Dipartimento di Agraria, University of Sassari, Viale Italia 39/A, 07100 Sassari, Italy.
Int J Mol Sci. 2023 Jan 16;24(2):1781. doi: 10.3390/ijms24021781.
S-layers are involved in the adaptation of bacteria to the outside environment and in pathogenesis, often representing special virulence factors. Vegetative cells of the entomopathogenic bacterium are characterized by an overproduction of extracellular surface layers that are released in the medium during growth. The purpose of this study was to characterize cell wall proteins of this bacterium and to investigate their involvement in pathogenesis. Electron microscopy observations documented the presence of multiple S-layers, including an outermost (OW) and a middle (MW) layer, in addition to the peptidoglycan layer covering the plasma membrane. After identifying these proteins (OWP and MWP) by mass spectrometry analyses, and determining their gene sequences, the cell wall multilayer-released fraction was successfully isolated and used in insect bioassays alone and in combination with bacterial spores. This study confirmed a central role of spores in bacterial pathogenicity to insects but also detected a significant virulence associated with fractions containing released cell wall multilayer proteins. Taken together, S-layer proteins appear to be part of the toxins and virulence factors complex of this microbial control agent of invertebrate pests.
S-层参与细菌对外界环境的适应和发病机制，通常代表特殊的毒力因子。昆虫病原细菌的营养细胞的特征是大量产生在生长过程中释放到培养基中的细胞外表面层。本研究的目的是表征该细菌的细胞壁蛋白，并研究它们在发病机制中的作用。电子显微镜观察记录了存在多种 S-层，包括最外层 (OW) 和中层 (MW) 层，以及覆盖质膜的肽聚糖层。通过质谱分析鉴定这些蛋白质（OWP 和 MWP）并确定其基因序列后，成功分离了细胞壁多层释放部分，并单独和与细菌孢子一起用于昆虫生物测定。本研究证实了孢子在细菌对昆虫的致病性中的核心作用，但也检测到与释放的细胞壁多层蛋白相关的分数具有显著的毒力。总之，S-层蛋白似乎是这种昆虫病原微生物控制剂的毒素和毒力因子复合物的一部分。
