Conjugative mobilization of the cloned M6 protein gene from Streptococcus pneumoniae to Streptococcus pyogenes

The host-vector system omega 6001-pDP36 was used to transfer the M6 protein gene (emm-6.1) of Streptococcus pyogenes to other S. pyogenes strains, isogenic and nonisogenic to D471, the strain from which emm-6.1 was originally cloned. The first step was to subclone emm-6.1 into the insertion vector pDP36. The resulting plasmid, pRMB20, was used as donor in transformation to insert emm-6.1 into the conjugative transposon omega 6001. Streptococcus pneumoniae DP1322, carrying omega 6001 integrated into the chromosome, was the recipient in the transformation experiment. omega 6001 containing emm-6.1 was then transferred by conjugation from S. pneumoniae to the chromosomes of M+ and M- S. pyogenes strains. S. pyogenes transconjugants contained one intact copy of emm-6.1 integrated into the chromosome, but no expression of M6 protein could be detected by Western blot analysis. We found no evidence of the positive transacting regulation of emm gene expression postulated by other authors. In fact, the cloned emm-6.1 was not expressed in three strains expressing their own M proteins (M5, M17 and a shorter M6). In these partial diploids M protein genes were expressed only when present in the original chromosomal locus.

Method and parameters for genetic transformation of Streptococcus sanguis Challis

A simple procedure for genetic transformation of Streptococcus sanguis Challis was developed and standardized. During the exponential phase of growth, cells became competent while growing as diplococci in broth containing 10% foetal calf serum. High levels of competence were maintained by the cultures for 60 min. Competent cells could be stored frozen without loss of competence for at least three years. Using total chromosomal DNA as donor, the dose-response curve for transformation of a point mutation (streptomycin resistance) showed one-hit kinetics, as the DNA concentration varied from 0.000001 to 10 micrograms/ml. At 10 micrograms/ml, more than 2.2% of the colony-forming units were transformed to streptomycin resistance, while transforming activity remained detectable with 1 pg of DNA/ml. Optimal time of exposure of competent cells to transforming DNA was 30 min. The transformation reaction was inhibited at 0 and 4 degrees C, whereas it occurred efficiently both at 25 and 37 degrees C.

Effects of FeSO4 on B16 melanoma cells differentiation and proliferation

The effects exerted by FeSO4, in the presence or absence of vitamin C, on melanogenesis and proliferation in mouse B16 melanoma cells in culture were analysed either in serum-free (MEM-N2) or in serum-supplemented media. These cellular parameters can be either stimulated or on the contrary inhibited, depending on the metal concentration, the presence or the absence of vitamin C and serum, and on the type of culture (subconfluent or clonal). Vitamin C toxicity for B16 cells was decreased in the presence of FeSO4.

Control of B16 melanoma cells differentiation and proliferation by CuSO4 and vitamin C

The effects exerted by CuSO4, in the presence or absence of vitamin C, on melanogenesis and proliferation in mouse B16 melanoma cells in culture were analysed either in serum-free (MEM-N2) or in serum-supplemented media. The stimulation or the inhibition of these cellular parameters can be induced, depending on the metal concentration, the presence or absence of vitamin C, the composition of the culture medium and on the type of culture (subconfluent or clonal). Vitamin C toxicity for B16 cells was generally increased in serum-free medium, in clonal cultures, or in the presence of CuSO4.

Prevalence of Streptococcus mutans and dental decay in school children from Siena (Italy)

Epidemiological indexes of dental decay and prevalence of Streptococcus mutans in dental plaque were studied in a group of 255 schoolchildren aged 6-11 from a suburban area near Siena (Italy). Mutans streptococci were isolated from 17.4% of subjects: a significant correlation with dental decay indexes and with the presence of active caries was observed.

DNA probe for identification of Streptococcus pneumoniae

A total of 287 clinical isolates of Streptococcus pneumoniae (pneumococcus) were tested for their ability to undergo autolysis when treated with sodium deoxycholate. The test was positive for all but one isolate, strain DOC-1. This autolysis required the activity of an enzyme which is unique and characteristic of S. pneumoniae: a choline-dependent N-acetylmuramoyl-L-alanine amidase, the gene product of the lytA gene. We used lytA as a DNA probe to test the distribution of the autolysin gene among clinical isolates of S. pneumoniae. In dot blot hybridization experiments our probe reacted with the DNA of 60 of 60 strains tested, including the autolysis-deficient clinical isolate DOC-1. No hybridization occurred when strains of Streptococcus sanguis, Streptococcus mutans, Streptococcus pyogenes, Streptococcus (Enterococcus) faecalis, Streptococcus (Enterococcus) faecium, Streptococcus agalactiae, and Streptococcus bovis were tested. The lytA gene appears to be an ideal candidate for use as a DNA probe for the identification of S. pneumoniae.

