Micro - Chapter 6 PDF

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Microbio Chapter 6 Notes...

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Chapter Six – Microbial Growth The Requirements for Growth 

Can be divided into two main categories: o Physical aspects: temperature, pH, osmotic pressure o Chemical aspects: sources of carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements, and organic growth factors

Physical Requirements  Temperature: o Most microorganisms grow well at temperatures that humans like o Microorganisms are classified into three groups based on temperature preference:  Psychrophiles: cold-loving  Mesophiles: moderate-temperature-loving (most common microbe)  Thermophiles: heat-loving  Extreme thermophiles (hyperthermophiles): loves extreme heat o Each species grows at a particular minimum, optimum and maximum temperature o Psychrotrophs: spoilage microorganisms  pH: o Most bacteria grow best in a pH range near neutrality (6.5 – 7.5)  Very few grow at pH below 4 o Acidophiles: bacteria that are extremely tolerant of acidity o Molds and yeast grow over a greater pH range than bacteria  Optimum pH for them is 5 – 6  Osmotic pressure: o Microorganisms obtain almost all nutrients in solution from surrounding water o 80-90% composition of water is required for growth o High osmotic pressures remove necessary water from a cell  When environment is hypertonic to cell: osmotic loss of water – plasmolysis – shrinkage of cell’s cytoplasm  Growth inhibited o Extreme halophiles (obligate halophiles): adapted to high salt concentration – need salt for growth o Facultative halophiles: do not require high salt concentration to grow but can grow in salt concentrations up to 2% (more common) o If osmotic pressure is really low (environment is hypotonic) – distilled water – cell can be caused to lysed Chemical Requirements  Carbon: o Carbon = structural backbone of living matter  Needed for all organic compounds that make up a living cell o Half dry weight of a typical bacteria cell = carbon  Nitrogen, sulfur, and phosphorus: o Protein synthesis needs nitrogen and some sulfur o Synthesis of DNA and RNA needs nitrogen and some phosphorus o Organisms mainly use nitrogen to form the amino group of amino acids of proteins o Nitrogen fixation: when bacteria use N 2 directly from the atmosphere

Phosphorus is needed for the synthesis of nucleic acids and phospholipids of cell membranes  Found in energy bonds of ATP Trace elements: o Trace elements: iron, copper, molybdenum, and zinc  Most are important for the functions of certain enzymes – usually as cofactors o Usually found in water – even distilled Oxygen: o Microbes that use molecular oxygen (aerobes) produce more energy from nutrients than microbes that do not (anaerobes) o Obligate aerobes: organisms that require oxygen to live o Obligate anaerobes: bacteria that are unable to use molecular oxygen for energyyielding reactions (most harmed by it) o Aerotolerant anaerobes: cannot use oxygen for growth but can tolerate it Organic growth factors: o Organic growth factors: essential organic compounds an organism is unable to synthesize  Example: vitamins (humans)  Example: amino acids, purines, pyrimidines (bacteria) o

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Biofilms  

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Microorganisms rarely live in isolated single-species colonies o They live in biofilms – communities Biofilms live in matrix mostly made of polysaccharides (contain DNA and proteins) – slime o Considered a hydrogel – complex polymer with many times its dry weight in water o Usually attached to a surface In a biofilm community, bacteria can share nutrients and are sheltered from harm in the environment Biofilm usually starts to grow when free-swimming bacterium (planktonic) attached to a surface Essential elements in proper functioning of sewage treatment systems

Culture Media    

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Culture medium: nutrient material prepared for growth of microorganism Inoculums: microbes that are introduced into a culture medium and initiate growth Culture: microbes that grow and multiply in or on a culture medium Agar: complex polysaccharide derived from a marine alga o Hard to degrade by microbes o Agar media contained in test tubes  Slants: when test tubes are allowed to solidify (held at an angle)  Deep: when agar solidifies in vertical tube Sterile: must initially contain no living microorganisms (so culture will only contain microbes)

Chemically Defined Media:  Medium must provide energy source to support microbial growth  Chemically defined medium: one whose exact chemical composition is known  For chemoheterotroph – chemically defined medium must contain organic growth factors that serve as source of carbon and energy

Complex Media:  Complex media: made up of nutrients including extracts from yeast, meat, or plants, or digests of proteins from there and other sources o Exact chemical composition varies slightly from batch to batch o Energy, carbon nitrogen and sulfur mainly provided by protein o Vitamins and organic growth factors are provided by meat or yeast  If complex medium is in liquid form = nutrient broth o When agar is added = nutrient agar Anaerobic Growth Media and Methods  Cultivation of anaerobic bacteria is hard because bacteria may be killed by exposure to oxygen o Reducing media is used – deplete oxygen in culture medium o Heated before use to drive off absorbed oxygen Special Culture Techniques  Many bacteria have never been successfully grown on artificial laboratory media  There are special carbon dioxide incubators to grow aerobic bacteria that need concentrations of CO2 at different levels than what is in the atmosphere o CO2 levels obtained with candle jars  Cultures placed in large sealed jar with candle (consumes oxygen). Candle stops burning when air in jar has a lowered CO2 level  Capnophiles: microbes that grow better at high CO2 concentrations Selective and Differential Media  Selective media: designed to suppress growth of unwanted bacteria and encourage growth of desired bacteria o Used to detect presence of specific microorganisms associated with disease and poor health  Differential media: make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate  Blood agar (medium) used to identify bacterial species that destroy red blood cells o Example: Streptococcus pyogenes (bacteria that causes strep throat) Enrichment Culture  Enrichment culture: medium for enrichment culture is usually liquid and provides nutrients and environmental conditions that favor the growth of a particular microbe but not others o Often used for soil and fecal samples o Selective medium o Designed to increase very small numbers of desired organism to detectable levels

Obtaining Pure Cultures   

Visible colony comes from a single spore or vegetative cell or from a group of the same microorganisms attached to one another in clumps or chains Bacteria must be distributed widely so colonies are visibly separated from each other Streak plate method: isolation method o Sterile inoculating loop dipped in mixed culture (contains more than one type of microbe) and is streaked in a pattern over surface of nutrient medium

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Works well when organisms are present in large numbers

Preserving Bacterial Cultures  

Short-term storage of bacterial cultures = refrigerator Long-term storage: o Deep-freezing: pure culture of microbes is placed in suspending liquid and quick-frozen at temperatures ranging -50ºC to -95ºC  Culture can be thawed and cultures even several years later o Freeze-drying (lyophilization): suspension of microbes quickly frozen at temperatures ranging -54ºC to -72ºC and water is removed by high vacuum (sublimation)  When under vacuum, container is sealed my melting glass  Result = powder-like residue that contains surviving microbes  Can be stored for years  Retrieved by hydration with liquid nutrient medium...