Microbiology Chapter 6 Microbial Nutrition and Growth 2018

Microbiology Chapter 6 Microbial Nutrition and Growth © 2018 Pearson Education, Inc.

Growth Requirements • Microbial growth • Increase in a population of microbes • Due to reproduction of individual microbes • Results of microbial growth • Discrete colony—an aggregation of cells arising from single parent cell • Biofilm—collection of microbes living on a surface in a complex community © 2018 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. © 2018 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 © 2018 Pearson Education, Inc.

Figure 6. 1 Four basic groups of organisms based on their carbon and energy sources. © 2018 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. © 2018 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 © 2018 Pearson Education, Inc.

Growth Requirements • Nutrients: Chemical and Energy Requirements • Oxygen requirements • Many organisms can live in various oxygen concentrations • Aerobes • Anaerobes • Facultative anaerobes • Aerotolerant anaerobes • Microaerophiles © 2018 Pearson Education, Inc.

Figure 6. 2 Using a liquid thioglycolate growth medium to identify the oxygen requirements of organisms. © 2018 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 for amino acids and nucleotides. Nitrogen fixation by certain bacteria is essential to life on Earth. © 2018 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 © 2018 Pearson Education, Inc.

Growth Requirements • Physical Requirements • 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. © 2018 Pearson Education, Inc.

Figure 6. 3 The effects of temperature on microbial growth. © 2018 Pearson Education, Inc.

Figure 6. 4 Five categories of microbes based on temperature ranges for growth. © 2018 Pearson Education, Inc.

Figure 6. 5 An example of a psychrophile. © 2018 Pearson Education, Inc.

Growth Requirements • Physical Requirements • p. H • Organisms sensitive to changes in acidity • Hydrogen ions interfere with H bonding. • Neutrophiles grow best in a narrow range around neutral p. H. • Acidophiles grow best in acidic habitats. • Alkalinophiles live in alkaline soils and water. © 2018 Pearson Education, Inc.

Growth 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 © 2018 Pearson Education, Inc.

Growth Requirements • Physical effects of water • Osmotic pressure • Pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross the 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 © 2018 Pearson Education, Inc.

Growth 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. © 2018 Pearson Education, Inc.

Growth Requirements • Associations and Biofilms • Organisms live in association with different species: • Antagonistic relationships • Synergistic relationships • Symbiotic relationships © 2018 Pearson Education, Inc.

Growth Requirements • Associations and 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 © 2018 Pearson Education, Inc.

Culturing Microorganisms • Inoculum introduced into medium • Environmental specimens • Clinical specimens • Stored specimens • Culture • Act of cultivating microorganisms or the microorganisms that are cultivated © 2018 Pearson Education, Inc.

Figure 6. 8 Characteristics of bacterial colonies. © 2018 Pearson Education, Inc.

Table 6. 2 Clinical Specimens and the Methods Used to Collect Them © 2018 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 © 2018 Pearson Education, Inc.

Figure 6. 9 The streak-plate method of isolation. © 2018 Pearson Education, Inc.

Figure 6. 10 The pour-plate method of isolation. © 2018 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 © 2018 Pearson Education, Inc.

Culturing Microorganisms • Culture Media • Majority of prokaryotes have not been grown in culture medium • Variety of liquid and solid media used to culture microbes • Nutrient broth is a common liquid medium. • Agar is a common addition to make media solid. • Used to make Petri plates and slant tubes © 2018 Pearson Education, Inc.

Figure 6. 11 Slant tubes containing solid media. © 2018 Pearson Education, Inc.

Culturing Microorganisms • Culture Media • Six types of general culture media: • • • Supportive media Selective media Differential media Enrichment media Anaerobic media Transport media © 2018 Pearson Education, Inc.

Culturing Microorganisms • Culture Media • Supportive Media • Supports growth of a wide variety of microorganisms • Useful when nutritional needs of an organism are unknown • Selective media • Contain substances that favor or inhibit growth of particular microorganisms © 2018 Pearson Education, Inc.

