Segregation of secondary metabolite biosynthesis in hybrids of Fusarium fujikuroi and Fusarium proliferatum

Fusarium fujikuroi and Fusarium proliferatum are two phylogenetically closely related species of the Gibberella fujikuroi species complex (GFC). In some cases, strains of these species can cross and produce a few ascospores. In this study, we analyzed 26 single ascospore isolates of an interspecific cross between F. fujikuroi C1995 and F. proliferatum D4854 for their ability to produce four secondary metabolites: gibberellins (GAs), the mycotoxins fusarin C and fumonisin B(1), and a family of red polyketides, the fusarubins. Both parental strains contain the biosynthetic genes for all four metabolites, but differ in their ability to produce these metabolites under certain conditions. F. fujikuroi C1995 produces GAs and fusarins, while F. proliferatum D4854 produces fumonisins and fusarubins. The segregation amongst the progeny of these traits is not the expected 1:1 Mendelian ratio. Only eight, six, three and three progeny, respectively, produce GAs, fusarins, fumonisin B(1) and fusarubins in amounts similar to those synthesized by the producing parental strain. Beside the eight highly GA(3)-producing progeny, some of the progeny produce small amounts of GAs, predominantly GA(1), although these strains contain the GA gene cluster of the non-GA-producing F. proliferatum parental strain. Some progeny had recombinant secondary metabolite profiles under the conditions examined indicating that interspecific crosses can yield secondary metabolite production profiles that are atypical of the parent species.

[Landscape components favouring the occurrence of anthrax in the Flooding Pampa grasslands (Buenos Aires province, Argentina)]

The authors studied the landscape components that favour the occurrence of anthrax in the Flooding Pampa grasslands (Buenos Aires province, Argentina). They made spatial locations of anthrax outbreaks diagnosed by registered veterinary laboratories in the study area's zone of influence. As variables for study, they differentiated areas that are flooded for 20% of the time or more from primary and secondary runoff channels. They also identified areas with low-productivity pasture. Logistic regression analysis of farm populations revealed that landscape components favouring the occurrence of anthrax outbreaks are shared runoff channels (odds ratio (OR) = 2.3; confidence interval (CI) = 1.2; 4.7) and > or = 40% low-productivity pasture (OR = 5.4; CI = 3.5; 8.3). Contrary to initial assumptions, susceptibility to flooding was not a significant variable (OR = 1.1; CI = 0.5; 2.1). The authors concluded that the first step in decision-making and ensuring more efficient implementation of future anthrax control and eradication plans was to identify risk variables.

Restoration of gibberellin production in Fusarium proliferatum by functional complementation of enzymatic blocks

Nine biological species, or mating populations (MPs), denoted by letters A to I, and at least 29 anamorphic Fusarium species have been identified within the Gibberella fujikuroi species complex. Members of this species complex are the only species of the genus Fusarium that contain the gibberellin (GA) biosynthetic gene cluster or at least parts of it. However, the ability of fusaria to produce GAs is so far restricted to Fusarium fujikuroi, although at least six other MPs contain all the genes of the GA biosynthetic gene cluster. Members of Fusarium proliferatum, the closest related species, have lost the ability to produce GAs as a result of the accumulation of several mutations in the coding and 5' noncoding regions of genes P450-4 and P450-1, both encoding cytochrome P450 monooxygenases, resulting in metabolic blocks at the early stages of GA biosynthesis. In this study, we have determined additional enzymatic blocks at the first specific steps in the GA biosynthesis pathway of F. proliferatum: the synthesis of geranylgeranyl diphosphate and the synthesis of ent-kaurene. Complementation of these enzymatic blocks by transferring the corresponding genes from GA-producing F. fujikuroi to F. proliferatum resulted in the restoration of GA production. We discuss the reasons for Fusarium species outside the G. fujikuroi species complex having no GA biosynthetic genes, whereas species distantly related to Fusarium, e.g., Sphaceloma spp. and Phaeosphaeria spp., produce GAs.

