Per Halkjær Nielsen is a Professor in Environmental Biotechnology and heading the Center for Microbial Communities at Aalborg University, Denmark. The main research activities are related to structure and function of microbial communities in engineered ecosystems, primarily related to used water treatment, biological recovery of resources (such as phosphorus) and bioenergy production. Uncultured microorganisms are investigated by various omics methods (metagenomics, metatranscriptomics, metaproteomics and metabolomics) in combination with single cell microbiology, e.g. by using microscopy and tracers. The main focus of his research is on organisms involved in biological P-removal, N-removal and organisms causing foaming and bulking. In addition, he also conducts research on medical microbiology and structure and function of extracellular polymeric substances with main focus on proteins such as functional amyloids.