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Stahl, University of Washington Seattle Daniel H. Buckley, Cornell University Kelly S. Bender, Southern Illinois University Carbondale Michael T. Madigan, Southern Illinois University Carbondale John M. Martinko, Southern Illinois University Carbondale productFormatCode=W22 productCategory=16 statusCode=5 isBuyable=false subType= path/ProductBean/courseSmart ISBN-10:. ISBN-13: 30292068398 ©2015. Pearson. Online Published 12 Aug 2014. Live.

LECTURE PRESENTATIONS For BROCK BIOLOGY OF MICROORGANISMS, THIRTEENTH EDITION Michael T. Madigan, John M. Martinko, David A. Stahl, David P. Clark Lectures by John Zamora Middle Tennessee State University © 2012 Pearson Education, Inc.

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Microbial Growth Chapter 5 I. Bacterial Cell Division 5.1Cell Growth and Binary Fission 5.2Fts Proteins and Cell Division 5.3MreB and Determinants of Cell Morphology 5.4Peptidoglycan Synthesis and Cell Division © 2012 Pearson Education, Inc.

5.1 Cell Growth and Binary Fission Growth: increase in the number of cells Binary fission: cell division following enlargement of a cell to twice its minimum size (Figure 5.1) Generation time: time required for microbial cells to double in number During cell division, each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell © 2012 Pearson Education, Inc. Animation: Binary Fission Animation: Binary Fission Animation: Overview of Bacterial Growth Animation: Overview of Bacterial Growth Figure 5.1 Septum Cell elongation Septum formation Completion of septum; formation of walls; cell separation One generation © 2012 Pearson Education, Inc.

5.2 Fts Proteins and Cell Division Fts (filamentous temperature-sensitive) Proteins (Figure 5.2) –Essential for cell division in all prokaryotes –Interact to form the divisome (cell division apparatus) FtsZ: forms ring around center of cell; related to tubulin ZipA: anchor that connects FtsZ ring to cytoplasmic membrane FtsA: helps connect FtsZ ring to membrane and also recruits other divisome proteins –Related to actin © 2012 Pearson Education, Inc. Figure 5.2 Cytoplasmic membrane Outer membrane Cytoplasmic membrane Divisome complex Peptidoglycan FtsZ ring © 2012 Pearson Education, Inc. 5.2 Fts Proteins and Cell Division DNA replicates before the FtsZ ring forms (Figure 5.3) Location of FtsZ ring is facilitated by Min proteins –MinC, MinD, MinE FtsK protein mediates separation of chromosomes to daughter cells © 2012 Pearson Education, Inc. Figure 5.3 Cell wall Min CD Cytoplasmic membrane Nucleoid MinE Divisome complex FtsZ ring Nucleoid Septum MinE Minutes 0 20 40 60 80 © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology Prokaryotes contain a cell cytoskeleton that is dynamic and multifaceted MreB: major shape-determining factor in prokaryotes –Forms simple cytoskeleton in Bacteria and probably Archaea –Forms spiral-shaped bands around the inside of the cell, underneath the cytoplasmic membrane (Figure 5.4a and b) –Not found in coccus-shaped bacteria © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology MreB (cont’d) –Localizes synthesis of new peptidoglycan and other cell wall components to specific locations along the cylinder of a rod-shaped cell during growth © 2012 Pearson Education, Inc. Figure 5.4a Cell wall Cytoplasmic membrane MreB Sites of cell wall synthesis FtsZ © 2012 Pearson Education, Inc.

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Figure 5.4b © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology Crescentin: shape-determining protein produced by vibrio-shaped cells of Caulobacter crescentus –Crescentin protein organizes into filaments 10 nm wide that localize on the concave face of the curved cells (Figure 5.4c) © 2012 Pearson Education, Inc.

