Transfection of protoplasts from Streptomyces lividans 66 with actinophage SH10 DNA

The plant natural product 2-methoxy-1,4-naphthoquinone stimulates therapeutic neural repair properties of olfactory ensheathing cells

Olfactory ensheathing cells (OECs) are crucial for promoting the regeneration of the primary olfactory nervous system that occurs throughout life. Transplantation of OECs has emerged as a promising therapy for nervous system injuries, in particular for spinal cord injury repair. Functional outcomes in both animals and humans are, however, highly variable, primarily because it is difficult to rapidly obtain enough OECs for transplantation. Compounds which can stimulate OEC proliferation without changing the phenotype of the cells are therefore highly sought after. Additionally, compounds which can stimulate favourable cell behaviours such as migration and phagocytic activity are desirable. We conducted a medium-throughput screen testing the Davis open access natural product-based library (472 compounds) and subsequently identified the known plant natural product 2-methoxy-1,4-naphthoquinone as a stimulant of OEC viability. We showed that 2-methoxy-1,4-naphthoquinone: (i) strongly stimulates proliferation over several weeks in culture whilst maintaining the OEC phenotype; (ii) stimulates the phagocytic activity of OECs, and (iii) modulates the cell cycle. We also identified the transcription factor Nrf2 as the compound’s potential molecular target. From these extensive investigations we conclude that 2-methoxy-1,4-naphthoquinone may enhance the therapeutic potential of OECs by stimulating proliferation prior to transplantation.

Involvement of host cell energy in the transfection of Lactobacillus casei protoplasts with phage PL-1 DNA

Transfection of Lactobacillus casei ATCC 27092 protoplasts with phage PL-1 DNA was studied under various conditions. The process of transfection was dependent on the incubation temperature, and the apparent activation energy was calculated to be about 11 kcal/mol. Transfection was inhibited by treating the cells before protoplasting either with monoiodoacetate, N,N'-dicyclohexylcarbodiimide (DCCD), or NaN3, without affecting both the viability of uninfected cells and protoplasting. The addition of DCCD after mixing protoplasts and DNA had no influence on transfection efficiencies. The transfection of L. casei protoplasts with phage PL-1 DNA was considered to require cell energy such as proton-motive force, probably in the initial stages, although the direct involvement of cell energy in the transfer of DNA across the cell membrane is still unclear.

Analysis of the nourseothricin-resistance gene (nat) of Streptomyces noursei

A gene (nat) conferring resistance to the streptothricin antibiotic nourseothricin (Nc) was cloned from the producer Streptomyces noursei into Streptomyces lividans on the vector pIJ702 to form pNAT1. The nat gene was localized on a 1-kb SalI-MboI fragment, which also carries the nat promoter. Divergent promoter activity from the nat promoter region was identified on the cloned fragment using promoter probe plasmids pIJ486 and pIJ487. The nat gene is not expressed from its own promoter in Escherichia coli as shown by its failure to promote cat expression in promoter-less plasmid pBB100 and by the expression of NcR in only one orientation, when cloned in pUC19. In S. lividans 7A, harbouring plasmid pNAT1, an Nc-acetylating activity (NAT) was associated with the cloned resistance gene. The substrate specificity of NAT correlated well with the substrate range of the acetyltransferase in S. noursei and Tn1825-determined streptothricin resistance in Gram-negative bacteria. Moreover, an extract of S. lividans carrying pNAT1 showed specific serological cross-reactivity with an extract of E. coli carrying Tn1825.

Transfection in Micromonospora spp

The introduction of bacteriophage DNA into Micromonospora protoplasts, resulting in the production of infective viral progeny, is reported. Transfection was affected by several factors. We observed that it reached a maximum when protoplasts from young mycelium (15 h old) were used. Maximum transfection took place when polyethylene glycol (PEG) was added to the mixtures at a final concentration of 20% (vol/vol) and did not occur at PEG concentrations under 10% or over 35%. The addition of positively charged liposomes to the mixtures was essential, since no transfectants were detected in the absence of liposomes at any PEG concentration. When DNA was present in nonlimiting amounts, a maximum efficiency of around 10(-3) to 10(-4) PFU per protoplast was obtained. The efficiency per DNA molecule showed a constant value of around 10(-4) to 10(-5) PFU, but the data suggest that transfection could be achieved by a single DNA molecule. The method proved to be equally efficient for the DNAs of at least five Micromonospora bacteriophages. On the contrary, we failed to transfect five of seven Micromonospora strains. These data suggest that only a minor subpopulation of protoplasts is competent and that the main factors influencing the transfection of Micromonospora protoplasts are neither the characteristics nor the origin of the DNA but the properties and status of the protoplasts.

