The isolation and characterization of a temperate phage, Y46/(E2), from Erwinia herbicola Y40.

A temperate phage was induced from exponential phase cells of Erwinia herbicola Y46 by treatment with mitomycin C. The phage was purified by single plaque isolation, and produced in bulk by successive cultivation in young cultures of E. herbicola Y 178. Phages were concentrated from culture filtrates by rate zonal centrifugation and resuspension in 0.02 M Tris buffer, pH 7.2, twice, yielding suspensions of about 5 times 10(11) PFU/ml. Purification was achieved by centrifugation in buffered sucrose solutions. The band at the 30/40% sucrose interface yielded intact particles having regular hexagonal heads and lonb contractile tails, with base plates. Fibers were not seen. The mean dimensions were head, 51 nm; neck length, 11 nm; overall tail length, extended, 98 nm and contracted, 75 nm; diameter of tail sheath, 24 nm. The phage was stable from pH 4.0 to 11.0, but unstable at pH 3.0, the response being independent of the suspending medium used. At pH 3.0, a survival curve having biphasic appearance was observed, which was not due to a mixed population of phages. Stability to heat was good up to 45 degrees C, above which a logarithmic decline with temperature increase occurred. The average inactivation rate constant at 50 degrees C and pH 6.8 was 0.15 min-1. Adsorption to E. herbicola Y 178 cells exhibited first-order kinetics, the adsorption rate constant being 2.5 times 10(-10) ml/min. One-step growth-curve experiments indicated a burst size of 35-40, and a minimum latent period of 80 min. Probit analysis gave a mean latent period of 140 min (SD 25). The phage caused lysis of only E. herbicola strains Y178 and Y186.     

Fructan from Erwinia herbicola.

Levan production by strains of Erwinia herbicola is common, and this property has some taxonomic significance for species differentiation within the "herbicola" group. The extracellular polysaccharide elaborated by strain 403 was characterized by nuclear magnetic resonance spectroscopy and methylation analysis. Results showed it to be a typical bacterial levan.     

Nucleoside phosphotransferase from Erwinia herbicola, a new membrane-bound enzyme.

A nucleoside phosphotransferase, which catalyzes the phosphorylation of nucleosides to nucleotides by low energy phosphate esters, has been isolated and purified 500-fold from the membrane fraction of Erwinia herbicola. Its most noteworthy difference from other enzymes of this class is that it is membrane bound and can be isolated and handled only in the presence of a detergent. With a ribonucleoside acceptor, adenosine, the reaction product is exclusively 5'-AMP; with deoxyadenosine, 5'- and 3'-nucleotide products appear in the approximate ratio of 2:1, respectively. The enzyme has no detectable phosphatase activity with the best phosphate donors, 5'-dAMP and 5'-dTMP, and very little with less active donors, such as p-nitrophenyl phosphate. This phosphotransferase should be a useful agent for preparing 5'-nucleotides from unusual synthetic bases.     

Partial purification and characterization of Naegleria fowleri beta-glucosidase

Naegleria fowleri cells, grown axenically, contain high levels of beta-D-glucosidase which catalyzes the hydrolysis of 4-methylumbelliferyl-beta-D-glucopyranoside (4MUGlc) (Km, 0.9 mM), octyl-beta-D-glucoside (Km, 0.17 mM), and p-nitrophenyl-beta-D-glucopyranoside at relative rates of 1.00, 2.88, and 1.16, respectively (substrate concentration, 3.0 mM). When the amebae are subjected to freeze-thawing, sonication, and centrifugation (100,000 g, 1 h), 85% of the beta-glucosidase activity appears in the supernatant fraction. The beta-glucosidase was purified 40-fold (34% yield) using a combination of chromatographic steps involving DE-52 cellulose, concanavalin A-Sepharose, and hydroxylapatite followed by isoelectric focusing. The predominant soluble beta-D-galactosidase activity in the Naegleria extract copurifies with the beta-D-glucosidase; the two activities have the same isoelectric point (pI, 6.9), similar heat stabilities, are both inhibited by lactobionic acid (Ki, 0.40 mM), and exhibit optima at pH 4.5, indicating that they are probably the same enzyme. The Naegleria beta-D-glucosidase has an apparent molecular weight of 66,000, a Stokes radius of 25 A, and a sedimentation coefficient of 4.2S. The beta-glucosidase is not inhibited by conduritol beta-epoxide or galactosylsphingosine but is completely inhibited by 1.25 mM bromo conduritol beta-epoxide. The latter compound, when present in the growth medium, inhibits the growth of the organism and profoundly alters its ultrastructure, the main effect being the apparent inhibition of cytokinesis and the generation of multinucleate cells. The issue of the role of the beta-glucosidase in the metabolism of the ameba and its possible role in pathogenic mechanisms are discussed.     

