3 Centre for Microbial Ecology and Genomics, University of Pretoria, 0028, South Africa; Department of Genetics, University of Pretoria, 0028, South Africa. Electronic address: don.cowan@up.ac.za.
4 Centre for Microbial Ecology and Genomics, University of Pretoria, 0028, South Africa; Department of Microbiology, University of Pretoria, 0028, South Africa.