Micro Exam 2 Study Guide Review

Chapter 6 – Microbial Growth Microbial growth is often defined as the increase in cell number, not cell size. Bacteria grow and divide into two identical cells through: binary fission. Physical Requirements: 3 types: temperature, pH and Osmotic pressure Temperature range: each species has its own specific growth response to temperature. Bacterial species grow at a – Minimum growth temperature: the lowest temperature, which it is able to grow Optimum growth temperature: the temperature at which the species grows best Maximum growth temperature: the highest temperature at which the species is able to grow  Psychotrophs/philes (cold loving) o Optimum at 15/10 C (fridge temperature is 4) o Grow between 0 and 20-30C  Mesophiles (moderate temperature loving) o Optimum (35-37) – body temperature o Most pathogens are mesophiles  Thermophiles (optimum 60C – hyper at 90-100) o Can grow at temperatures that would pasteurize most mesophiles o They are rarely pathogenic, usually spoiling microbes. o (we pasteurize milk at 63C) pH      Bacterial growth between 5-9 Most bacterial grow optimally in a narrow range between 6.5-7.5 Acidity is sometimes added to foods to prevent spoilage Molds and yeasts have a grater range of growth in pH, some can grow in environments <4 Acidophiles are bacteria that are tolerant of acidity. Usually are able to grow between 4-5 Osmotic Pressure: Microorganisms obtain their nutrients in solutions from the surroundings, they are 80-90% water. High osmotic pressure can remove necessary water from the cell. When a cell is in solution, and the concentration of solute is higher than inside the cell, the environment is considered hypotonic.  A hypotonic environment causes plasmolysis, or shriveling  Cellular water passes through the plasma membrane to the high solute concentration  Extreme or obligate halophiles require high salt concentrations for growth, or high osmotic pressure  Facultative halophiles – do not require high concentrations of solutes or high osmotic pressure, but are able to tolerate them. Microbio Exam 2 Review Chemical Requirements for Growth: carbon, nitrogen, sulfur, phosphorus, trace elements, oxygen and organic growth factors. Carbon  Besides water, one of the most important requirements for microbial growth is carbon it is the structural backbone of living matter, it is needed for all organic compounds that make up a cell. Almost half of the dry weight of a microbe is carbon  It is a structural organic molecule, as well as an energy source  Chemoheterotrophs – use organic carbon sources such as proteins, carbs lipids.  Autotrophs – derive their carbon from CO2 Nitrogen  Amino acid and protein synthesis requires nitrogen  Most bacteria decompose proteins  Some bacteria use nitrogen from ammonium (NH4+) or nitrate (NO3-)  Very few use N2 in nitrogen fixation Sulfur  Used in amino acids: thiamine and biotin  Most bacteria decompose proteins  Use SO42- or H2S as a source Phosphorus  Used in DNA RNA and ATP synthesis as well as membranes  PO43- is a source Trace Elements:  Microbes require very small amounts of other inorganic minerals referred to as trace elements.  Most are essential for the functions of certain enzymes and act as COFACTORS  Carbon, Hydrogen, Oxygen, Phospohorus, Potassium, Iodine, Nitrogen, Sulphur, Calcium, Iron, Sodium, Chlorine, Magnesium, Manganese, Zinc.  C.HOPKINS CaFe – Mighty nice Mighty good. Oxygen: