Investigating and managing the nitrogen cycle in soil and water was the key focus for Prof. Eppe Mulder’s research. He had established the essential role of molybdenum in the nitrogen-fixing capacity of Rhizobium and continued, together with his PhD fellows, research on how plants and rhizobium bacteria collaborate and communicate in acquiring their nitrogen-fixing capacity.
Alternative to chemical fertilizers
Dr Li Tek An, who obtained his PhD in 1964, built up an impressive and valuable Rhizobium mutant collection that formed the basis for later insights into plant-microbe communication. His applied research, on nodule formation in peas and other leguminosa, later led to the establishment of (what we would now call) a spin-off company, in Bolivia, which provided Rhizobium bacteria to people who could not afford chemical fertilizers. His colleague Jan Woldendorp – who later became director of the Netherlands Institute of Ecology (NIOO) – obtained his PhD on denitrification in the rhizosphere, the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. This undesired conversion can lead to large nitrogen losses in agricultural soils.
Work on the nitrogen cycle was further advanced by Dr Antoon Akkermans who continued the work on microbes, notably Frankia spp., that could fix nitrogen in trees such as Alnus. Later, he laid the foundations for the field of Microbial Molecular Ecology, by applying DNA-based technologies to microbes in natural environments.