microbiology

Theodor Wilhelm Engelmann was a German microbiologist whose 1882 experiment measured the effects of different colors of light on photosynthetic activity and showed that the conversion of light energy to chemical energy took place in the chloroplast. In 1881, he observed the movement of bacteria towards the chloroplasts in a strand of “Spirogyra” algae. Engelmann hypothesized that the bacteria were moving in response to oxygen generated by the photo synthetically active chloroplasts in the algae. This was one of the first documented observations of positive aero taxis in bacteria. In 1882, he performed his famous action spectrum experiment using a device designed and built by Carl Zeiss. The modified microscope had a prism which could produce a microscopic spectrum on a microscope slide. The device could also distinguish and measure different wavelengths of light making it a “micro-spectroscope.” Engelmann used this device to illuminate a strand of Cladophora with light from the visible spectrum, exposing different sections to different wavelengths. He added the oxygen seeking bacteria B. termo to this setup and noted where they accumulated. Their clumping allowed him to see which regions had the highest concentration of oxygen. He concluded that the most photo synthetically active regions will have the highest concentrations of bacteria. The bacteria accumulated in the regions of red and blue light, showing that these wavelengths of light generated the most photosynthetic activity. However, his experiment was somewhat flawed because he used the sun as his light source. He failed to account for the fact that the sun does not emit all visible wavelengths of light at the same intensity. However, further analysis of plant pigments proved that his results were valid. A year later Engelmann discovered that purple bacteria utilize ultraviolet light in the same way. In 1883, Thomas Engelmann devised an experiment to learn which wavelengths of light were the most effective