Insertional inactivation of the major autolysin gene of Streptococcus pneumoniae

The lytA gene encoding the major pneumococcal autolysin (N-acetylmuramoyl-L-alanine amidase) was inactivated by inserting the 2-kilobase MspI fragment of pE194 containing the staphylococcal ermC gene. Stable autolysis-deficient (Lyt-) mutants and their isogenic Lyt+ parents were used in experiments designed to test possible physiological functions of the amidase. No autolysis could be induced in the mutants grown at 37 degrees C by deoxycholate, by incubation in stationary phase, or by treatment with penicillin. On the other hand, the Lyt- mutants exhibited normal growth rates and yields and normal adaptive responses during shifts from one growth temperature or nutritional condition to another. There was no evidence for impeded cell separation (chain formation). Colonies of Lyt- insertional mutants produced normal hemolytic zones on blood agar; they showed normal (high) levels of competence for genetic transformation. Lyt- mutants were also able to produce type 3 and 6 capsular polysaccharides, and such strains showed the same degree of virulence in mice as did the isogenic Lyt+ parent. The physiological function(s) of the amidase remains a puzzle.

Host-vector system for integration of recombinant DNA into chromosomes of transformable and nontransformable streptococci

We describe a genetic system in which transformation of Streptococcus pneumoniae and Streptococcus sanguis was used to insert recombinant DNA into the conjugative chromosomal element omega (cat tetM) 6001 (omega 6001). The element containing the recombinant DNA was then transferred by conjugation to the chromosome of transformable and nontransformable streptococci. When Escherichia coli plasmid pDP36 was used as donor in transformation, it was capable of inserting 5.9 kilobases of heterologous DNA into the chromosome of competent streptococcal strains carrying omega 6001; the transformants were scored for erythromycin resistance. Genetic analysis showed that in a fraction of the erythromycin-resistant transformants the integration via flanking homology of the heterologous DNA caused inactivation of the tetM gene of omega 6001. By analyzing the stability of the resistance markers, we found that stable integration of heterologous DNA was achieved only in the erythromycin-resistant, tetracycline-sensitive transformants. It was possible to detect conjugal transfer of the heterologous sequences from stable transformants to strains of S. pneumoniae, S. sanguis, Streptococcus pyogenes, and Streptococcus faecalis. The omega 6001-pDP36 host-vector system opens new possibilities for gene transfer in streptococci. By this method cloned streptococcal DNA (possibly mutagenized in vitro) can be returned to the original host, greatly facilitating complementation tests and fine physiological studies.

Two genes for chloramphenicol resistance common to staphylococci and streptococci

Southern blot hybridization and pneumococcal transformation were used to study the epidemiology at a molecular level of the genes for chloramphenicol resistance (cat) in streptococci and staphylococci. The cat gene of staphylococcal plasmid pC194 showed homology to the cat genes of the chromosomal elements of 5 different strains of Streptococcus pneumoniae and of Streptococcus agalactiae B109. DNA sequence homology was also detected between the cat gene of staphylococcal plasmid pC221 and the cat gene of broad host range conjugative plasmid pIP501, originally isolated from S. agalactiae. Two different cat genes appear to be present in clinical isolates of both streptococci and staphylococci.

Cellular uptake and metabolic reduction of pentavalent to trivalent arsenic as determinants of cytotoxicity and morphological transformation

