LIGHT-INDUCED MOTILITY OF THERMOPHILIC SYNECHOCOCCUS ISOLATES FROM OCTOPUS SPRING, YELLOWSTONE-NATIONAL-PARK

This study demonstrates light-induced motility of two thermophilic Syn echococcus isolates that are morphologically similar but that belong t o different cyanobacterial lineages. Both isolates migrated away from densely inoculated streaks to form fingerlike projections extending to ward or away from the light source, depending on the light intensity. However, the two isolates seemed to prefer widely different light cond itions. The behavior of each isolate was controlled by several factors , including temperature, preacclimation of inocula, acclimation during the experiment, and strain-specific genetic preferences for different light conditions (adaptation). Time-lapse microscopy confirmed that t hese projections were formed by actively gliding cells and were not si mply the outcome of directional cell division. The observed motility r ates of individual cells of 0.1 to 0.3 mu m s(-1) agreed well with the distance traversed by the projections, 0.3 to 0.5 mm h(-1), suggestin g that most cells in each projection are travelling in the same direct ion. The finding of motility among two phylogenetically unaffiliated u nicellular cyanobacteria suggests that this trait may be widespread am ong this group. If so, this would have important implications for expe riments on colonization, succession, diel positioning, and photosynthe tic activity in hot spring mats dominated by Synechococcus-like cyanob acteria.