Pathogenicity and oxidative stress in Nile tilapia caused by Aphanomyces laevis and Phoma herbarum isolated from farmed fish.

Identified (n = 17) and unidentified (n = 1) fish-pathogenic fungal species from 10 genera of Oomycetes and soil fungi were isolated from 40 infected freshwater fish samples of the species Oreochromis niloticus niloticus (Nile tilapia) and Clarias gariepinus (African catfish). Samples were collected from various fish farms in the Nile Delta, Egypt. Nile tilapia were tested in aquaria for their susceptibility to the commonest Oomycetes species, Aphanomyces laevis and Achlya klebsiana, and also against the 2 most prevalent pathogenic soil fungi, Paecilomyces lilacinus and Phoma herbarum. Two techniques were used: water bath exposure and intramuscular (subcutaneous) injection. Water bath exposure to the 2 species of Oomycetes caused greater mortalities of O. niloticus niloticus than intramuscular injection, but the reverse was true of the soil fungal species. Regardless of the infection method, the 2 Oomycetes species were more potent pathogens than the soil fungal species. In both gills and mytomal muscles of fish infected by A. laevis and P. herbarum, we measured and compared with controls the oxidative stress parameters total peroxide (TP), lipid peroxidation (LPO) and nitric oxide (NO), as well as levels of the antioxidants vitamin E and glutathione (GSH), and superoxide dismutase (SOD) and catalase (CAT) activities. Infection by these 2 fungal species through either spore suspension or spore injection significantly increased oxidative damage in gills and induced marked decrease in most studied antioxidants. In addition, both routes showed similar effects and A. laevis depressed the antioxidants CAT, vitamin E and GSH more than P. herbarum.

Potential of Epicoccum purpurascens Strain 5615 AUMC as a Biocontrol Agent of Pythium irregulare Root Rot in Three Leguminous Plants.

Epicoccum purpurascens stain 5615 AUMC was investigated for its biocontrol activity against root rot disease caused by Pythium irregulare. E. purpurascens greenhouse pathogenicity tests using three leguminous plants indicated that the fungus was nonpathogenic under the test conditions. The germination rate of the three species of legume seeds treated with a E. purpurascens homogenate increased significantly compared with the seeds infested with P. irregulare. No root rot symptoms were observed on seeds treated with E. purpurascens, and seedlings appeared more vigorous when compared with the non-treated control. A significant increase in seedling growth parameters (seedling length and fresh and dry weights) was observed in seedlings treated with E. purpurascens compared to pathogen-treated seedlings. Pre-treating the seeds with the bioagent fungus was more efficient for protecting seeds against the root rot disease caused by P. irregulare than waiting for disease dispersal before intervention. To determine whether E. purpurascens produced known anti-fungal compounds, an acetone extract of the fungus was analyzed by gas chromatography mass spectrometry. The extract revealed a high percentage of the cinnamic acid derivative (trimethylsiloxy) cinnamic acid methyl ester. The E. purpurascens isolate grew more rapidly than the P. irregulare pathogen in a dual culture on potato dextrose agar nutrient medium, although the two fungi grew similarly when cultured separately. This result may indicate antagonism via antibiosis or competition.

Comparative study of the effect of stress by the heavy metals Cd+2, Pb+2, and Zn+2 on morphological characteristics of Saprolegnia delica Coker and Dictyuchus carpophorus Zopf.

The effects of essential (Zn+2) and non-essential (Cd+2 and Pb+2) heavy metals on morphogenesis of two represantatives of informal group zoosporic fungi namely; Saprolegnia delica Coker and Dictyuchus carpophorus Zopf. were studied. These two species varied in their tolerance of each amended heavy metal. Lead had the most potent effect amongst the tested heavy metals in inhibiting the radial extension of the vegetative hyphae of the two tested species. The vegetative hyphae of S. delica and D. carpophorus assumed different morphological alterations compared with that at controls depending upon the applied heavy metal and the dose concentration. Both zoosporangial formation and discharges of the two tested fungi were greatly inhibited even at the low concentrations of Cd. Zoosporangia of D. carpophorus appeared curved at high concentrations of Cd. Zoosporangial formation and discharge of the two zoosporic fungi showed variable deformation when treated with Pb. The different applications of Zn nearly stimulated sporangial elongation in both zoosporic fungi. Sex organs varied in their numbers and morphogenesis at each treatment of the applied heavy metal. The gemmae of S. delica were greatly reduced or missed at the elevated toxic levels of Cd whereas they enhanced in numbers and size at most Pb treatments and little affected at Zn applications.

Removal Efficiency of the Heavy Metals Zn(II), Pb(II) and Cd(II) by Saprolegnia delica and Trichoderma viride at Different pH Values and Temperature Degrees.

The removal efficiency of the heavy metals Zn, Pb and Cd by the zoosporic fungal species Saprolegnia delica and the terrestrial fungus Trichoderma viride, isolated from polluted water drainages in the Delta of Nile in Egypt, as affected by various ranges of pH values and different temperature degrees,was extensively investigated. The maximum removal efficiency of S. delica for Zn(II) and Cd(II) was obtained at pH 8 and for Pb(II) was at pH 6 whilst the removal efficiency of T. viride was found to be optimum at pH 6 for the three applied heavy metals. Regardless the median lethal doses of the three heavy metals, Zn recorded the highest bioaccumulation potency by S. delica at all pH values except at pH 4, followed by Pb whereas Cd showed the lowest removal potency by the fungal species and vice versa in case of T. viride. The optimum biomass dry weight production by S. delica was found when the fungus was grown in the medium treated with the heavy metal Pb at pH 6, followed by Zn at pH 8 and Cd at pH 8. The optimum biomass dry weight yield by T. viride amended with Zn,Pb and Cd was obtained at pH 6 for the three heavy metals with the maximum value at Zn. The highest yield of biomass dry weight was found when T. viride treated with Cd at all different pH values followed by Pb whilst Zn output was the lowest and this result was reversed in case of S. delica. The maximum removal efficiency and the biomass dry weight production for the three tested heavy metals was obtained at the incubation temperature 20℃ in case of S. delica while it was 25℃ for T. viride. Incubation of T. viride at higher temperatures (30℃ and 35℃) enhanced the removal efficiency of Pb and Cd than low temperatures (15℃ and 20℃) and vice versa in case of Zn removal. At all tested incubation temperatures, the maximum yield of biomass dry weight was attained at Zn treatment by the two tested fungal species. The bioaccumulation potency of S. delica for Zn was higher than that for Pb at all temperature degrees of incubation and Cd bioaccumulation was the lowest whereas T. viride showed the highest removal efficiency for Pb followed by Cd and Zn was the minor of the heavy metals.

