Environmental Influences

• Nutrients


  Chemical substances acquired from the environment and used in cellular activities
• Essential nutrients


  • C
  • N2
  • O2
  • H2
  • P
  • S
• Micronutrients


  Required in small amounts, involved in enzyme function and maintenance of protein structure
• Macronutrients


  Required in large amounts, play principal role in cell structure and metabolism
• Cytoplasmic (cell) membrane


  • Controls passage of nutrients into the cell
  • Semi-permeable
  • Selectively permeable

  
• Only relatively small, non-polar materials can move through the lipid bilayer (lipids, oxygen, carbon dioxide and alcohol)

  
• Water-soluble materials like glucose, amino acids and electrolytes need some assistance to cross the membrane
• Cell envelope


  • Comprises the cell membrane, the cell wall and outer membrane if present

  
• Gram-negative bacteria outer membrane


  • Plays a role in regulating the passage of solutes
  • Semi-permeable
  • No proteins are known to pump solutes across it although some activity facilitate passage

  
• Concentration gradient


  The difference in concentration of a substance across a space

  
• Diffusion


  The movement of particles from an area of higher concentration to an area of lower concentration

  
• Types of diffusion

  • Passive diffusion (simple diffusion)
  • Facilitated diffusion
  • Active diffusion
  • Group translocation
• Passive diffusion


  A process in which molecules from a region of higher concentration moves to one of lower concentration
• Facilitated diffusion


  Diffusion in and out of the cell of certain compounds mediated by specific membrane proteins (permeases, carrier proteins, channel proteins)
• Active transport


  Metabolic energy is utilized for the transport of substances through carrier proteins embedded in the membrane

  
• Electrical gradients


  Difference in charge across plasma membrane because atoms and molecules can form ions and carry positive or negative electrical charges
• Proton motive force (PMF)

  The transfer of hydrogen molecule (H+) through a proton pump generates an electrochemical gradient of protons that drives the conversion of ADP to ATP through ATP synthase

  
• Electron transport system (ETS)


  Involved in active transport
• Endocytosis


  A form of active transport that does not involve membrane carriers
• Exocytosis


  A form of active transport that does not involve membrane carriers
• ATP-binding cassette (ABC) transporters


  One of the largest and most diverse superfamily of proteins that can be found in all eukaryotic and prokaryotic organisms, important membrane proteins implicated in uptake and expulsion of a variety of substrates

  
• Types of active transport

  • Uniport (transports one solute at a time)
  • Symport (transports the solute and a co-transported solute at the same time in the same direction)
  • Antiport (transports the solute in (or out) and the co-transported solute the opposite direction)
• Secondary active transport


  Establishment of a proton motive force by proton extrusion associated with the passage of electrons through a membrane-bound transport chain or by hydrolysis of ATP by the membrane-bound ATPase

  
• Group translocation


  A process in which a molecule is chemically modified as it is brought into the cell, uptake of certain sugars like glucose and mannose, source of energy is Phosphoenolpyruvate (PEP), Phosphotransferase System (PTS)
• Phosphate-carrying proteins in group translocation

  • Heat stable carrier protein (HPr) histidine – containing protein
  • Enzyme I
  • Enzyme II
  • Enzyme III
• Exoenzymes


  Enzymes that are inactive while inside the cell but become active upon release from the cell
• Characteristics of exoenzymes


  • Inactive while inside the cell
  • Become active upon release from the cell
• Osmotic pressure


  The force with which water moves through the cytoplasmic membrane from a solution containing a low concentration of dissolved substances (solute) to one containing a high solute concentration
• Bacteria based on osmotic requirement

  • Osmophiles (grow in solution of increased osmolarity)
  • Halophiles (grow in solution of increased salt concentration)
• Sodium requirement of bacteria

  Detected only for growth at the expense of certain specific carbon and energy sources, required by bacteria of marine origin, most moderate halophiles and extreme halophiles, plays a number of different roles indispensable to the maintenance of cellular function
• Hydrostatic pressure


  Pressure exerted on the cells by the movement of water resting on top of them
• Barophiles


  Metabolize or function better at high pressure than at atmospheric pressure, organisms that need a high-pressure environment in order to grow, found in deep-sea environment
• Cardinal temperatures


  Minimum, Optimum, Maximum
• Cardinal temperature of a particular microbial species may vary depending on the stage in the life cycle of the microorganism and the nutritional content of the medium
• High temperatures damage microbes by denaturing enzymes, transport carriers and other proteins, and disrupting microbial membranes
• As the incubation temperature is lowered, enzymatic activity and growth rate decreases
• Barophiles


  Organisms that metabolize or function better at high pressure than at atmospheric pressure
• Barophiles


  • Need a high-pressure environment in order to grow
  • Found in deep-sea environment (ocean floors, deep lakes-pressure exceeds 380 atm)
• Temperature


  Most important factor that determines the rate of growth, multiplication, survival and death of all microorganisms
• Higher temperature


  Increases the rate of enzyme reaction