Cloning and regulation of Erwinia herbicola pigment genes.

The genes coding for yellow pigment production in Erwinia herbicola Eho10 (ATCC 39368) were cloned and localized to a 12.4-kilobase (kb) chromosomal fragment. A 2.3-kb AvaI deletion in the cloned fragment resulted in the production of a pink-yellow pigment, a possible precursor of the yellow pigment. Production of yellow pigment in both E. herbicola Eho10 and pigmented Escherichia coli clones was inhibited by glucose. When the pigment genes were transformed into a cya (adenylate cyclase) E. coli mutant, no expression was observed unless exogenous cyclic AMP was provided, which suggests that cyclic AMP is involved in the regulation of pigment gene expression. In E. coli minicells, the 12.4-kb fragment specified the synthesis of at least seven polypeptides. The 2.3-kb AvaI deletion resulted in the loss of a 37K polypeptide and the appearance of a polypeptide of 40 kilodaltons (40K polypeptide). The synthesis of the 37K polypeptide, which appears to be required for yellow pigment production, was not repressed by the presence of glucose in the culture medium, as was the synthesis of other polypeptides specified by the 12.4-kb fragment, suggesting that there are at least two types of gene regulation involved in yellow pigment synthesis. DNA hybridization studies indicated that different yellow pigment genes exist among different E. herbicola strains. None of six pigmented plant pathogenic bacteria examined, Agrobacterium tumefaciens C58, Cornyebacterium flaccumfaciens 1D2, Erwinia rubrifaciens 6D364, Pseudomonas syringae ATCC 19310, Xanthomonas campestris 25D11, and "Xanthomonas oryzae" 17D54, exhibited homology with the cloned pigment genes.     

Enhanced production of extracellular ice nucleators from Erwinia herbicola

The effects of growth conditions and chemical or physical treatments on the production of extracellular ice nucleators (ECINs) by Erwinia herbicola cells were investigated. The spontaneous release of ECINs, active at temperatures higher than -4 degrees C, into the environment depended on culture conditions, with optimal production when cells were grown in yeast extract to an early stationary phase at temperatures below 22 degrees C. ECINs were vesicular, released from cell surfaces with sizes ranging from 0.1 to 0.3 &mgr;m as determined by ultrafiltration and transmission electron microscopy. Protein profiles of ECIN fractions during bacterial growth were examined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), and Ina proteins were detected by Western blotting. ECIN production was enhanced 5-fold when cells were treated with EDTA and 20- to 30-fold when subjected to sonication. These conditions provide a means for large-scale preparationage> ECINs by E. herbicola.     

Ice nucleating activity of Pseudomonas syringae and Erwinia herbicola.

Chemical and biological properties of the ice nucleating sites of Pseudomonas syringae, strain C-9, and Erwinia herbicola have been characterized. The ice nucleating activity (INA) for both bacteria was unchanged in buffers ranging from pH 5.0 to 9.2, suggesting that there were no essential groups for which a change in charge in this range was critical. The INA of both bacteria was also unaffected by the addition of metal chelating compounds. Borate compounds and certain lectins markedly inhibited the INA of both types of bacterial cells. Butyl borate was not an inhibitor, but borate, phenyl borate, and m-nitrophenyl borate were, in order, increasingly potent inhibitors. These compounds have a similar order of affinity for cis hydroxyls, particularly for those found on sugars. Lentil lectin and fava bean lectin, which have binding sites for mannose or glucose, inhibited the INA of both bacteria. All other lectins examined had no effect. The inhibition of INA by these two types of reagents indicate that sugar-like groups are at or near the ice nucleating site. Sulfhydryl reagents were potent inhibitors of the INA of both bacteria. When treated with N-ethylmaleimide, p-hydroxymercuribenzoate, or iodoacetamide, the INA was irreversibly inhibited by 99%. The kinetics of inactivation with N-ethylmaleimide suggested that E. herbicola cells have at least two separate ice nucleating sites, whereas P. syringae cells have possibly four or more separate sites. The effect of infection with a virulent phage (Erh 1) on the INA of E. herbicola was examined. After multiple infection of a bacterial culture the INA was unchanged until 40 to 45 min, which was midway through the 95-min latent period. At that time, the INA activity began falling and 99% of the INA was lost by 55 min after infection, well before any cells had lysed. This decrease in INA before lysis is attributed to phage-induced changes in the cell wall.     

