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Volume 135,
Issue 7,
1989
Volume 135, Issue 7, 1989
- Article
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- Biochemistry
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The Lipid Composition and Permeability to the Triazole Antifungal Antibiotic ICI 153066 of Serum-grown Mycelial Cultures of Candida albicans
More LessThe total lipid content of Candida albicans (serotype A; NCPF 3153) exponential-phase mycelial cultures grown in tissue-culture medium 199 (containing 10%, v/v, foetal calf serum) was 29·8 ± 8 mg (g dry weight)-1 (mean ± sd). The weight ratios of phospholipid to neutral lipid and phospholipid to non-esterified sterol were 2·6 ± 0·4 and 24·9 ± 0·5, respectively. The major phospholipid was phosphatidylcholine with smaller amounts of phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidylglycerol and diphosphatidylglycerol; the most abundant fatty acids were palmitic, palmitoleic, oleic and linoleic acids. The major neutral lipids comprised esterified sterol, triacylglycerol and non-esterified fatty acid with a smaller amount of non-esterified sterol. The fatty acid compositions of the three fatty-acid-containing neutral lipids were distinct from each other and the phospholipids. Comparison with previous data on yeast cultures of C. albicans A grown in glucose broth shows that mycelial cultures have a larger lipid content, lower phospholipid to neutral lipid ratio and higher phospholipid to non-esterified sterol ratio. We now show that mycelial cultures were more permeable to a [14C]triazole antifungal antibiotic compared with exponentially growing yeast cultures of several azole-sensitive strains. Taken together these data are consistent with there being a relationship between the phospholipid/non-esterified sterol ratio of a culture and its ability to accumulate a triazole.
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Metabolism of 1,8-Cineole by a Rhodococcus Species: Ring Cleavage Reactions
More LessA Rhodococcus sp. (strain C1) was isolated by elective culture with 1,8-cineole as sole carbon source. 6-endo-Hydroxycineole and 6-oxocineole accumulated transiently during the latter part of the exponential growth phase and, together with 1,8-cineole, were oxidized rapidly by 1,8-cineole-grown cells. Although a putative 1,8-cineole monooxygenase was not detected in cell-free systems an induced 6-endo-hydroxycineole dehydrogenase and an induced NADPH-linked 6-oxocineole oxygenase were readily demonstrated. The lactone 5,5-dimethyl-4-(3′-oxobutyl)-4,5-dihydrofuran-2(3H)-one was isolated from oxygenation reactions with 6-oxocineole as substrate. This was not the immediate product of oxygenation but resulted from non-enzymic lactonization of the ring cleavage intermediate 3-(1-hydroxy-1-methylethyl)-6-oxoheptanoic acid during extraction procedures. 2,5-Diketocamphane 1,2-monooxygenase purified from (+)-camphor-grown Pseudomonas putida ATCC 17453 was also able to utilize 6-oxocineole as a substrate with formation of the same isolated product. The established oxygen-insertion specificity of this enzyme coupled with an unequivocal absence of esterase activity allowed the nature of the oxygen insertion into 6-oxocineole by the enzyme from Rhodococcus C1 to be inferred and a reaction sequence for cleavage of both rings of 1,8-cineole to be proposed. It provides an explanation for the reported isolation of (R)-5,5-dimethyl-4-(3′-oxobutyl)-4,5-dihydrofuran-2(3H)-one from culture media of Pseudomonas flava grown with 1,8-cineole.
