Isolation and purification of mosquito larvicidal compounds from extracts of a basidiomycete jo5289

Abstract

Mosquitoes present a worldwide, public health and nuisance challenge since they transmit human diseases including west Nile virus, malaria, dengue, Japanese encephalitis, filiarisis and other viral diseases throughout the globe. An obvious method for preventing the spread of these diseases is to control mosquito vector population by insecticides and synthetic agents, which have been developed and employed in the field with considerable success. As a result of insects’ resistance and adverse non-target effects, the current trend is to reduce or eliminate many of these older insecticides and develop safer, biodegradable, low costs larvicides for vector control. The secondary metabolites from higher fungi were thus investigated for possible mosquito larvicidal activity to control mosquitoes. A basidiomycete serialized JO5289 was collected from undisturbed habitat in Londiani forest in Rift Valley province. The strain was preserved as agar slant and the corresponding herbarium material kept in a fungal culture collection in the Integrated Biotechnology Research Laboratory (IBRL) at Egerton University. On initial screening it was found to produce active compounds in liquid culture against Aedes aegypti larvae. It was cultured in sterile submerged nutrient liquid malt media and growth conditions were manipulated to trigger the generation of secondary metabolites. From the culture two sets of crude extracts were prepared with intracellular secondary metabolites prepared from mycelium (Mex) while extracellular secondary metabolites prepared from the cultured filtrate (Kex). The crude extracts were tested for larvicidal activities against late third instar larvae and early fourth instar larvae of Ae. Aegypti before activity guided purification of the active compounds was carried out. These afforded eleven purified compounds which were subjected to NMR experiments (both 1D and 2D), that were used to determine the chemical structures of the compounds. Two mosquito larvicidal compounds were purified; 4-(2-hydroxyethyl)phenol and 3-methoxy-5-methyl-1,2-benzenediol with LC50 values of 231 and 237ppm, respectively against Ae. aegypti larvae after 24 hours. The third compound that was purified 2-hydroxy-4-(4-hydroxychroman-7-yl)but-3-enal whose larvicidal activity was not determined due to low yield. These compounds (4-(2-hydroxyethyl)phenol and 3-methoxy-5- methyl-1,2-benzenediol) have been produced from cultures of a basidiomycete and reported to have mosquito larvicidal activity for the first time. Despite the limitations of necessary research equipment, the study has demonstrated the potential of a basidiomycete JO5289 as a source of mosquito larvicidal compounds. It is the recommendation of this work that these compounds can be evaluated further for product development.