PowerPoint ® Lecture Presentations prepared by Mindy Miller-Kittrell, North Carolina State University C H A P T E R © 2014 Pearson Education, Inc. 6 Microbial Nutrition and Growth

© 2014 Pearson Education, Inc. Growth Requirements Microbial growth Increase in a population of microbes Due to reproduction of individual microbes Result of microbial growth is discrete colony An aggregation of cells arising from single parent cell

© 2014 Pearson Education, Inc. Growth Requirements Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures Most common nutrients contain necessary elements such as carbon, oxygen, nitrogen, and hydrogen Microbes obtain nutrients from variety of sources

© 2014 Pearson Education, Inc. Growth Requirements Nutrients: Chemical and Energy Requirements Sources of carbon, energy, and electrons Two groups of organisms based on source of carbon Autotrophs Heterotrophs Two groups of organisms based on source of energy Chemotrophs Phototrophs

© 2014 Pearson Education, Inc. Figure 6.1 Four basic groups of organisms based on their carbon and energy sources.

© 2014 Pearson Education, Inc. Growth Requirements Nutrients: Chemical and Energy Requirements Sources of carbon, energy, and electrons Two groups of organisms based on source of electrons Organotrophs Lithotrophs

© 2014 Pearson Education, Inc. Growth Requirements Nutrients: Chemical and Energy Requirements Oxygen requirements Oxygen is essential for obligate aerobes Oxygen is deadly for obligate anaerobes How can this be true? Toxic forms of oxygen are highly reactive and excellent oxidizing agents Resulting oxidation causes irreparable damage to cells

© 2014 Pearson Education, Inc. Growth Requirements Nutrients: Chemical and Energy Requirements Oxygen requirements Four toxic forms of oxygen Singlet oxygen Superoxide radicals Peroxide anion Hydroxyl radical

© 2014 Pearson Education, Inc. Growth Requirements Nutrients: Chemical and Energy Requirements Nitrogen requirements Anabolism often ceases due to insufficient nitrogen Nitrogen acquired from organic and inorganic nutrients All cells recycle nitrogen from amino acids and nucleotides Nitrogen fixation by certain bacteria is essential to life on Earth

© 2014 Pearson Education, Inc. Growth Requirements Nutrients: Chemical and Energy Requirements Other chemical requirements Phosphorus Sulfur Trace elements Only required in small amounts Growth factors Necessary organic chemicals that cannot be synthesized by certain organisms

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Growth Requirements Physical Requirements Temperature Temperature affects three-dimensional structure of proteins Lipid-containing membranes of cells and organelles are temperature sensitive If too low, membranes become rigid and fragile If too high, membranes become too fluid

© 2014 Pearson Education, Inc. Figure 6.5 Four categories of microbes based on temperature ranges for growth.

© 2014 Pearson Education, Inc. Growth Requirements Physical Requirements pH Organisms sensitive to changes in acidity H + and OH – interfere with H bonding Neutrophiles grow best in a narrow range around neutral pH Acidophiles grow best in acidic habitats Alkalinophiles live in alkaline soils and water

© 2014 Pearson Education, Inc. Growth Requirements Physical Requirements Physical effects of water Microbes require water to dissolve enzymes and nutrients Water is important reactant in many metabolic reactions Most cells die in absence of water Some have cell walls that retain water Endospores and cysts cease most metabolic activity Two physical effects of water Osmotic pressure Hydrostatic pressure

© 2014 Pearson Education, Inc. Growth Requirements Physical Requirements Physical effects of water Osmotic pressure Pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross membrane Hypotonic solutions have lower solute concentrations Cell placed in hypotonic solution swells Hypertonic solutions have greater solute concentrations Cell placed in hypertonic solution shrivels Restricts organisms to certain environments Obligate and facultative halophiles

© 2014 Pearson Education, Inc. Growth Requirements Physical Requirements Physical effects of water Hydrostatic pressure Water exerts pressure in proportion to its depth Barophiles live under extreme pressure Their membranes and enzymes depend on pressure to maintain their three-dimensional, functional shape

