Characterization of Mosquito-Specific Bacillus thuringiensis Strains Coisolated from a Soil Population

Bacillus thuringiensis serovar mogi (flagellar serotype 3a3b3d), a novel serogroup with a mosquitocidal activity

The flagellated vegetative cells of the Bacillus thuringiensis strain K4 were agglutinated with the H3 reference antiserum and further, agglutinated with 3b and 3d monospecific factor sera but non-reactive for 3c and 3e factor sera. This creates a new serogroup with flagellar antigenic structure of 3a3b3d: B. thuringiensis serovar mogi. The strain K4 showed high activity against dipteran larvae, Anopheles sinensis and Culex pipienspallens while no lepidopteran toxicity. It produced ovoidal parasporal inclusions (crystals) whose SDS-PAGE protein profile consisted of several bands ranging from 75 to 30kDa. Through the protein identification by nano-LC-ESI-IT MS analysis, the putative peptides of Cry19Ba, Cry40ORF2, Cry27Aa and Cry20Aa were detected.

Occurrence of parasporin-producing Bacillus thuringiensis in Vietnam

A total of 63 Bacillus thuringiensis isolates were recovered from urban soils of Hanoi, Vietnam. Of these, 34 were identified to 12 H serogroups. None of the isolates showed larvicidal activities against three lepidopterous insects. Three isolates belonging to the two serovars, colmeri (H21) and konkukian (H34), were highly toxic to larvae of the mosquito Aedes aegypti. Parasporal inclusion proteins of four isolates exhibited cytocidal activities against HeLa cells. Immunologically, proteins of four isolates were closely related to parasporin-1 (Cry31Aa), a parasporal protein that preferentially kills human cancer cells. Haemolytic activities were associated with parasporal proteins of the three mosquitocidal isolates but not with those of the four cancer-cell-killing isolates. PCR experiments and nucleotide sequence analysis revealed that the genes of four anti-cancer isolates are closely related to the gene parasporin-1 (cry31Aa) but are dissimilar to those of the three other existing parasporins. Our results suggest that the soil of northern Vietnam is a good reservoir of parasporin-producing B. thuringiensis.

Bacillus thuringiensis soil populations naturally occurring in the Ryukyus, a subtropic region of Japan

Of 809 soil samples collected from the seven islands of the Ryukyus, Japan, 107 samples (13.2%) contained Bacillus thuringiensis. The frequency of B. thuringiensis among the B. cereus group was 1.1% (235/21842) on the average. The B. thuringiensis soil populations of the Ryukyus consisted of more than 22 H serogroups. The predominant H serotype was the H5ac/21 (serovar canadensis/colmeri), followed by the H3ad (serovar sumiyoshiensis) and H16 (serovar indiana). Geographically, most widely distributed H serogroups were the H16 and H10ac (serovar londrina); the former was recovered from five islands and the latter from three islands. Parasporal inclusions of the isolates were morphologically heterogeneous, roughly grouped into four categories: bipyramidal/cuboidal, spherical/ovoid, irregularly-pointed, and irregular-shaped. About 53% of the isolates formed spherical to ovoid parasporal inclusions. None of the isolates exhibited larvicidal activity against the silkworm, Bombyx mori. Only four isolates belonging to four different serotypes killed larvae of the mosquito, Aedes aegypti. These mosquito-specific isolates all produced spherical parasporal inclusions.

Larval susceptibility of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), to Bacillus thuringiensis H serovars isolated in Japan

A total of 1700 Japanese strains of Bacillus thuringiensis, belonging to at least 47 H serogroups, were examined for insecticidal activity against larvae of the diamondback moth, Plutella xylostella. The high-level toxicity was associated with 612 isolates (36.0%). Of these, 608 isolates (99.3%) fell into 13 H serogroups belonging to the low-numbered H serotypes, H1-H10. Conversely, most isolates belonging to the high-numbered serotypes (>H10) had little or no larvicidal activity; only one isolate of the serovar japonensis H23 was active. P xylostella larvae were susceptible to 89.8% of the serovar morrisoni H8a:8b strains and 85.7% of galleriae H5a:5b strains. High values of 60-80% were also obtained in six serovars (thuringiensis H1, alesti H3a:3c, kurstaki H3a:3b:3c, kenyae H4a:4c, aizawai H7, and tolworhi H9), while relatively low values of <60% in two other common serovars, sotto H4a:4b and darmstadiensis H10a:10b. Five selected isolates, belonging to H serovars other than kurstaki and aizawai, were 10-60 times less toxic than the reference strain HD-1 (serovar kurstaki). Parasporal inclusion proteins of these strains were immunologically unrelated to those of the strain HD-1 and the aizawai type strain.

