van Niel, C. B

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van Niel, C. B.

Dutch Microbiologist and Educator 1897-1985

Cornelis Bernardus van Niel was a Dutch microbiologist whose experiments with bacteria helped explain how photosynthesis occurs in plants. Sulfur bacteria particularly interested van Niel, because there was a controversy in the early 1900s concerning the bacteria. Scientists were not sure if the bacteria got their energy from chemicals in their environment or from sunlight. They knew that the bacteria used sulfur compounds and did take in carbon dioxide to create more complex carbon compounds, and van Niel wanted to determine which energy source the bacteria used to do this.

One problem was that previous scientists had usually studied cultures of bacteria that contained several different species. They knew that the bacteria needed light and also needed and stored sulfur compounds, but the interactions between different species in the cultures made experimentation difficult. Van Niel decided he would have to do his work on pure cultures. He began the labor of isolating and studying pure cultures of purple and green sulfur bacteria in the Netherlands and he continued this work after he transferred to the Hopkins Marine Station in California, in 1929.

Van Niel carefully examined his cultures, using very specific growing conditions. He measured as accurately as possible the amounts of carbon, sulfur, and other chemicals that the bacteria used up or released. In this way, he saw that in the light, the amount of carbon dioxide the bacteria could convert into other carbon compounds depended precisely on how much hydrogen sulfide was available. He worked out a formula for this bacterial photosynthesis and he noticed it was very similar to the formula known for plant photosynthesis. The only difference was that the bacteria used hydrogen sulfide in the reaction where plants used water, and the bacteria produced sulfur compounds where the plants produced oxygen. This led him to make a general formula for the reactions of photosynthesis in both bacteria and plants that is still used today.

The most striking part of van Niel's ideas about photosynthesis was that light was used to split water or hydrogen sulfide. The energy and hydrogen released would then be used to reduce carbon dioxide into more complex compounds. This was new and interesting at the time, because it meant that the oxygen given off by plants during photosynthesis came from the split water molecule, and not from carbon dioxide as previously thought. Later researchers confirmed van Niel's theory by doing experiments using heavy isotopes of oxygen to label the oxygen and observe its origins in photosynthesis. Van Niel's research originated the study of the electron transport chain involved in transferring the energy in photosynthesis.

Other van Niel studies became the foundation for studying bacterial evolution and for the classification of organisms as prokaryotes or eukaryotes. Van Niel died in 1985.

see also Photosynthesis, Light Reactions and; Physiologist; Physiology; Physiology, History of.

Jessica P. Penney