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Acta Mycologica
|
2009
|
tom 44
|
nr 1
125-138
Sixteen identified and three unidentified species belonging to six genera of zoosporic fungi were isolated from forty water samples which were collected from different fish and fish hatcheries farms at Abbassa city, Sharkiya governorate, Egypt, using sesame seeds baiting technique at 20±2°C. Saprolegnia and Achlya contributed the broadest spectra of species diversity amongst the other genera of zoosporic fungi. Saprolegnia diclina and Aphanomyces sp. were the most prevalent species of zoosporic fungi. The abundance of zoosporic fungal species in these aquacultures was correlated with some physicochemical characteristics of the water samples. The two dominant species of zoosporic fungi were tested for their tolerance of NaCl solution and its impact on some morphological and metabolic activities of these fungi. Saprolegnia diclina tolerated concentrations of NaCl solution till 12000 μg/ml whereas the maximum resistance of Aphanomyces sp. was 8000 μg/ml. The examined morphological aspects of the two studied fungal species, which included the colony diameters, the vegetative hyphae, zoosporogenesis, zoospores discharge, sexual reproductive structures and gemmae formation, were generally affected depending upon the tested fungal species and the applied dose of NaCl solution. The low treatments of NaCl solution were significantly stimulative compared with the control for protease production by S. diclina but higher doses were significantly suppressive. A significant decline in protease activity at all applications was found when Aphanomyces sp. was treated with NaCl solution. The total free amino acids and total protein content of S. diclina and Aphanomyces sp. mycelia were almost significantly increased relative to untreated controls at the low dose of NaCl solution and they were significantly dropped at the higher concentrations by the two zoosporic fungi.
Thirty-four identified in addition to five unidentified species appertaining to ten genera of zoosporic fungi were identified and isolated from eighty four polluted water samples, which were randomly collected from different polluted sites of the water drainages along the Niles Delta in Lower Egypt. Baiting sesame seeds culture technique was employed at 20±2°C for the recovery of zoosporic fungi. The genera; Pythium and Saprolegnia (8 and 7 zoosporic fungal species, respectively) showed the broadest spectra of species diversity whereas Aqualinderella was only represented by one species (A. fermentans). Saprolegnia delica and Dictyuchus carpophorus(the greatest fungal populations) were the most dominant isolated zoosporic fungal species where they were highly occurred especially at the hyperpolluted waters with the heavy metals. These two species could be considered as indicators for the response of the structure and function of microbial communities for water pollution. Several zoosporic fungal species were rarely encountered. Both Aqualinderella fermentansand Pythium rostratumwere recovered in moderate frequency of occurrence. Water samples which had high concentrations in heavy metals were the poorest in the species diversity of zoosporic fungi. Despite that, fungal species belonging to the family Saprolegniaceaeflourished in hyper polluted water samples whilst those belonging to the family Pythiaceae predominated in more diluted water samples. Also, the prevalent species; S. delica andD. carpophoruswere not affected by heavy metals concentrations being as indicators for water pollution with the heavy metals. pH values of the polluted water samples had no influence on the occurrence of zoosporic fungi. Water samples characterized by high organic matter content and low total soluble salts were the richest in zoosporic fungal species.
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 defonnation 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.
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