Speculation and hoopla: Is diversity expected in cyanobacterial circadian timing systems?

Abstract

Cyanobacteria are an extremely diverse group of photoautotrophic prokaryotes. Synechococcus elongatus PCC 7942 has become the model cyanobac-terium for biological research directed at understanding the circadian timing mechanism and its central role in prokaryote circadian biology. Working primarily with S. elongatus, genetic and biochemical experimentation over the past two decades has identified the key components (and their functions) of a fascinating circa-dian timing mechanism. Of course, many basic questions remain regarding cyanobacterial circadian biology. Among those questions: is there a model system that can accurately represent such a diverse group of organisms? As a first step toward addressing that question, this chapter introduces several aspects of cyano-bacterial diversity and then discusses the similarities and differences among likely circadian clock protein components from 39 different species of cyanobacteria. Although sound conclusions remain elusive, the information within the chapter should at least serve as a reminder to interpret model system data within the biological context under which it was determined. Ecology and evolutionary history are always important components of understanding molecular biological data.