Figure 5.4c © 2012 Pearson Education, Inc. 5.3 MreB and Determinants of Cell Morphology Most archaeal genomes contain FtsZ and MreB-like proteins, thus cell morphology is similar to that seen in Bacteria © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Production of new cell wall material is a major feature of cell division –In cocci, cell walls grow in opposite directions outward from the FtsZ ring –In rod-shaped cells, growth occurs at several points along length of the cell © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Preexisting peptidoglycan needs to be severed to allow newly synthesized peptidoglycan to form –Beginning at the FtsZ ring, small openings in the wall are created by autolysins –New cell wall material is added across the openings –Wall band: junction between new and old peptidoglycan © 2012 Pearson Education, Inc. Figure 5.5 FtsZ ring Wall bands Growth zone Septum © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Bactoprenol: carrier molecule that plays major role in insertion of peptidoglycan precursors –C 55 alcohol (Figure 5.6) –Bonds to N-acetylglucosamine/ N-acetylmuramic acid/pentapeptide peptidoglycan precursor © 2012 Pearson Education, Inc. Figure 5.6 Hydrophobic portion © 2012 Pearson Education, Inc.

5.4 Peptidoglycan Synthesis and Cell Division Glycolases: enzymes that interact with bactoprenol (Figure 5.7a) –Insert cell wall precursors into growing points of cell wall –Catalyze glycosidic bond formation © 2012 Pearson Education, Inc. Figure 5.7a Transglycosylase activity Growing point of cell wall Cytoplasmic membrane Autolysin activity Pentapeptide Bactoprenol Peptidoglycan Out In © 2012 Pearson Education, Inc. 5.4 Peptidoglycan Synthesis and Cell Division Transpeptidation: final step in cell wall synthesis (Figure 5.7b) –Forms the peptide cross-links between muramic acid residues in adjacent glycan chains –Inhibited by the antibiotic penicillin © 2012 Pearson Education, Inc. Figure 5.7b Transpeptidation © 2012 Pearson Education, Inc.

Population Growth 5.5The Concept of Exponential Growth 5.6The Mathematics of Exponential Growth 5.7The Microbial Growth Cycle 5.8Continuous Culture: The Chemostat © 2012 Pearson Education, Inc. 5.5 The Concept of Exponential Growth Most bacteria have shorter generation times than eukaryotic microbes Generation time is dependent on growth medium and incubation conditions © 2012 Pearson Education, Inc. 5.5 The Concept of Exponential Growth Exponential growth: growth of a microbial population in which cell numbers double within a specific time interval During exponential growth, the increase in cell number is initially slow but increases at a faster rate (Figure 5.8) © 2012 Pearson Education, Inc. Figure 5.8 Time (h) Logarithmic plot Arithmetic plot Number of cells (arithmetic scale) Number of cells (logarithmic scale) 1000 500 100 0 1 2 3 4 5 1 10 10 2 10 3 © 2012 Pearson Education, Inc.

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5.6 The Mathematics of Exponential Growth A relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth: N = N 0 2 n N is the final cell number N 0 is the initial cell number n is the number of generations during the period of exponential growth © 2012 Pearson Education, Inc. 5.6 The Mathematics of Exponential Growth Generation time (g) of the exponentially growing population is g = t/n t is the duration of exponential growth n is the number of generations during the period of exponential growth © 2012 Pearson Education, Inc.

5.6 The Mathematics of Exponential Growth Specific growth rate (k) is calculated as k = 0.301/g Division rate (v) is calculated as v = 1/g © 2012 Pearson Education, Inc. 5.7 The Microbial Growth Cycle Batch culture: a closed-system microbial culture of fixed volume Typical growth curve for population of cells grown in a closed system is characterized by four phases (Figure 5.10): –Lag phase –Exponential phase –Stationary phase –Death phase © 2012 Pearson Education, Inc. Animation: Bacterial Growth Curve Animation: Bacterial Growth Curve Figure 5.10 Time Log 10 viable organisms/ml Optical density (OD) 10 9 8 7 6 1.0 0.75 0.50 0.25 0.1 Viable count Turbidity (optical density) Lag ExponentialStationaryDeath Growth phases © 2012 Pearson Education, Inc. 5.7 The Microbial Growth Cycle Lag phase –Interval between when a culture is inoculated and when growth begins Exponential phase –Cells in this phase are typically in the healthiest state Stationary phase –Growth rate of population is zero –Either an essential nutrient is used up or waste product of the organism accumulates in the medium © 2012 Pearson Education, Inc. 5.7 The Microbial Growth Cycle Death Phase – If incubation continues after cells reach stationary phase, the cells will eventually die © 2012 Pearson Education, Inc.

