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Unformatted text preview: Vol. 174,No. 2 MINIREVIEW LifeAfterLog DEBORAH A. SIEGELE AND ROBERTO KOLTER* Department of Microbiology andMolecular Genetics, HarvardMedical School, 200LongwoodAvenue, Boston, Massachusetts 02115 A remarkablefeatureofbacterialspeciesistheircapacity forrapidgrowthwhen nutrientsare availableandconditions are appropriateforgrowth.Perhapseven more remarkable is theirabilitytoremainviableunderconditionsnot propitious forgrowth.Many bacteriahaveevolvedhighlysophisticated mechanisms thatallowthemto maintaincellviabilityduring starvationand resume growth rapidlywhen nutrientsagain becomeavailable.Some speciesformdormant spores, while others form multicellular aggregates and fruiting bodies in response to starvationconditions (26,34).But even without theformation ofsuch elaboratelydifferentiatedcells, many bacteria, among them Escherichia, Salmonella, and Vibrio spp., enter a starvation-induced program that results in a metabolically lessactiveand more resistantstate. Examination of starved cells using light microscopy re- veals changes in cell morphology. Escherichia coli cells become much smallerand almostsphericalwhen theyenter stationary phase (22, 31). This phenomenon is even more striking for a number of marine bacteria which greatly decreaseinsizeduringstarvationandform ultramicrocells, as small as 0.03 ,um3 (28). Ultramicrocells result from cells that undergo several cell divisions without an increase in biomass and thena furtherdecrease intheirsize as a result ofendogenous metabolism. One possible selective advan- tage ofthereductive divisions seen inmarine bacteria is to improve the survivaloftheclonalpopulation by increasing theprobabilitythat some cellswill encounter nutrients(38). InE. coli,these changes incellsizeand shape are accom- panied by changes in the subcellular compartments; the cytoplasm iscondensed and the volume ofthe periplasm increases(48). The surface properties ofstarved cells are also different from those ofgrowing cells. The surface of many marine bacteria becomes increasingly hydrophobic and the cells becomemore adhesiveduringstarvation(28).Changesinthe fattyacidcompositionofthecellmembranes havebeen seen duringstarvationofseveralspecies(28).Forexample, inE. colithereis a conversion of allunsaturatedmembrane fatty acidstothecyclopropylderivativesas cellsenterstationary phase (14). Vibrio sp. strain S14 acquires new fimbraelike structures and forms cellular aggregates or clumps after prolongedstarvation(1).InE. coli,suchstarvation-induced aggregates appear to form as the resultofa self-generated and secreted attractant that is sensed by the chemotaxis machinery (7). Thecellwallsynthesizedduringaminoacidstarvationhas a different structure from the cellwall synthesized during growth(46,56).Thesechangesinstructureappear toprotect cells against the autolysis induced by either penicillin or * Correspondingauthor....
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