The chromatographic properties of the DNA-dependent DNA polymerases from Acholeplasma laidlawii PG-8]

The DNA-dependent DNA-polymerase (DNA polymerase I which is not sorbed on the column with DEAE-cellulose, and DNA-polymerase II, which is absorbed by this column and is eluted from it by 0.3 M of NaCl), have been isolated from Acholeplasma laidlawii PG-8. DNA-polymerase I in homogeneous state was obtained as a result of the stepwise treatment by heparin-sepharose (elution at 0.35 M of NaCl) and poly-U-sepharose (elution at 0.3 M of NaCl). It was presented on the electrophoregram by one polypeptide with molecular weight of 72 kDalton. The second form of DNA polymerase was also obtained in homogeneous state as a result of sequential treatment on heparin-sepharose (elution at 0.3 M of NaCl) and on poly-A-sepharose (elution at 0.25 M of NaCl): the protein which had manifested polymerase activity was a polypeptide with molecular weight of 45 kDalton.     

The isolation and partial purification of 2 DNA-dependent DNA polymerases from Acholeplasma laidlawii PG-8]

Two forms of DNA-dependent DNA-polymerase have been isolated and partially purified from the limited amount of biomass of cells Acholeplasma laidlawii PG-8, a typical representative of genus Acholeplasmataceae, as a result of successive chromatography on the columns with DEAE-cellulose DE-52 and Green A-sepharose. The first form of DNA-polymerase is eluted from the ion-exchange column with NaCl concentration of 0.1 M from the column with Green A-sepharose of 0.27 M, while the second form-with NaCl concentrations of 0.6 and 0.4 M, respectively. The both enzymatic activities are able to implement DNA synthesis. The conditions of DNA-polymerase production proved to be rather convenient for isolation of the concentrated and highly active enzymes.     

The effect of physicochemical factors on the activity of DNA-dependent DNA polymerases in Acholeplasma laidlawii PG-8]

The biological and physico-chemical properties of DNA-dependent DNA-polymerases of Acholeplasma laidlawii PG-8 have been studied. The optimal parameters of maximal enzymatic activity are determined. It is stated that N-ethylmaleimide in concentration of 1 mM activated DNA-polymerase I by 52%, whereas DNA-polymerase II with reagent concentration of 0.5 mM demonstrated the peak of activity exceeding the control only by 10%. Spermidine in concentration of 1.5 mM for the first form of DNA-polymerase and 0.15 mM-for the second one increased the ability of both forms of polymerases to synthesize DNA by 10%. Aphidicolin added to the reaction medium up to concentration of 10 mg/ml decreased activity of forms I and II of enzymes by 83 and 68%, respectively. The presence of 0.6 mM of EDTA in the medium also negatively affected the activity of polymerases inhibiting it by 83% in form I and by 77%-in form II.     

Role of mutations in the A-subunit of Acholeplasma laidlawii PG-8B topoisomerase IV in formation of resistance to fluoroquinolones

Nucleotide sequence of Acholeplasma laidlawii genome site PG-8B (1000 n.p.), containing topoisomerase IV subunit genes (parE and parC), has been determined. Sequenced genome site contains a gene fragment coding for the C-terminal region of ParE and gene fragment coding for N-terminal region of ParC. Topoisomerase IV subunite genes in A. laidlawii genome are situated near each other and overlapping by 4 nucleotides. Selection in liquid nutrient medium with ascending antibiotic concentrations resulted in derivation of A. laidlawii PG-8B cells resistant to ciprofloxacin, a fluoroquinolone. The resistant clones contain a mutation in the parC QRDR region determining fluoroquinolone resistance: Ser(91) (corresponding to Ser(80) in Escherichia coli ParC) replacement) for Leu.     

Acholeplasma laidlawii PG8 ultramicroforms amplificate selectivelyrrnB nucleotide sequences

Mycoplasmas are frequent contaminants ofin vitro animal cell cultures. Despite a broad spectrum of modern methods, detection of mycoplasmas remains a serious problem. The situation is complicated by the fact that mycoplasmas may be presented in cell cultures or biological samples by viable but unculturable forms (ultramicroforms). We found that the DNA ofAcholeplasma laidlawii PG8 ultramicroforms showed selective amplification of therrnB nucleotide sequences while vegetative cells of the mycoplasma showed amplification both forrrnA andrrnB sequences. The role of enzyme deproteinization in PCR results was also shown. The results presented in this report indicate that the optimisation of primer sequences as well as PCR regime may be crucial steps in detection and differentiation of vegetative forms and ultramicroforms ofA. laidlawii.     