Morphological and biochemical alterations of oomycete fish pathogen Saprolegnia parasitica as affected by salinity, ascorbic acid and their synergistic action.

Vegetative growth of Saprolegnia parasitica decreased by increasing the concentration of NaCl and ascorbic acid. Under these conditions, the morphological features of the vegetative hyphae were distinguishable from those used as controls. NaCl and ascorbic acid in combination improved the tolerance of S. parasitica to high levels of salinity. Sporangial formation, release and proliferation were very sensitive to even lower levels of salinity. For instance, at 0.03 M NaCl sporangia formation was rarely observed. Ascorbic acid alone had a little effect on sporangial formation and release, but when combine with NaCl the developmental processes were improved. Reduction of numbers and plasmolysis of oogonia were found at various NaCl concentrations, whereas ascorbic acid stimulated the formation of these reproductive organs at low concentrations. The synergistic effect of NaCl and ascorbic acid improved and overcomed the symptoms of oogonial plasmolysis. Protease activity of S. parasitica was significantly reduced at all NaCl concentrations, whilst ascorbic acid significantly increased and inhibited it at low concentrations and at moderate and high concentrations, respectively. The combination of these compounds reduced protease activity at all tested concentrations with significant difference at the highest concentration. The total free amino-acids content of S. parasitica mycelia was significantly reduced at all the NaCl concentrations, whereas ascorbic acid significantly increased it at low but inhibited it at higher concentrations. The combination of NaCl and ascorbic acid significantly increased the accumulation of free amino-acids at low and moderate concentrations, but decreased them at high concentrations. Total protein content was reduced at all tested concentrations of NaCl and ascorbic acid had also similar effect. However, the combined effect of NaCl and ascorbic acid significantly enhanced and reduced total protein content at low and high concentrations, respectively. Treatments with NaCl induced proline accumulation in S. parasitica, which paralleled the salt concentration.

Effects of Some Amino Acids on Ammonia Secretion and Extracellular Protease Activity by Three Oomycetes in Synthetic Medium with or without Glucose.

The effects of different concentrations of three amino acids as carbon and or nitrogen sources on mycelial dry weights, changes in pH values of synthetic medium, ammonia secretion and extracellular protease activity by three zoosporic fungi, pathogens of fish and shellfish, were studied. As compared with the control, the addition of isoleucine and aspartic acid as nitrogen sources were generally stimulative for mycelial dry weight production whereas phenylalanine was inhibitory irrespective to the tested fungal species. When amino acids served as carbon and nitrogen sources, the mycelial dry weights of the three fungi were increased (mostly non-significantly) relative to untreated control but weights were decreased as the concentrations of the three amino acids raised. The addition of individual amino acids as carbon and nitrogen sources to the medium significantly increased pH values of the medium comparable to the control. The addition of each of the three amino acids as carbon and nitrogen sources to the medium significantly induced ammonia secretion by the three species of zoosporic fungi. Ammonia secretion in synthetic medium amended with amino acids as nitrogen source raised by the three zoosporic fungi relative to untreated control except in case of Achlya racemosa treated with isoleucine. Extracellular protease activity was almost promoted in case of Achlya proliferoides and Saprolegnia furcata cultures treated with isoleucine and aspartic acid individually in presence of glucose and vice versa in case of phenylalanine. However, extracellular protease activity of A. racemosa decreased compared with the control at various concentrations of isoleucine and both phenylalanine and aspartic acid assumed inconsistent effects. Extracellular protease activity of the three zoosporic fungi in the medium devoid of glucose varied depending upon zoosporic fungal species, the tested amino acid and the applied concentrations. The values of protease activity were approximately less two folds than that obtained in presence of glucose.

Distribution of zoosporic fungi in the mud of major Egyptian lakes.

Twenty-six identified and three unidentified species belonging to eight genera of zoosporic fungi were recovered from seventy-six mud samples of Egyptian lakes using sesame seeds as baits. Nineteen samples were collected along the borders of four major lakes. Pythium, Phytophthora and Allomyces, yielded the highest spectra of zoosporic species, while Aqualinderella, Blastocladia and Dictyuchus, had one species. Pythium, Aphanomyces, Allomyces, Aqualinderella, Phytophthora and Saprolegnia were the dominant zoosporic genera while Blastocladia and Dictyuchus were rare. The most prevalent species of zoosporic fungi were Aqualinderella fermentans, Aphanomyces laevis and unidentified Pythium species while the other isolated species in this study were rare. Menzalah was the richest lake with zoosporic species followed by Borolous and Karoon. Some zoosporic fungal genera were recovered from the mud of the four tested lakes (participator genera) and others from three lakes or from only two lakes. Physicochemical characteristics of the mud samples (pH, total soluble salts and organic matter) revealed no correlation with the fungal occurrence and distribution in these lakes.