Consequences of producing DNA gyrase from a synthetic gyrBA operon in Salmonella enterica serovar Typhimurium

• Published in: Molecular microbiology 2021-06, Vol.115 (6), p.1410-1429
• Main Authors: Pozdeev, German, Mogre, Aalap, Dorman, Charles J.
• Format: Article
• Language: English
• Subjects: Bacteria; Chromosomes; Deoxyribonucleic acid; DNA; DNA gyrase; DNA supercoiling; DNA topoisomerase; Genes; Genomes; gyrA; gyrB; Macrophages; Salmonella; Salmonella enterica serovar Typhimurium; SPI‐1; SPI‐2; Supercoiling; Topology; Transcription; Virulence
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14689

DNA gyrase is an essential type II topoisomerase that is composed of two subunits, GyrA and GyrB, and has an A2B2 structure. Although the A and B subunits are required in equal proportions to form DNA gyrase, the gyrA and gyrB genes that encode them in Salmonella (and in many other bacteria) are at separate locations on the chromosome, are under separate transcriptional control, and are present in different copy numbers in rapidly growing bacteria. In wild‐type Salmonella, gyrA is near the chromosome's replication terminus, while gyrB is near the origin. We generated a synthetic gyrBA operon at the oriC‐proximal location of gyrB to test the significance of the gyrase gene position for Salmonella physiology. Although the strain producing gyrase from an operon had a modest alteration to its DNA supercoiling set points, most housekeeping functions were unaffected. However, its SPI‐2 virulence genes were expressed at a reduced level and its survival was reduced in macrophage. Our data reveal that the horizontally acquired SPI‐2 genes have a greater sensitivity to disturbance of DNA topology than the core genome and we discuss its significance in the context of Salmonella genome evolution and the gyrA and gyrB gene arrangements found in other bacteria. DNA gyrase is an essential topoisomerase in bacteria that plays critical roles in the management of nucleoid structure, DNA replication, transcription and recombination. It is also a major drug target. The gyrA and gyrB genes that encode the two subunits of DNA gyrase are located at widely separated sites on the chromosome of Salmonella and other bacteria. In contrast, many bacteria, such as Mycobacterium tuberculosis, Bacillus subtilis and Listeria monocytogenes, maintain the gyrA and gyrB genes in an operon. We report an investigation of the effects on Salmonella physiology and virulence of producing DNA gyrase from an operon, and the patterns of gyrase gene arrangements found in a wide range of bacteria. We believe that our findings will be of interest to those studying DNA gyrase, bacterial nucleoid architecture, gene regulation and Salmonella virulence. Our work can also assist those interested in the application of synthetic biology to bacterial chromosome design.