Analysis of the DNA gyrase genes ofAcholeplasma laidlawii PG-8B

A 5-kb region of theAcholeplasma laidlawii PG-8B genome was sequenced. The region contained the genes for RecF, DNA gyrase subunits A and B (GyrA and GyrB), and a fragment of the ATP-binding subunit of the hypothetical ABC transporter. In phylogenetic analysis,A. laidlawii GyrA and GyrB formed statistically significant, stable clusters with the corresponding proteins ofClostridium acetobutylicum, Staphylococcus aureus, Bacillus subtilis, andStreptococcus pneumoniae. A laidlawii PG-8B clones resistant to fluoroquinolone (FQ) antibiotic ciprofloxacin (Cff) were obtained on a selective medium. The clones carried mutations in the quinolone resistance-determining region (QRDR) ofgyrA, which resulted in substitutions Ser83→Ala, Ser83→Phe, or Asp91→Asn. No mutations were found ingyrB QRDR of the resistant clones.     

Acylated proteins in Acholeplasma laidlawii.

The covalent modification of membrane proteins by long-chain fatty acids was determined in two strains of Acholeplasma laidlawii by one-dimensional gel electrophoresis of radiolabeled membranes. Of the more than 50 membrane polypeptides detected, approximately 30 were labeled with [3H]palmitate, whereas covalent binding of [3H]oleate to membrane proteins could not be demonstrated. We suggest that in these wall-less bacteria, membrane protein acylation with saturated fatty acids may serve to ensure the structural integrity of the membrane.     

The stability of the alkylating derivatives of oligodeoxyribonucleotides containing a cholesterol or phenazine radical added to the 3'-termination during their interaction with Acholeplasma laidlawii PG-8]

Stability of alkylating derivatives of decathymidylates protected on the 3'-terminal by cholesterol and phenazine residues has been studied in the process of their interaction with cells of Acholeplasma laidlawii PG-8. It is shown that the studied reagents are not split by nucleases of A. laidlawii PG-8 for the time necessary for alkylation of mycoplasma biopolymers.     

Two cholesterol pools in Acholeplasma laidlawii membranes

Cholesterol exchange kinetics between [14C]cholesterol-labeled Acholeplasma laidlawii and Mycoplasma gallisepticum cells and phosphatidylcholine-cholesterol vesicles followed a biphasic curve, with faster exchange rates for A. laidlawii. The same biphasic curve was obtained with isolated membranes. Cholesterol exchange between lipid vesicles and A. laidlawii cells depleted of phospholipids by phospholipase A2, fitted a monophasic linear curve. The data support the hypothesis that the biphasic cholesterol exchange kinetics do not result from the transbilayer distribution of cholesterol, but reflect the presence in the membrane of two cholesterol pools associated with lipids of high and low affinity for cholesterol.     

Adenylate energy charge in Acholeplasma laidlawii.

Adenosine 5'-triphosphate, adenosine 5'-diphosphate, and adenosine 5'-monophosphate were produced by Acholeplasma laidlawii B-PG9 growing in modified Edward medium. The adenylate energy charge was calculated to be 0.84 +/- 0.07 and ranged from 0.91 to 0.78 during exponential growth (12 to 24 h). During exponential growth, A. laidlawii contained, at 17.5 h, 2.3 X 10(-17) mol of adenosine 5'-triphosphate per colony-forming unit and, at 16 h, 27.3 nmol of adenosine 5'-triphosphate per mg (dry weight). The medium supported a doubling time of 0.95 h. The molar growth yields (Yglucose = grams [dry weight] per mole of glucose used) were 40.2 +/- 3.4 (16 h) and 57.1 +/- 9.7 (20 h) during midexponential growth. A maximum yield of 8.3 X 10(9) colony-forming units was reached at 24 h, when 56% of the initial concentration of glucose had been used. At 40 h, during the stationary phase, 14.95 +/- 3.75 mumol of glucose per ml of medium had been used. At this time, the culture fluids contained 21.86 +/0 mumol of lactate per ml and 3.14 +/- 0.13 mumol of pyruvate per ml.     

Chloride fluxes across Acholeplasma laidlawii membranes.

Chloride fluxes across the cytoplasmic membrane of Acholeplasma laidlawii were studied by using the chloride sensitive fluorescent dye, 6-methoxy-N-(sulfopropyl)quinolinium. Chloride was found to penetrate the membrane passively. Chloride flux was dependent upon the transmembrane electric potential.