1. ELEMENTS OF MICROBIAL NUTRITION, ECOLOGY, & GROWTH
Chapter 7
ELEMENTS OF MICROBIAL NUTRITION, ECOLOGY, & GROWTH

2. Microbial Nutrition, Ecology & Growth
Sources of Nutrition - Nutrition consists of taking in chemical substances (nutrients) and assimilating and extracting energy from them
Essential nutrients – substances required for survival; can be macronutrients or micronutrients
Macronutrients are required in relatively large quantities and play principal roles in cell structure and metabolism
Carbon - supplied in media as either carbohydrates (sugars) and/or peptones
Nitrogen, sulfur, and phosphorus - needed for proteins & nucleic acids; supplied as peptones
Micronutrients, or trace elements are present in smaller amounts and are involved in enzyme function and maintenance of protein structure
Trace elements (Fe, Cu, Mg, and Zn) - needed for coenzymes; usually present in water

3. Microbial Nutrition, Ecology & Growth
Organic nutrients contain carbon and hydrogen atoms and are usually the products of living things
Organic growth factors - needed by fastidious (have special growth requirements) organisms
Essential compounds not synthesized by organisms
Supplied in media in purified form or as body fluids (e.g. blood, serum, etc.)
Examples: vitamins, amino acids, purines, pyrimidines, hemin, NAD, etc.
Inorganic nutrients are atoms or simple molecules that contains a combination of atoms other than carbon and hydrogen

4. Nutritional Categories
An autotroph depends on carbon dioxide for its carbon needs
If its energy needs are met by light, it is a photoautotroph, but if it extracts energy from inorganic substances, such as soil and minerals, it is a chemoautotroph
A heterotroph acquires carbon from organic molecules
A saprobe is a decomposer that feeds upon dead organic matter
A parasite feeds from a live host and usually causes harm
Disease-causing parasites are pathogens

5. Saprobes

6. Requirements for Growth
Environmental factors - can be used in selective isolation
Temperature - range and optimum different for each species; related to protein (enzyme) stability
Psychrophile (cold loving) - 5 C - 30 C
Mesophile C
Thermophile C

7. Requirements for Growth
pH - range and optimum differ with organism; most = ; buffers used in media to maintain pH in proper range
Acidophiles prefer lower pH
Alkalinophiles prefer higher pH
Osmotic pressure (solute concentration) - maintains water conc.; most cells require isotonic (0.9%) solutions; some can tolerate hypertonic (halophiles - e.g. vibrios & staphylococci) and hypotonic solutions; used as preservatives

8. Requirements for Growth
Oxygen - requirements based on presence of catalase, peroxidase and superoxide dismutase (enzymes that handle toxic by-products)
Source = atmosphere or chemical (organic or inorganic)
Classification based on oxygen requirement
Strict (obligate) aerobes - use molecular oxygen; have catalase and dismutase - e.g. Pseudomonas
Strict (obligate) anaerobes - free oxygen is toxic; use inorganic oxygen-containing salts; generally lack both catalase and dismutase - e.g. Clostridium
Facultative anaerobes - prefer molecular oxygen but can grow without it; have catalase and dismutase - e.g. Escherichia
Aerotolerant anaerobe - cannot use oxygen but not killed if exposed; have dismutase - streptococci
Microaerophilic - grow best at low oxygen tension; lack cytochromes; lack catalase but have dismutase; Campylobacter

9. Transport Mechanisms
A microbial cell must take on nutrients from its surroundings by transporting them across the cell membrane
Passive transport involves the natural movement of substances down a concentration gradient and requires no additional energy (diffusion)

10. Osmosis is diffusion of water through a selectively permeable membrane

11. Form of passive transport that can move specific substances is facilitated diffusion

12. Diffusion

13. Transport Mechanisms
Osmotic changes that affect cells are hypotonic solutions, which contain a lower solute concentration, and hypertonic solutions, which contain a higher solute concentration
Isotonic solutions have the same solute concentration as the inside of the cell

14. In active transport, substances are taken into the cell by a process that consumes energy

15. In group translocation, molecules are altered during transport

16. Transport Mechanisms
Phagocytosis and pinocytosis are forms of active transport in which bulk quantities of solid and fluid material are taken into the cell

18. Microbial Growth Definitions Growth - increase in numbers
Binary fission - method of reproduction used by prokaryotes in which each cell divides; doubles population (logarithmic)

19. Microbial Growth
Generation time (doubling time) - time required for a cell to divide and multiply (double) its population (20 min hrs.)

20. Phases of growth
Lag - occurs at inoculation; little or no change in numbers; enzymes being synthesized and cells increasing in size preparing to divide; time increased if media is cold
Log or exponential - cell mass and number increases in logarithmic manner; consistent rate and activity; organisms are most sensitive to adverse conditions
Stationary - population stabilizes; production = death; may be due to accumulation to toxic wastes or decrease in nutrients
Death (logarithmic decline) - deaths exceed production; cells usually most resistant and often assume unusual shapes (pleomorphic)