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Updated: Aug 11, 2026
Isolation and Selection of Entomopathogenic Fungi from Soil Samples and Evaluation of Fungal Virulence against Insect Pests
Published on: September 28, 2021
Unusual envelopes associated with parasporal inclusions of a mosquitocidal Bacillus thuringiensis serovar
Noriko Shisa1, Minoru Maeda, Michio Ohba
1Bioresources and Management Laboratory, Graduate School of Agriculture, Kyushu University, Fukuoka 812-8581, Japan.
Abstract:
A mosquitocidal soil isolate of Bacillus thuringiensis serovar fukuokaensis (H3ade) produced spherical parasporal inclusions measuring 0.6-0.7 microm in diameter. Inclusion matrix was homogeneous substance surrounded by a thick, highly electron-dense envelope 30-50 nm in thickness. The envelopes were associated with both intracellular and extracellular inclusions. Densely woven network was the inner structure of the envelope. Often, inclusions had round-shaped, enveloped small protrusions on the surface.
Insights
Bacillus thuringiensis fukuokaensis (H3ade) produces spherical, electron-dense parasporal inclusions. These inclusions, crucial for mosquitocidal activity, feature a unique, densely woven envelope structure.
Area of Science:
- Microbiology
- Insecticide Research
Background:
- Bacillus thuringiensis (Bt) is a soil bacterium known for its insecticidal properties.
- Specific serovars of Bt produce crystalline parasporal inclusions toxic to various insect larvae.
Purpose of the Study:
- To characterize the morphology of parasporal inclusions produced by Bacillus thuringiensis serovar fukuokaensis (H3ade).
- To investigate the ultrastructure of the inclusion envelope and its association with the matrix.
Main Methods:
- Isolation and culturing of Bacillus thuringiensis serovar fukuokaensis (H3ade).
- Transmission electron microscopy (TEM) to visualize parasporal inclusions.
- Analysis of inclusion size, shape, and envelope characteristics.
Main Results:
- Spherical parasporal inclusions measuring 0.6-0.7 micrometers were observed.
- Inclusions possessed a homogeneous matrix enclosed by a thick (30-50 nm), electron-dense envelope.
- The envelope's inner structure revealed a densely woven network, with some inclusions exhibiting surface protrusions.
Conclusions:
- The unique ultrastructure of the H3ade parasporal inclusions, particularly the electron-dense envelope, may contribute to its mosquitocidal efficacy.
- Further research into the composition and function of the envelope is warranted.
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