Abstract: The present invention relates to the field of molecular biology and genetic tool development in thermophilic bacteria. In particular, it relates to the use of positive and/or negative selection markers that can be used to efficiently select modified strains of interest. By providing such capabilities, the disclosed invention facilitates the recycling of genetic markers in thermophilic bacterial host cells. The present invention also allows the creation of unmarked strains. The genetic tools disclosed in the present invention are prerequisites for making targeted higher order mutations in a single thermophilic strain background.