Caro-Astorga Joaquín, Pérez-García Alejandro, de Vicente Antonio, Romero Diego
Departamento de Microbiología, Facultad de Ciencias, Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora" (IHSM-UMA-CSIC), Universidad de Málaga Málaga, Spain.
Front Microbiol. 2015 Jan 13;5:745. doi: 10.3389/fmicb.2014.00745. eCollection 2014.
Bacillus cereus is a bacterial pathogen that is responsible for many recurrent disease outbreaks due to food contamination. Spores and biofilms are considered the most important reservoirs of B. cereus in contaminated fresh vegetables and fruits. Biofilms are bacterial communities that are difficult to eradicate from biotic and abiotic surfaces because of their stable and extremely strong extracellular matrix. These extracellular matrixes contain exopolysaccharides, proteins, extracellular DNA, and other minor components. Although B. cereus can form biofilms, the bacterial features governing assembly of the protective extracellular matrix are not known. Using the well-studied bacterium B. subtilis as a model, we identified two genomic loci in B. cereus, which encodes two orthologs of the amyloid-like protein TasA of B. subtilis and a SipW signal peptidase. Deletion of this genomic region in B. cereus inhibited biofilm assembly; notably, mutation of the putative signal peptidase SipW caused the same phenotype. However, mutations in tasA or calY did not completely prevent biofilm formation; strains that were mutated for either of these genes formed phenotypically different surface attached biofilms. Electron microscopy studies revealed that TasA polymerizes to form long and abundant fibers on cell surfaces, whereas CalY does not aggregate similarly. Heterologous expression of this amyloid-like cassette in a B. subtilis strain lacking the factors required for the assembly of TasA amyloid-like fibers revealed (i) the involvement of this B. cereus genomic region in formation of the air-liquid interphase pellicles and (ii) the intrinsic ability of TasA to form fibers similar to the amyloid-like fibers produced by its B. subtilis ortholog.
蜡样芽孢杆菌是一种细菌病原体，因食物污染导致多次疾病暴发。孢子和生物膜被认为是蜡样芽孢杆菌在受污染新鲜蔬菜和水果中最重要的储存库。生物膜是细菌群落，由于其稳定且极强的细胞外基质，很难从生物和非生物表面根除。这些细胞外基质包含胞外多糖、蛋白质、细胞外DNA和其他次要成分。虽然蜡样芽孢杆菌能够形成生物膜，但控制保护性细胞外基质组装的细菌特征尚不清楚。我们以研究充分的枯草芽孢杆菌为模型，在蜡样芽孢杆菌中鉴定出两个基因组位点，它们编码枯草芽孢杆菌淀粉样蛋白TasA的两个直系同源物和一种信号肽酶SipW。在蜡样芽孢杆菌中删除该基因组区域会抑制生物膜组装；值得注意的是，假定的信号肽酶SipW发生突变会导致相同的表型。然而，tasA或calY发生突变并不能完全阻止生物膜形成；这两个基因中任何一个发生突变的菌株形成了表型不同的表面附着生物膜。电子显微镜研究表明，TasA聚合在细胞表面形成长而丰富的纤维，而CalY不会以类似方式聚集。在缺乏组装TasA淀粉样纤维所需因子的枯草芽孢杆菌菌株中异源表达这个淀粉样蛋白盒，结果显示：（i）蜡样芽孢杆菌的这个基因组区域参与气液界面菌膜的形成；（ii）TasA具有形成与其枯草芽孢杆菌直系同源物产生的淀粉样纤维相似的纤维的内在能力。
