1. Department of Environmental Science, College of Agriculture and Environmental Science, UNISA, P.O. Box 392, Pretoria, South Africa
2. Microbiology and Environmental Biotechnology Research Group, Institute for Soil, Climate and Water- Agricultural Research Council, Private Bag X79, Pretoria 0001, South Africa
3. Unit for Environmental Science and Management, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom, South Africa