A novel isolate of Bacillus thuringiensis serovar leesis that specifically exhibits larvicidal activity against the moth-fly, Telmatoscopus albipunctatus

A soil isolate designated 88-KO-14-45, belonging to Bacillus thuringiensis serovar leesis (H33), exhibited larvicidal activity against the moth-fly, Telmatoscopus albipunctatus (Diptera: Psychodidae), but not for larvae of the culicine and aedine mosquitoes and Lepidoptera. Purified parasporal inclusions had an LC50 value of 5.78 micrograms/ml for the larval moth-fly, but gave no mortality against larvae of Culex pipiens molestus (Diptera: Culicidae) at protein concentrations up to 10 mg/ml. Electron microscopic observations revealed that the parasporal inclusions are homogeneous round-shaped bodies enclosed with thick, electron dense envelopes. Haemolytic activity against sheep erythrocytes was not detected in the solubilized inclusions. SDS-PAGE showed that the inclusions are composed of 72, 68, 56 and 30 kDa proteins. Immunologically, these proteins were unrelated to the inclusion proteins of B. thuringiensis serovar israelensis, while a 70 kDa protein of the strain 73-E-10-2 (B. thuringiensis serovar darmstadiensis) was seroactive to antibodies against proteins of 88-KO-14-45.

Larvicidal activity of Bacillus thuringiensis natural isolates; indigenous to Japan, against two nematoceran insect pests occurring in urban sewage environments

A total of 1449 Bacillus thuringiensis strains, indigenous to Japan, were screened for larvicidal activity against two nematoceran insect pests, the mosquito, Culex pipiens molestus (Culicidae), and the moth-fly, Telmatoscopus albipunctatus (Psychodidae). Mosquito specific strains were abundant in H serotypes 3abc (serovar kurstaki), 3ade (fukuokaensis), 4ac (kenyae), 7 (aizawai), 11ac (kyushuensis) and 29 (amagiensis), while moth-fly specific strains were predominantly found in H serotype 17 (tohokuensis). Strains toxic to both insects were most frequently detected in H serotypes 10 (darmstadiensis) and 17/27. Seven selected B. thuringiensis strains were highly toxic to Culex and/or Telmatoscopus. There was a diversity in SDS-PAGE profiles of inclusion proteins of these strains.

Bacillus thuringiensis serovar higo (flagellar serotype 44), a new serogroup with a larvicidal activity preferential for the anopheline mosquito

Eight strains of Bacillus thuringiensis, isolated in Japan, formed spherical parasporal inclusions and exhibited low to moderate larvicidal activities for two mosquito species, Anopheles stephensi and Culex pipiens molestus, but not for another dipteran, Telmatoscopus albipunctatus, or two lepidopterans, Bombyx mori and Hyphantria cunea. The anopheline toxicity (LC50 = 6.3 micrograms ml-1) was > 10 times greater than the activity on the Culex mosquito. These strains were assigned to a previously undescribed flagellar (H) antigenic group. On the basis of the representative strain, 92-KU-137-4, a serogroup with H antigen 44, Bacillus thuringiensis serovar higo was established as new.

Haemolytic activity associated with parasporal inclusion proteins of mosquito-specific Bacillus thuringiensis soil isolates: a comparative neutralization study

Solubilized parasporal inclusions of the three mosquito-specific Bacillus thuringiensis isolates belonging to three different H serovars, co-isolated from a single soil microhabitat, showed haemolytic activity towards mammalian erythrocytes. Neutralization tests with antibodies against whole inclusion proteins resulted in crossed neutralization of haemolytic activity among the isolates and the type strain of B. thuringiensis serovar kyushuensis, indicating that the three soil isolates produce toxins related to the CytB toxin. No cross-neutralization occurred between the type strain of B. thuringiensis serovar israelensis and the three soil isolates.