SEARCH FOR NATURAL ISOLATES OF Bacillus thuringiensis FOR DEVELOPMENT OF ECOLOGICALLY FRIENDLY BIOLOGICALS

Two Bacillus thuringiensis var. kurstaki HD-1 mutants, two Bacillus thuringiensis var. israelensis HD-500 mutants, and four rice grain dust isolates were characterized using microscopic examination and protein profiles of purified crystals on sodium dodecyl sulfate – polyacrylamide gel electrophoresis. Specific detection of cryI- and cryIV-type genes was performed in a polymerase chain reaction using cryI and cryIV-specific oligonucleotide primers. The cry-type genes under study consisted of cryIA(a), cryI(A)b, cryI(A)c, cryIB, and cryIV. Presence or absence of the cryI- and cryIV-type genes was further confirmed by Southern blotting followed by hybridization with specific cryI and cryIV gene fragments. A genetically modified strain of B. thuringiensis var. kurstaki HD-1, called OZK-13 and obtained following mutagenesis with ozone, was shown to contain cryIA(a), cryIA(b), and cryIA(c) genes. Another kurstaki HD-1 mutant, called NGK-13 and obtained following treatment with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), was shown to have lost the cryIA(b) gene while retaining the cryIA(a) and cryIA(c) genes. NGI-23-1, an oligosporogenous–multicrystalliferous mutant of B. thuringiensis var. israelensis (Bti) HD-500, obtained following treatment with MNNG contained cryIV-type genes. NGI-22, an oligosporogenous–acrystalliferous mutant of Bti HD-500, contained no cryI- nor cryIV-type genes. The rice grain dust isolate BT-285 contained the cryIA(a) and cryIA(c) genes. Isolate BT-14 contained only the cryIA(c) gene, whereas isolate BT-209 contained cryIA(a), cryIA(b), and cryIB genes. Isolate BT-205 contained no cryI- nor cryIV-type genes. Bacillus thuringiensis mutants and natural isolates shown to contain cryI-type genes were tested for their insecticidal activities in a series of bioassays against Hyphantria cunea Drury (Lepidoptera: Arctiidae). All cryI-carrying strains were toxic against the insect larvae. BT-205 was also tested and exhibited no toxicity against the insect larvae.Key words: Bacillus thuringiensis, δ-endotoxin crystal, cry-type genes, polymerase chain reaction.

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The impact of strain diversity and mixed infections on the evolution of resistance to Bacillus thuringiensis

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2013.1497 ◽

2013 ◽

Vol 280 (1769) ◽

pp. 20131497 ◽

Cited By ~ 9

Author(s):

Ben Raymond ◽

Denis J. Wright ◽

Neil Crickmore ◽

Michael B. Bonsall

Keyword(s):

Bacillus Thuringiensis ◽

Transmission Rate ◽

Diamondback Moth ◽

Mixed Infections ◽

Ecological Interactions ◽

Significant Difference ◽

Natural Isolates ◽

Evolution Of Resistance ◽

Insect Populations ◽

The Impact

Pesticide mixtures can reduce the rate at which insects evolve pesticide resistance. However, with live biopesticides such as the naturally abundant pathogen Bacillus thuringiensis ( Bt ), a range of additional biological considerations might affect the evolution of resistance. These can include ecological interactions in mixed infections, the different rates of transmission post-application and the impact of the native biodiversity on the frequency of mixed infections. Using multi-generation selection experiments, we tested how applications of single and mixed strains of Bt from diverse sources (natural isolates and biopesticides) affected the evolution of resistance in the diamondback moth, Plutella xylostella, to a focal strain. There was no significant difference in the rate of evolution of resistance between single and mixed-strain applications although the latter did result in lower insect populations. The relative survivorship of Bt- resistant genotypes was higher in the mixed-strain treatment, in part owing to elevated mortality of susceptible larvae in mixtures. Resistance evolved more quickly with treatments that contained natural isolates, and biological differences in transmission rate may have contributed to this. Our data indicate that the use of mixtures can have unexpected consequences on the fitness of resistant and susceptible insects.

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Occurrence and Linkage Between Secreted Insecticidal Toxins in Natural Isolates of Bacillus thuringiensis

Current Microbiology ◽

10.1007/s00284-003-4097-2 ◽

2003 ◽

Vol 47 (6) ◽

Cited By ~ 19

Author(s):

Sylvain Espinasse ◽

Josette Chaufaux ◽

Christophe Buisson ◽

St�phane Perchat ◽

Michel Gohar ◽

...

Keyword(s):

Bacillus Thuringiensis ◽

Insecticidal Toxins ◽

Natural Isolates

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Correspondence of High Levels of Beta-Exotoxin I and the Presence of cry1B in Bacillus thuringiensis

Applied and Environmental Microbiology ◽

10.1128/aem.68.9.4182-4186.2002 ◽

2002 ◽

Vol 68 (9) ◽

pp. 4182-4186 ◽

Cited By ~ 15

Author(s):

Sylvain Espinasse ◽

Michel Gohar ◽

Josette Chaufaux ◽

Christophe Buisson ◽

Stéphane Perchat ◽

...

Keyword(s):

Bacillus Thuringiensis ◽

Insect Species ◽

Anthonomus Grandis ◽

Genetic Determinants ◽

Natural Isolates ◽

Culture Supernatants

ABSTRACT Examination of 640 natural isolates of Bacillus thuringiensis showed that the 58 strains (9%) whose supernatants were toxic to Anthonomus grandis (Coleoptera: Curculionidae) produced between 10 and 175 μg of β-exotoxin I per ml. We also found that 55 (46%) of a sample of 118 strains whose culture supernatants were not toxic to A. grandis nevertheless produced between 2 and 5 μg/ml. However, these amounts of β-exotoxin I were below the threshold for detectable toxicity against this insect species. Secretion of large amounts of β-exotoxin I was strongly associated with the presence of cry1B and vip2 genes in the 640 natural B. thuringiensis isolates studied. We concluded that strains carrying cry1B and vip2 genes also possess, on the same plasmid, genetic determinants necessary to promote high levels of production of β-exotoxin I.

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