene using in vivo-methylated targeted vectors. Our optimized electroporation parameters provide a useful tool for genetic manipulation of Bacteroides species.

Survey of genome organization and gene content of Corynebacterium pseudotuberculosis

Corynebacterium pseudotuberculosis is an intracellular pathogen that causes Caseous lymphadenitis (CLA) disease in sheep and goats. The widespread occurrence and the economic importance of this pathogen have prompted investigation of its pathogenesis. We used a genomic library of C. pseudotuberculosis to generate 1440 genomic survey sequences (GSSs); these were analyzed in silico with bioinformatics tools, using public databases for comparative analyses. We employed non-redundant unique sequences as a query for BLAST searches against the genome, the translated genome and the proteome of four other Corynebacterium species that have been completely sequenced. We were able to characterize approximately 8% of the genome of C. pseudotuberculosis, including previously undescribed functional group genes, based on the COG database; the GSSs classification into categories gave 13% information storage and processing, 14% cellular processes and 23% metabolism. We found a close relation between C. pseudotuberculosis and C. diphtheriae conserved-gene synteny in Corynebacteria species.

Double deletion of dtsR1 and pyc induce efficient L: -glutamate overproduction in Corynebacterium glutamicum

Corynebacterium glutamicum strains are used for the fermentative production of L-glutamate. Five C. glutamicum deletion mutants were isolated by two rounds of selection for homologous recombination and identified by Southern blot analysis. The growth, glucose consumption and glutamate production of the mutants were analyzed and compared with the wild-type ATCC 13032 strain. Double disruption of dtsR1 (encoding a subunit of acetyl-CoA carboxylase complex) and pyc (encoding pyruvate carboxylase) caused efficient overproduction of L-glutamate in C. glutamicum; production was much higher than that of the wild-type strain and DeltadtsR1 strain under glutamate-inducing conditions. In the absence of any inducing conditions, the amount of glutamate produced by the double-deletion strain DeltadtsR1Deltapyc was more than that of the mutant DeltadtsR1. The activity of phosphoenolpyruvate carboxylase (PEPC) was found to be higher in the DeltadtsR1Deltapyc strain than in the DeltadtsR1 strain and the wild-type strain. Therefore, PEPC appears to be an important anaplerotic enzyme for glutamate synthesis in DeltadtsR1 derivatives. Moreover, this conclusion was confirmed by overexpression of ppc and pyc in the two double-deletion strains (DeltadtsR1Deltappc and DeltadtsR1Deltapyc), respectively. Based on the data generated in this investigation, we suggest a new method that will improve glutamate production strains and provide a better understanding of the interaction(s) between the anaplerotic pathway and fatty acid synthesis.

In vivo insertional mutagenesis in Corynebacterium pseudotuberculosis: an efficient means to identify DNA sequences encoding exported proteins

The reporter transposon-based system TnFuZ was used to identify exported proteins of the animal pathogen Corynebacterium pseudotuberculosis. Thirty-four out of 1,500 mutants had detectable alkaline phosphatase (PhoZ) activity. This activity was from 21 C. pseudotuberculosis loci that code for fimbrial and transport subunits and for hypothetical and unknown-function proteins.