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Degradation of p-Toluenesulphonic Acid via Sidechain Oxidation, Desulphonation and meta Ring Cleavage in Pseudomonas (Comamonas) testosteroni T-2
More LessPseudomonas (Comamonas) testosteroni T-2 completely converted p-toluenesulphonic acid (TS) or p-sulphobenzoic acid (PSB) to cell material, CO2 and sulphate, with growth yields of about 5 g protein (mol C)−1. PSB and sulphite were excreted as transient intermediates during growth in TS-salts medium. All reactions of a catabolic pathway involving sidechain oxidation and cleavage of the sulphonate moiety as sulphite were measurable in the soluble portion of cell extracts. Degradation of TS and PSB was inducible and apparently involved at least two regulons. TS was converted to p-sulphobenzyl alcohol in a reaction requiring NAD(P)H and 1 mol O2 (mol TS)−1. This alcohol was in an equilibrium (in the presence of NAD+) with p-sulphobenzaldehyde, which was converted to PSB in an NAD(P)+-dependent reaction. PSB was desulphonated to protocatechuic acid in a reaction requiring NAD(P)H and 1 mol O2 (mol PSB)−1. Experiments with 18O2 confirmed involvement of a dioxygenase, because both atoms of this molecular oxygen were recovered in protocatechuate. Protocatechuate was converted to 2-hydroxy-4-carboxymuconate semialdehyde by a 4,5-dioxygenase.
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Steroid Catechol Degradation: Disecoandrostane Intermediates Accumulated by Pseudomonas Transposon Mutant Strains
More LessEleven transposon mutant strains affected in bile acid catabolism were each found to form yellow, muconic-like intermediates from bile acids. To characterize these unstable intermediates, media from the growth of one of these mutants with deoxycholic acid was treated with ammonia, then the crude product was methylated with diazomethane. Four compounds were subsequently isolated; spectral evidence suggested that they were methyl 12a-hydroxy-3-oxo-23,24-dinorchola-1,4-dien-22-oate, methyl 4-aza-12β-hydroxy-9(10)-secoandrosta-1,3,5-triene-9,17-dione-3-carboxylate, methyl 4-aza-9α, 12β-dihydroxy-9(10)-secoandrosta-1,3,5-trien-17-one-3-carboxylate and 4a-[3′-propionic acid]-5-amino-7β-hydroxy-7αβ-methyl-3aα,4,7,7α-tetra-hydro-1-indanone-d-lactam. It is proposed that the mutants are blocked in the utilization of such muconic-like compounds as the 3,12-dihydroxy-5,9,17-trioxo-4(5),9(10)-disecoandrosta-1(10),2-dien-4-oic acid formed from deoxycholic acid. A further mutant was examined, which converted deoxycholic acid to 12a-hydroxyandrosta-1,4-dien-3,17-dione, but accumulated yellow products from steroids which lacked a 12α-hydroxy function, such as chenodeoxycholic acid. The products from the latter acid were treated as above; spectral evidence suggested that the two compounds isolated were methyl 4-aza-7-hydroxy-9(10)-secoandrosta-1,3,5-triene-9,17-dione-3-carboxylate and 4a-[1′α-hydroxy-3′-propionic acid]-5-amino-7aβ-methyl-3aα,4,7,7α-tetrahydro-1-indanone-δ-lactam.
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Malic Enzyme Activity in Bacteroids from Soybean Nodules
More LessSoluble extracts of Bradyrhizobium japonicum bacteroids from soybean root nodules showed substantial rates of NAD+ and NADP+ reduction which were malate and MnCl2 dependent. Pyruvate was formed stoichiometrically and the NAD- and NADP-dependent rates were additive, indicating the presence of two malic enzymes. The NADP-dependent malic enzyme had a high affinity for malate (apparent K m = 0·1 mm) and was stimulated by ammonium. The NAD-dependent malic enzyme had a lower affinity for malate (apparent K m = 1·9 mM) and was stimulated by potassium and ammonium salts. The maximum velocities of the two enzymes were similar and of comparable magnitude to the activities of tricarboxylic acid cycle enzymes in the extracts. Possible roles of the malic enzymes in the metabolism of malate and succinate in bacteroids are discussed.
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A Hexokinase Associated with Catabolite Repression in Pachysolen tannophilus
More LessA hexokinase (ATP:d-hexose 6-phosphotransferase; EC 2.7.1.1) associated with catabolite repression was isolated and purified from the yeast Pachysolen tannophilus. The enzyme phosphorylated d-fructose at a rate 15 times greater than that for d-glucose. The K m values for d-glucose and d-fructose were 0·36 and 2·28 mm, respectively. Neither xylose reductase nor xylitol dehydrogenase were subject to catabolite repression in mutants defective in this enzyme.
