UC Berkeley

Despite their diminutive size and seemingly simple construction, bacteria lead remarkably complex lives. In order to fulfill their biological roles of growth and reproduction, they must integrate a wealth of information about their environment and, depending upon the suitability of the available conditions for survival, they can act to relocate themselves to more preferred locales. Doing so requires that bacteria be able to sense environmental stimuli and relay signals induced by those stimuli to various locomotive apparatuses. Once a cell has fulfilled its nutrient quota to support replication, cell division can occur. Cell division is also intricately timed and regulated in bacterial cells, which are now known to possess intracellular organization, cytoskeletal features, and, in some species, compartmentalization. Therefore, division of a bacterial cell must coordinate disassembly, reassortment, and segregation of these cell biological features. In this work, I investigate the connection between the cell cycle and bacterial organelle formation in the magnetotactic bacterium Magnetospirillum magneticum AMB-1. Magnetotactic bacteria, including AMB-1, are defined by their ability to synthesize chains of intracellular membrane-bounded magnetic minerals, which facilitate bacterial alignments with and responses to geomagnetic fields. To determine the role of the cell cycle in governing the production of these bacterial organelles, called magnetosomes, I disrupted homologs of regulatory factors known to control the progression of the cell cycle as well as polar organelle development in related Alphaproteobacteria. Surprisingly, mutants in the CtrA regulatory pathway were viable, indicating alternative mechanisms of cell cycle progression in AMB-1; in addition, magnetosome formation was also unaffected. Notably, motility was the only feature of AMB-1 disrupted by the CtrA pathway mutations. While subsequent studies to probe upstream regulators of motility in AMB-1 failed to yield additional insight, my results suggest a terminal role for CtrA in the transcription of flagellar biosynthesis genes. This role appears to be ancestral in the Alphaproteobacteria. Further, I have developed protocols which should enable future investigations of the cell cycle in AMB-1 and the temporal changes in gene expression which allow its progression. Preliminary studies indicate that genes involved in signal transduction and possibly magnetosome membrane formation vary their expression throughout the AMB-1 cell cycle. Continued investigation of the connections between the CtrA pathway, magnetosome gene expression, and the cell cycle may elucidate regulation of motility in magnetotactic bacteria and illustrate novel mechanisms of cell cycle progression in these unique organisms.