It has become increasingly clear that bacterial cells are highly organized with many ultrastructural similarities to eukaryotic cells. In addition to a dynamic cytoskeleton composed of homologues of actin, tubulin and intermediate filaments, many bacteria also possess intracellular membranous organelles. The Komeili lab uses magnetosomes as a model system for studying the molecular mechanisms of organelle biogenesis and maintenance in bacteria.
The magnetosome chains of magnetotactic bacteria are one of the best-studied examples of membranous bacterial organelles. Magnetosome chains (see figure to the right) contain 15-20 approximately 50-nm magnetite crystals that act like the needle of a compass to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic environments. The unique properties of magnetosomal magnetite crystals have drawn attention to their potential use in biotechnology, bioremediation, and geobiology and have made them a genetically tractable system for the study of biomineralization. In addition to these applications, the cell biological characteristics of magnetosomes make them ideal for the study of organelle biology in bacteria. Each magnetite crystal within a magnetosome is surrounded by a lipid bilayer, and specific soluble and transmembrane proteins are sorted to the magnetosome membrane. These results suggest that to build a magnetosome a bacterium must be able to generate a membranous comparmtent, target the appropriate set of proteins to this membrane and control their number and position within a cell.
The Komeili Lab uses a combination of cell biological, genetic and biochemical approaches to define the physical characteristics of the magnetosome and identify key genes involved in controlling its production and function. Their earlier work showed that the magnetosome membrane is an independent organelle that pre-exists the formation of magnetite and that magnetite synthesis proceeds simultaneously from multiple adjacent magnetosomes. Recently, the work of several groups including theirs has led to the identification of a large genomic region with many genes encoding proteins that are localized to the magnetosome and are essential for magnetite formation. The challenge now is to understand the specific functions of these genes and how their products interact to form a magnetosome.
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A microscopy expert at UC Berkeley has won a grant to purchase an amazingly powerful new microscope that will enable scientists to study the tiniest of organisms. The new $600,000 instrument, purchased with a National Institutes of Health grant, is a "Structured Illumination Microscope" that allows researchers to image and differentiate different parts of a cell, using different fluorescent dyes.