The mosquito-larvicidal binary toxin of Bacillus sphaericus 2297 was expres
sed in Enterobacter amnigenus, a Gram-negative bacterium isolated from Anop
heles dirus larvae gut. The toxin was placed under the regulation of variou
s promoters in order to improve the expression level of the toxin. Amongst
the recombinants obtained, E. amnigenus harboring pBS373, a plasmid which c
ontains the toxin genes under the control of the native B. sphaericus promo
ter, expressed a significant amount of protein, comparable to that found in
B. sphaericus 2297. In addition, this recombinant provided approximately t
wenty times higher toxicity against second-instar Anopheles dirus larvae wh
en compared to B. sphaericus 2297. The procedure of obtaining this environm
entally isolated bacterium from larvae gut and introducing the system for m
osquito-larvicidal toxin synthesis is noteworthy. The promising result pres
ented here provides a substantial degree of confidence for further field st
udies.