Characterization and control of symbiotic Bacillus cereus isolated from the mid gut of Anopheles subpictus Grassi.

An investigation was done to find out the role of gut bacterium on the larval development and survival of Anopheles subpictus, the vector responsible for the transmission of malaria. An. subpictus mosquitoes breed exclusively in stagnant water, including shrimp/fish ponds with high nutrient level. One bacterial strain (CX2) was isolated from the midgut of late third instar of mosquito larvae. The bacterial isolate was sensitive to recommended doses of tetracyclin (30 µg/disc), doxycycline (30 µg/disc), kanamycin (30 µg/disc), gentamycin (10 µg/disc), streptomycin (10 µg/disc), vancomycin (30 µg/disc), ofloxacin (5 µg/disc), levofloxacin (5 µg/disc), gatifloxacin (10 µg/disc), but resistant to ampicillin (10 µg/disc).The larvae which were fed with the mixture of two antibiotics tetracylin (30 µg/disc) and doxycyclin (30 µg/disc) (1:1) could not survive in rice-field water. In the control experiments without any antibiotic treatment, 95-100 % survival and 95 % adult emergence were observed. The study indicates that the elimination of gut bacteria suppressed larval growth. Phylogenetic analysis of the 16S rRNA gene sequence was also done. Based on the morphological, biochemical, FAME analysis and phylogenetic analysis, the bacterial isolate CX2 was identified as Bacillus cereus. Poly acrylamide gel electrophoresis analysis revealed that the isolate showed discrete bands ranging from 24.272 to 60.049 kDa proteins. Water extract and methanol extract of Tamarindus indica showed inhibitory effect against B. cereus.