Genotypic Diversity of Mosquitocidal Bacteria: An editorial

摘要

The genus Bacillusencompasses Gram-positive rod shaped, endospore-forming or facultatively anaerobic bacteria, and is a phenotypically and phylogenetically diverse taxon [1]. Bacillusspecies are distributed widely in nature. Members of this group can be isolated from soil, plants, insect guts, foods and diseased animals. The Bacillus cereus(Bc)group comprises closely related gram-positive bacteria that exhibit highly divergent pathogenic properties. Many bacteria classified as B.cereusare widely distributed in the environment, with probable reservoirs in the soil, and as commensal inhabitants of the intestines of insects. Occasionally they are associated with food poisoning. This is due to mainly four main enterotoxins, named cereulide, emolysin-T, non-hemolytic enterotoxin complex and cytotoxin-K. B.thuringiensisare the other members of insect pathogens and it is a gram positive bacteria that synthesizes crystal inclusions during sporulation constituted by 6 endotoxins (M.wt: 134, 127, 68 and 27 kDa) 2,3] encoded by the Cryand Cytgenes. The geometry of these crystals allows a first classification system of Bf strains. In addition, Bthas other insecticidal proteins that are secreted during its vegetative cycle. The Cry toxins of Bthave specific activities against insect species of the orders Lepidoptera, Diptera, Coleoptera, Hymenopteraand nematodes 4]. Thus, B. thuringiensisproduces crystalline protein inclusions with insecticidal properties. When insects ingest toxin crystals, the alkaline H of their digestive tract activates the toxin. Cry toxin gets inserted into the insect gut cell membrane, forming a pore. The pore results in cell lysis and eventual death of the insect. Occasionally, Bt strains are responsible for human infections, similar to those caused by strains of B.cereus. B.thuringiensissubsp. kurstaki(Btk)is another subspecies that roduces crystal proteins and are pathogenic to agricultural pests.B. sphaericus (Bs) is also aerobic, mesophilic, spore-forming and gram- ositive bacterium, commonly isolated from soil [5]. Most of the strains are pathogenic to mosquito larvae and have been widely used as biocontrol agents for disease transmitting mosquitoes. The larvicidal activity of Bsmainly originates from the binary toxins (Bin proteins), which are produced during sporulation a major toxic component of commercial Bsstrains. A new component of Cry toxins (Cry48Aa and Cry49Aa) with high specificity against Culexquinquefasciatushas also been reported [6].