Cytotoxicity, morphological neoplastic transformation, cellular uptake and metabolic reduction were determined in BALB/3T3 Cl A31-1-1 cells for trivalent arsenic (sodium arsenite, As3+) and for pentavalent arsenic (sodium arsenate, As5+). The levels of cellular uptake of 73As-labelled sodium arsenite and arsenate were dose-dependent and highest in the first hour. At equimolar concentration (3 X 10(-6) M), cellular uptake was 4-fold higher for As3+ than for As5+. Cytotoxicity was higher for As3+ than for As5+, but when correlated to total As cell burden it showed no significant difference for the two forms. Morphological transformation focus assays showed transforming activity for both As3+ and As5+, with relative transformation frequencies also of approximately 4:1. Recovery from the cytosol after exposure for 1-24 h was greater than 90% for either form of absorbed As. Exposure to As3+ yielded 100% as As3+ in cytosol, but exposure to As5+ yielded greater than 70% as As3+, showing a high rate of intracellular metabolic reduction. No methylated metabolites were detected by ion-exchange chromatography. After 24-h incubation in cell-free medium, oxidation of As3+ to As5+ occurred up to 30% of the dose, but incubation in the presence of cells lowered the oxidation level to 4%. As5+ was recovered unchanged from cell-free medium (24-h incubation), but in the presence of the cells it yielded up to 5% as As3+ within 24 h and the cumulative release of As3+ by cells exposed to As5+ was dose-dependent. Glutathione depletion by diethylmaleate inhibited reduction of As5+ to As3+ by these cells up to 25% of controls, showing that As5+ reduction is partly dependent on glutathione. These results suggest that As3+ is the form responsible for the cytotoxic and transforming effects, independently of the valence state of the inorganic arsenic in the culture medium.

Cloning and physical characterization of chromosomal conjugative elements in streptococci

We used a directed insertion method to introduce a nonreplicating vector plasmid into the large conjugative cat-tet element found in the chromosome of Streptococcus pneumoniae BM6001 and derivatives. To direct insertion preferentially to the conjugative element, we transferred it by conjugation to Streptococcus faecalis and then used DNA from this strain as a source of restriction nuclease fragments for ligation to digests of the vector pVA891, which can replicate in Escherichia coli but not in streptococci. This ligation mix was used to transform pneumococcal cells carrying the cat-tet element, with selection for the erythromycin resistance carried by pVA891. Eight such isolates were found, and transformation and conjugation tests showed that in each case the vector had inserted into the conjugative element, as expected. DNA from these pneumococcal strains generated a variety of E. coli plasmids which provide tools for obtaining a detailed restriction map and for defining other structural features of the streptococcal conjugative element.

Transformation as a tool for studying the epidemiology of tet determinants in Streptococcus pneumoniae

Transformation of pneumococcus was used to detect homology among tetracycline resistance determinants of clinical isolates of Streptococcus pneumoniae. A strain of pneumococcus containing a mutated tet determinant (tet-3), of class M, integrated into the chromosome was used as a recipient in transformation experiments, where donor DNA was from the tetracycline resistant isolates. 34/34 strains appeared to have tet determinants homologous to tet-3 (i.e. tet M). Still using transformation it was possible to determine that the tet-3 transforming activity of DNA from Tn916 and S. pneumoniae BM6001 was contained in a 5 kb HincII fragment. For this purpose a transformation technique where donor DNA was directly taken from low melting point agarose gels was standardized and used.

Modes of integration of heterologous plasmid DNA into the chromosome of Streptococcus pneumoniae

We compared the efficiencies of two different processes that can direct integration of plasmids into chromosomes of recipient cells during transformation. A donor-recipient system was constructed to allow a single donor plasmid to use either flanking homology, involving an apparent double crossover, or the insertion duplication process that has been described as due to a "Campbell-like" single crossover between the chromosome and a circular duplex. The latter process gave 600-fold fewer insertions that did the former, confirming expectations from prior work showing that insertion of heterologous DNA by use of flanking homology is highly efficient. It has some advantages for cloning and mapping purposes and can be exploited once it is recognized.

Bronchial hyperreactivity and arterial carboxyhemoglobin as detectors of air pollution in Milan: a study on normal subjects

Research has been carried out in the town area of Milan on 275 subjects. For each patient the following data have been measured: ventilatory profile, aspecific bronchial reactivity, arterial concentration in CO and acid-base balance. The results obtained have been divided into four groups, according to the level of SO2 in the area of residence of the subjects, who have also been studied with reference to the habit of smoking. The data obtained have shown (1) an alteration of the ventilatory function, with decrease of oxygen tension in arterial blood in all subjects. (2) Increase of bronchial irritability and CO concentration in arterial blood have been found in these subjects, with rates higher than those established by the WHO (1.5-1.7). (3) The division of our results according to the level of SO2 pollution in the areas of residence of the patients showed the presence, in the most polluted areas of Milan (NE and SW), of higher levels of bronchial irritability and higher CO rates in arterial blood. (4) Cigarette smoking does not seem to play a major role in causing bronchial irritability. It certainly increases CO concentration: smokers have HbCO concentration higher than nonsmokers in all four areas. (5) Air pollution is more important than cigarette smoking in determining CO saturation of blood. Nonsmokers living in the most polluted areas of Milan (NE) show a higher concentration of CO in arterial blood than smokers living in the less polluted areas (SW).