Blanca Fontaniella

Secreted arginases from phylogenetically far-related lichen species act as cross-recognition factors for two different algal cells

Purified arginases secreted from Evernia prunastri and Xanthoria parietina thalli hydrolyze arginine in a Mn2+ -dependent reaction. Ca2+ cannot replace Mn2+, but its addition to reaction mixtures in the presence of Mn2+ significantly inhibited arginase activity. Arginases from both lichen species also show lectin function, binding to the cell wall of both homologous and heterologous algae. Such binding is enhanced by both Ca2+ and Mn2+ and results in cytoagglutination, which is counteracted by alpha-D-galactose. A putative ligand for these lectins consists of a glycosylated urease, the polysaccharide moiety of which is uniquely composed of alpha-D-galactose. Binding of lectins inhibits its enzymatic activity, which is recovered after desorption of the lectin with alpha-D-galactose. Urease is also eluted from arginase-agarose columns by using alpha-D-galactose as eluent. Data demonstrate ligand-dependent retention of the fungal lectin on the algal cell surface and this is consistent with a model of recognition of compatible algae, through which algal cells would form a lichen with a lectin-secreting fungus only when these cells contain the specific ligand for the lectin in their cell walls. This is, lectin binding is used as a mechanism for ensuring specificity in the association.

A role for sugarcane glycoproteins in the resistance of sugarcane to Ustilago scitaminea

Smut is a major disease of sugarcane caused by Ustilago scitaminea. Germination of fungal teliospores is achieved on the internode surface of plants, and it is followed by the formation of appressoria. A primary response of sugarcane plants to the infection seems to be the production of several glycoproteins, defined as mid-molecular mass (MMMG) or high molecular mass (HMMG) macromolecules. Teliospore germination in the presence of both MMMG and HMMG decreased about 50% following 5 h of teliospore contact with glycoproteins. This may be related to the ability of glycoproteins to produce cytoagglutination. Binding of fluorescein-labelled glycoproteins was studied by fluorescence microscopy, showing that staining of cells was not uniform, but mainly in the contact zone between two individual teliospores when aggregated. HMMG was composed of only one fraction that was completely retained by smut teliospores, whereas three of the five different glycoproteins occurring in the MMMG fraction were retained by teliospore cell walls. Moreover, a unique application of salicylic acid, naturally produced by sugarcane stalks after experimental fungal infection, enhanced the production of both glycoprotein pools. A hypothesis about the role of both HMMG and MMMG as defence glycoproteins is discussed.

Gluconacetobacter diazotrophicus, a sugar cane endosymbiont, produces a bacteriocin against Xanthomonas albilineans, a sugar cane pathogen

Gluconacetobacter diazotrophicus in liquid culture secretes proteins into the medium. Both medium containing Gluconacetobacter protein and a solution of this protein after acetone precipitation appeared to inhibit the growth of Xanthomonas albilineans in solid culture. This apparent inhibition of bacterial growth has, in fact, been revealed to be lysis of bacterial cells, as demonstrated by transmission electron microscopy. Fractionation of the Gluconacetobacter protein mixture in size-exclusion chromatography reveals a main fraction with lysozyme-like activity which produces lysis of both living bacteria and isolated cell walls.

Improvement of the analysis of dansylated derivatives of polyamines and their conjugates by high-performance liquid chromatography.

The paper described a method for improving the hydrolysis of conjugated polyamines in PH fraction, isolated from the lichen Evernia prunastri, as well as the optimization of dansylation procedure of these polyamines on the basis of the pH value to which derivatization is achieved. Dansylated polyamines have been later separated by high-performance liquid chromatography (HPLC) using a gradient elution. Hydrolysis of conjugates requires acid treatment at room temperature rather than at 110 degrees C, as usually described. Dansylation is improved at high pH values, whereas removal of phenolics (mainly evernic acid), from the conjugates requires low pH values.

Identification of xanthans isolated from sugarcane juices obtained from scalded plants infected by Xanthomonas albilineans.

