The Bacillus subtilis spore coat provides "eat resistance" during phagocytic predation by the protozoan Tetrahymena thermophila
The Bacillus subtilis spore coat provides "eat resistance" during phagocytic predation by the protozoan Tetrahymena thermophila
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DOI：
10.1073/pnas.0507121102
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发表时间：
2006-01-03
影响因子：
11.1
通讯作者：
Setlow, P
中科院分区：
文献类型：
--
作者：
Klobutcher, LA;Ragkousi, K;Setlow, P
芽孢杆菌孢子对许多环境胁迫具有很高的抵抗力，部分原因是由于存在多个“胞外”层。虽然这些胞外层中的一些在抵抗特殊胁迫方面的作用是已知的，但最外层之一的孢子皮的功能还不完全清楚。这项研究试图确定孢子被是否在抵抗纤毛原生动物四膜虫的捕食方面发挥作用，四膜虫利用吞噬作用来吞噬和降解其他微生物。原生动物嗜热四膜虫能有效摄取枯草芽孢杆菌的野生型休眠孢子，但既不能被消化，也不能被杀死。然而，有各种被毛缺陷的孢子被杀死和消化，只留下一个被称为外壳的外壳，并支持四膜虫的生长。当只用溶菌酶处理有外壳缺陷的孢子时，也会产生类似的果皮。具有不同外壳缺陷的孢子对嗜热假单胞菌捕食的敏感性与其对溶菌酶的敏感性一致。嗜热假单胞菌通过原生动物吞噬体内的裂解酶杀死孢子，而不是先萌发后杀灭。这些发现表明，芽孢杆菌种的孢子皮的一个主要功能是保护孢子免受捕食。我们还发现，即使在外壳蛋白的交联度大大降低的孢子中也会产生无法消化的皮肤，这意味着存在一种高度抵抗降解酶的外壳结构。
Bacillus spores are highly resistant to many environmental stresses, owing in part to the presence of multiple "extracellular" layers. Although the role of some of these extracellular layers in resistance to particular stresses is known, the function of one of the outermost layers, the spore coat, is not completely understood. This study sought to determine whether the spore coat plays a role in resistance to predation by the ciliated protozoan Tetrahymena, which uses phagocytosis to ingest and degrade other microorganisms. Wild-type dormant spores of Bacillus subtilis were efficiently ingested by the protozoan Tetrahymena thermophila but were neither digested nor killed. However, spores with various coat defects were killed and digested, leaving only an outer shell termed a rind, and supporting the growth of Tetrahymena. A similar rind was generated when coat-defective spores were treated with lysozyme alone. The sensitivity of spores with different coat defects to predation by T. thermophila paralleled the spores' sensitivities to lysozyme. Spore killing by T. thermophila was by means of lytic enzymes within the protozoal phagosome, not by initial spore germination followed by killing. These findings suggest that a major function of the coat of spores of Bacillus species is to protect spores against predation. We also found that indigestible rinds were generated even from spores in which cross-linking of coat proteins was greatly reduced, implying the existence of a coat structure that is highly resistant to degradative enzymes.