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Glucose-negative Mutants of Pachysolen tannophilus
More LessMutants of the yeast Pachysolen tannophilus, exhibiting decreased ability to utilize d-glucose as the sole carbon source, were obtained by selecting for resistance to 2-deoxyglucose. Enzyme studies confirmed that these strains are defective in the hexose-phosphorylating enzymes and are unable to phosphorylate d-glucose to d-glucose 6-phosphate. The results confirmed the presence of two hexokinases, A and B, with ratios of d-glucose to d-fructose phosphorylation activity of 1·3/1·0 and 3·0/1·0, respectively, and a d-glucose-specific glucokinase. The behaviour of a hexose-negative strain, able to ferment d-xylose in the presence of d-glucose, is described.
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Purification and Characterization of Two Aminopeptidases Produced by Brevibacterium linens
More LessTwo aminopeptidases, designated as aminopeptidase A and B, were purified 1720- and 1950-fold, respectively, from the culture filtrate of Brevibacterium linens F by ammonium sulphate fractionation, a series of column chromatography steps on DEAE-Sephadex, DEAE-Trisacryl M and Mono-Q, and gel filtration on Superose-6. Aminopeptidase A accounted for 85% of the aminopeptidase activity remaining by the end of purification. The purified enzymes were homogeneous as judged by disc gel electrophoresis. Aminopeptidases A and B showed the same pH optimum of 9·3 and apparent temperature optimum of 40 °C, although the former showed slightly higher pH stability than the latter. NaCl or KC1 concentrations to 2 m did not affect the activities or stabilities of aminopeptidases A and B. Both enzymes were completely inhibited by incubation with EDTA, indicating that they are metalloenzymes, and were reactivated by incubation with Ca2+, Co2+, Mg2+, Zn2+ or Mn2+. The M r values of aminopeptidases A and B were estimated as 150000 and 110000, respectively, by gel filtration on Superose-6, and as 36000 and 26000, respectively, by SDS-PAGE. It was thus assumed that each of the native enzymes exists as a tetramer. The K m values of aminopeptidase A and B for l-leucine-p-nitroanilide were calculated to be 16·1 and 15·2 mm, respectively. The substrate specificities of aminopeptidases A and B were similar to each other.
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Purification and Characterization of d(-)-Mandelate Dehydrogenase from Rhodotorula graminis
More LessA soluble, NAD+-dependent d(-)-mandelate dehydrogenase has been purified to homogeneity from the yeast Rhodotorula graminis strain KGX 39, using DEAE-Sephacel, Phenyl Sepharose and Matrex Gel Orange A affinity chromatography. The M r of the native enzyme was 77000 (as determined by gel filtration) and the subunit M r was 38000 (as determined by SDS-polyacrylamide-gel electrophoresis), indicating that the enzyme exists as a dimer. Amino acid analysis showed only one cysteine residue per subunit. There was no spectroscopic evidence for the presence of cofactors such as flavin or cytochrome. The enzyme was neither inhibited nor stimulated by a wide range of salts and metal ions, nor was it inhibited by various metal chelating agents, indicating that the enzyme has no absolute requirement for salt or metal ions. The enzyme was not inhibited by various thiol reagents. The isoelectric point was 5·9. d(-)-Mandelate dehydrogenase catalyses the oxidation of d(-)-mandelate (forward reaction) and the reduction of phenylglyoxylate (reverse reaction). Activities of the forward reaction and reverse reactions were maximal at pH 9·5 and pH 5·85 respectively. Oxidation of d(-)-mandelate produced equimolar amounts of phenylglyoxylate and NADH, and the equilibrium constant was 1·59 × 10−11 m, pH 9·2. At pH 9·5, the K m values for d(-)-mandelate and NAD+ were 319 μm and 71 μm respectively, and the maximum velocity was 123 μmol min−1 (mg of protein)−1. The apparent K m and V values with respect to d(-)-mandelate, NAD+, phenylglyoxylate and NADH at pH 5·85, pH 7·0 and pH 9·5 are recorded. d(-)-Mandelate dehydrogenase uses various substituted mandelates as substrates. Several aliphatic 2-hydroxy and 2-oxocarboxylic acids did not act as substrates but were capable of inhibiting the enzyme. Comparisons are made with other mandelate dehydrogenases and NAD+-dependent dehydrogenases.