Figure 6. 12 An example of the use of a selective medium. © 2018 Pearson Education, Inc.

Culturing Microorganisms • Culture Media • Selective media • Enrichment culture • Selective medium used to increase small numbers of a microbe to observable levels • Cold enrichment • Enrich a culture with cold-tolerant species. © 2018 Pearson Education, Inc.

Figure 6. 13 The use of blood agar as a differential medium. © 2018 Pearson Education, Inc.

Figure 6. 14 The use of carbohydrate utilization tubes as differential media. © 2018 Pearson Education, Inc.

Figure 6. 15 The use of Mac. Conkey agar as a selective and differential medium. © 2018 Pearson Education, Inc.

Culturing Microorganisms • Culture Media • Transport media • Used by health care personnel to ensure clinical specimens are not contaminated and to protect people from infection • Rapid transport of samples is important. © 2018 Pearson Education, Inc.

Culturing Microorganisms • Special Culture Techniques • Techniques developed for culturing microorganisms • Animal and cell culture • Used when artificial media is inadequate • Viruses only grow within living cells. • Low-oxygen culture • Carbon dioxide incubators mimic the environment of certain body tissues. • Candle jars create environment with low oxygen and high CO 2 levels. © 2018 Pearson Education, Inc.

Figure 6. 16 An anaerobic culture system. © 2018 Pearson Education, Inc.

Culturing Microorganisms • Preserving Cultures • Refrigeration • Stores for short periods of time • Deep-freezing • Stores for years • Lyophilization • Stores for decades © 2018 Pearson Education, Inc.

Growth of Microbial Populations • Most microorganisms reproduce by binary fission. • One divides in half to produce two daughter cells. • Involves four steps © 2018 Pearson Education, Inc.

Figure 6. 17 Binary fission. © 2018 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 © 2018 Pearson Education, Inc.

Figure 6. 18 A comparison of arithmetic and logarithmic growth. © 2018 Pearson Education, Inc.

Figure 6. 19 Two growth curves of logarithmic growth. © 2018 Pearson Education, Inc.

Figure 6. 20 A typical microbial growth curve. © 2018 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 © 2018 Pearson Education, Inc.

Growth of Microbial Populations • Measuring Microbial Reproduction • Estimating the number of microorganisms is useful • Determine severity of certain infections • Determine effectiveness of food preservation techniques • Measure the degree of contamination of water supplies • Evaluate disinfectants and antibiotics • Direct methods not requiring incubation • Microscopic counts © 2018 Pearson Education, Inc.

Figure 6. 22 The use of a cell counter for estimating microbial numbers. © 2018 Pearson Education, Inc.

Growth of Microbial Populations • Measuring Microbial Reproduction • Direct methods not requiring incubation • Electronic counters • Coulter counter • Counts cells as they interrupt an electrical current • Flow cytometry • Detects changes in light transmission as cells pass a detector © 2018 Pearson Education, Inc.

Growth of Microbial Populations • Measuring Microbial Reproduction • Direct methods requiring incubation • Serial dilution and viable plate counts • Membrane filtration © 2018 Pearson Education, Inc.

Figure 6. 23 A serial dilution and viable plate count for estimating microbial population size. © 2018 Pearson Education, Inc.

Figure 6. 24 The use of membrane filtration to estimate microbial population size. © 2018 Pearson Education, Inc.

Growth of Microbial Populations • Measuring Microbial Growth • Indirect methods • Turbidity • Often the more turbid a culture, the greater the bacterial population © 2018 Pearson Education, Inc.

Figure 6. 26 Turbidity and the use of spectrophotometry in indirect measurement of population size. © 2018 Pearson Education, Inc.

Growth of Microbial Populations • Measuring Microbial Growth • Indirect methods • Metabolic activity • Dry weight • Molecular methods • Isolate DNA sequences of unculturable prokaryotes © 2018 Pearson Education, Inc.