Optical properties of Erwinia herbicola bacteria at 0.190-2.50 microm

We measure the complex index of refraction of Erwina herbicola (also known as Enterobacter agglomerans or Pantoea agglomerans) bacteria (ATTC 33243) over the spectral region from 0.190 to 2.50 microm (4000-52,632 cm(-1)). Transmission measurements are made on solid films of E. herbicola and on suspensions of the bacteria in water. These measurements, combined with spectral reflectance and Kramers-Kr?nig analysis, allow the determination of the real and imaginary parts over the entire wavelength interval. Accurate and consistent results are obtained for this complex and difficult to measure material. This is part of a continuing series of measurements of the optical constants of representative biological materials that are applicable to the development of methods for detection of airborne biological contaminants, where the material under study is used as a surrogate for a pathogenic agent.     

Release of cell-free ice nuclei by Erwinia herbicola.

Several ice-nucleating bacterial strains, including Erwinia herbicola, Pseudomonas fluorescens, and Pseudomonas syringae isolates, were examined for their ability to shed ice nuclei into the growth medium. Only E. herbicola isolates shed cell-free ice nuclei active at -2 to -10 degrees C. These cell-free nuclei exhibited a freezing spectrum similar to that of ice nuclei found on whole cells, both above and below -5 degrees C. Partially purified cell-free nuclei were examined by density gradient centrifugation, chemical and enzymatic probes, and electron microscopy. Ice-nucleating activity in these cell-free preparations was associated with outer membrane vesicles shed by cells and was sensitive to protein-modifying reagents.     

Metabolism of phloridzin by Erwinia herbicola: nature of the degradation products, and the purification and properties of phloretin hydrolase

Erwinia herbicola Y46 degrades phloridzin to yield phloretin, phloroglucinol, and phloretic acid, when grown on defined medium containing phloridzin as the sole source of carbon. The identities of the intermediates isolated from culture filtrates were established by co-chromatography and by ultraviolet absorption spectra. Only 3 of 11 strains of this species, and none of the 12 species of bacterial phytopathogens tested could effect this breakdown. Some of the latter organisms possessed beta-glucosidase activity which liberated d-glucose from phloridzin. The enzyme phloretin hydrolase was purified from cells of E. herbicola Y46 grown on Yeast Beef Broth, by treatment of crude extracts with protamine sulfate, ammonium sulfate precipitation, elution from calcium phosphate gel, elution from diethylaminoethyl-cellulose, and concentration by ultrafiltration. The final preparation was free of beta-glucosidase, had a specific activity of 213 units per mg of protein, and represented a 142-fold purification over the crude extract. The enzyme had a pH optimum of 6.7 to 6.8, and produced only phloroglucinol and phloretic acid as products of phloretin breakdown, there being an equimolar relationship between the cleavage of phloretin and the formation of the products. The Michaelis constant (K(m)) for the enzyme with phloretin as substrate was 3.8 x 10(-5)m, and the enzyme was sensitive to Hg(2+) and Cu(2+) ions. Phloroglucinol, phloretic acid, p-chloromercuribenzoate and iodoacetamide were without effect on the activity. The enzyme did not react with phloridzin, naringin, or naringenin. The physiological significance of the results is discussed.     

Partial purification and characterization of a soybean beta-glucosidase with high specific activity towards isoflavone conjugates.

A beta-glucosidase with high specific activity towards isoflavone conjugates was purified from soybean [Glycine max] roots by high salt extraction from a low speed centrifugal pellet and subsequent anion and cation exchange chromatography. Purification required stabilization throughout fractionation in 10% glycerol. The enzyme is most likely a dimer (approximate M(r) 165 kDa) with potential subunits of M(r) 80 and/or 75 kDa. The pH and temperature optima are pH 6 and 30 degrees C, respectively. The enzyme was highly heat-stable. Of the various potential effectors examined, silver and mercury ions were the most inhibitory. The IC(50) of silver ions was increased from 140 microM to 14 mM in the presence of 250 microM beta-mercaptoethanol. Glucono-delta-lactone was not strongly inhibitory (IC(50) 24 mM). The activity was highly active against isoflavone conjugates, with a specificity constant 160-1000 fold higher for isoflavone conjugates over the generic chromogenic substrate, p-nitrophenyl beta-glucoside. The enzyme was inactive against the flavonol glycosides tested. The partially purified enzyme had similar K(m) and k(cat) towards 7-O-glucosyl- and 7-O-glucosyl-6"-malonyl-isoflavones, suggesting that it may be able to cleave the esterified glucosyl conjugate. We hypothesize that the enzyme is involved in the release of daidzein and genistein, both of which play central roles in soybean defense.     

