Effect of ultraviolet-A radiation on the production of Leptolegnia chapmanii (Saprolegniales: Saprolegniaceae) zoospores on dead Aedes aegypti (Diptera: Culicidae) larvae and their larvicidal activity.

Impact of UV-radiation in entomopathogens in aquatic environments remains little investigated. The present study reports on the effect of UV-A on the larvicidal activity of Leptolegnia chapmanii zoospores in Aedes aegypti; on the production of zoospores in larvae killed by the pathogen and then exposed to UV-A; and on the activity of these zoospores against healthy larvae. Whereas the virulence of free zoospores in A. aegypti larvae was affected by a UV-A exposure time longer than 10min, production of zoospores in larvae and their virulence were not hampered at a maximal 8h exposure of dead larvae to UV-A. Findings suggest that dead larvae and zoosporangia provide a certain protection to zoospores against UV-A and emphasize the susceptibility of free encysted zoospores to such radiation.

Irreversible magnetoporation of micro-organisms in high pulsed magnetic fields.

Electroporation is an appealing way of stimulating living cells, which causes permanent or temporary nanoporosities in the structure of the biological objects. However, the technique has a disadvantage such as a requirement of contact between the electrodes and the cell medium. In this review, a methodology of contactless treatment of the biological objects using pulsed magnetic fields is proposed. The eukaryotic micro-organisms Achlya americana and Saprolegnia diclina have been used in the study and magnetic fields up to 7 T were applied, which caused effects similar to irreversible electroporation resulting in the death of the species. The proposed technique is applicable for different types of the biological cells or micro-organisms and possibly can be used in the area of cancer, antifungal treatment and other biotechnological fields.

Treatment of microbiologically polluted aquaculture waters by a novel photochemical technique of potentially low environmental impact.

The applicability of a novel procedure for the disinfection of microbiologically polluted waters from fish-farming ponds, based on the combined action of visible light (including sunlight) and porphyrin-type photosensitising agents, has been investigated using (a) cell cultures of a Gram-positive bacterium (meticillin-resistant Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli) and a fungal pathogen (Saprolegnia spp.); (b) pilot aquaculture plants involving either spontaneously or artificially Saprolegnia-infected rainbow trout (Oncorhynchus mykiss). The results obtained by using two cationic porphyrins, namely a tetra-substituted N-methyl-pyridyl-porphine (C1) and its analogue where one N-methyl group had been replaced by a N-tetradecyl chain (C14), and low intensity visible light irradiation showed an extensive (up to 6-7 log) decrease in the bacterial/fungal population after short incubation and irradiation times in the presence of micromolar photosensitiser concentrations. Moreover, C14 showed some toxic effect also in the absence of light. Extension of these studies to the pilot plants indicated that both C1 + light and C14 can prevent Saprolegnia infections or promote the cure of saprolegniasis in infected trout by treatments with submicromolar porphyrin doses. The procedure appears to be of low cost and to have a low environmental impact.