1. Dynamics of Prokaryotic Growth
Chapter 4

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

3. Assume t = 20 min (3 per hour)
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 sterile loop
Streak the plate to deposit individual bacteria at sites on the plate
Incubate for hr
Single bacterium grows to millions, forming a colony on the plate

11. 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

12. 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

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

15. 4.5 Environmental Factors that Influence Microbial Growth

16. 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

17. 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

18. More expensive than complex media Selective Media
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

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

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