Presentation on theme: "Microbial Nutrition and Growth Microbial Population Growth"— Presentation transcript:
1 Microbial Nutrition and Growth Microbial Population Growth Microbiology of the Health Sciences
2 The Study of Microbial Growth Growth takes place on two levelsCell synthesizes new cell components and increases in sizeThe number of cells in the population increasesThe Basis of Population Growth: Binary Fission
4 The Rate of Population Growth Generation or doubling time: The time required for a complete fission cycleEach new fission cycle or generation increases the population by a factor of 2As long as the environment is favorable, the doubling effect continues at a constant rateThe length of the generation time- a measure of the growth rate of an organismAverage generation time- 30 to 60 minutes under optimum conditionsCan be as short as 10 to 12 minutesThis growth pattern is termed exponential
5 Basic Nutrients for Growth ATP for cellular processes Carbon is necessary for the production of many macromolecules (proteins, lipids, and carbohydrates) Oxygen for metabolism Nitrogen for amino acid synthesis Sulfur for vitamins, amino acids, structural stability of proteins
6 Basic Nutrients for Growth Phosphorous makes ATP and membranes Trace elements are used for metabolic reaction in the cell and cell component stabilization cobalt Co potassium K molybdenum Mo magnesium Mg manganese Mn calcium Ca iron Fe zinc Zn
7 Basic Nutrients for Growth Organic growth factors such as vitamins, amino acids, and nucleic acids some growth factors cannot be synthesized by own cellular processes Water water activity
8 How Microbes Obtain Nutrients Heterotroph: uses organic carbon source Autotroph: uses inorganic carbon dioxide Phototroph: uses light as energy source Chemotroph: uses chemical compounds (ie. glucose) Saprobe Parasite
10 Culturing Microorganisms Inoculum introduced into medium (broth or solid)Environmental specimensClinical specimensStored specimensCulture – refers to act of cultivating microorganisms or the microorganisms that are cultivated
14 Media Enriched Media added nutrient encourages the growth of microorganisms
15 Media Selective Media Selects form a microorganism while inhibiting most othersPhenol Ethanol AgarDeoxycholate Agar
16 Media Differential Media Allow for the differentiation of microorganisms based onaction that occurs on the mediaor a color change within themedia that is based on a pHchangeMannitol Salt AgarMacConkey Agar
17 Media Question What type of media is Blood Agar considered? Enriched SelectiveDifferential
18 The Population Growth Curve A population of bacteria does not maintain its potential growth rate and double endlesslyA population displays a predictable pattern called a growth curveThe method to observe the population growth pattern:Place a tiny number of cells in a sterile liquid mediumIncubate this culture over a period of several hoursSampling the broth at regular intervals during incubationPlating each sample onto solid mediaCounting the number of colonies present after incubation
19 The Rate of Population Growth Generation or doubling time: The time required for a complete fission cycleEach new fission cycle or generation increases the population by a factor of 2As long as the environment is favorable, the doubling effect continues at a constant rateThe length of the generation time- a measure of the growth rate of an organismAverage generation time- 30 to 60 minutes under optimum conditionsCan be as short as 10 to 12 minutesThis growth pattern is termed exponential
20 Stages in the Normal Growth Curve Data from an entire growth period typicallyproduce a curve with a series of phasesLag PhaseExponential Growth PhaseStationary Growth PhaseRapidly Declining PhaseDeath Phase
21 Lag Phase Relatively “flat” period Newly inoculated cells require a period of adjustment, enlargement, and synthesisThe cells are not yet multiplying at their maximum rateThe population of cells is so sparse that the sampling misses themLength of lag period varies from one population to another
22 Exponential Growth (Logarithmic or log) Phase When the growth curve increases geometricallyCells reach the maximum rate of cell divisionWill continue as long as cells have adequate nutrients and the environment is favorableThe number of cells growing greatly out number the number of cells dying.
23 Stationary Growth Phase The population enters a survival mode in which cells stop growing or grow slowlyThe rate of cell inhibition or death balances out the rate of multiplicationDepleted nutrients and oxygenExcretion of organic acids and other biochemical pollutants into the growth mediumThe number of cells growing will equal the amount of cells dying.Endospores begin to form in this phase.
24 Rapidly Declining Phase The curve dips downwardCells begin to die at an exponential rateThe amount of cells dying out numbers the amount of cells growing.The dead cells become nutrients for the growing cells.
25 Death Phase The curve continues to dips downward Most cellular activity stopsEndospores are formed and released from the parent cells.
26 Phases of Growth Basic phases of growth: 1. Lag phase: new growth medium, period of delay while cells prepare to divide2. Log phase (exponential growth phase): cellular reproduction most active during this period, generation time reaches a constant minimum3. Stationary phase: state of equilibrium where number of cell deaths equals number of cell divisions
27 Phases of GrowthBasic phases of growth: 4. Rapidly Declining Phase: cells die logarithmically, endospores formed 5. Death phase: number of deaths exceeds number of new cells
28 Potential Importance of the Growth Curve Implications in microbial control, infection, food microbiology, and culture technologyGrowth patterns in microorganisms can account for the stages of infectionUnderstanding the stages of cell growth is crucial for working with culturesIn some applications, closed batch culturing is inefficient, and instead, must use a chemostat or continuous culture system
29 Graphing Bacterial Growth The data from growing bacterial populations are graphed by plotting the number of cells as a function of timeIf plotted logarithmically- a straight lineIf plotted arithmetically- a constantly curved slopeTo calculate thesize of a population over time: Nf = (Ni)2gNf is the total number of cells in the population at some point in the growth phaseNi is the starting numberg denotes the generation number