Salamitou Sylvie, Ramisse Françoise, Brehélin Michel, Bourguet Denis, Gilois Nathalie, Gominet Myriam, Hernandez Eric, Lereclus Didier
Unité de Lutte Biologique, INRA, La Minière, 78285 Guyancourt cedex, France2.
Unité de Biochimie Microbienne, CNRS (URA2172), Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris cedex, France1.
Microbiology (Reading). 2000 Nov;146 ( Pt 11):2825-2832. doi: 10.1099/00221287-146-11-2825.
Bacillus thuringiensis has been widely used for 40 years as a safe biopesticide for controlling agricultural pests and mosquitoes because it produces insecticidal crystal proteins. However, spores have also been shown to contribute to overall entomopathogenicity. Here, the opportunistic properties of acrystalliferous B. thuringiensis Cry(-) and Bacillus cereus strains were investigated in an insect species, Galleria mellonella, and in a mammal, BALB/c mice. In both animal models, the pathogenicity of the two bacterial species was similar. Mutant strains were constructed in which the plcR gene, encoding a pleiotropic regulator of extracellular factors, was disrupted. In larvae, co-ingestion of 10(6) spores of the parental strain with a sublethal concentration of Cry1C toxin caused 70% mortality whereas only 7% mortality was recorded if spores of the DeltaplcR mutant strain were used. In mice, nasal instillation of 10(8) spores of the parental strain caused 100% mortality whereas instillation with the same number of DeltaplcR strain spores caused much lower or no mortality. Similar effects were obtained if vegetative cells were used instead of spores. The cause of death is unknown and is unlikely to be due to actual growth of the bacteria in mice. The lesions caused by B. thuringiensis supernatant in infected mice suggested that haemolytic toxins were involved. The cytolytic properties of strains of B. thuringiensis and B. cereus, using sheep, horse and human erythrocytes and G. mellonella haemocytes, were therefore investigated. The level of cytolytic activity is highly reduced in DeltaplcR strains. Together, the results indicate that the pathogenicity of B. thuringiensis strain 407 and B. cereus strain ATCC 14579 is controlled by PlcR.
苏云金芽孢杆菌作为一种安全的生物杀虫剂，因其能产生杀虫晶体蛋白，已被广泛用于控制农业害虫和蚊子达40年之久。然而，研究表明孢子也对整体昆虫致病性有贡献。在此，研究了无晶体苏云金芽孢杆菌Cry(-)菌株和蜡样芽孢杆菌菌株在一种昆虫物种——大蜡螟以及一种哺乳动物——BALB/c小鼠中的机会性特性。在这两种动物模型中，这两种细菌的致病性相似。构建了突变菌株，其中编码细胞外因子多效调节因子的plcR基因被破坏。在幼虫中，将亲本菌株的10⁶个孢子与亚致死浓度的Cry1C毒素共同摄入导致70%的死亡率，而如果使用ΔplcR突变菌株的孢子，死亡率仅为7%。在小鼠中，经鼻腔滴注亲本菌株的10⁸个孢子导致100%的死亡率，而滴注相同数量的ΔplcR菌株孢子导致的死亡率则低得多或无死亡。如果使用营养细胞代替孢子，也会得到类似的结果。死亡原因不明，不太可能是由于细菌在小鼠体内实际生长所致。苏云金芽孢杆菌上清液在感染小鼠中引起的病变表明溶血毒素参与其中。因此，研究了苏云金芽孢杆菌和蜡样芽孢杆菌菌株对绵羊、马和人的红细胞以及大蜡螟血细胞的溶细胞特性。在ΔplcR菌株中，溶细胞活性水平大幅降低。总之，结果表明苏云金芽孢杆菌407菌株和蜡样芽孢杆菌ATCC 14579菌株的致病性受PlcR控制。