© 2014 Pearson Education, Inc. Growth Requirements Associations and Biofilms Biofilms Complex relationships among numerous microorganisms Form on surfaces, medical devices, mucous membranes of digestive system Form as a result of quorum sensing Many microorganisms more harmful as part of a biofilm Scientists seeking ways to prevent biofilm formation

© 2014 Pearson Education, Inc. Figure 6.7 Biofilm development. Free-swimming microbes are vulnerable to environmental stresses. Bacteria Some microbes land on a surface, such as a tooth, and attach. The cells begin producing an intracellular matrix and secrete quorum-sensing molecules. Quorum sensing triggers cells to change their biochemistry and shape. New cells arrive, possibly including new species, and water channels form in the biofilm. Some microbes escape from the biofilm to resume a free-living existence and perhaps, form a new biofilm on another surface. Chemical structure of one type of quorum- sensing molecule Matrix Water flow Water channel Escaping microbes

© 2014 Pearson Education, Inc. Culturing Microorganisms Obtaining Pure Cultures Cultures composed of cells arising from a single progenitor Progenitor is termed a colony-forming unit (CFU) Aseptic technique prevents contamination of sterile substances or objects Two common isolation techniques Streak plates Pour plates

© 2014 Pearson Education, Inc. Culturing Microorganisms Obtaining Pure Cultures Other isolation techniques Some fungi isolated with streak and pour plates Protozoa and motile unicellular algae isolated through dilution of broth cultures Can individually pick single cell of some large microorganisms and use to establish a culture

© 2014 Pearson Education, Inc. Culturing Microorganisms Culture Media Majority of prokaryotes have not been grown in culture medium Agar is a common addition to many media Six types of general culture media Defined media Complex media Selective media Differential media Anaerobic media Transport media

© 2014 Pearson Education, Inc. Culturing Microorganisms Preserving Cultures Refrigeration Stores for short periods of time Deep-freezing Stores for years Lyophilization Stores for decades

© 2014 Pearson Education, Inc. Binary Fission PLAY

© 2014 Pearson Education, Inc. Cytoplasmic membrane Chromosome Cell wall Replicated chromosome Septum Completed septum 30 minutes 60 minutes 90 minutes 120 minutes Septum Figure 6.17 Binary fission.

© 2014 Pearson Education, Inc. Growth of Microbial Populations Generation Time Time required for a bacterial cell to grow and divide Dependent on chemical and physical conditions

© 2014 Pearson Education, Inc. Figure 6.20 A typical microbial growth curve.

© 2014 Pearson Education, Inc. Growth of Microbial Populations Continuous Culture in a Chemostat Chemostat used to maintain a microbial population in a particular phase of growth Open system Requires addition of fresh medium and removal of old medium Used in several industrial settings

© 2014 Pearson Education, Inc. Growth of Microbial Populations Measuring Microbial Reproduction Direct methods not requiring incubation Microscopic counts

© 2014 Pearson Education, Inc. Growth of Microbial Populations Measuring Microbial Reproduction Direct methods not requiring incubation Electronic counters Coulter counters Flow cytometry

© 2014 Pearson Education, Inc. Growth of Microbial Populations Measuring Microbial Reproduction Direct methods requiring incubation Serial dilution and viable plate counts Membrane filtration Most probable number

© 2014 Pearson Education, Inc. 1 ml of original culture 9 ml of broth + 1 ml of original culture 0.1 ml of each transferred to a plate Incubation period 1.0 ml 1:10 dilution (10 -1 ) Too numerous to count (TNTC) TNTC 65 colonies6 colonies 0 colonies 1:100 dilution (10 -2 ) 1:1000 dilution (10 -3 ) 1:10,000 dilution (10 -4 ) 1:100,000 dilution (10 -5 ) 1.0 ml 0.1 ml Figure 6.23 A serial dilution and viable plate count for estimating microbial population size.

© 2014 Pearson Education, Inc. Growth of Microbial Populations Measuring Microbial Growth Indirect methods Turbidity

© 2014 Pearson Education, Inc. Growth of Microbial Populations Measuring Microbial Growth Indirect methods Metabolic activity Dry weight Genetic methods Isolate DNA sequences of unculturable prokaryotes