5.8 Continuous Culture: The Chemostat Continuous culture: an open-system microbial culture of fixed volume Chemostat: most common type of continuous culture device (Figure 5.11) –Both growth rate and population density of culture can be controlled independently and simultaneously Dilution rate: rate at which fresh medium is pumped in and spent medium is pumped out Concentration of a limiting nutrient © 2012 Pearson Education, Inc. Figure 5.11 Fresh medium from reservoir Sterile air or other gas Flow-rate regulator Gaseous headspace Culture vessel Culture Overflow Effluent containing microbial cells © 2012 Pearson Education, Inc. 5.8 Continuous Culture: The Chemostat In a chemostat –The growth rate is controlled by dilution rate –The growth yield (cell number/ml) is controlled by the concentration of the limiting nutrient In a batch culture, growth conditions are constantly changing; it is impossible to independently control both growth parameters (Figure 5.12) © 2012 Pearson Education, Inc. Figure 5.12 Only yield affected Growth rate ( ) Nutrient concentration (mg/ml) Growth yield ( ) 0 0.1 0.20.30.40.5 Rate and yield affected © 2012 Pearson Education, Inc. 5.8 Continuous Culture: The Chemostat Chemostat cultures are sensitive to the dilution rate and limiting nutrient concentration (Figure 5.13) –At too high a dilution rate, the organism is washed out –At too low a dilution rate, the cells may die from starvation –Increasing concentration of a limiting nutrient results in greater biomass but same growth rate © 2012 Pearson Education, Inc.

Figure 5.13 5 Bacterial concentration Doubling time Doubling time (h) Steady-state bacterial concentration (g/l) Steady state Washout 4 3 2 1 0 0 0.25 0.50.75 1.0 4 6 2 0 Dilution rate (h  1 ) © 2012 Pearson Education, Inc. Measuring Microbial Growth 5.9 Microscopic Counts 5.10 Viable Counts 5.11 Turbidimetric Methods © 2012 Pearson Education, Inc. 5.9 Microscopic Counts Microbial cells are enumerated by microscopic observations (Figure 5.14) –Results can be unreliable © 2012 Pearson Education, Inc. Figure 5.14 Coverslip Ridges that support coverslip To calculate number per milliliter of sample: 12 cells  25 large squares  50  10 3 Number/mm 2 (3  10 2 ) Number/mm 3 (1.5  10 4 ) Number/cm 3 (ml) (1.5  10 7 ) Sample added here. Care must be taken not to allow overflow; space between coverslip and slide is 0.02 mm ( mm. Whole grid has 25 large squares, a total area of 1 mm 2 and a total volume of 0.02 mm 3. Microscopic observation; all cells are counted in large square (16 small squares): 12 cells.