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Purification and Activity Gel Analysis of Polynucleotide Phosphorylase from the Cyanobacterium Nostoc sp. MAC
More LessPolynucleotide phosphorylase has been purified from the cyanobacterium Nostoc sp. MAC. The enzyme requires a divalent cation such as Mg2+, has a pH optimum of 10·5 and catalyses the polymerization of ADP into polynucleotide in a primer-independent reaction at a rate of 2 mol min−1 (mg protein)−1. It has an apparent native M r of 215000–240000. Non-denaturing polyacrylamide activity gels reveal a heterogeneous pattern of active bands similar to those previously observed with the corresponding enzyme from Micrococcus luteus, while SDS-denaturing activity gels reveal a single band of activity of M r 91000 in both crude extracts and the most highly purified fraction. Activity has also been demonstrated in a cetyltrimethyl-ammonium bromide non-denaturing activity gel. By analogy with other known polynucleotide phosphorylases, the Nostoc enzyme is probably a trimer of the 91000-M r subunit.
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Purification and Characterization of Cell-associated Glucosyltransferase Synthesizing Insoluble Glucan from Streptococcus mutans Serotype c
More LessStreptococcus mutans Ingbritt (serotype c) was shown to have a significant amount of cell-associated glucosyltransferase activity which synthesizes water-insoluble glucan from sucrose. The enzyme was extracted from the washed cells with SDS, renatured with Triton X-100, adsorbed to 1,3-α-d-glucan gel, and then eluted with SDS. The enzyme preparation was electrophoretically homogeneous, and the specific activity was 7·3 i.u. (mg protein)-1. The enzyme had an M r of 158000 as determined by SDS-PAGE, and was a strongly hydrophilic protein, as judged by its amino acid composition. The enzyme gradually aggregated in the absence of SDS. The enzyme had an optimum pH of 6·5 and a K m value of 16·3 mm for sucrose. Activity was stimulated 1·7-fold by dextran T10, but was not stimulated by high concentrations of ammonium sulphate. Below a sodium phosphate buffer concentration of 50 mm, activity was reduced by 75 %. This enzyme synthesized an insoluble d-glucan consisting of 76 mol % 1,3-α-linked glucose and 24 mol % 1,6-α-linked glucose.
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- Biotechnology
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The Effects of Temperature on Growth and Production of the Antibiotic Granaticin by a Thermotolerant Streptomycete
More LessThe synthesis of granaticin, a polyketide-derived antibiotic synthesized as a secondary metabolite by Streptomyces thermoviolaceus strain NCIB 10076, was studied at different growth temperatures. Quantitative measurements of the antibiotic made during batch fermentations showed that the yield was greatest at 45°C, whereas the rate of synthesis was most rapid at 37 °C. The timing of the appearance of granaticin in culture could not be assigned to any particular phase of growth or to de-repression due to depletion of any particular nutrient. However, at all temperatures, appearance of the antibiotic coincided with a rise in ammoniacal nitrogen presumably due to deamination of glutamate, the carbon source for growth. We have previously shown that production of the antibiotic is pH sensitive and that some carbon sources result in higher titres than others. This paper examines the effect of temperature on the physiology of growth and on antibiotic production in more detail under conditions that also allow an exact measurement of granaticin yield.