Partial purification and properties of a nucleoside hydrolase from Crithidia

An enzyme catalyzing the hydrolysis of nucleosides was found to occur in Crithidia fasciculata and was partially purified (30- to 40-fold) by treatment with either streptomycin sulfate or MnCl₂, ammonium sulfate fractionation, acidification and neutralization, passage through Sephadex G-200, and isoelectric focusing. The specific activity of these preparations was about 6 μmnoles of uridine hydrolyzed per mg protein per min. Specificity for the puriue or pyrimidine base was very broad; uridine gave the maximum rate of hydrolysis. Deoxyribosides were not hydrolyzed. The enzyme is relatively stable to heat and to acidification and can be stored frozen. Hydrolysis of uridine is inhibited by borate ions and by adenosine, inosine, and guanosine, but not by cytidine or xanthosine.     

Aspartate transcarbamoylase from Phaseolus aureus. Partial purification and properties

1. Aspartate transcarbamoylase from 4-day-old radicles of Phaseolus aureus was purified 190-fold by (NH₄)₂SO₄ fractionation, DEAE-cellulose and DEAE-Sephadex chromatography and Sephadex-gel filtration. The partially purified enzyme, which required P_i for maximum stability, had an apparent molecular weight of 83000±5000. 2. Uridine nucleotides were found to inhibit the activity; UMP was the most potent inhibitor, followed by UDP and UTP. No other nucleotide was found to affect the enzyme, nor could UMP inhibition be overcome by adding another nucleotide. Aspartate gives a hyperbolic substrate-saturation curve, both with and without UMP. The nucleotide inhibitor is non-competitive with respect to this substrate. Carbamoyl phosphate also yields a hyperbolic substrate-saturation curve in the absence of feedback inhibitor, but when UMP is added a sigmoidal pattern results, and the inhibition is competitive with carbamoyl phosphate. 3. The degree of inhibition by UMP is not affected by p-chloromercuribenzoate, urea, mild heat pretreatment or change in pH over the range 8.5–10.5, but is affected by temperature. 4. The aspartate analogue, succinate, both activates and inhibits the reaction, depending on the concentrations of aspartate and succinate used. 5. Kinetic studies with the partially purified enzyme showed that the K_m for carbamoyl phosphate (0.091 mm) is much lower than that for aspartate (1.7mm). A sequential reaction mechanism was inferred from product-inhibition kinetics, with carbamoyl phosphate binding to the enzyme before aspartate, and the product, carbamoylaspartate, being released ahead of P_i. Initial-velocity studies gave a set of parallel reciprocal plots, compatible with an essentially irreversible step occurring before the binding of aspartate.     

Hypoxanthine-DNA glycosylase from Escherichia coli. Partial purification and properties

Hypoxanthine-DNA glycosylase from Escherichia coli was partially purified by ammonium sulfate fractionation and by chromatography on Sephacryl S-200, DEAE-cellulose, and phosphocellulose P-11 columns. Analysis of the enzymatic reaction products was carried out on a minicolumn of DEAE-cellulose and/or by paper chromatography, by following the release of the free base [3H]hypoxanthine from [3H]dIMP-containing phi X174 DNA. In native conditions, the enzyme has a molecular mass of 60 +/- 4 kDa, as determined by gel filtration on Sephadex G-150 and Sephacryl S-200 columns. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed a major polypeptide band of an apparent molecular mass of 56 kDa, and glycerol gradient centrifugation indicated a sedimentation coefficient of 4.0 S. Hypoxanthine-DNA glycosylase from E. coli has an obligatory requirement for Mg2+ and is totally inhibited in the presence of EDTA. Co2+ can only partially replace Mg2+. The enzyme is inhibited by hypoxanthine which at 4 mM causes 85% inhibition. The optimal pH range of the enzymatic activity is 5.5-7.8, and the apparent Km value is 2.5 x 10(-7) M.     

Characterization and purification of thermostable beta-glucosidase from Clostridium thermocellum.

A β-glucosidase was isolated from $\text{Clostridium thermocellum}$; the enzyme was localized in the periplasmic space.It was purified in a five-step procedure including ion-exchange chromatography on DEAE-Cellulose, chromatography on HA-Ultrogel and DEAE-Sephadex, gel filtration on AcA 34 Ultrogel and isoelectric focusing.The final preparation was purified 944-fold with a recovery of about 5% of the initial enzyme activity.Polyacrylamide disc electrophoresis of the purified enzyme gave a single band at pH 8.3. The enzyme is active towards cellobiose and p-nitrophenyl-β-D-glucoside(PNPG) and developed maximum activities at pH 6.0 and 65°C. A molecular weight of 50,000 daltons was estimated by gel filtration and the enzyme was isoelectric at pH 4.68.