Cell biology of bacterial sensory modules.

Despite their small size, bacterial cells possess very efficient sensory apparatus that allow them to perceive and respond to the external environment with cell movement. In enteric bacteria, these apparatus are complex lattices of different chemoreceptors working in concert and forming clusters positioned at the cell poles. Since the study of chemotaxis has been expanded to other bacterial species, examples of chemosensory systems regulating functions different than taxis have been described and chemoreceptors localizing in ways divergent from the enteric paradigm have been visualized. The scope of this review is to revise and summarize the architecture of different bacterial chemoreceptors. Then, hypotheses will be proposed on how chemoreceptor distribution in cells is coupled to specific functions and life styles in well-characterized bacterial model systems, such as Escherichia coli, Rhodobacter sphaeroides, Caulobacter crescentus and Myxococcus xanthus.