Abstract
The thermotolerant representative of the Bacillus cereus group, Bacillus cytotoxicus, reliably harbors the coding gene of cytotoxin K-1 (CytK-1). This protein is a highly cytotoxic variant of CytK toxin, initially recovered from a diarrheal foodborne outbreak that caused the death of three people. In recent years, the cytotoxicity of B. cytotoxicus has become controversial, with some strains displaying a high cytotoxicity while others show no cytotoxicity towards cell lines. In order to better circumscribe the potential pathogenic role of CytK-1, knockout (KO) mutants were constructed in two B. cytotoxicus strains, E8.1 and E28.3. The complementation of the cytK-1 KO mutation was implemented in a mutant strain lacking in the cytK-1 gene. Using the tetrazolium salt (MTT) method, cytotoxicity tests of the cytK-1 KO and complemented mutants, as well as those of their wild-type strains, were carried out on Caco-2 cells. The results showed that cytK-1 KO mutants were significantly less cytotoxic than the parental wild-type strains. However, the complemented mutant was as cytotoxic as the wild-type, suggesting that CytK-1 is the major cytotoxicity factor in B. cytotoxicus.
Highlights
Cytotoxin K-1 (CytK-1) is a highly cytotoxic and necrotic variant of cytotoxin K (CytK)
Numerous new species have been described as B. cereus s.l. members, the primary members of the group are B. cereus sensu stricto (s.s.), Bacillus thuringiensis, Bacillus anthracis, Bacillus mycoides, Bacillus pseudomycoides, and Bacillus weihensphanensis
To help circumscribe the role of CytK-1 toxin, we knocked out the cytK-1 gene in two B. cytotoxicus strains, E28.3 and E8.1
Summary
Cytotoxin K-1 (CytK-1) is a highly cytotoxic and necrotic variant of cytotoxin K (CytK) It was initially recovered from a specific Bacillus cereus strain isolated from a food poisoning outbreak fatal to three elderly people in France in 1998. This B. cereus strain and its kin were later described as a new species, Bacillus cytotoxicus, the thermotolerant representative of the B. cereus group [1,2]. Numerous new species have been described as B. cereus s.l. members, the primary members of the group are B. cereus sensu stricto (s.s.), Bacillus thuringiensis, Bacillus anthracis, Bacillus mycoides, Bacillus pseudomycoides, and Bacillus weihensphanensis. While B. mycoides, B. pseudomycoides, and B. weihensphanensis have not reportedly been implicated in any human infections or foodborne diseases yet [3], many B. thuringiensis have been used for several decades as bio-pesticides in agriculture and control of disease vectors, due to their ability to produce insecticidal molecules [4]
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