Cell biology of micro-organisms and the evolution of the eukaryotic cell

Abstract

A comparative or evolutionary approach is a powerful addition to the cell biologist's armory. It can provide context for observations in more classical model systems; it can elucidate the forces shaping the morphology, organization, and complexity of the cell; and it can identify new phenomena that may eventually be recognized as crucial to how cells work. Over the past 15 years, genome sequencing has facilitated comparative work in microbial eukaryotes, while advances in cellular imaging technologies have opened up prokaryotes as models for the study of cell biology. At the 2011 ASCB meeting, the Minisymposium entitled “Cell Biology of Micro-organisms and the Evolution of the Eukaryotic Cell” highlighted mechanisms that underpin the evolution of complexity in cells, described new and unexpected microbial cellular phenomena, and reported the development of technologies that will allow us to explore new avenues in the study of microbial cells. The session began with the theme of eukaryotic cell evolution and emergent complexity. Using a combination of comparative genomics and structural modeling Fred Mast (University of Alberta) described an evolutionary model for how multiple organellar cargoes compete for transport by myosin V (Mast et al., 2011 ). Aaron Turkewitz (University of Chicago) extended this theme by discussing evidence that evolutionary diversification of the Rab family of small GTPases scales with increasing complexity of cellular membrane trafficking and compartmentalization (Bright et al., 2010 ). Mark Slabodnick (University of California, San Francisco) concluded the session's presentations on unicellular eukaroytes with his progress report on the development of new molecular tools to study cell division and regeneration in the giant ciliate, Stentor. The second half of the minisymposium centered on the biology of bacterial cells, and began with Alex Valm (Marine Biological Laboratory–Woods Hole), who described an exciting new fluorescence imaging method. Combinatorial labeling and spectral imaging fluorescence in situ hybridization (CLASI-FISH) uses dozens of combinations of fluorescent probes that provide an unprecedented look at the spatial composition of complex bacterial cell communities (Valm et al., 2011 ). Joel Kralj (Harvard University) reported the development of a voltage-sensitive fluorescent protein known as the proteorhodopsin optical proton sensor (PROPS). Expression of PROPS in Escherichia coli revealed unexpected, high-frequency electrical spiking (Kralj et al., 2011 ) that coincided with efflux of a small fluorophore from the cell. The results of these studies suggest that some bacterial cell efflux processes may be electrically regulated. Finally, Sean Crosson (University of Chicago) described recent data on molecular and genetic determinants of cell cycle control and cell differentiation in the bacterium Caulobacter crescentus. These studies have defined how the broadly conserved regulatory molecules guanosine tetraphosphate and inorganic polyphosphate link nutrient limitation to cell differentiation at the G1–S cell cycle transition in a bacterial cell (Boutte et al., 2012 ). All of these talks make us rethink our ideas about “normal” cell biology and awakened us to the “endless forms most beautiful and most wonderful” into which the cell has evolved.