Development of a pyrE-based selective system for Thermotoga sp. strain RQ7

To fully unlock the biotechnological potentials of Thermotoga species, this study aimed to expand the genetic toolbox of Thermotoga by developing a new selective system. The developed system was composed of two components: a recipient strain bearing a deletion in its orotate phosphoribosyltransferase gene pyrE and a shuttle vector expressing a heterologous pyrE as the selectable marker. A spontaneous uracil auxotroph, T. sp. strain RQ7-15, was isolated at 70 °C with 2 mg/ml 5-fluoroorotic acid. The mutant carried a 112 bp deletion in pyrE and was a suitable recipient strain. To avoid homologous recombination, the pyrE gene from another thermophilic bacterium Caldicellulosiruptor saccharolyticus was used as the selectable marker. The gene was cloned into two Thermotoga-E. coli shuttle vectors, controlled by different promoters: the promoter of Thermus S-layer protein (P _slpA ) in pDH25 and the promoter of the pyrimidine synthesis operon of T. sp. strain RQ7 (P _RQ7.pyr ) in pDH28. After being introduced into the mutant strain RQ7-15 through natural transformation, both vectors allowed the host to thrive in a minimal medium. Single colonies of transformants were isolated and confirmed by polymerase chain reactions and restriction digestions. In summary, a pyrE-based selective system has been established in T. sp. strain RQ7.