Copy number mutants of the broad-host-range Streptomyces plasmid pMG200

pMG200, isolated from the bacteriocin-releasing strain Streptomyces chrysomallus, was further physically mapped. Variants of S. chrysomallus were isolated which inhibited the parental strain. Two types of plasmids, pMG210 and pMG220, were isolated from these variants, with copy numbers of 10-30 and 300, respectively, compared with 1-3 for pMG200. pMG210 is apparently physically identical to pMG200 but presumably differs at a level not detected by simple restriction mapping; pMG220 is deleted for 1.6 kb. Genes for thiostrepton and viomycin resistance were subcloned from pIJ364 on to pMG200 and a fragment containing the gene for nourseothricin resistance was subcloned on to pMG220. In this way nonessential sites were identified.

Polyethylene glycol-dependent transfection of Acholeplasma laidlawii with mycoplasma virus L2 DNA

Phenol-extracted DNA from mycoplasma virus L2 was able to transfect Acholeplasma laidlawii in the presence of polyethylene glycol. Transfection was sensitive to DNase and was most efficient with 36% (wt/vol) polyethylene glycol 8000 and cells in logarithmic growth. Virus production by the transfected cells was similar to that of the cells infected by intact virus. L2 DNA transfected A. laidlawii with a single-hit dose-response curve, reaching saturation at high DNA concentrations. Optimum transfection frequencies were about 10(-7) transfectants per L2 DNA molecule and 10(-4) transfectants per CFU. When DNA was present in saturating amounts, the number of transfectants increased linearly with the number of CFU present in the transfection mixture, suggesting that DNA uptake does not occur by a mechanism involving cell fusion. The cleavage of the superhelical mycoplasma virus L2 genome with restriction endonucleases that cleave the DNA molecule once reduced the transfection frequency. Host cell modification and restriction of transfecting L2 DNA were similar to those for infecting L2 virions.

Advances in protoplast fusion and transformation in Streptomyces

Rapid advances have been made in recent years on protoplast research in the economically important Streptomyces. The use of protoplasts has facilitated the development of efficient techniques for intra- and interspecific genetic recombination by fusion and by gene cloning. This report summarizes current protoplast methodologies as they relate to both protoplast fusion and genetic transformation, points out some genetic instabilities associated with protoplast techniques, and speculates on future directions to broaden the applications of protoplasts for heterospecific gene recombination and cloning in Streptomyces.

Restriction enzyme mapping of the DNA of Streptomyces bacteriophage B alpha and its deletion derivatives

Cleavage analysis of actinophage B alpha DNA was done with several restriction enzymes, and a restriction map of the DNA was determined. The DNA appeared to carry cohesive ends. Deletion mutants of actinophage B alpha were isolated by five cycles of treatment with 15 mM PPi. Both mutants had deletions of 2.5 of 1.8 megadaltons near one end of the genome, and one of them lost the single EcoRI cleavage site.

Small DNA-free liposomes stimulate transfection of streptomyces protoplasts

DNA of the bacteriophage phi C31 was rendered DNase resistant by entrapment in liposomes. Liposome-entrapped phi C31 DNA transfected Streptomyces protoplasts in the presence of 50% polyethylene glycol (PEG), providing a potential alternative route to conventional PEG-mediated transfection of protoplasts. However, probably partially because of low entrapment of DNA, this system did not result in an effective increase in transfection efficiency over the conventional transfection procedure. A more effective use of liposomes for stimulating transfection was provided by the discovery that supernatants obtained during the washing of DNA-free liposome preparations stimulated PEG-mediated transfection of protoplasts. This effect appeared to involve small (0.1- to 0.3-micrometer diameter) poorly sedimented liposomes. It was most effective (more than 100-fold stimulation) with positively charged liposome supernatants and high (about 50% [wt/vol]) PEG concentrations. Stimulation of transfection was also observed with cloning ligation mixtures containing phi C31 DNA as the vector. Transformation by plasmids (but not by chromosomal DNA fragments) was also significantly more efficient in these conditions than in conventional protoplast transformation.

Restriction endonuclease analysis of DNA from the Streptomyces phages SH3, SH5, SH10 and SH13

Using 26 restriction endonucleases, a cleavage site survey was undertaken for DNAs of several unrelated Streptomyces phages SH3, SH5, SH10 and SH13. Only EcoRI was found to produce single cleavage in SH3 and SH10 DNA. The complete maps were prepared for the 2, 9 and 11 fragments of SH10 DNA, as generated by EcoRI, KpnI and BglII, respectively. The evidence is presented that SH10 DNA contains cohesive ends. Moreover, a clear-plaque mutant of SH10 was shown to contain a deletion of 790 bp in the right part of the genome, including two KpnI sites.