Chapter 6: Microbial Growth

How do bacteria grow?  Not in size  Increase in population size  One cell divides into 2 new cells – binary fission

Binary fission

Binary fission:  Attachment of chromosome to p.m.; replication of DNA; new p.m. and cell wall laid down between the 2 chromosomes  This is the way that each new daughter cell gets one chromosome

Number of generations Number of cellsLog of # of cells 10 X = #

How can we describe growth? 2 n = no. of cells in n generation Generation time N t = N 0 x 2 n

Growth problems If Staphylococcus aureus has a doubling time (generation time) of 30 minutes and 5 hours have passed, how many generations have been produced? a. How many 30 minute time chunks are in 5 hours? = 10 ANSWER: 10 generations

Growth problems If Staphylococcus aureus has a generation time of 30 minutes and 5 hours have passed, how many bacteria will be present at the end of the time period? a. We have already determined that 10 generations will occur. b. 2 n = # cells at n generation c = # cells at the 10 th generation ANSWER = 1024 cells

Growth problems If Staphylococcus aureus has a generation time of 30 minutes and 5 hours have passed, how many bacteria will be present at the end of the time period if we start with 3,000 cells? N t = N 0 x 2 n N t = 3,000 x 2 10 = 3,072,000 cells at the end of 5 hours

 Growth curve: lag, log, stationary, and death phases  What occurs in each?

How can population size be counted? (Advantages and disadvantages of each method) 1. Direct methods A. Microscopic count with hemacytometer/ Petroff Hauser counting chamber

 B. Plate counts – dilution series and plates

 C. Filtration

 D. Coulter counter/flow cytometer/Fluorescence activated cell sorter (FACS)

2. Indirect methods A. Dry weight B. Metabolic activity C. Turbidity

Turbidity

Growth requirements of microbes A. Temperature: Thermophiles Mesophiles Psychrophiles

B. pH: acidophiles C. Osmotic pressure (# of solutes in solution) Halophiles D. Oxygen: Types: Obligate aerobe Facultative anaerobe Obligate anaerobe Aerotolerant anaerobe Microaerophilic

Enzymes needed to survive in presence of oxygen: Catalase Peroxidase Super oxide dismutase (SOD)

E. Nutrients C, N, P, S elements needed Mg, Fe, etc. trace elements needed Media: Defined or complex Selective vs. differential Special

Mannitol salt agar – selective medium

Blood agar – differential medium

The End