Cell aggregation of the cyanobacterium Synechococcus elongatus: Role of the electron transport chain

Cell aggregation, the formation of irregular clusters of individual cells o r filaments, is frequently observed in many cyanobacterial species. The mec hanism(s) and potential causes of cell aggregation were studied in a thermo philic strain of the unicellular cyanobacterium Synechococcus elongatus Nag . We found that cell aggregation occured as the natural response of a healt hy, well-growing culture to a sudden increase in irradiance, We propose tha t aggregation represents a fast (time scale in minutes), light-adapting mec hanism, affected by both light quality and the presence of substances alter ing photosynthetic electron transfer. Our data suggest an involvement of el ectron transfer downstream of PSI, with reactive oxygen species triggering the signal, Aggregation was an ATP-independent process and did not require de novo protein synthesis. We suggest a specific role of glutathione in thi s process based on its ability to induce aggregation in the dark.