Functional characterization of two cytochrome P450 monooxygenase genes, P450-1 and P450-4, of the gibberellic acid gene cluster in Fusarium proliferatum (Gibberella fujikuroi MP-D)

Gibberella fujikuroi is a species complex with at least nine different biological species, termed mating populations (MPs) A to I (MP-A to MP-I), known to produce many different secondary metabolites. So far, gibberellin (GA) production is restricted to Fusarium fujikuroi (G. fujikuroi MP-C), although at least five other MPs contain all biosynthetic genes. Here, we analyze the GA gene cluster and GA pathway in the closest related species, Fusarium proliferatum (MP-D), and demonstrate that the GA genes share a high degree of sequence homology with the corresponding genes of MP-C. The GA production capacity was restored after integration of the entire GA gene cluster from MP-C, indicating the existence of an active regulation system in F. proliferatum. The results further indicate that one reason for the loss of GA production is the accumulation of several mutations in the coding and 5' noncoding regions of the ent-kaurene oxidase gene, P450-4.

Immune response to Babesia bigemina infection in pregnant cows

The objective of this study was to characterize the immune response of Babesia bigemina-infected cows during the second trimester of pregnancy. Twelve animals were divided into four groups (I, II, III, IV); groups I and II were pregnant cows, groups III and IV were non-pregnant cows. Groups I and III were infected with a virulent strain of Babesia bigemina, the doses utilized was 1 x 10(7) infected red blood cells IM. Groups II and IV were noninfected control groups. All the infected animals were severely affected; at days 5-7 post-inoculation (DPI) they showed clinical signs: fever (40-41.5 degrees C), packed cell volume reduction, and parasitemia, and specific treatment was required. The immune response was monitored daily from 0-11 DPI. As shown by flow cytometry analysis, in infected animals the distribution in peripheral blood of the T-cells subpopulations (CD4+, CD8+, gammadelta T-cells) was not affected when compared to the control groups. By ELISA, IFN-gamma production showed a trend to increase in plasma between 6-10 DPI; noninfected cows showed the lowest optical density values. By RT-PCR, a Th1 predominant response was observed, TNFalpha, INF-gamma and iNOs were detected. In contrast IL-4 and IL-10 were weak or undetected. The results of this trial will be discussed.

Immune response to Babesia bigemina infection in pregnant cows

Babesiosis is a tick-borne disease of cattle caused by Babesia bigemina and Babesia bovis and is transmitted by the tick vector Boophilus microplus. In this study, we investigate B. bigemina infection regarding the clinical infection, T cell distribution, and cytokine profile during the acute phase of an experimental infection in pregnant cows.

The P450-1 gene of Gibberella fujikuroi encodes a multifunctional enzyme in gibberellin biosynthesis

Recent studies have shown that the genes of the gibberellin (GA) biosynthesis pathway in the fungus Gibberella fujikuroi are organized in a cluster of at least seven genes. P450-1 is one of four cytochrome P450 monooxygenase genes in this cluster. Disruption of the P450-1 gene in the GA-producing wild-type strain IMI 58289 led to total loss of GA production. Analysis of the P450-1-disrupted mutants indicated that GA biosynthesis was blocked immediately after ent-kaurenoic acid. The function of the P450-1 gene product was investigated further by inserting the gene into mutants of G. fujikuroi that lack the entire GA gene cluster; the gene was highly expressed under GA production conditions in the absence of the other GA-biosynthesis genes. Cultures of transformants containing P450-1 converted ent-[(14)C]kaurenoic acid efficiently into [(14)C]GA(14), indicating that P450-1 catalyzes four sequential steps in the GA-biosynthetic pathway: 7beta-hydroxylation, contraction of ring B by oxidation at C-6, 3beta-hydroxylation, and oxidation at C-7. The GA precursors ent-7alpha-hydroxy[(14)C]kaurenoic acid, [(14)C]GA(12)-aldehyde, and [(14)C]GA(12) were also converted to [(14)C]GA(14). In addition, there is an indication that P450-1 may also be involved in the formation of the kaurenolides and fujenoic acids, which are by-products of GA biosynthesis in G. fujikuroi. Thus, P450-1 displays remarkable multifunctionality and may be responsible for the formation of 12 products.

