School of Yunkang Medicine and Health, Nanfang College, Guangzhou, Guangdong, China.
School of Life Science, Liaoning University, Shenyang, Liaoning, China.
PLoS One. 2022 May 19;17(5):e0262974. doi: 10.1371/journal.pone.0262974. eCollection 2022.
Bacillus cereus is a food contaminant with widely varying enterotoxic potential due to its virulence proteins. In this article, phylogenetic analysis of the amino acid sequences from the whole-genomes of 41 strains, evolutionary distance calculation of the amino acid sequences of the virulence genes, and functional and structural predictions of the virulence proteins were performed to reveal the taxonomically diverse distribution of virulence factors. The genome evolution of the strains showed a clustering trend based on the protein-coding virulence genes. The strains of B. cereus have evolved into non-toxic risk and toxic risk clusters with medium-high- and medium-low-risk subclusters. The evolutionary transfer distances of incomplete virulence genes relative to housekeeping genes were greater than those of complete virulence genes, and the distance values of HblACD were higher than those of nheABC and CytK among the complete virulence genes. Cytoplasmic localization was impossible for all the virulence proteins, and NheB, NheC, Hbl-B, and Hbl-L1 were predicted to be extracellular. Nhe and Hbl proteins except CytK had similar spatial structures. The predicted structures of Nhe and Hbl mainly showed 'head' and 'tail' domains. The 'head' of NheA and Hbl-B, including two α-helices separated by β-tongue strands, might play a special role in the formation of Nhe trimers and Hbl trimers, respectively. The 'cap' of CytK, which includes two 'latches' with many β-sheets, formed a β-barrel structure with pores, and a 'rim' balanced the structure. The evolution of B. cereus strains showed a clustering tendency based on the protein-coding virulence genes, and the complete virulence-gene operon combination had higher relative genetic stability. The beta-tongue or latch associated with β-sheet folding might play an important role in the binding of virulence structures and pore-forming toxins in B. cereus.
蜡样芽胞杆菌是一种食源性污染物，由于其毒力蛋白的存在，具有广泛的肠毒性潜力。在本文中，对 41 株全基因组的氨基酸序列进行了系统发育分析，对毒力基因的氨基酸序列进行了进化距离计算，并对毒力蛋白进行了功能和结构预测，以揭示毒力因子的分类多样性分布。菌株的基因组进化显示出基于蛋白质编码毒力基因的聚类趋势。蜡样芽胞杆菌的菌株已进化为非毒性风险和毒性风险聚类，具有中高和中低风险亚群。与管家基因相比，不完全毒力基因的进化转移距离大于完整毒力基因，而在完整毒力基因中，HblACD 的距离值高于 nheABC 和 CytK。所有毒力蛋白均不可能定位于细胞质，NheB、NheC、Hbl-B 和 Hbl-L1 被预测为细胞外。除 CytK 外，Nhe 和 Hbl 蛋白具有相似的空间结构。Nhe 和 Hbl 蛋白的预测结构主要显示“头”和“尾”域。NheA 和 Hbl-B 的“头”，包括由β舌链隔开的两个α-螺旋，可能分别在 Nhe 三聚体和 Hbl 三聚体的形成中发挥特殊作用。CytK 的“帽”包括两个具有许多β-片层的“闩锁”，形成具有孔的β-桶结构，“边缘”平衡结构。蜡样芽胞杆菌菌株的进化显示出基于蛋白质编码毒力基因的聚类趋势，完整的毒力基因操纵子组合具有更高的相对遗传稳定性。与β-片层折叠相关的β-舌或闩锁可能在蜡样芽胞杆菌中发挥重要作用，与毒力结构和孔形成毒素的结合。
