The riddle of the 'green streaks'

C. E. Dobell identified these organisms (in 1932) as Spirogyra, filamentous algae with coiled chloroplasts. In our article we question this identification. Most of the clues in Van Leeuwenhoek's description either do not match or only partly match with Spirogyra.

Among others, Spirogyra is benthic, not planktic in a large lake. It forms floating mats but these are yellow/brown not whitish. Moreover, filaments of Spirogyra are straight and not shaped as a coil, individual cells do not resemble little balls.

A much more likely candidate is Dolichospermum, a genus of planktic cyanobacteria that often form blooms. They create a whitish layer with green clouds on or near the surface of the water. These organisms form filaments shaped as a regular coil, made out of individual cells that look like interconnected little balls. There are several species with regular coils as big as the width of a human hair. In the Netherlands these blooms are still common in lakes rich in fish.

Implication: If Dolichospermum was being described and not Spirogyra, this would make it the first reported microscopical study of bacteria, predating by two years his later description of bacteria in his famous 'pepper water' letter dated October 9th 1676. It would also be the first microscopical study and description of a cyanobacterial bloom.