Jim Prosser is a microbial ecologist who has made significant contributions to our understanding of the diversity and ecosystem function of microorganisms in natural environments. He studied Microbiology at Queen Elizabeth College, London and obtained a PhD at the University of Liverpool, under the supervision of Professor Tim Gray. After postdoctoral research he moved to the University of Aberdeen, where is Professor of Environmental Microbiology. A major focus of his research has been the ecology of soil ammonia oxidising bacteria and archaea, which significantly reduce the efficiency of nitrogen fertilisers and generate greenhouse gases. His research has determined links between the remarkably high diversity of soil ammonia oxidisers and their ecosystem function and he has demonstrated niche specialisation and differentiation in bacterial and archaeal ammonia oxidisers. Jim’s research exploits laboratory experimental systems to test ecological concepts and he has developed molecular techniques for characterisation of the diversity and activities of complex communities of microorganisms, most of which cannot be cultivated. In 2013 he received an OBE for services to environmental science.