Brock Biology Of Microorganisms 14th

(In practice, several large squares are counted and the numbers averaged.) 1 50 © 2012 Pearson Education, Inc. 5.9 Microscopic Counts Limitations of microscopic counts –Cannot distinguish between live and dead cells without special stains –Small cells can be overlooked –Precision is difficult to achieve –Phase-contrast microscope required if a stain is not used –Cell suspensions of low density (9) –Some have sodium motive force rather than proton motive force © 2012 Pearson Education, Inc. 5.15 Acidity and Alkalinity The internal pH of a cell must stay relatively close to neutral even though the external pH is highly acidic or basic –Internal pH has been found to be as low as 4.6 and as high as 9.5 in extreme acido- and alkaliphiles, respectively © 2012 Pearson Education, Inc. 5.15 Acidity and Alkalinity Microbial culture media typically contain buffers to maintain constant pH © 2012 Pearson Education, Inc. 5.16 Osmotic Effects on Microbial Growth Water activity (a w ): water availability; expressed in physical terms –Defined as ratio of vapor pressure of air in equilibrium with a substance or solution to the vapor pressure of pure water © 2012 Pearson Education, Inc. 5.16 Osmotic Effects on Microbial Growth Typically, the cytoplasm has a higher solute concentration than the surrounding environment, thus the tendency is for water to move into the cell (positive water balance) When a cell is in an environment with a higher external solute concentration, water will flow out unless the cell has a mechanism to prevent this © 2012 Pearson Education, Inc. 5.16 Osmotic Effects on Microbial Growth Halophiles: organisms that grow best at reduced water potential; have a specific requirement for NaCl (Figure 5.25) Extreme halophiles: organisms that require high levels (15–30%) of NaCl for growth Halotolerant: organisms that can tolerate some reduction in water activity of environment but generally grow best in the absence of the added solute © 2012 Pearson Education, Inc.

Example: Staphylococcus aureus Example: Aliivibrio fischeri Example: Halobacterium salinarum Example: Escherichia coli NaCl (%) Growth rate 0 5 10 15 20 Nonhalophile Halotolerant Halophile Extreme halophile Figure 5.25 © 2012 Pearson Education, Inc. 5.16 Osmotic Effects on Microbial Growth Osmophiles: organisms that live in environments high in sugar as solute Xerophiles: organisms able to grow in very dry environments © 2012 Pearson Education, Inc. 5.16 Osmotic Effects on Microbial Growth Mechanisms for combating low water activity in surrounding environment involve increasing the internal solute concentration by –Pumping inorganic ions from environment into cell –Synthesis or concentration of organic solutes compatible solutes: compounds used by cell to counteract low water activity in surrounding environment © 2012 Pearson Education, Inc. 5.17 Oxygen and Microorganisms Aerobes: require oxygen to live Anaerobes: do not require oxygen and may even be killed by exposure Facultative organisms: can live with or without oxygen Aerotolerant anaerobes: can tolerate oxygen and grow in its presence even though they cannot use it Microaerophiles: can use oxygen only when it is present at levels reduced from that in air © 2012 Pearson Education, Inc. 5.17 Oxygen and Microorganisms Thioglycolate broth (Figure 5.26) –Complex medium that separates microbes based on oxygen requirements –Reacts with oxygen so oxygen can only penetrate the top of the tube © 2012 Pearson Education, Inc. Figure 5.26 Oxic zone Anoxic zone © 2012 Pearson Education, Inc.

5.17 Oxygen and Microorganisms Special techniques are needed to grow aerobic and anaerobic microorganisms (Figure 5.27) Reducing agents: chemicals that may be added to culture media to reduce oxygen (e.g., thioglycolate) © 2012 Pearson Education, Inc. Figure 5.27 © 2012 Pearson Education, Inc. 5.18 Toxic Forms of Oxygen Several toxic forms of oxygen can be formed in the cell (Figure 5.28): –Single oxygen –Superoxide anion –Hydrogen peroxide –Hydroxyl radical © 2012 Pearson Education, Inc. Figure 5.28 Reactants Products Outcome: (superoxide) (hydrogen peroxide) (hydroxyl radical) (water) © 2012 Pearson Education, Inc. 5.18 Toxic Forms of Oxygen Enzymes are present to neutralize most of these toxic oxygen species (Figure 5.29) –Catalase (Figure 5.30) –Peroxidase –Superoxide dismutase –Superoxide reductase © 2012 Pearson Education, Inc. Figure 5.29 Peroxidase Catalase Superoxide dismutase Superoxide dismutase/catalase in combination Superoxide reductase © 2012 Pearson Education, Inc.

Figure 5.30 © 2012 Pearson Education, Inc.