- Volume 54, Issue 1, 1968
Volume 54, Issue 1, 1968
- Articles
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Development of the Zygospore Wall in Rhizopus sexualis (Smith) Callen
More LessSUMMARY: As the zygospore of Rhizopus sexualis enlarges it develops a thick wall. Studies with the transmission and stereoscan electron microscopes show that this wall is formed in the following manner.(1) The gametangial septa increase in thickness by the deposition of new material, which is laid down more rapidly on the inner or zygospore side than on the suspensor side. These septa form the ‘end walls’ of the zygospore. Fine plasmodesmatal tubules remain at intervals in the wall and are in direct connexion with the tubules of a dense zone of endoplasmic reticulum situated on either side of the septa. It is considered likely that the plasmodesmata allow the passage of nutrients from the parent hyphae into the developing zygospore.(2) The ‘side walls’ of the zygospore is formed by the development of new patches within the original wall of the fused gametangia. At first these ‘patches’ are shaped like inverted saucers and are separate from each other, except that there is a more continuous zone adjacent to the end walls of the spore. Then, the ‘patches’ become larger, by the deposition of new material at the rim, finally becoming shaped like inverted flower pots and coalescing at the rims to give a continuous warted layer. Until this stage the zygospore wall is permeable to water and dissolved substances. Meanwhile the original wall first becomes gelatinous, then membranous, and finally tears and is sloughed off exposing the newly-formed sculptured wall.(3) Finally a new inner wall, impermeable to water and dissolved substances, is laid down within the ornamented wall.
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The Membrane of the Streptobacillus moniliformis L-phase
More LessSUMMARY: Membranes of the stable L-phase of Streptobacillus moniliformis were isolated after lysis of the organisms by osmotic shock combined with ultrasonic treatment. The membranes were composed of about 53% protein and 40‥ lipid. About two-thirds of the lipids were polar; the rest consisted almost entirely of cholesterol. Radioactive oleic and palmitic acids were incorporated most efficiently from the growth medium into the membrane lipids. The L-phase membranes were solubilized by sodium dodecyl sulphate and sodium deoxycholate. Most of the solubilized membrane proteins could be separated from membrane lipid by ammonium sulphate precipitation. The precipitated proteins were very hydrophobic. The solubilized membrane proteins reassociated with membrane lipids after removal of the detergent by dialysis. The lipid: protein ratio in the resulting membrane re-aggregates depended on the magnesium concentration in the dialysis buffer. Polyacrylamide-gel electrophoresis showed that most of the protein species of the original membrane were incorporated into membrane re-aggregates. The protein composition of the re-aggregate was similar to, but not identical with, that of the hydrophobic protein fraction. The data obtained indicate that membranes of the stable L-phase of S. moniliformis resemble Mycoplasma membranes.
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The Isolation and Comparative Biological and Physical Characteristics of T-mycoplasmas of Cattle
More LessSUMMARYT-mycoplasmas were isolated by a ‘colour-change’ technique, involving the metabolism of urea, from 16 of 49 slaughtered cows (33%). They were encountered more often in the urethra and bladder than in the vagina. Isolations were made usually within 2 days of incubation but occasionally 5 days was required. T-mycoplasmas were isolated in medium without inhibitors from urethral scrapings of a cow and from seminal fluid of a bull. On solid medium, bovine T-mycoplasmas produced colonies of 5-12μ which were similar to those produced by a T-mycoplasma from the human urogenital tract. In liquid medium, the growth cycle of bovine T-mycoplasmas was similar to that of human T-mycoplasmas, being more rapid than that of large colony-forming (classical) mycoplasmas. The presence of serum in the medium was necessary for growth. T-mycoplasmas of bovine origin were affected in a similar way to those of human origin when subjected to ether, heat, freezing and thawing, freeze-drying, antibiotics and thallium acetate; they were more sensitive to erythromycin and thallium acetate than some classical mycoplasmas. The size of the minimal reproductive forms of bovine and human T-mycoplasmas and a classical mycoplasma, Mycoplasma hyorhinis, was similar as judged by filtration experiments. Electron microscopy of bovine and human T-mycoplasmas revealed cells which varied in size from 80 mμ, to 420 mμ, and which were bounded by a triple-layered membrane, features similar to known classical mycoplasmas.
