Microbial Growth and Nutrition - MIC 101 PDF

MIC 101 INTRODUCTION TO MICROBIOLOGY MICROBIAL GROWTH AND NUTRITION ABDULROKEEB JAKKARI (B.Sc., M.Sc.)  MICROBIAL GROWTH Microbial growth refers to an increase in the number of microbial cells in a population. It can also be stated as an increase i...

MIC 101 INTRODUCTION TO MICROBIOLOGY MICROBIAL GROWTH AND NUTRITION ABDULROKEEB JAKKARI (B.Sc., M.Sc.)  MICROBIAL GROWTH Microbial growth refers to an increase in the number of microbial cells in a population. It can also be stated as an increase in total cell mass. Prokaryotic organisms grow largely by binary fission. Some may also grow by budding. The growth of microorganisms is dependent on chemical requirements It is also influenced by physical (environmental) factors CHEMICAL FACTORS (NUTRIENT REQUIREMENTS) Oxygen Carbon source Nitrogen source Sulphur source Phosphorus source Trace elements e.g., iron, copper, zinc  Based on oxygen Based on carbon source, requirements, there are: there are: Obligate aerobes e.g., Neisseria Heterotrophs: they use organic Obligate anaerobes e.g., compounds such as Clostridium carbohydrates, proteins, vitamins etc. as carbon source. Facultative anaerobes e.g., Escherichia Aerotolerant anaerobes e.g., Lactobacillus Autotrophs: they obtain their Microaerophiles e.g., carbon from inorganic sources Campylobacter usually CO2 Physical (Environmental) Requirements pH Acidophile: they grow optimally at pH 0 – 5.5 Neutrophile: they grow optimally at pH 5.5 – 8.0 Alkaliphile: they grow optimally at pH 8.0 – 11.5 Temperature Psychrophile: has an optimum growth temperature between 0oC and 20oC Mesophile: has an optimum growth temperature between 20oC and 45oC Thermophile: has an optimum growth temperature between 50oC and 60oC Osmotic pressure Water activity Hydrostatic pressure- Barophiles/Piezophiles  Acidophiles e.g., Sulfolobus, Ferroplasma Neutrophiles e.g., Escherichia Alkaliphiles e.g., B. alcalophilus Psychrophiles e.g. B. psychrophilus Psychrotrophs e.g., Listeria Mesophiles e.g., Escherichia Thermophiles e.g., Thermus aquaticus Hyperthermophiles e.g. Pyrococcus THE MICROBIAL GROWTH CURVE There are 4 distinct phases observed when microorganisms are grown in a closed culture system Lag phase Log/ Exponential phase Stationary phase Death/Senescence  Lag Phase No noticeable increase in cell population Cells are adjusting to their new environment They synthesise new components necessary for their function The cells also repair themselves from damages suffered during transfer Exponential (Log) Phase Cells begin to divide actively Metabolic activity is highest at this stage Growth rate is constant The population is most uniform in physical and physiological properties Cells in the exponential phase are used for biochemical studies.  Stationary Phase The population of cells remain constant Possibly due to the establishment of a balance between cell division and cell death Nutrients are depleted at this stage Metabolic waste get accumulated Senescence/Death The depletion of nutrients and accumulation of toxic waste eventually lead to loss of cells. Number of viable cells decrease exponentially as death rate becomes constant The microbial growth curve in a closed culture system  Generation time: The interval it takes for the population of cells to double. The population of cells at any point is expressed as: Nn = N02n Where N = Initial number of cells 0 n = Number of generations LABORATORY CULTURE OF MICROORGANISMS The process of cultivating microorganisms in the laboratory is referred to as culturing. This is possible with the use of culture media. Culture media are solid or liquid media containing essential nutrients for microbial growth used to grow, store and transport microorganisms. Culture media can be classified based on different parameters Parameters for classifying culture media 1. Based on Chemical Composition Defined Media Complex Media 2. Based on Physical Nature Liquid media (Broth) Semi-solid media Solid media (Agar) 3. Based on Function General purpose, Enriched, Selective, Differential, Enrichment Preparation of a solid medium A plate of solid medium with bacterial colonies Classification based on chemical composition Defined media are media in which all chemical components are known. Such media can contain sodium carbonate as carbon source Ammonia as nitrogen source etc. Complex media contain some ingredients of unknown chemical composition. E.g., meat extract, yeast extract etc. Classification based on physical nature Liquid media are liquid at room temperature They are referred to as broths. They are useful for investigating biochemical characteristics such as gas production. Examples include: Nutrient broth, Trypic soy broth. Solid media exist as solids at room temperature. They contain agar which serves as the solidifying agent. Semi-solid media contain a reduced concentration of agar. They are useful in performing motility tests.  General purpose media support the growth of a wide range of microorganisms E.g., Nutrient agar, Mueller Hinton agar Enriched media contain additional nutrients to support the growth of fastidious organisms. E.g., Blood agar, Chocolate agar Selective media support the growth of a particular organism or group of organisms while inhibiting the growth of others. E.g., Mac Conkey agar, Mannitol Salt agar Differential media distinguish between microorganisms on the basis of biochemical/physiological characteristics E.g., MacConkey agar, Blood agar Additional Definitions Inoculum: Microbes that are introduced into a culture medium to initiate growth. Culture: The microbes growing in or on a culture medium. Colony: A macroscopically visible cluster of microorganisms on a solid medium. Batch (Closed) culture: A culture in which no fresh medium is added during incubation. Continuous (Open) culture: A culture system in which fresh medium is added during incubation.