Monooxygenases involved in GA12 and GA14 synthesis in Gibberella fujikuroi

A microsomal preparation from mycelia of the gibberellin (GA)-producing fungus Gibberella fujikuroi catalyzed the first two steps in the conversion of the biosynthetic intermediate GA12-aldehyde to gibberellic acid (GA3). [14C]GA12-Aldehyde was converted to radiolabelled GA14, the major product, together with smaller amounts of non-hydroxylated GA12. The microsomal activities required reduced pyridine nucleotides and molecular oxygen. However, GA12 and GA14 synthesis differed markedly in the preferred electron source. Formation of GA12 required NADH or NADPH, while GA14 synthesis from GA12-aldehyde occurred only with NADPH. Marked differences were also found in the activating effect of FAD. When NADPH was the reductant, the rate of GA14 synthesis was enhanced 3.5 times by 5 microM FAD while this flavin nucleotide did not alter the synthesis of GA12. In contrast, GA12 synthesis was activated 3.8 times by 50 microM FAD in the presence of NADH. Both activities were inhibited by carbon monoxide and cytochrome c. These properties suggest that the 3beta-hydroxylation of GA12-aldehyde and further oxidation of carbon 7 are catalyzed by cytochrome P-450 monooxygenases in Gibberella fujikuroi.

Indole-3-Acetic Acid Control on Acidic Oat Cell Wall Peroxidases

Incubation of oat coleoptile segments with 40 µm indoleacetic acid (IAA) induced a decrease of 35-60% in peroxidase activity at the cell wall compartment. Treatment with IAA also produced a similar decrease in the oxidation of NADH and IAA at the cell wall. Isoelectric focusing of ionic, covalent, and intercellular wall peroxidase fractions showed that acidic isoforms (pI 4.0-5.5) were reduced preferentially by IAA treatment. Marked differences were found between acidic and basic wall isoperoxidases in relation to their efficacy in the oxidation of IAA. A peroxidase fraction containing acidic isoforms oxidized IAA with a V(max)/s(0.5) value of 2.4 x 10(-2) min(-1). g fw(-1), 4.0 times higher than that obtained for basic peroxidase isoforms (0.6 x 10(-2) min(-1). g fw(-1)). In contrast, basic isoforms were more efficient than acidic isoperoxidases in the oxidation of coniferyl alcohol or ferulic acid with H(2)O(2) (5.6 and 2.1 times, respectively). The levels of diferulate and lignin in the walls of oat coleoptile segments were not altered by treatment with IAA. The decrease in cell wall peroxidase activity by IAA was related more to reduced oxidative degradation of the hormone than to covalent cell wall cross-linking.Key Words. IAA-Auxin-Wall peroxidases-Oat-Avena sativa-Diferulic acid-Ligninhttp://link.springer-ny.com/link/service/journals/00344/bibs/18n1p25.html

Identification of reactive vicinal cysteines in Saccharomyces cerevisiae (ATP) and cytosolic rat liver (GTP) phospho enol pyruvate carboxykinases

Saccharomyces cerevisiae (ATP) and cytosolic rat liver (GTP) phospho enol pyruvate carboxykinases (EC 4.1.1.49/32) have been labeled with N-(1-pyrenyl)-iodoacetamide. Reagent incorporation was completely prevented by the presence of the respective nucleoside diphosphate plus MnCl2. Under appropriate conditions, 2 mol of reagent per mol of enzyme subunit were incorporated. The fluorescence spectra of the labeled proteins showed the pyrene excimer emission band. The pyrenyl-derivatized enzymes were digested with trypsin after carboxymethylation, and two labeled peptides were isolated for each carboxykinase upon reverse-phase high-performance liquid chromatography. Automated Edman degradation of the labeled peptides indicated that cysteines 364 and 457 (yeast enzyme), and cysteines 288 and 413 (rat enzyme) were labeled with the fluorescence SH-specific reagent. The relative reactivity of these residues was characterized. Labeling experiments utilizing the 5,5'-dithiobis(2-nitrobenzoate)-oxidized enzymes suggested that the reactive SH-groups occupy a vicinal position in the tertiary structure of the proteins, probably in the nucleotide-binding region.

