Interactive image analysis system to determine the motility and velocity of cyanobacterial filaments.

An interactive image analysis system has been developed to analyse and quantify the percentage of motile filaments and the individual linear velocities of organisms. The technique is based on the "difference" image between two digitized images taken from a time-lapse video recording 80 s apart which is overlaid on the first image. The bright lines in the difference image represent the paths along which the filaments have moved and are measured using a crosshair cursor controlled by the mouse. Even short exposure to solar ultraviolet radiation strongly impairs the motility of the gliding cyanobacterium Phormidium uncinatum, while its velocity is not likewise affected. These effects are not due to either type I (free radical formation) or type II (singlet oxygen production) photodynamic reactions, since specific quenchers and scavengers, indicative of these reactions, failed to be effective.