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Influence of Mutagenic Agents on the Integration of the F Episome into the Chromosome of Escherichia coli k12 F+
More LessSUMMARY: Escherichia coli F+ donor bacteria were treated with u.v. radiation, mitomycin C, nitrous acid, hydroxylamine or caffeine, and then incubated for various periods in broth at 37° before conjugation. U.v. radiation, mitomycin C and nitrous acid increased the fertility of F+ populations, but hydroxylamine and caffeine did not. The maximal effect of u.v. irradiation was obtained after using a dose 50-100 ergs/mm.2 and after 45 min. incubation in broth of irradiated bacteria before conjugation. The maximal effect of mitomycin C occurred after treatment with 1‐3 µg./ml. and after 110 min. incubation in broth. Depending on the strain used, the fertility of the population increased 8-20 times after u.v. irradiation and 5-21 times after mitomycin C. The effect of u.v. irradiation could be photoreactivated up to 50%. Following treatment of strain W 1655 with nitrous acid (0·01 M), a three-to four-fold increase in the yield of conjugation was obtained, although irregularly. Caffeine (0·01%) enhanced the effect of u.v. irradiation about two-fold. Chloramphenicol blocked the expression of the effect of u.v. irradiation and mitomycin C. The effect of chloramphenicol was not permanent, because after its removal followed by further incubation the fertility of the F+ population increased to the same degree as in the samples in which the bacteria, previously exposed to u.v. radiation or mitomycin C, were incubated in broth without chloramphenicol.
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Osmotic Fragility of Bacteria Deprived of Carbon Dioxide
B. K. CHOE and G. BERTANISUMMARY: An absolute requirement for external carbon dioxide can easily be demonstrated for Escherichia coli strains B, C and K-12, and for a Serratia marcescens strain under anaerobic conditions, even in the presence of a very rich complex medium. During carbon dioxide deprivation such bacteria (with the exception of E. coli B) become extremely sensitive to the challenge of a sudden decrease in the osmotic pressure of the medium. This challenge does not seem to disrupt the gross structure of the bacteria, but it impairs in an apparently irreversible manner their ability to multiply.
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Properties of a Proteus morganii Bacteriocin
More LessSUMMARYThe bacteriocin produced by Proteus morganii strain MR 336 is a thermolabile glycoprotein with a sedimentation constant of 4·0. Activity is dependent on the integrity of the complex and the bacteriocin is inactivated by oxidation. Bacteriocinogeny could not be transmitted to other strains of P. morganii but was eliminated by 30 μg./ml. acridine orange at pH 7·45. Bacteriocin-resistant mutants of a sensitive P. morganii strain were readily obtained.
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The Effect of Glutamate on Toxin Production by Clostridium tetani
More LessSUMMARY: The addition of sodium-L-glutamate (1%, w/v) to the Mueller medium in which Clostridium tetani was grown initially stimulated growth and toxin production, then caused early lysis, and resulted finally in a marked suppression in the titre of tetanus toxin in the culture measured after 7 days. The suppression of production of tetanus toxin was not associated with any general suppression of protein production or with a decrease in the production of any major antigen.
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The Metabolism of Bacterial Nucleic Acid and of Free Components of Nucleic Acid by the Rumen Ciliate Entodinium caudatum
More LessSUMMARY:Washed suspensions of Entodinium caudatum grown in vitro and incubated anaerobically in the presence of penicillin and neomycin for up to 6 hr incorporated 14C-adenine, guanine and uracil into the cell. The 14C was distributed between the cell pool of the protozoa and the nucleic acid. 14C-Thymine was incorporated only into the pool. There was some interconversion of the nucleic acid bases: guanine was converted to adenine and uracil to cytosine. Adenine and guanine were broken down in the medium to a mixture of hypoxanthine and xanthine, and uracil and thymine were reduced to their dihydro-derivatives. E. caudatum suspensions also incorporated purine and pyrimidine bases, ribose and phosphate from bacterial nucleic acid into protozoal nucleic acid and evidence was obtained that the former was degraded as far as individual nucleotides before incorporation into the latter. No evidence was obtained for the synthesis of protozoal ribose from other carbohydrates.
