Distinct Roles of ComK1 and ComK2 in Gene Regulation in <em>Bacillus cereus</em>

The B. subtilis transcriptional factor ComK regulates a set of genes coding for DNA uptake from the environment and for its integration into the genome. In previous work we showed that Bacillus cereus expressing the B. subtilis ComK protein is able to take up DNA and integrate it into its own genome. To extend our knowledge on the effect of B. subtilis ComK overexpression in B. cereus we first determined which genes are significantly altered. Transcriptome analysis showed that only part of the competence gene cluster is significantly upregulated. Two ComK homologues can be identified in B. cereus that differ in their respective homologies to other ComK proteins. ComK1 is most similar, while ComK2 lacks the C-terminal region previously shown to be important for transcription activation by B. subtilis ComK. comK1 and comK2 overexpression and deletion studies using transcriptomics techniques showed that ComK1 enhances and ComK2 decreases expression of the comG operon, when B. subtilis ComK was overexpressed simultaneously.枯草芽孢杆菌（Bacillus subtilis）的ComK转录因子可调控一组编码环境DNA摄取及DNA基因组整合功能的基因。本课题组前期研究已证实，表达枯草芽孢杆菌ComK蛋白的蜡样芽孢杆菌（Bacillus cereus）能够摄取外源DNA并将其整合至自身基因组。为进一步探明枯草芽孢杆菌ComK在蜡样芽孢杆菌中过表达的调控效应，本研究首先鉴定了该菌体内发生显著表达变化的基因。转录组分析结果显示，仅感受态基因簇的部分区域出现显著上调表达。蜡样芽孢杆菌中存在两种ComK同源蛋白，二者与其他来源ComK蛋白的同源性存在差异：其中ComK1与其他ComK蛋白的同源性最高，而ComK2则缺失了此前被证实对枯草芽孢杆菌ComK转录激活功能至关重要的C端结构域。通过转录组学技术开展的comK1与comK2过表达及敲除实验结果表明，当同时过表达枯草芽孢杆菌ComK时，ComK1可上调comG操纵子的表达，而ComK2则会抑制该操纵子的转录。