Comparison of NheA toxin production and doubling time between Bacillus cereus and Bacillus thuringiensis

Abstract

In this study, we compared the toxin gene expression, NheA toxin production, doubling time, and viable cell number for several strains of the food poisoning bacteria Bacillus cereus and the microbial pesticide Bacillus thuringiensis. The two B. cereus and six B. thuringiensis strains evaluated were confirmed to possess and transcribe the nheABC, hblCDA, and cytK genes using polymerase chain reaction (PCR) and reverse-transcription PCR. NheA toxin production was compared based on the absorbance at 414 nm using a Tecra BDE-VIA kit. The NheA-specific production (absorbance/viable cell number) values indicated that the two B. thuringiensis var. kurstaki isolates from microbial pesticide produced the highest amount of toxin (0.66-0.95) than other B. thuringiensis (0.14-0.45) and the B. cereus strains (0.19-0.31). However, the B. thuringiensis strains had longer doubling time (20-26 min) than the B. cereus strains (18-19 min). Interestingly, two B. thuringiensis var. kurstaki isolates produced the highest amount of NheA toxin, and their doubling times (20-22 min) were close to those of the B. cereus strains tested.