Professor Thies began her research career at the NifTAL Project (Nitrogen Fixation in Tropical Agricultural Legumes) in Hawaii where she worked on rhizobial ecology in tropical agricultural systems. She has worked on various aspects of microbial ecology at Oregon State University, the Cooperative Research Centre for Legumes in Mediterranean Agriculture (CLIMA) in Perth, Australia, and at the University of Western Sydney in NSW, Australia. Since coming to Cornell, she has developed a large research program on soil microbial ecology.