Chemotaxis and Other Cell Motility Mechanisms PDF

Chemotaxis best studied in E. coli (peritrichous) “run and tumble” behavior (Figure 2.36) run: smooth forward motion, flagellar motor rotates counterclockwise tumble: stops and jiggles, flagellar motor rotates clockwise, flagellar bundle comes apart move by rotation https:...

Chemotaxis best studied in E. coli (peritrichous) “run and tumble” behavior (Figure 2.36) run: smooth forward motion, flagellar motor rotates counterclockwise tumble: stops and jiggles, flagellar motor rotates clockwise, flagellar bundle comes apart move by rotation https://www.youtube.com/watch?v=PBrxh3N8CuA  Many (e.g., Pseudomonas) can fully reverse flagellar rotation, avoiding tumbling and reversing direction. Some (e.g., Rhodobacter) stop and are affected by Brownian motion. Figure 2.36  Bacteria respond to temporal, not spatial, difference in chemical concentration. Sensory information is fed through an elaborate cascade of proteins that eventually affect the direction of rotation of the flagellar motor. monitor/sample environment with chemoreceptors that sense attractants and repellents  Phototaxis and other taxes Phototaxis using photoreceptors allows phototrophic organisms to optimize position for light harvest. (Figure 2.44a) Scotophobotaxis: Entering darkness causes cell to tumble, reverse direction, head back to light. aerotaxis, osmotaxis, hydrotaxis  Scotophobic accumulation of the phototrophic purple bacterium Thiospirillum jenense at wavelengths of light at which its pigments absorb. Phototaxis of an entire colony of the purple phototrophic bacterium Rhodospirillum centenum. These strongly phototactic cells move in unison toward the light source at the top.  Eukaryotic Microbial Cells Eukaryotes contain a membrane-enclosed nucleus Other organelles include mitochondria, Golgi complex, lysosomes, endoplasmic reticula, microtubules, and microfilaments. (Figure 2.45) Some have motility (flagella or cilia). Some have cell walls. Membranes contain sterols that lend structural strength. Figure 2.45 Features of the Nucleus and Cell Division Nucleus: contains the chromosomes and histones Cell division mitosis (Figure 2.47) normal form of nuclear division in eukaryotic cells results in two diploid (two copies of each chromosome) daughter cells meiosis specialized form of nuclear division results in four haploid (one copy of each chromosome) gametes  Mitochondria, Chloroplasts, and Hydrogenosomes All specialize in energy metabolism. Hydrogenosomes: Present in anaerobic eukaryotic microorganisms which lack mitochondria. The major biochemical reaction in the hydrogenosome oxidation of pyruvate to H2, CO2, and Consumed to acetate. And produce ATP. produce CH4 in methane- Examples: human parasite and producing various protists that inhabit Archaea the rumen of ruminant animals. Excreted  Flagella and cilia organelles of motility that allow cells to move by swimming Cilia are short flagella. structurally distinct from prokaryotic flagella and do not rotate; instead whip (flagella) or beat in synchrony (cilia) bundle of nine pairs of microtubules surrounding a central pair of microtubules Dynein is attached to the microtubules and uses ATP to drive motility. Complex structure Cross section through a flagellum of the fungus Blastocladiella showing the outer sheath, the outer nine pairs of microtubules, and the central pair of microtubules.