Calcium Signaling in Prokaryotes

Abstract

Calcium (Ca 2+ ) functions as a universal messenger in eukaryotes and regulates many intracellular processes such as cell division and gene expression. However, the physi- ological role of Ca 2+ in prokaryotic cells remains unclear. Indirect evidence suggests that Ca 2+ is involved in a wide variety of bacterial cellular processes including membrane transport mechanisms (channels, primary and secondary transporters), chemotaxis, cell division and cell differentiation processes such as sporulation and heterocyst formation. In addition, Ca 2+ signaling has been implicated in various stages of bacterial infections and host-pathogen interactions. The most significant discovery is that similar to eukary - otic cells, bacteria always maintain very low cytosolic free Ca 2+ , even in the presence of millimolar extracellular Ca 2+ . Furthermore, Ca 2+ transients are produced in response to stimuli by several agents. Transport systems, which may be involved in Ca 2+ homeostasis are present in bacteria but none of these have been examined critically. Ca 2+ -binding proteins have also been identified, including proteins with EF motifs but their role as intracellular Ca 2+ targets is elusive. Genomic studies indicate that changes in intracellular Ca 2+ up and downregulate hundreds of genes and proteins suggesting a physiological role. This chapter presents an overview of the role of Ca 2+ in prokaryotes summarizing recent developments.