In his native country, the Netherlands, Cornelis B. van Niel (1897 – 1985) earned a degree in chemical engineering from the Technological University at Delft. The "Delft School", as it is often called, had an outstanding general and applied microbiology program within the Department of Chemical Technology, chaired in succession by two prominent microbiologists – Martinus Beijerinck and Albert Kluyver.

After earning his degree in 1923, van Niel accepted a position as assistant to Kluyver, caring for an extensive culture collection, and helping prepare demonstrations for lecture courses. Kluyver was relatively new to the school, but he had a vast knowledge of microbiology and biochemistry. Although little was known at the time about metabolic pathways, Kluyver believed that biochemical processes were fundamentally the same in all cells and that microorganisms, which can be grown in pure culture, could serve as an important research tool, serving as a model to study biochemical processes. Thirty years later, Kluyver and van Niel would present lectures that would be published in a book entitled "The Microbes Contribution to Biology". Under Kluyver’s direction, van Niel began studying the photosynthetic activities of vividly colored purple bacteria such as Chromatium species, a subject for which he developed a life-long interest.

Shortly after earning his Ph.D. in 1928, van Niel moved to the United States, bringing with him the intense appreciation for general microbiology that had been fostered at the Delft School. Settling at the Hopkins Marine Station in California, he continued his work on purple photosynthetic bacteria. Using systematic methods, he conclusively showed that the growth of these organisms is light dependant, yet they do not evolve O₂. Furthermore, his experiments showed that in order to incorporate CO₂ into cellular material, these anoxygenic phototrophs oxidize hydrogen sulfide. He noted that the reaction stoichiometry of this process was remarkably similar to that of the photosynthesis of green plants and algae, except hydrogen sulfide was used in place of water, and oxidized sulfur compounds were produced instead of O₂. This finding raised the possibility that O₂ generated by plants did not come from carbon dioxide, as was believed at the time, but rather, from water.

In addition to his scientific contributions, van Niel was recognized as an outstanding teacher. During the summers at Hopkins Marine Station, he taught a bacteriology course, inspiring many microbiologists with his enthusiasm for the diversity of microorganisms and their importance in nature. His keen memory and knowledge of the literature, along with his appreciation for the remarkable abilities of microorganisms, enabled him to successfully impart the awe and wonder of the microbial world to his students.