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- Development And Structure
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Increased Cell Wall Porosity in Saccharomyces cerevisiae after Treatment with Dithiothreitol or EDTA
More LessIntact cells of Saccharomyces cerevisiae were able to endocytose FITC-dextrans of 70 kDa, but not of 150 kDa, whereas spheroplasts took up both components. The rate of uptake of 70 kDa dextrans by spheroplasts was about three times higher than that by intact cells. Pretreatment of intact cells with dithiothreitol (DTT) or EDTA increased the rate of uptake of 70 kDa dextrans considerably, but 150 kDa dextrans were still excluded. Release of periplasmic invertase activity into the medium by glucose-derepressed cells was negligible in control cell suspensions, but was strongly stimulated in the presence of DTT. The released invertase had an apparent molecular mass of 320 kDa, indicating that the dimeric form was released. In the presence of EDTA only a slight increase in the release of invertase was observed. Pretreatment with DTT was accompanied by an increased loss of cell wall proteins. This suggests that the loss of mannoproteins, in combination with a more general opening up of the wall by reducing disulphide bridges, increases cell wall porosity. It is argued from the Stokes radius of 70 kDa dextran (5·8 nm) that yeast cell walls are, in principle, permeable to globular proteins with a molecular mass up to 400 kDa.
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- Genetics And Molecular Biology
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Molecular Cloning and Sequence Determination of the lpd Gene Encoding Lipoamide Dehydrogenase from Pseudomonas fluorescens
The lpd gene encoding lipoamide dehydrogenase (dihydrolipoamide dehydrogenase; EC 1.8.1.4) was isolated from a library of Pseudomonas fluorescens DNA cloned in Escherichia coli TG2 by use of serum raised against lipoamide dehydrogenase from Azotobacter vinelandii. Large amounts (up to 15% of total cellular protein) of the P. fluorescens lipoamide dehydrogenase were produced by the E. coli clone harbouring plasmid pCJB94 with the lipoamide dehydrogenase gene. The enzyme was purified to homogeneity by a three-step procedure. The gene was subcloned from plasmid pCJB94 and the complete nucleotide sequence of the subcloned fragment (3610 bp) was determined. The derived amino acid sequence of P. fluorescens lipoamide dehydrogenase showed 84% and 42% homology when compared to the amino acid sequences of lipoamide dehydrogenase from A. vinelandii and E. coli, respectively. The lpd gene of P. fluorescens is clustered in the genome with genes for the other components of the 2-oxoglutarate dehydrogenase complex.
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Physical and Genetic Mapping of the Protein A Gene in the Chromosome of Staphylococcus aureus 8325-4
More LessThe gene coding for protein A (spa) has been mapped close to nov on the genetic map of the chromosome of Staphylococcus aureus 8325–4. A rapid mapping procedure has been developed which first allowed the region of the chromosome carrying the spa gene to be identified by blot hybridization of large DNA fragments which had been separated by pulsed-field gel electrophoresis. Restriction endonuclease Smal fragment G was shown to carry the spa gene. An insertion mutation in spa was constructed by in vitro insertion of a fragment of DNA expressing resistance to kanamycin and neomycin. A spa::KanrNeor mutation was isolated in S. aureus 8325–4 by allele replacement. This provided a selectable marker which allowed the spa gene to be mapped by transformation analysis.
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Characterization and Complementation of a Mutant of Rhodobacter sphaeroides with a Chromosomal Deletion in the Light-harvesting (LH2) Genes
More LessAn LH2− strain of Rhodobacter sphaeroides, DBC1, has been constructed by deleting the puc operon, which encodes the LH2 α and β polypeptides, from the chromosome and replacing it with a kanamycin resistance gene. Southern blot analysis indicates that the 950 bp BamHI restriction fragment which contains the puc operon has been lost and has been replaced by the 1·25 kb KmR cassette derived from Tn903. Strain DBC1 lacked the LH2 complex, as shown by loss of the characteristic absorbance bands at 800 and 850 nm. The LH2 polypeptides were also found to be absent after SDS-PAGE. The wild-type phenotype was restored to DBC1 by the transfer of a 3·8 kb BscI fragment containing the puc operon in plasmid pMA81. Transconjugants possessed a wild-type absorbance spectrum and LH2 polypeptides.
