MMG301 1st Edition Lecture 16Outline of Last Lecture I. BacteriaOutline of Current Lecture II. Bacterial growthIII. Bacterial divisionIV. Methods to measure bacterial populationsCurrent Lecture-growth: increase in the number of cells – not in the size of individual cells-up to ~2,000 simultaneous biochemical reactions-differentiation: new structures formed as part of the life cycle-binary fission: used by most bacteria; cells elongate in both directions, septum forms when cell is almost twice as long, septum separates cell into 2 identical daughter cells -all cell constituents increase proportionally -generation time varies per species and growth conditions-MinCD: oscillate back and forth under surface of cell; rotate inside cytoplasmic membrane; block FtsZ from binding to the membrane-MinE: antagonist of MinCD; also oscillates; pushes MinCD; is trying to make room for FtsZ-FtsZ ring: assembles into a ring exactly in the center of the cell; can contain up to about 2000 molecules of FtsZ-divisome: synthesizing new cell wall and cytoplasmic membrane while cell is dividing-FtsK: responsible for partitioning DNA in daughter cells; makes sure both daughter cells get sufficient DNA-MreB: gives their shapes to bacteria; forms flat spiral-shaped bands; helix turns to cause cell wall to expand longitudinally onlyThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-new cell wall synthesized-the MreB helix rotates in the cell-MreB distributes cell wall synthesis all along the cell-MreB mutants: coccus-shaped cells-methods to measure bacterial populations-1. direct microscope count: the Petrov-Hausser counting chamber-advantages: quick, direct, can be linked to computer and image analysis-disadvantages: counts both living and dead cells, population must exceed ~106 cells per ml-2. turbidimetric (light scattering) methods-use a spectrophotometer to measure light scattered by bacteria-advantages: quick-disadvantages: counts live and dead cells; inaccurate below 106 cells per ml-3. Viable cell count by plating-advantages: counts only live cells, very sensitive-disadvantages: material and time consuming, expensive-over 99% of bacteria in nature are viable but non-culturable: plate counts will underestimate the full microbial population and diversity in many natural samples-still gives the best estimate of viable cells in a sample, widely used-4. viable cell count by filtration-for very low population densities-advantages: very sensitive, measures only live cells, large sample sizes (very dilute samples), little preparation-disadvantages: incubation takes time-uses: Water
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