Rap-Phr Systems from Plasmids pAW63 and pHT8-1 Act Together To Regulate Sporulation in the Bacillus thuringiensis Serovar kurstaki HD73 Strain

• Published in: Applied and environmental microbiology Vol. 86; no. 18
• Main Authors: Cardoso, Priscilla, Fazion, Fernanda, Perchat, Stéphane, Buisson, Christophe, Vilas-Bôas, Gislayne, Lereclus, Didier
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.09.2020
• Subjects: Bacillus thuringiensis; Bacillus thuringiensis - genetics; Bacillus thuringiensis - physiology; Bacteria; Crosstalk; Deoxyribonucleic acid; DNA; Genes; Insects; Invertebrate Microbiology; Life Sciences; Peptides; Phr gene; Plasmids; Plasmids - genetics; Quorum Sensing; Serogroup; Spores, Bacterial - physiology; Sporulation; Synergism; Toxins; quorum sensing; Rap-Phr; plasmids; Bacillus; sporulation
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.01238-20

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. contains a remarkable number of extrachromosomal DNA molecules and a great number of plasmid genes. Rap-Phr quorum-sensing systems regulate different bacterial processes, notably the commitment to sporulation in 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 serovar kurstaki HD73 strain. Rap63 has moderate activity on sporulation and is inhibited by the Phr63 peptide. The genes are cotranscribed, and the gene is also transcribed from a σ -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 and genes in the same strain has a greater negative effect on sporulation than the sum of the loss of each 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 at the end of the infectious cycle in insects, thus pointing out the roles of the plasmids in the fitness of the bacterium. The life cycle of in insect larvae is regulated by quorum-sensing systems of the RNPP family. After the toxemia caused by Cry insecticidal toxins, the sequential activation of these systems allows the bacterium to trigger first a state of virulence (regulated by PlcR-PapR) and then a necrotrophic lifestyle (regulated by NprR-NprX); ultimately, sporulation is controlled by the Rap-Phr systems. Our study describes a new operon carried by a plasmid and shows that the Rap protein has a moderate effect on sporulation. However, this system, in combination with another plasmidic operon, provides effective control of sporulation when the bacteria develop in the cadavers of infected insect larvae. Overall, this study highlights the important adaptive role of the plasmid Rap-Phr systems in the developmental fate of and its survival within its ecological niche.