BIOCHEMICAL AND MOLECULAR CHARACTERIZATION OF SYMBIOTIC MID-GUT BACTERIUM BACILLUS CEREUS (PQ324272) OF CULEX QUINQUEFASCIATUS LARVAE AND ITS CONTROL BY INDIGENOUS PLANT EXTRACTS

–Gut of insects harbors a diverse microorganism which can thrive and multiply within the insect, play a crucial role in digestion, nutrition and overall growth. Midgut bacteria significantly influence development and survival of Culex quinquefasciatus larvae also. Through this investigation we have identified a bacterium CGB1 from the midgut of third instar larvae of Culex mosquito and its symbiotic relationship has been undertaken. Phenotypic and molecular characteristics of CGB1 reveals it is a rodshaped bacterium that forms round, off-white and flat colonies. It produces spores and utilizes sodium malonate as sole carbon source. It is positive for catalase, methyl-red and urease production; nitrate reduction, citrate utilization and starch and gelatine hydrolysis tests, while negative for lipid and esculin hydrolysis, Voges-Proskauer, indole, ONPG and oxidase tests. It produces acid from trehalose and sucrose, but unable to utilize other twenty carbon sources like lactose,maltose, xylose, fructose, dextrose, mannose, galactose, raffinose, mellibiose, rhamnose, cellobiose, melezitose, a-methyl-d-mannoside, xylitol, darabinose, sorbose, inositol, salicin, mannitol and ducital. CGB1 is sensitive to kanamycin, vancomycin, amoxicillin, nalidixic acid, chloramphenicol, levofloxacin, gentamicin, ofloxacin, norfloxacin, tetracycline, ciprofloxacin, rifampicin, fusidic acid, azithromycin and doxycycline but resistant to ampicillin, bacteriocin and penicillin. Antimicrobial potential of Moringa oleifera extracts was assessed by well diffusion against the isolate. Inhibition zone (IZ) for fresh leaf juice and aqueous, methanol and ethyl acetate extracts against the bacterium measured 21.33±0.58, 25.0±0.53, 24.0±0.58 and 14.67±0.58 mm, respectively. Elimination of midgut bacteria using antibiotics in the breeding water had an adverse effect on the development of wild mosquito larvae leading to reduced survival and growth rates. Addition of fresh leaf juice extract of M. oleifera to the breeding habitat water also lowered larval development and pupal emergence.