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English: Possible roles of calcium in bacteria
Calcium (Ca2+) functions as a universal messenger in eukaryotes and regulates many intracellular processes such as cell division and gene expression. However, the physiological role of Ca2+ in prokaryotic cells remains unclear. Indirect evidence suggests that Ca2+ 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, Ca2+ signaling has been implicated in various stages of bacterial infections and host-pathogen interactions. The most significant discovery is that similar to eukaryotic cells, bacteria always maintain very low cytosolic free Ca2+, even in the presence of millimolar extracellular Ca2+. Furthermore, Ca2+ transients are produced in response to stimuli by several agents. Transport systems, which may be involved in Ca2+ homeostasis are present in bacteria but none of these have been examined critically. Ca2+-binding proteins have also been identified, including proteins with EF motifs but their role as intracellular Ca2+ targets is elusive. Genomic studies indicate that changes in intracellular Ca2+ up and downregulate hundreds of genes and proteins suggesting a physiological role.