Semiautomated quantification of cytotoxic damage induced in cultured insect cells exposed to commercial Bacillus thuringiensis biopesticides

Early murine immune responses from endotracheal exposures to biotechnology-related Bacillus strains

An immunology-based in vivo screening regime was used to assess the potential pathogenicity of biotechnology-related microbes. Strains of Bacillus cereus (Bc), Bacillus subtilis (Bs), Bacillus thuringiensis (Bt), and Bt commercial products (CPs) were tested. Balb/c mice were endotracheally instilled with purified spores, diluted CP, or vegetative cells (VC) (live or dead). Exposed mice were evaluated for changes in behavioral and physical symptoms, bacterial clearance, pulmonary granulocytes, and pulmonary and circulatory pyrogenic cytokines (interleukins (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α), as well as acute phase biomarkers (fibrinogen and serum amyloid A). Except for some differences in clearance rates, no marked effects were observed in mice exposed to any spore at 10(6) or 10(7) colony forming units (cfu). In contrast, live Bc or Bt VCs (10(5) or 10(6) cfu) produced shock-like symptoms (lethargy, hunched appearance, ruffled fur, and respiratory distress), and 11-200-fold elevations in pyrogenic cytokines at 2-h post-exposure. In the study, 4-h effects included increased lethargy, ocular discharge, and 1.5-4-fold rise in circulatory acute phase markers, but no indications of recovery. Bs VC did not produce any changes in symptoms or biomarkers. After 2 or 4 h of exposure to dead VC, increases of only plasma IL-1? and TNF-α (4.6- and 12.4-fold, respectively) were observed. These findings demonstrate that purified spores produced no marked effects in mice compared to that of metabolically active bacteria. This early screening regime was successful in distinguishing the pathogenicity of the different Bacillus species, and might be useful for assessing the relative hazard potential of other biotechnology-related candidate strains.

Cell-cycle-dependent resistance to Bacillus thuringiensis Cry1C toxin in Sf9 cells

The Sf9 cell line, derived from the moth Spodoptera frugiperda, is highly and specifically sensitive to the Bacillus thuringiensis Cry1C toxin. Upon exposure to Cry1C, ionic pores are formed in the plasma membrane leading to cell swelling and death. Here, we describe a unique transient tolerance to Cry1C of dividing cells, which allowed completion of the division process in the presence of Cry1C. Correlatively, arresting the cells at G2-M phase by nocodazole treatment rendered them insensitive to Cry1C. When the arresting agent was removed, the cells completed their division and gradually regained Cry1C sensitivity. In comparison to normal cells with 1-2% cell-division frequency, the M-phase arrested cells bound less toxin in binding assays. Moreover, no lipid rafts could be isolated from the membranes of M-phase arrested cells. Caveolin-1, identified here for the first time in insect cells, was immunodetected as a lipid raft component of normal cells, but was only present in the membrane-soluble fraction of G2-M-arrested cells. Thus M-phase-linked changes in lipid raft organization may account for diminished Cry1C binding and toxicity. Furthermore, considering the pivotal role of lipid rafts in different cell functions of many cell types, the lack of organized lipid rafts in dividing cells may transiently affect cell susceptibility to pathogens, toxins and other lipid raft-linked functions.

Cell integrity markers for in vitro evaluation of cytotoxic responses to bacteria-containing commercial insecticides

Toxicity of two commercial "BT" products, containing Bacillus thuringiensis subsp. kurstaki spores (Btk) and associated parasporal inclusion body proteins, was tested in vitro using two unrelated lepidoperan cell lines and several markers of cell integrity (morphology, quantification of loss of adherence and electron transport (redox) activity, and degradation of nuclear DNA, actin, hsp-70, and beta-tubulin). With doses of 10(-7), 10(-5), and 10(-3) International Units (IU)/target cell, these markers measured exposure-dependent effects closely linked to cell death, which occurred rapidly once Btk spores germinated, unless inhibited by antibiotic. Derivation of marker half-lives (HL50) revealed that temperature critically affected product performance. Between 34 and 37 degrees C, HL50 was < or = 5 hr, but dose discrimination between 10(-5) and 10(-3) IU was poor. At temperatures less than 34 degrees C, the resolution between different HL50s and doses increased in a manner directly relating to published data obtained from in vivo BT-spore-induced LD50 assays. It was concluded that BT product toxification is complex, essentially enabled by an autobiotransformation process in which dose-response lag is affected by temperature-dependent temporal expression of spore germination and critical buildup of vegetative cells and byproduct toxicants. The in vitro dosimetry assays described here are potentially useful for obtaining mechanistic toxicologic data and in vivo relevant quantifications of subingredient activities in various commercial BT formulations as well as in other microbe-based biotechnology products.