pH, temperature, radiation, osmotic pressure, salinity
physical factors affecting growth
o2, carbon, nitrogen, phosphorus
chemical factors affecting growth
Cryophiles
capable of growth and reproductionfrom -20oC to 10oC
Mesophiles
–growth between 20oC- 45oC
Thermophiles
growth at 50oC or higher
Hyperthermophiles
growth between 80oC-113oC
Lag phase
No increase in cell no. • Cells are synthesizing new components such as DNA replication, protein synthesis
Log or Exponential phase
Rate of growth is constant • M.o. are growing and dividing at a maximal rate possible given the genetic potential, the nature of the medium or conditions of growth
Stationary phase
Population growth ceases and the growth curve becomes horizontal • Total number remains constant due to a balance between cell division and cell death due to nutrient limitation, O2 availability for aerobic microbes and accumulation of waste products limit the growth
Death phase
Detrimental environment changes like nutrient deprivation and the build up of toxic wastes lead to the decline in the number of viable cells characteristic of the death phase.
Logarithmic manner
Most of the microbial population also dies in
Direct count methods
counts both dead and live bacteria
hemacytometer
direct count methods example
Viable count methods
count live cells only.
Dilution plating methods
viable count emthods example
Turbidometric method
needs to be used together with dilution plate method initially to create a standard curve which can repeatedly be used later
Spectrophotometer
Measures turbidity (% absorbed light) of bacterial suspension or % light transmitte