While the role of calcium ions as secondary chemical messengers has been well described in eukaryotic cells, little is known about calcium homeostasis in bacteria at the physiological and molecular level. No calcium influx gene has been identified so far. This dissertation focuses on calcium regulation of gene expression by (i) determining the effects of elevated and depleted calcium levels on global gene expression in wild-type cells (MG1655), (ii) employing transposon mutants (calcium-sensitive) and mutants that are defective in calcium transport, and (iii) performing quantitative analysis of a specific subset of 15 genes to elucidate their possible involvement in calcium transport and homeostasis. The results of the systematic research approach corroborate existing knowledge regarding the involvement of genes ftsZ, atpD, cheB, atoA in calcium regulation. Quantitative real time PCR data revealed very high upregulation of genes yjeE and secA indicating their possible role as overactive calcium efflux systems in E. coli. My data also raises the distinct possibility of calcium's involvement in stress response as evidenced by upregulation of marB in transposon mutants and by 10-fold induction of rpoS in elevated calcium condition in mutants defective in calcium transport. The results also reveal calcium-regulation of yfaD and ybbO, however, their functions are yet unknown. Cumulatively, a comprehensive picture emerges wherein it seems likely that calcium homeostasis represents a dynamic state with hitherto unknown regulatory activity throughout E. coli genome.
Biology, Microbiology, Molecular, Genetics
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