Presentation on theme: "Bacterial response to environment"— Presentation transcript:
1 Bacterial response to environment Rapid response crucial for survivalSimultaneous transcription and translationCoordinate regulation in operons and regulonsGlobal genetic control through modulonsBacteria respondChange from aerobic to anaerobicPresence/absence of glucoseAmount of nutrients in generalPresence of specific nutrientsPopulation size
2 Quorum Sensing Bacteria monitor their own population size Pathogenesis: do not produce important molecules too soon to tip off the immune system.Light production: a few bacteria make feeble glow, but ATP cost per cell remains high.Bacteria form spores when in high numbers, avoid competition between each other.System requirementsA signaling molecule that increases in concentration as the population increases; LMWA receptor; activation of a set of genes
3 Chemotaxis and other taxes Movement in response to environmental stimulusPositive chemotaxis, attraction towards nutrientsNegative: away from harmful chemicalsAerotaxis: motility in response to oxygenPhototaxis: motility to certain wavelengths of lightMagnetotaxis: response to magnetic fieldsTaxis is movementIncludes swimming through liquid using flagellaSwarming over surfaces with flagellaGliding motility, requiring a surface to move over
6 Motility summarizedFlagella: protein appendages for swimming through liquid or across wet surfaces.Axial filament: a bundle of internal flagellaBetween cell membrane and outer membrane in spirochetesFilament rotates, bacterium corkscrews through mediumGlidingNo visible structures, requires solid surfaceSlime usually involved.
8 Gliding Motility Movement on a solid surface. Cells produce, move in slime trails.Cells glide in groups, singly, andcan reverse directions.Unrelated organism glide:myxobacteria, flavobacteria,cyanobacteria;Recent data support polysaccharide synthesis, extrusion model.
9 Starvation Responses Bacteria frequently on verge of starvation Rapid utilization of nutrients by community keeps nutrient supply lowNormal life typical of stationary phaseBacteria monitor nutritional status and adjust through global genetic mechanismsTypes of responsesLower metabolic rates, smaller size (incr surface:volume)Release of extracellular enzymes, scavenging moleculesProduction of resting cells, sporesInduction of low Km uptake systems
10 Type of molecule affects transport Small molecules can pass through a lipid bilayerWater; otherwise, no osmosisGases such as O2 and CO2Lipid molecules canDissolve in lipid bilayer, pass through membraneMany antibiotics, drugs are lipid solubleLarger, hydrophilic molecules cannotIons, sugars, amino acids cannot pass through lipidsTransport proteins required
11 Extracellular molecules EnzymesPolymers cannot enter cellsProteins, starch, cellulose all valuable nutrientsEnzymes produced and released from the cellLMW products taken up; nutrients gathered exceed energy costs.Low molecular weight aidsSiderophores, hemolysins collect ironAntibiotics may slow the growth of competition when nutrients are in short supply
12 Sporulation Resting cells Cells respond to low nutrients by sporulation or slowing down metabolic rate, decr size.Some cells change shape, develop thick coatEndospores form within cells; very resistant.Spores in bacteria generally are for survivalNot reproductionA spore structure protects cells against drying, heat, etc. until better nutrient conditions returnAn inactive cell can’t protect itself well
13 Endospore formationGenetic cascade producing alternative sigma factors.
14 Responses of microbes to other environmental stresses Compatible solutes: small neutral molecules accumulated in cytoplasm when external environment is hypertonic.Heat shock proteins and other stress proteinsBacteria express additional genes that code for protective proteins.