Bacterial Growth l Introduction –Population vs. Cellular Growth –Exponential vs. Arithmetic Growth –Bacterial Growth - Binary Fission

Bacterial Growth

l Bacterial Growth Curve –Lag Phase –Log Phase –Stationary Phase –Death Phase

Bacterial Growth Lag Log Stationary Death

Bacterial Growth l Calculations - Number of cells l Example: Initial Cells = Number x 2 number of generations of cells

Bacterial Growth Sample calculation: How many cells would be in a culture if the starting number were 100,000 and the culture was allowed to divide 5 times?

Bacterial Growth l Calculations - Number of Generations l Example: Generations = log n 2 – log n 1 /log 2 Generations = log n 2 – log n 1 /0.301 where n = number of cells at a given time

Bacterial Growth Sample calculation: How many generations have elapsed if the cell count in a culture went from 3 x 10 8 to 8 x in 1.5 hours?

Bacterial Growth l Calculations - Generation Time l Time for single cell to double l Example: Generation Time = Elapsed time Number of Generations between n 1 and n 2

Bacterial Growth l Calculations - Generation Time l Time for single cell to double l Example: Generation Time = 5 hours (Log 1,720,320 – log 100)/.301 = 5/((6.23 – 2)/.301) =.356 hrs or 21 min

Bacterial Growth l Measurement of Growth –Biomass –Viable Counts –Total Counts –Most Probable Number (MPN)

Bacterial Growth l Biomass –Dry weight –Turbidity –Metabolic Activity

Bacterial Growth l Dry Weight –Mass increases in proportion to growth –Filter onto pre-weighed paper –Dry under vacuum –Time consuming but usually accurate

Bacterial Growth l Metabolic Activity –Dissolved oxygen »Decrease in oxygen as cells increase –pH »Use indicator change or pH meter –Monitor a metabolite »Glucose use or ethanol production or carbon dioxide

Bacterial Growth l Viable Counts –Plate counts –Membrane filters

Bacterial Growth l Total Counts –Direct Microscopic Count –Most Probable Number –Electronic Counter

Bacterial Growth l Most Probable Number –5 tubes at 10 mL, 1 mL and 0.1 mL sized inoculum –Use combinations with table to calculate the most probable number –Confidence limits set range

Bacterial Growth l Electronic counter –Cells move past light source in very narrow tube –Each cell passing is counted –Counts both live and dead cells so must be used before culture gets to stationary phase