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Dynamics of Prokaryotic Growth

Dynamics of Prokaryotic Growth. Chapter 4. 4.1 Principles of Prokaryotic Growth. Robert Koch (1843-1910) Developed the strategies for cultivating bacteria Defined growth requirements Media formulations First to use agar for semisolid media. Bacterial replication Binary fission

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Dynamics of Prokaryotic Growth

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  1. Dynamics of Prokaryotic Growth • Chapter 4

  2. 4.1 Principles of Prokaryotic Growth • Robert Koch (1843-1910) • Developed the strategies for cultivating bacteria • Defined growth requirements • Media formulations • First to use agar for semisolid media

  3. Bacterial replication • Binary fission • Doubling time varies by species and conditions • Growth can be calculated Nt = N0 x 2n Nt = total cells in a given time N0 = starting population of cells n = number of cell divisions Assume t = 20 min (3 per hour) 3 x 4 hours = 12 doublings If N0 = 10 then 10 x 212 = 40,960 bacteria

  4. 4.2 Bacterial Growth in Nature • Biofilms • Bacteria in nature tend to attach to solid surfaces • These bacteria encase themselves in polysaccharide coatings to form communities • Collectively, these communities are referred to as biofilms

  5. Biofilm communities are highly organized • Intracellular communication • Channels • Cellular movement within the biofilm (usually mediated by pili)

  6. Biofilm Activities • Ear infections • Dental decay • Bioremediation • Sewage treatment • Toxic waste sites • Heavy metals • Intracellular “warfare” (i.e., competition)

  7. 4.3 Obtaining a Pure Culture • Isolation of pure cultures is mandatory for studying bacteria • This is usually accomplished using semi-solid media composed with agar • Agar is a polysaccharide obtained from marine algae • It melts at about 95° C and remains liquid to 45° C

  8. Media are made with agar and usually sterilized in an autoclave • Media are cooled to 60° C, then dispensed into Petri dishes or tubes • After cooling, the agar solidifies, providing a semi-solid surface

  9. The streak plate method for obtaining a pure culture • Agar media in Petri dish • Collect a broth culture with a sterileloop • Streak the plate to deposit individual bacteria at sites on the plate • Incubate for 24-48 hr • Single bacterium grows to millions, forming a colony on the plate

  10. Maintaining a Stock Culture • Once a colony is obtained it is considered pure • This colony can be picked and inoculated into another tube or plate (subculturing) to provide a stock of the purified culture for short-term use (weeks) • Long-term storage (years) • This purified culture can also be grown in broth and lyophilized (freeze-dried) • It can also be diluted 1:2 in glycerol and frozen at -70° C

  11. 4.4 Bacterial Growth in Laboratory Conditions • The Growth Curve • Bacteria exhibit distinct kinetic profiles of growth in the laboratory in closed cultures (systems) • These profiles generally are the same, although time-course between species can be different

  12. Continuous (Open) Cultures • Removal of toxic metabolites • Replenishment of medium • Conducted in culture tanks called fermenters • Internal sensors • Computer controlled

  13. 4.5 Environmental Factors that Influence Microbial Growth

  14. 4.6 Nutritional Factors that Influence Microbial Growth • Heterotrophs • Carbon source is organic carbon • Medically important bacteria • Autotrophs • Carbon source is inorganic carbon • Perform carbon fixation, the conversion of inorganic carbon into organic carbon • Photoautotrophs use photosynthesis CO2 + H2O ➔ Glucose + O2

  15. 4.7 Cultivating Prokaryotes in the Laboratory • Complex Media • Contain a variety of biomolecule precursors • Concentrations of precursors can vary between media • Often, the source of the precursors are extracts, which are water-soluble substances • Examples • Nutrient agar • Tryptic soy agar • Blood agar

  16. Defined Media • Known amounts of chemicals and biomolecules are formulated into the medium • More expensive than complex media • Selective Media • Generally used for the propagation of particular bacteria • MacConkey agar selects for Gram- enterics • Bismuth sulfite agar cultures Salmonella and Proteus species to the exclusion of other bacteria

  17. Differential Media • Media that can distinguish two or more groups of bacteria in a mixed culture

  18. Providing Appropriate Atmospheric Conditions • Increased CO2 • Capnophiles (15% CO2) • Hemophilus • Neisseria • Microaerophilic - low levels of oxygen • Anaerobe - killed by prolonged exposure to oxygen

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