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Unformatted text preview: 1 Microbial Growth Microbial Growth Environmental influences and adaptations Environmental influences and adaptations Bio3124 Bio3124 Lecture #5 Lecture #5 Growth Under favorable nutritional conditions Biosynthesis leads to increase in cellular constituents Cells divide and population increase Cells divide and population increases Growth: increase in population size not individual cells size 2 Binary Fission and Exponential Growth 1 st division 2 nd division 3 rd division 2 =1 2 1 =2 2 2 =4 3 4 th division N = N o . 2 n n = number of divisions (generations) 2 3 =8 2 4 =16 2 The Mathematics of Growth Two parameters are important 1. Generation time (g) time required for the population to double in size Varies depending on species of microorganism and environmental conditions range is from 10 minutes for some bacteria to several days for some eukaryotic microorganisms 4 The Mathematics of Growth 2. Mean growth rate constant (k) Mean number of generations (divisions) per hour This shows how fast the cells are growing under culture conditions during log phase it is the inverse of g value ie. k=1/g (hr1 ) How do you find the generation time? 5 The Mathematics of Growth The Mathematics of Growth N cells after n generations produce N cells over a given incubation time ( t ) Since population increases exponentially, then the final cell yield is an 6 exponential function, N= N 2 n log N= log (N . 2 n ) log N= log N + n.log2 n.log2=log Nlog N 3 Solving for n (number of generations) n = (log N  log N )/log2 n = (log N  log N )/0.301 Since n generations happened The Mathematics of Growth The Mathematics of Growth 7 over t incubation time Then the mean generation time: g=t/n (min or hr) Graphically this corresponds to the time interval that cells doubled in the linear portion of log phase. Problem A bacterial culture grows from 1 X 10 6 cells/ml to 6.4 X 10 7 cells/ml in 2 hours. What is the generation time, number of generations and the average growth rate constant of this bacterial culture? N = 1 X 10 6 , N= 6.4 X 10 7 , t=120 min n = (log N log N )/0 301 n = (log N  log N )/0.301 n = (log 6.4 X 10 7 log 1 X 10 6 )/0.301 n= 6 generations G=120/6 G=20 min or 0.33 hr K=1/g K=1/0.33 K=3 generations per hour 8 Experimental Growth Curve Plot of population vs time batch culture culture incubated in a closed vessel with a single batch of medium usually plotted as logarithm of cell number versus time Has four distinct phases 9 4 Growth Curve 10 Has four distinct phases Lag Phase Lag Phase cells synthesizing new components reorganizing gene expression adapt to new medium varies in length...
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 Spring '11
 RezaNokhbeh
 Nutrition

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