300: Chapter 7 - Exponential Growth and Measurement

How does bacterial growth come to be? What are the general steps? (5)

Binary Fission: cells volume increases, chromosomes are replicated, cells contents are divided and distributed, septum forms, and cell divides to become two new daughter cells

What is the purpose of a microbial growth curve? In general terms, how is it created/formulated?

To study bacterial population growth in batch culture. It is created via a closed system.

What is a closed system?

It is a method of studying bacterial population growth. Within a flask, there is enough nutrients for the microbes with proliferate but once it is sealed, nothing goes in and nothing comes out.

What are the phases and their expected results for a microbial growth curve?

1. Lag phase: The cell increases in volume and doubles its DNA

2. Exponential phase: binary fission and maximal growth is occurring at a constant rate

3. Stationary phase: # of living cells = # of dead cells (plateau)

4. Death phase: exponential cell death as nutrients decline and waste increases

What is the equation for bacterial growth? What do the variables represent?

Nt = N0 × 2^n

g=generation time

n = # of generations or time (t) it takes to double

N0 = # of bacteria at t=0 (original #)

Nt = # of bacteria at a given time (total #)

What is the relationship between growth rate and generation time?

The less time it takes to double, the faster the growth rate

The more time it takes to double, the slower the growth rate

The more the bacteria favor the environment, the faster they reproduce therefore take less time to double

What factors affect bacterial growth?

Temp, water availability, pH, pressure, and O2 concentration

What are the categories that classify bacteria in regard to temperature?

Psychrophiles (<= 15 deg C ~ fridge cold)

Psychotrophs (20-30 deg C but can live at 0)

Mesophiles (20-40 deg C) tends to be pathogens as human body temp ~ 37 deg C

Thermophiles (55-65 deg C) boiling

What are the categories that classify bacteria in regard to water availability?

Hypotonic: high water availability

Isotonic: ~-0.98

Hypertonic (halophiles): low water availability

What are the categories that classify bacteria in regard to pH?

Acidophiles (1-5.5)

Neutrophiles (5.5-8.0)

Alkophiles (8.5-11.5)