Chapter 7 Microbial Growth

Topics • Binary fission –Microbial Growth • Generation time • Growth curve –Factors that affect microbial • Enumeration of growth –Microbial Nutrition

Definition of growth Binary fission - Unicellular increase in size to approximately two times the original size • The division of a bacterial - At that time the mother cell divides into two • Parental cell enlarges and duplicates daughter cells by binary fission its DNA • Septum formation divides the cell - The daughter cells grow - become mother into two separate chambers cells and divide • Complete division results in two identical cells With each division, the population doubles

Steps in Binary Fission Generation time

• The time required for a complete division cycle (doubling) • Length of the generation time is a Should measure of the growth rate be pink – • Exponentials are used to define the RIGHT?? numbers of bacteria after growth

1 Log

Synchronous growth vs. nonsynchronous growth

Growth curve

• Lag phase • Log phase • Stationary phase • Death phase

2 Enumeration of bacteria One bacterium results in one bacterial colony • Direct cell count - multiple methods • Turbidity Countable number of colonies • Automated devices – Coulter counter – Flow cytometer Limitation = 30 to 300 per plate Differences in techniques - can you tell the difference between live/dead?

Direct counts by microscopy - can take Turbidity advantage of staining techniques we learned in Chapter 3

3 Mechanical or automated counters Factors that Effect Microbial Growth

• Temperature • Gas • pH • Osmotic pressure • Other factors • Microbial association

Temperature -Psychrophiles obligate ( Bacillus globisporus ), facultative ( Xanthomonas pharmicola ) – optimal temperature for growth below 15°C - Mesophiles - 20 to 40 oC - thermoduric organisms can survive elevated temperatures, but grow best at moderate temperatures - Thermophiles – organisms that normally grow best at >45°C

Oxygen -

Gases - Obligate aerobes

• Two gases that most influence - Obligate anaerobes microbial growth - Facultative anaerobes – Oxygen • Respiration - Microaerophiles - do not grow at normal • Oxidizing agent atmospheric concentrations of O 2- soil microorgansims – Carbon dioxide - Capnophiles - microaerophiles that are

CO 2 loving

4 Obligate aerobe Facultative anaerobe

• Requires oxygen for • Does not require oxygen for • Possess enzymes that can neutralize metabolism, but can grow in its presence the toxic oxygen metabolites • During oxygen limitation states, anaerobic – Superoxide dismutase and respiration or fermentation occurs catalase • Possess superoxide dismutase and catalase • Ex. Most fungi, , and bacteria • Ex. Gram negative pathogens

Obligate anaerobes pH

• Cannot use oxygen for metabolism pH - negative logarithm of the • Do not possess superoxide dismutase hydrogen ion concentration of an and catalase aqueous solution • The presence of oxygen is toxic to the • Most cells grow best between pH 6 - 8 cell • Exceptions would be acidophiles (pH 0) • Ex - dental pathogens, intestinal and alkalinophiles (pH 10). pathogens, deep in tissues

Osmotic pressure Other factors? • Halophiles • Require high salt concentrations • Barophiles – withstand high • Withstand hypertonic conditions pressures • Ex. • and cysts- can survive dry • Facultative halophiles habitats – Can survive high salt conditions but is not required – Ex.

5 Ecological association Hydrostatic pressure • Influence have on other microbes Most microorganisms can withstand reasonable pressures, but barophiles – Symbiotic relationship are highly evolved microorganisms that – Non-symbiotic relationship grow only at intense pressure • Organisms that live in close nutritional relationship Some barophiles are also thermophiles • Types - deep thermal vents in oceans – Mutualism – both benefit – Commensalism – one organisms benefits – Parasitism – host/microbe relationship

Ecology of Communities Clint Eastwood Style

Good – help each other in community setting Bad – kill one another with antibiotics – take spoils of victory

Ugly – live together to cause disease

Oral cavity biofilms and Co-aggregation

Two Biofilm Formed by: S. oralis & P. acnes

6 Microbial Nutrition Carbon source

• Sources of essential nutrients • Heterotroph ( depends on other forms ) - Macronutrients : Carbon, Nitrogen, Oxygen, – Organic molecules and Hydrogen – Ex. Sugars, proteins, lipids - Micronutrients : Magnesium, Manganese, Zinc, and Nickel • Autotroph ( self-feeders ) – Inorganic molecules • Transport mechanisms – Ex. CO 2

- Water movement Transport mechanisms - Selectively permeable membrane • Osmosis - Concentration gradient • Diffusion • Active transport • Endocytosis

Osmosis – water movement Diffusion

• Net movement of molecules from a high concentrated area to a low concentrated area • No energy is expended (passive) • Concentration gradient and permeability Equal In  Burst Out Shrink affect movement

7 Sugar diffusion in coffee Facilitated diffusion • Transport of polar molecules and ions across the membrane • No energy is expended (passive) • Carrier protein facilitates the binding and transport – Specificity – Saturation – Competition

Facilitated diffusion Active transport

• Transport of molecules against a gradient • Requires energy (active) • Ex. Permeases and protein pumps transport sugars, amino acids, organic acids, phosphates and metal ions

• Ex. Group translocation transports and modifies specific sugars

Permeases Group translocation - usually entities are modified

8 Endocytosis

• Substances are taken, but are not transported through the membrane. • Requires energy (active) • Common for • Ex. Phagocytosis , pinocytosis

In summary

The growth and division of microorganisms requires a carefully choreographed arrangement of a large number of processes. Little things can be exceedingly complex.

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