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The Ultrastructure of a Rickettsia Pathogenic to a Saturnid Moth
More LessSUMMARY: The rickettsia pathogenic to the saturnid moth Samia cynthia x ricini mainly attacks mid-gut cells and multiplies in the cytoplasm. It is pleomorphic with a mean size of 1.50 0.7 as measured on micrographs of negatively stained preparations of purified organisms. The limiting membrane consists of two zones, the outer being about 20 mμ thick and slightly rippled and the inner a finely granular layer about 30 mμ thick. Actively growing organisms have a fairly dense granular cytoplasm with only few and small osmiophilic bodies; on their surfaces there are usually many small evaginations of the limiting membrane which measure up to 200 mμ long, have a basal diameter of about 20 mμ and often extend into the host cytoplasm. When the wall evaginations are absent the cytoplasm is less dense and osmiophilic bodies are up to 120 mμ in diameter. Some rickettsias, lying in the lumen of tracheae, have no osmiophilic bodies and very degenerate wall evaginations.
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Aminoacetone Formation and Utilization by Pseudomonads Grown on DL-1-Aminopropan-2-ol
More LessSUMMARY:Pseudomonas sp. 8/IX isolated from soil and Pseudomonas sp. NCIB 8858 are capable of growth on DL-I-aminopropan-2-ol or aminoacetone as sole sources of carbon, nitrogen and energy. During growth on the amino alcohol, small amounts of aminoacetone initially accumulate in the medium but disappear during the early logarithmic phase. Aminoacetone accumulation is favoured by high pH and high growth-substrate concentrations.
Washed suspensions of the pseudomonads grown on DL-I-aminopropan-2-ol accumulate aminoacetone when incubated with the amino alcohol in the presence of metabolic inhibitors, and rapidly utilize aminoacetone in their absence. Aminoacetone formation is optimal at about pH 10 in the presence or absence of the most effective inhibitor iodoacetate.
Aminoacetone utilization occurs optimally at pH 7·7, the apparent K m for the amino ketone being about 0·1 mM. At an initial concn. of 1·0 mM, the rate of utilization is proportional to cell density up to at least 0·5 mg. dry wt organisms/ml. and is constant with time over almost the entire course of the reaction. The maximum rate of utilization is approximately 150 mμmoles/mg. dry wt organisms/min. at 30˚. The phenyl analogue 2'-aminoacetophenone is utilized at a comparable rate but 5-aminolaevulate is virtually unaffected. Anaerobic conditions and metabolic inhibitors prevent amino ketone utilization.
Growth conditions markedly affect the ability of suspensions both to accumulate and utilize aminoacetone. Of the growth substrates tested, only L-threonine enabled Pseudomonas sp. 8/IX to utilize aminoacetone, the rate being approx. 60 % of that found after growthon DL-I-aminopropan-2-ol
The patterns of oxidation of possible intermediates of DL-I-aminopropan-2-ol catabolism are similar using washed organisms grown on either the amino alcohol or aminoacetone. Organisms grown on acetate plus glycine oxidize such compounds at relatively low rates. Methylglyoxal is not a substrate for either growth or oxidation. Comparison of the rates of oxygen uptake and aminoacetone utilization, and measurement of the total oxygen consumed, indicate about 70% complete oxidation of the amino ketone by organisms grown on the amino alcohol.
Similar maximum crop-sizes are obtained in media in which ammonium sulphate or different relative amounts of D- and L-I-aminopropan-2-ol serve as the sole sources of growth-limiting nitrogen.
