Bacillus thuringiensis is a Gram-positive spore-forming bacterium pathogenic to various insect species. This property is due to the Cry toxins encoded by plasmid genes and mostly produced during sporulation. B. thuringiensis contains a remarkable number of extrachromosomal DNA molecules and a great number of plasmid rap-phr genes. Rap-Phr quorum-sensing systems regulate different bacterial processes, notably the commitment to sporulation in Bacillus species. Rap proteins are quorum sensors acting as phosphatases on Spo0F, an intermediate of the sporulation phosphorelay, and are inhibited by Phr peptides that function as signaling molecules. In this study, we characterize the Rap63-Phr63 system encoded by the pAW63 plasmid from the B. thuringiensis serovar kurstaki HD73 strain. Rap63 has moderate activity on sporulation and is inhibited by the Phr63 peptide. The rap63-phr63 genes are cotranscribed, and the phr63 gene is also transcribed from a σ^H-specific promoter. We show that Rap63-Phr63 regulates sporulation together with the Rap8-Phr8 system harbored by plasmid pHT8_1 of the HD73 strain. Interestingly, the deletion of both phr63 and phr8 genes in the same strain has a greater negative effect on sporulation than the sum of the loss of each phr gene. Despite the similarities in the Phr8 and Phr63 sequences, there is no cross talk between the two systems. Our results suggest a synergism of these two Rap-Phr systems in the regulation of the sporulation of B. thuringiensis at the end of the infectious cycle in insects, thus pointing out the roles of the plasmids in the fitness of the bacterium.

中文翻译：

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来自质粒pAW63和pHT8-1的Rap-Phr系统共同作用，以调节苏云金芽孢杆菌库尔斯塔克HD73菌株的孢子形成。

苏云金芽孢杆菌是对多种昆虫致病的革兰氏阳性孢子形成细菌。该性质归因于质粒基因编码的Cry毒素，并且大多数在孢子形成过程中产生。苏云金芽孢杆菌含有大量染色体外DNA分子和大量质粒rap-phr基因。Rap-Phr群体感应系统调节不同的细菌过程，特别是芽孢杆菌物种中形成孢子的承诺。Rap蛋白是定型传感器，在Spo0F（孢子形成磷酸化的中间产物）上充当磷酸酶，并被用作信号分子的Phr肽抑制。在这项研究中，我们表征了由pAW63质粒编码的Rap63-Phr63系统。苏云金芽孢杆菌血清型库尔斯塔基HD73菌株。Rap63对孢子形成具有中等活性，并被Phr63肽抑制。所述rap63-phr63基因cotranscribed，并且phr63基因也由σ转录^ħ特异性启动子。我们显示，Rap63-Phr63调节孢子形成与HD73株的质粒pHT8_1所具有的Rap8-Phr8系统一起。有趣的是，同一菌株中phr63和phr8基因的缺失对孢子形成的负面影响要比每个phr的损失总和更大。基因。尽管Phr8和Phr63序列相似，但两个系统之间没有串扰。我们的结果表明，在昆虫的感染周期结束时，这两个Rap-Phr系统在苏云金芽孢杆菌孢子形成的调控中具有协同作用，从而指出了质粒在细菌适应性中的作用。