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Chapter 4: Dynamics of Prokaryotic Growth. Important Point:. If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!. Bacteria are incredibly diverse, but...
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Important Point: If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!
Bacteria are incredibly diverse, but... • Each bacterial species can grow in only a limited set of environments. • Each bacterial species can grow only if presented with the right nutrients/conditions. • In addition, bacteria produce characteristic by-products (e.g., waste products). • We can take advantage of these growth characteristics to identify bacteria phenotypically. • To do these identifications we first have to get organisms in Pure Culture. • Unfortunately, only about 1% of microorganisms currently can be grown in pure culture. Each Species is Unique
Sterile = completely free of microbes. • Aseptic Technique = procedures that minimize unintentional introduction of microorganisms to media (cultures) or from cultures to surrounding environment. • Solid media is usually employed to obtain pure cultures. • Agar is usually employed to make solid media. • Agar melts at 95°C and solidifies below 45°C. • Colony = pile of cells descended from single cell (or clump of cells). • Petri Dish = container to which agar is added to obtain pure culture. • Agar Plate (plate) = agar-containing petri dish. Pure-Culture Basics
Stored pure cultures are often called “Stock Cultures” • Stock cultures often are stored as/using: • Frozen in glycerol solution • Lyophilized = freeze drying • On agar slants • As stabs Storing Pure Cultures
This is how most bacteria undergo cell division (how they replicate). Binary Fission The interval, division to division, is called the Generation or Doubling Time. Note that not all daughter cells fully separate after division, e.g. streptococci, etc.
Optimum Growth Temperature Growth temperature optimum.
Max due to enzyme denaturation. Temperature Ranges Min due to enzyme & membrane fluidity problems.
Psychotrophs Important for food spoilage.
Most human pathogens are mesophiles. I.e., organisms adapted to growth at body temperature. Mesophiles
Important source of heat-stable enzymes (e.g., Taq polymerase or laundry detergent enzymes). Thermophiles
Oxygen Requirements: The Shake Tube Aerotolerant Anaerobe! Note maximum growth nearer to surface (where oxygen is plentiful; this is not shown well in image). Don’t worry about enzyme names. Just recall “O2 (product) detoxification”.
Medically Important Examples Pseudomonas spp. are obligate aerobes. E.g., Clostridium spp. such as C.botulinum. Enterics such as Escherichia coli are facultative anaerobes
Water Availability Plasmolysis Food preservation: jams, jellies, bacon, anchovies, etc.
Heterotrophs = require organic carbon (e.g., glucose). • Autotrophs convert CO2 to organic carbon. • Carbon fixation = conversion of CO2 to organic carbon. • Nitrogen fixation = conversion of N2 to non-gaseous form(i.e., ammonia). • Growth factors = small organic molecules (e.g., vitamins, amino acids) that must be provided for growth(some bacteria require no “exogenous” “growth factors”). • E.g., Neisseria spp. can require 40 growth factors to grow.We would describe such a bacterium as fastidious. • E. coli requires no growth factors.We would describe such a bacterium as non-fastidious. Terms for Nutrient Needs
Energy & Carbon Source Types “Chemoautotroph” is good enough for now. “Chemoheterotroph” is good enough for now. Chemoheterotrophs differ in the number (and types) of organic compounds they can use. Some Pseudomonas species can utilize 80 different compounds. Other bacteria are limited to as little as only a single organic compound type.
Culture Media Types Peptone = predigested protein
Culture Media Types Note that, confusingly, many media are both selective and differential, e.g., MacConkey agar.
Enrichment Culture Means of isolating rare organisms with specific characteristics from heterogeneous populations.
Direct Microscopic Count Requires relatively high bacterial densities. Usually can’t distinguish living cells from dead cells.
Viable Counts: Plate Counts Note the enumeration of colony-forming units (CFUs). Quantifies number of cells (CFUs) capable of replicating.
Serial Dilutions Note Serial Dilution.
Most Probable Number (MPN) These are gas-filled tubes, an indication of bacterial growth (fermentation). Looking for sufficient dilution that ~half of tubes show growth. Reciprocal of that dilution bacterial density.
Most Probable Number (MPN) Useful particularly when enumerating organisms that won’t grow on/in agar media. Durham tube.
Growth Curve Constant per-capita death rate (exponential). Death rate = Birth rate. Division at constant rate (exponential). Time of gearing up for division following change in culture conditions.
Continuous Culture, Chemostat Chemostats are a means of keeping a culture in log phase indefinitely.
Biofilms are polysaccharide-encased bacterial communities attached to environmental surfaces. • Biofilms include slippery rocks (in aquatic environments), slime coating sink drains, yuck yucking up what was once your clean toilet bowl, tarter on your teeth, etc. • “It is estimated that 65% of human bacterial infections involve biofilms.” • “Biofilms are particularly troublesome because they protect organisms against harmful chemicals such as disinfectants” and antibiotics. • They can accumulate on non-sterile medical devices kept in contact with patients over relatively long periods, e.g., on catheters. Biofilms
Don’t worry too much about the details of Glycolysis, Cellular Respiration, or Photosynthesis onward. • These topics are covered on pp. 144-151 and pp. 156-163. • Note, however, that we will cover Glycolysis and Cellular Respiration in class at least from the perspectives of the importance of NAD+ regeneration. Chapter 6 Notes