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Purification and Properties of L-1-Aminopropan-2-o1:NAD Oxidoreductase from a Pseudomonad Grown on DL-1-Aminopropan-2-o1
More LessSUMMARY:Two pseudomonad strains grown on DL- I -aminopropan-2-01 as sole source of carbon + nitrogen provided rich sources of L (+)- I -aminopropan- 2-01 : NAD+ oxidoreductase. The activity of this enzyme in crude extracts of Pseudomona's sp. strain NCIB 8858 was about 400 mpmoles aminoacetone formed/mg. protein/min., under optimum conditions. Growth on media containing other carbon sources commonly repressed enzyme formation. Enzyme formation was induced by incubating succinate-grown bacteria in media containing DL-I -aminopropan-2-ol, aminoacetone or L -threonine ; but induction was inhibited by DL -2-hydroxy-2-phenylethylamine or DL -2-phenylserine. The enzyme was purified twenty-fold by treatment with protamine sulphate and ammonium sulphate followed by gel-filtration.The molecular weight of the enzyme was estimated to be 70 to 80 thousand. The partly purified enzyme was optimally active at pH 9·5. The Km values for DL- I-aminopropan-2-o1 and NAD+ were about 0· 1 and 0·3 mM, respectively. Activity with NADP+ as the coenzyme was about the same as that with NADf, the Km being about 0·2 mM.The e nzyme was inactive with a-NAD+. Activity was unaffected by a variety of thiols, thiol-alkylating and metalchelating agents. The enzyme was virtually inactive with twenty-one potential substrates but oxidized DL-I -aminobutan-2-ol, DL -2-hydroxy-2-phenylethylamine and DL -phenylserine at significant rates and DL-I ,3-diaminopropan-2-ol and DL -3-hydroxybutyrate slowly. Enzyme activity towards I -amino-propan-2-ol was stereospecific for the L (+)-isomer, which was oxidized about six times more rapidly than the racemic substrate. The D( -)-enantiomorph was a competitive inhibitor of the reaction, Ki = about 0·3 m M , and no dehydrogenase activity towards this isomer was observed with either purified enzyme preparations or crude cell-free extracts. Aminoacetone-dependent oxidation of NADH occurred optimally at pH 5 in acetate buffer; a second peak of activity was found at pH 8·4 in diethanolamine + HCl buffers. Several buffers appeared to inhibit activity at pH 7·5. 2'-Aminoacetophenone was active as a substrate, but 5-aminolaevulate had little activity. NADPH was also active as coenzyme.
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Transductional Analysis of Arginineless Mutants in Proteus mirabilis
More LessSUMMARY: A genetic map of eight structural genes involved in arginine synthesis in Proteus mirabilisstrain 13 was obtained by transduction. Genes argE, C, B, G, Hform a cluster linked to the gene cysE, the argDgene is linked to a locus which controls resistance to 1 mg./ml. streptomycin, argFis linked to a pyrimidine marker, while the argAgene could not be co-transduced with other markers. The clustering and order of argE, C, B, H, the linkage of argDto str-rand the non-linkage of argFand argAto other arginine genes are features shared by P. mirabilis, Escherichia coliand Salmonella typhimurium. Proteus mirabilisdiffers from the other organisms in that argGis included in the argE, C, B, G, Hcluster. This cluster is closely linked to cysEand not to methionine markers. ArgF, which is the gene for the sixth step in the pathway, is linked to a pyrimidine marker whilein E. colithis step is governed by two genes, one of which (argI) is linked to pyrB.
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Production of ω-Haloesters from Alkyl Halides by Micrococcus cerificans
More LessSUMMARY: Micrococcus cerificans grows with n-alkyl chlorides and bromides containing 16 to 20 carbon atoms as the sole source of carbon and forms waxy esters. The esters produced from n-Hexadecyl chloride were identified to be 16-chlorohexadecyl-16-chlorohexadecanoate (74%) and 16-chlorohexa-decylhexadecanoate (23%). More than 80% of the fatty acids of the more polar cellular lipids also contained chlorine at the ω-carbon. These results show that the mechanism of utilization of alkyl halides by this organism is similar to that of alkanes and the initial attack is specifically at the non-halogenated methyl carbon.
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Morphology of Mycoplasma mycoides Thread-phase Growth
More LessSUMMARY: Examination of threads of Mycoplasma mycoides var. mycoides by optical and electron microscopy revealed organisms within a homogeneous mucinous matrix. This matrix stained with the periodic acid-Schiff (PAS) reagent method was almost electron-transparent and was probably lipo-polysaccharide (galactan) material. Treatment of threads with specific antibody produced a clearly visible microscopic precipitate strongly outlining the threads. By electron microscopy this precipitate was electron-dense, homogeneous, and finely granular; it could frequently be seen surrounding individual mycoplasma cells as a well-defined capsule.
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- Corrigendum
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