An efficient genetic transformation system and suitable promoters are essential prerequisites for gene expression studies and genetic engineering in streptomycetes. In this study, firstly, a genetic transformation system based on intergeneric conjugation was developed in Streptomyces rimosus M527, a bacterial strain which exhibits strong antagonistic activity against a broad range of plant-pathogenic fungi. Some experimental parameters involved in this procedure were optimized, including the conjugative media, ratio of donor to recipient, heat shock temperature, and incubation time of mixed culture. Under the optimal conditions, a maximal conjugation frequency of 3.05×10^-5 per recipient was obtained. Subsequently, based on the above developed and optimized transformation system, the synthetic promoters SPL-21 and SPL-57, a native promoter potrB, and a constitutive promoter permE^* commonly used for gene expression in streptomycetes were selected and their activity was analyzed using gusA as a reporter gene in S. rimosus M527. Among the four tested promoters, SPL-21 exhibited the strongest expression activity and gave rise to a 2.2-fold increase in β-glucuronidase (GUS) activity compared with the control promoter permE^*. Promoter SPL-57 showed activity comparable to that of permE^*. Promoter potrB, which showed the lowest activity, showed a 50% decrease in GUS activity compared with the control permE^*. The transformation system developed in this study and the tested promotors provide a basis for the further modification of S. rimosus M527.
Conjugation, Genetic ; Glucuronidase/genetics* ; Promoter Regions, Genetic ; Streptomyces rimosus/genetics*

Conjugal plasmid pGH112 has been developed based on the replicons of Streptomyces coelicolor plasmid SCP2 and E. coli ColE. The plasmid contains ampicilin resistance gene(amp) for selection in E. coli and thiostrepton resistance gene (tsr) for selection in Streptomycetes, and a 0.76 kb oriT fragment of (IncP) RK2. Conjugal transfer of pGH112 was performed from E. coli to S. coelicolor A3(2), S. avermitilis, S. lividans TK54, S. toxytricini NNRL15443, S. venezuelae ISP5230 and Sacc. erythraea by conjugation, results show that the plasmid was able to transfer efficenctly from E. coli to Streptomycetes, was stably inherited in the recipients. pGH113 was constructed from pGH112 by combining the constitutive ermE promoter with green fluorescent protein gene(gfp).
Ampicillin Resistance ; genetics ; Conjugation, Genetic ; Escherichia coli ; genetics ; Green Fluorescent Proteins ; genetics ; Plasmids ; Streptomycetaceae ; genetics ; Thiostrepton ; pharmacology

Mitochondria are subcellular organelles composed of two discrete membranes in the cytoplasm of eukaryotic cells. They have long been recognized as the generators of energy for the cell and also have been known to associate with several metabolic pathways that are crucial for cellular function. Mitochondria have their own genome, mitochondrial DNA (mtDNA), that is completely separated and independent from the much larger nuclear genome, and even have their own system for making proteins from the genes in this mtDNA genome. The human mtDNA is a small (~16.5 kb) circular DNA and defects in this genome can cause a wide range of inherited human diseases. Despite of the significant advances in discovering the mtDNA defects, however, there are currently no effective therapies for these clinically devastating diseases due to the lack of technology for introducing specific modifications into the mitochondrial genomes and for generating accurate mtDNA disease models. The ability to engineer the mitochondrial genomes would provide a powerful tool to create mutants with which many crucial experiments can be performed in the basic mammalian mitochondrial genetic studies as well as in the treatment of human mtDNA diseases. In this review we summarize the current approaches associated with the correction of mtDNA mutations in cells and describe our own efforts for introducing engineered mtDNA constructs into the mitochondria of living cells through bacterial conjugation.
Conjugation, Genetic ; Cytoplasm ; DNA ; DNA, Circular ; DNA, Mitochondrial ; Eukaryotic Cells ; Genome ; Genome, Mitochondrial ; Humans ; Membranes ; Metabolic Networks and Pathways ; Mitochondria ; Organelles ; Proteins

Base Sequence ; Conjugation, Genetic ; Drug Resistance, Bacterial ; Electrophoresis, Gel, Pulsed-Field ; Escherichia coli ; drug effects ; enzymology ; Humans ; Klebsiella pneumoniae ; drug effects ; enzymology ; Microbial Sensitivity Tests ; Molecular Sequence Data ; Polymerase Chain Reaction ; Transformation, Bacterial ; beta-Lactamases ; genetics

BACKGROUNDAmpC beta-lactamases and extended-spectrum beta-lactamases (ESBLs) are becoming predominant causes of resistance to third and forth-generation cephalosporins in Klebsiella pneumoniae (K. pneumoniae). It is very difficult to treat infectious diseases caused by multidrug-resistant K. pneumoniae. The purpose of the present study was to investigate transconjugation and characteristics of beta-lactamase genes in K. pneumoniae producing AmpC beta-lactamases and ESBLs.

METHODSAmpC beta-lactamases were detected by three-dimension test and ESBLs by disc confirmatory test. Minimum inhibitory concentrations (MICs) were determined by agar dilution. Transfer of resistance to EC600 (Rif(r)) was attempted by conjugation in broth and screened on agar containing cefotaxime (2 microg/ml) plus rifampin (1024 microg/ml). The genes encoding AmpC or ESBLs and their transconjugants were detected by PCR and verified by DNA sequencing.

RESULTSThe resistant rates to ampicillin and piperacillin were 100% in 18 isolates of K. pneumoniae. However, imipenem was still of great bactericidal activity on K. pneumoniae, and its MIC(50) was 0.5 microg/mL. Eleven beta-lactamase genes, including TEM-1, TEM-11, SHV-13, SHV-28, CTX-M-9, CTX-M-22, CTX-M-55, OXA-1, LEN, OKP-6 and DHA-1, were found from 18 isolates. And at least one beta-lactamase gene occurred in each isolate. To our surprise, there were six beta-lactamase genes in the CZ04 strain. Among 18 isolates of K. pneumoniae, the partial resistant genes in 8 isolates were conjugated successfully, which had 100% homological sequence with donors by sequence analysis. Compared with donors, 8 transconjugants had attained resistance to most beta-lactams, including ampicillin, piperacillin, cefoxitin, cefotaxime and aztreonam, or even amikacin and gentamicin.

CONCLUSIONSR plasmids can be easily transferred between the resistant and sensitive negative bacilli. It is very difficult to block and prevent the spread of antimicrobial resistance. So more attention should be paid to reducing the frequency, times and dosage of antimicrobials, especially third or fourth cephalosporins.

Ampicillin ; pharmacology ; Anti-Bacterial Agents ; pharmacology ; Bacterial Proteins ; genetics ; physiology ; Cefotaxime ; pharmacology ; Conjugation, Genetic ; genetics ; physiology ; Drug Resistance, Multiple, Bacterial ; genetics ; Genotype ; Imipenem ; pharmacology ; Klebsiella pneumoniae ; drug effects ; genetics ; Microbial Sensitivity Tests ; Piperacillin ; pharmacology ; Plasmids ; genetics ; physiology ; Rifampin ; pharmacology ; beta-Lactamases ; genetics ; physiology