3. pattern of growth

GROWTH OF BACTERIAL COLONIES

• generation time- time between bacterial divisions

• at first no. of bacteria in a colony can increase exponentially (doubling each cycle)

• limited nutrition/space and a build up of waste products then slows reproduction and growth

LOGARITHMIC SCALE

• used to work with large sets of data

• log numbers are used because diff in no. from initial organisms and billions of descendants is too great to represent on a graph using standard no.

LOGARITHMIC SCALE- GRAPH

• top graph shows bacterial no. against time

• as the scale is so large on y-axis it’s difficult to see bacterial growth

• when no. are converted to logarithms (log10) a clear trend of growth can be seen and represented

• as only y-axis values have been converted we call this a semi-logarithmic graph

  • means each no. on y-axis represents a power of 10 (10^n) (e.g. 1 = 10^1 or 10)

NO. OF BACTERIA IN A POPULATION AT A GIVEN TIME- FORMULA

• can calculate no. of bacteria in a pop at a given time using that formula

• where:

  • Nt = the number of organisms at a time t

  • N0 = the number of organisms at time 0

  • k = the exponential growth rate constant

  • t = the time the colony has been growing

EXPONENTIAL GROWTH RATE CONSTANT- FORMULA

• no. of times a pop will double in 1 unit of time

PHASES OF BACTERIAL GROWTH

• lag phase

• log phase

• stationary phase

• death phase

LAG PHASE

• bacteria are adapting to new env and aren’t yet reproducing at a measurable rate

LOG PHASE

• also known as exponential phase

• rate of reproduction is at or close to its theoretical max rate (doubling in a time period)

STATIONARY PHASE

• total growth rate is 0

• no. of cells made is equal to no. dying

DEATH PHASE

• reproduction has almost stopped and death rate is increasing

BACTERIAL GROWTH CURVE

REASONS FOR SLOWING GROWTH RATE- 1

• REDUCTION IN AVAILABLE NUTRIENTS

  • at the start, nutrients are in excess but as exponential growth occurs, excess is used up

  • unless more nutrients are added there will not be enough to support further growth and reproduction

  • limits growth of bacteria

REASONS FOR SLOWING GROWTH RATE- 2

• BUILD UP OF WASTE PRODUCTS

  • at the beginning, bacterial waste products in growth medium are minimal

  • as cell no. start to increase, build up of toxic substances becomes sufficient to inhibit further growth

  • can even poison and kill the culture

  • CO2 build up from respiration has a particularly neg effect

    • causes the pH to fall to a point where bacteria can no longer grow