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Characterization of Alpha and Beta Tubulin Genes in the Dimorphic Fungus Histoplasma capsulatum
More LessEvidence from our laboratory indicates that microtubules are involved in the differentiation of the dimorphic, pathogenic fungus Histoplasma capsulatum; therefore, we cloned the tubulin genes from a virulent strain of the organism. We report that the H. capsulatum genome contains a single alpha (TUB1) and a single beta (TUB2) tubulin gene rather than the more typical multigene family which is common in even the simplest eukaryotes. Sequence data from these genes reveal a high degree of nucleotide and protein sequence conservation relative to tubulins from other species. The coding regions of TUB1 and TUB2 contain five and eight intervening sequences, respectively. Field inversion gel electrophoresis of H. capsulatum chromosome-sized DNA fragments indicates that the TUB1 and TUB2 genes are unlinked. Potential regulatory elements common to both genes have been identified in the 5′ promoter regions. These elements may direct the coordinate expression of TUB1 and TUB2 during differentiation. The cloning and characterization of alpha and beta tubulin genes from H. capsulatum provides the first description of gene structure in this widely distributed pathogenic fungus. Isolation of the tubulin genes will facilitate future studies of tubulin gene expression during the dimorphic phase transitions and clarify the role of microtubules in the differentiation process.
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Structure and Expression of the Lactococcus lactis Gene for Phospho-β-galactosidase (lacG) in Escherichia coli and L. lactis
More LessThe Lactococcus lactis subsp. lactis 712 lacG gene encoding phospho-β-galactosidase was isolated from the lactose mini-plasmid pMG820 and cloned and expressed in Escherichia coli and L. lactis. The low phospho-β-galactosidase activity in L. lactis transformed with high-copy-number plasmids containing the lacG gene contrasted with the high activity found in L. lactis containing the original, low-copy-number lactose plasmid pMG820, and indicated that the original lactose promoter was absent from the cloned DNA. In E. coli the phospho-β-galactosidase could be overproduced using the strong inducible λ PL promoter, which allowed a rapid purification of the active enzyme. The complete nucleotide sequence of the L. lactis lacG gene and its surrounding regions was determined. The deduced amino acid sequence was confirmed by comparison with the amino acid composition of the purified phospho-β-galactosidase and its amino-terminal sequence. This also allowed the exact positioning of the lacG gene and identification of its characteristic Gram-positive translation initiation signals. The homologous expression data and the sequence organization of the L. lactis lacG gene indicate that the gene is organized into a large lactose operon which contains an intergenic promoter located in an inverted repeat immediately preceding the lacG gene. The organization and sequence of the L. lactis lacG gene were compared with those of the highly homologous lacG gene from Staphylococcus aureus. A remarkable bias for leucine codons was observed in the lacG genes of these two species. Heterogramic homology was observed between the deduced amino acid sequence of the L. lactis phospho-β-galactosidase, that of the functionally analogous E. coli phospho-β-glucosidase, and that of an Agrobacterium β-glucosidase (cellobiase).
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Isolation and Characterization of Actinophages Infecting Streptomyces Species and Their Interaction with Host Restriction-Modification Systems
More LessNine different phages, øA1 to øA9, were isolated from soil samples on Streptomyces antibioticus ATCC 11891, a strain which produces the macrolide antibiotic oleandomycin. Each phage displayed a different host-range which did not extend beyond Streptomyces species. Host-range was mainly limited by adsorption specificity and host-controlled restriction-modification systems. All the phages except øA3 and øA9 formed turbid plaques on S. antibioticus, but did not lysogenize this host. However, three of the phages (øA5, øA7 and øA8) were identified as temperate, since they were able to lysogenize other Streptomyces strains. All of the phages were morphologically similar and belonged to group B of Bradley’s classification. They had polyhedral heads and long, non-contractile tails. øA5, øA6 and øA7 had a base plate at the terminal end of the tail. Analysis with restriction endonucleases indicated that the nine phages contained double-strandpd DNA. Hybridization studies between the phage genomes, together with results on genome structure, allowed classification of the phages into five groups: (I) øA2, øA4 and øA9, (II) øA3 and øA8, (III) øA7, (IV) øA5 and øA6, and (V) øA1.
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