The exudate gum produced by Xanthomonas albilineans, a specific sugarcane pathogen, has been isolated from juices of diseased sugarcane stalks, hydrolyzed with hydrochloric acid, and the hydrolysate analyzed by capillary electrophoresis. Sucrose. cellobiose, mannose, glucose, glucose-1-P and glucuronic acid were identified as the major components of the polysaccharide isolated from diseased stalks. Juices from healthy stalks contained maltose instead of cellobiose. The chemical nature of this polysaccharide is discussed.

The cryoprotective role of polyols in lichens : Effects on the redistribution of RNase in Evernia prunastri thallus during freezing

Abstract The effect of low temperatures on the distribution of RNase (EC 3.1.26.1) in the lichen Evernia prunastri (L.) Ach. has been studied in laboratory conditions. Freezing of lichen thalli produces solubilization of part of the particulate enzyme from the cell wall of both mycobiont and phycobiont to the corresponding cytoplasm. A supply of exogenous ribitol (naturally produced by the algal partner) totally prevents the solubilization of the enzyme whereas mannitol (naturally produced by the fungal partner) impedes the enzyme solubilization to a minor extent. RNase is preferably located in the phycobiont cells in terms of specific activity. Ribitol also impedes the solubilization of algal enzyme whereas mannitol strongly promotes the loss of RNase from algal cell wall to the soluble fraction. Solubilization of fungal enzyme is enhanced by both polyols, with a preference for ribitol.

Ultrastructural Changes and Production of a Xanthan-Like Polysaccharide Associated with Scald of Sugarcane Leaves Caused by Xanthomonas albilineans

Leaf scald is a vascular disease of sugarcane caused by Xanthomonas albilineans. Scalded leaves show white-yellowish streaks alternating with green zones in parallel to the main veins. These zones develop large bulliform cells, probably as a consequence of the wilting process. Moreover, a gum exudate occludes phloem and bundle vessels, and partially enters mesophyll cells. Some lysigenic cavities appear near the xylem. However, the white-yellowish streaks show both phloem and xylem completely occluded by the gum and the overall mesophyll appears to be full of this bacterial secretion, as revealed by scanning electron microscopy. The gum in conducting tissues has been purified from juice obtained from scalded stalks by precipitation with isopropyl alcohol and size-exclusion chromatography. It was identified as a xanthan-like polysaccharide and found to be composed of glucose, mannose and glucuronic acid by acidic hydrolysis and capillary electrophoresis.

Bioskin as an affinity matrix for the separation of glycoproteins

Bioskin is a natural product produced by a mixed culture of Acetobacter xylinum, Saccharomyces cerevisiae and S. pombe cultured on media containing sucrose. It is of fibrillar nature able to retain some proteins, such as cytochrome c, by adsorption, and mainly composed of glucosamine and N-acetyl-D-glucosamine. This makes it possible that, at an adequate pH value, proteins charged as polyanionic molecules, such as catalase, can be retained by ionic adsorption using the positively charged amino groups of the matrix. In addition, bioskin can also be used as an affinity matrix to retain glycoproteins able to perform specific affinity reactions with the amino sugars of the matrix, such as invertase, fetuin or ovalbumin. Its possible use as a chromatographic support is discussed.

Determination by high performance liquid chromatography of ornithine and lysine decaboxylases in sugar cane juices

SummaryAccurate and very sensitive HPLC methods which allow the simultaneous determination of the diamines putrescine (PUT) and cadaverine (CAD), resulting from ornithine decarboxylase (ODC) and lysine decarboxylase (LDC) activities or naturally occurring in sugarcane juices, are presented. Diamines were detected as their dansyl derivatives by fluorescence emission. The corresponding limits of detection were 21 ng mL−1 for PUT and 5 ng mL−1 for CAD. HPLC methods were compared with routine spectrophotometric assays.

Requirements to produce fumarprotocetraric acid using alginate-immobilized cells of Cladonia verticillaris

The biosynthesis of the depsidone, fumarprotocetraric acid, a compound previously considered to be only produced by lichens, has been confirmed by using alginate-immobilized cells of Cladonia verticillaris. Immobilized cells only produce the depsidone when they are supplemented with FMN and acetate. This implies that fumaric acid which esterifies an alcohol function in the C3 of a depsidone precursor is added through a reducing, flavin-dependent, coupling reaction that uses the pool of succinyl-CoA from the fungal partner.