Comparative steady-state fluorescence studies of cytosolic rat liver (GTP), Saccharomyces cerevisiae (ATP) and Escherichia coli (ATP) phospho enol pyruvate carboxykinases

Two members of the ATP-dependent class of phospho enol pyruvate (PEP) carboxykinases (Saccharomyces cerevisiae and Escherichia coli PEP carboxykinase), and one member of the GTP-dependent class (the cytosolic rat liver enzyme) have been comparatively analyzed by taking advantage of their intrinsic fluorescence. The S. cerevisiae and the rat liver enzymes show intrinsic fluorescence with a maximum emission characteristic of moderately buried tryptophan residues, while the E. coli carboxykinase shows somewhat more average exposure for these fluorophores. The fluorescence of the three proteins was similarly quenched by the polar compound acrylamide, but differences were observed for the ionic quencher iodide. For the ATP-dependent enzymes, these last experiments indicate more exposure to the aqueous media of the tryptophan population of the E. coli than of the S. cerevisiae enzyme. The effect of nucleotides on the emission intensities and quenching efficiencies revealed substrate-induced conformational changes in the E. coli and cytosolic rat liver PEP carboxykinases. The addition of Mn2+ or of the adenosine nucleotides in the presence of Mg2+ induced an enhancement in the fluorescence of the E. coli enzyme. The addition of guanosine or inosine nucleotides to the rat liver enzyme quenched its fluorescence. From the ligand-induced fluorescence changes, dissociation constants of 40 +/- 6 microM, 10 +/- 0.8 microM, and 15 +/- 1 microM were obtained for Mn2+, MgATP and MgADP binding to the E. coli enzyme, respectively. For the cytosolic rat liver PEP carboxykinase, the respective values for GDP, IDP and ITP binding are 6 +/- 0.5 microM, 6.7 +/- 0.4 microM and 10.1 +/- 1.7 microM. A comparison of the dissociation constants obtained in this work with those reported for other PEP carboxykinases is presented.

Fluorescent labeling of the nucleotide site in cytosolic rat liver phosphoenolpyruvate carboxykinase

Reaction of rat liver phosphoenolpyruvate carboxykinase (GTP: oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32) with the alkylating fluorescent probe N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid (1,5-I-AEDANS), results in complete loss of enzymatic activity. One mole of the fluorescent reagent is incorporated per mole of the inactivated enzyme. When the modification is carried out in the presence of GDPMn, the enzyme retains 97% of its activity with almost no incorporation of label. The specificity of the reaction is further supported by the detection of a unique fluorescent peptide from the trypsin-treated modified enzyme. Fluorescence emission of enzyme-bound AEDANS shows a broad band centered at 470 nm and presents a monoexponential decay with a lifetime of 19 ns. These data indicate that the probe-binding site is considerably less polar than water and similar in polarity to ethanol. Anisotropy determinations give evidence for restricted rotational freedom for AEDANS bound to the rat carboxykinase, while acrylamide quenching studies reveal limited accessibility to the probe site. The results are consistent with specific labeling of rat liver phosphoenolpyruvate carboxykinase at or near the GDP site. The characteristics of the nucleotide-binding sites of rat liver and yeast (ATP) phosphoenolpyruvate carboxykinase are compared.

Substrate and metal specificity in the enzymic synthesis of cyclic monoterpenes from geranyl and neryl pyrophosphate

A partially purified enzyme (carbocyclase) from the flavedo of Citrus limonum formed alpha-pinene, beta-pinene, limonene, and gamma-terpinene from geranyl pyrophosphate (GPP) and neryl pyrophosphate. The maximum specific activities obtained were 7.0 and 3.6 nmol/min/mg, respectively. Cross-inhibition by the two substrates were observed and the ability to utilize neryl pyrophosphate was almost completely lost with aging. Citronellyl pyrophosphate and dimethylallyl pyrophosphate were the most effective inhibitors of carbocyclase. Isopentenyl pyrophosphate, the monophosphate esters of nerol and geraniol, as well as inorganic pyrophosphate were much less effective inhibitors. The enzyme had an absolute requirement for Mn2+. It could be replaced with about 2% effectiveness by Mg2+ and Co2+. Kinetic studies showed that the observed reaction rate correlates with the calculated concentration of the GPP (Mn2+)2 species. Previous evidence with nonenzymatic reactions and the results presented support the view that the mechanism of carbocyclase may be the intramolecular analog of prenyltransferase.