Microbiology Lecture 21: Influence of Environmental Factors PDF

MICR 0490-105 Chapter 07MICR 0490-105 MicrobiologyMicrobiology Bacterial and Archaeal Growth Lecture 19 Lecture 21 Influence of Environmental Factors Prescott’s Microbiology Fermentation Twelfth edition Joanne Willey, Kathleen Sandman, Dorothy Wood Ana...

MICR 0490-105 Chapter 07MICR 0490-105 MicrobiologyMicrobiology Bacterial and Archaeal Growth Lecture 19 Lecture 21 Influence of Environmental Factors Prescott’s Microbiology Fermentation Twelfth edition Joanne Willey, Kathleen Sandman, Dorothy Wood Anaerobic respiration Photosynthesis  Influence of Environmental Factors on Growth In general, most microorganisms grow in fairly moderate environmental conditions. Extremophiles, Grow under harsh conditions that would kill most other microorganisms. All microorganisms respond to changes in their environment. The optimal range of environmental parameters result in the best growth.  Solutes Affect Osmosis and Water Activity Changes in solute concentrations results in changes in osmotic concentrations in the environment that affect microbial cells: Hypotonic solution Contains lower solute concentration outside the cell than inside the cell that result in entrance of water that may lead to cell burst. Hypertonic solution Contains higher solute concentration outside the cell than inside the cell that force water to leave the cell that shrinks the membrane. Isotonic solution Contains same solute concentration outside and inside the cell that do not affect the movement of water.  Microbial Adaptation to hypotonic environments In hypotonic environments: the cell wall protects the cell by preventing the plasma membrane from overexpansion. Protists use contractile vacuoles to expel excess water. Mechanosensitive (MS) channels in plasma membrane allow solutes to leave.  Solutes and Water Activity Water activity (aw) Measure of the degree of water availability. Low water activity means most water is bound, not available to microorganisms. Most microorganisms grow well at water activities around 0.98. Osmotolerant are microorganisms that can grow over wide ranges of water activity but optimally at higher levels. Xerotolerant are microorganisms that withstand high solute concentrations. Halophiles are one type of osmophiles: Halophiles require NaCl at a concentration above about 0.2 M. Extreme halophiles require salt concentrations between 3 M and 6.2 M.  pH pH is the negative logarithm of the hydrogen ion concentration. pH is a measure of the relative acidity of a solution. Acidophiles Growth best between pH 0 and 5.5. Alkaliphiles (alkalophiles) Growth best between pH 8 and 11.5. Most bacteria and protists are neutrophiles. Most fungi prefer more acidic surroundings, about pH 4 to 6.  Temperature Microorganisms cannot regulate their internal temperature. Temperature fluctuation affect enzyme activity. Enzymes have optimal temperature for optimal function. Below optimum temperature, enzymes are not functional. High temperatures may inhibit enzyme function and be lethal. Cardinal temperatures Minimum Maximum Optimal Temperature Ranges for Microbial Growth Psychrophiles— 0oC to 20oC Psychrotrophs— 0oC to 35oC Mesophiles— 20oC to 45oC Thermophiles— 45oC to 85oC Hyperthermophiles— 85oC to 100oC  Adaptations of Thermophiles Have heat-stable enzymes and protein synthesis systems that function at high temperatures. Their membrane is stabilised by more saturated and more branched fatty acids.  Oxygen Concentration Five types of microbial relationships to O2 Obligate aerobe—requires O2. Obligate anaerobe—usually killed in presence of O2. Microaerophile—requires 2 to 10% O2. Facultative anaerobes—do not require O2 but grow better in its presence. Aerotolerant anaerobes—grow with or without O2. Oxygen and Bacterial Growth  Pressure Microbes that live on land and water surface live at a pressure of 1 atmosphere (atm). Some Bacteria and Archaea live in deep sea with very high hydrostatic pressures. Barotolerant—unfavorably affected by increased pressure, but not as severely as nontolerant organisms. Peizophilic (barophilic)—requires high pressure for growth. Their membrane fatty acids are more unsaturated and shorter to adapt to increasing pressure  Radiation The Electromagnetic Spectrum  Harmful Radiation Ionizing radiation X-rays and gamma rays Cause mutations that indirectly result in death. Disrupts chemical structure of many molecules. Breaks H-bonds and destroys ring structures. Bacterial endospores and Deinococcus radiodurans are extremely resistant to ionizing radiation. Ultraviolet (U V) radiation Most lethal wavelength is 260 nm because it is absorbed by DNA. DNA damage can be repaired by several repair mechanisms.