An ABC transporter from Bacillus thuringiensis is essential for beta-exotoxin I production.
beta-Exotoxin I is a nonspecific insecticidal metabolite secreted by some Bacillus thuringiensis strains. Several studies of B. thuringiensis strains that have lost the capacity to produce beta-exotoxin I have suggested that there is a strong correlation between high levels of beta-exotoxin I production and the ability to synthesize crystal proteins. In this study, we showed that a mutant strain, B. thuringiensis 407-1(Cry(-))(Pig(+)), with no crystal gene, produced considerable amounts of beta-exotoxin I together with a soluble brown melanin pigment. Therefore, beta-exotoxin I production can take place after a strain has lost the plasmids bearing the cry genes, which suggests that these curable plasmids probably contain determinants involved in the regulation of beta-exotoxin I production. Using a mini-Tn10 transposon, we constructed a library of strain 407-1(Cry(-))(Pig(+)) mutants. We screened for nonpigmented mutants with impaired beta-exotoxin I production and identified a genetic locus harboring two genes (berA and berB) essential for beta-exotoxin I production. The deduced amino acid sequence of the berA gene displayed significant similarity to the ATP-binding domains of the DRI (drug resistance and immunity) family of ATP-binding cassette (ABC) proteins involved in drug resistance and immunity to bacteriocins and lantibiotics. The berB gene encodes a protein with six putative transmembrane helices, which probably constitutes the integral membrane component of the transporter. The demonstration that berAB is required for beta-exotoxin I production and/or resistance in B. thuringiensis adds an adenine nucleotide analog to the wide range of substrates of the superfamily of ABC proteins. We suggest that berAB confers beta-exotoxin I immunity in B. thuringiensis, through active efflux of the molecule.
Espinasse
Sylvain
S
Unité de Recherches de Lutte Biologique, INRA La Minière, 78285 Guyancourt, France.
Gohar
Michel
M
Lereclus
Didier
D
Sanchis
Vincent
V
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000241:Adenosine / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000096:biosynthesis*; D001483:Base Sequence; D003470:Culture Media; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004731:Endotoxins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D006460:Hemolysin Proteins; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D018411:Spodoptera; D013400:Sugar Acids; D013997:Time Factors
D018528:ATP-Binding Cassette Transporters; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003470:Culture Media; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004731:Endotoxins; D006460:Hemolysin Proteins; D013400:Sugar Acids; C030956:insecticidal crystal protein, Bacillus Thuringiensis; C068295:thuringiensin; D000241:Adenosine