Orbita exam

• Binary fission


  The process by which prokaryotic organisms divide and reproduce (asexual reproduction)
• Binary fission is not the same as mitosis or meiosis (will only happen in eukaryotic cells)
• How Binary Fission Works

  1. Grow and elongate

  2. Replicate genetic material (DNA replication)
• Generation time/Doubling time


  (in prokaryotes) The time it takes for a bacterial population to double in size
• Some bacteria can divide into 2 cells once every 20 minutes under optimum conditions
• The Bacterial Growth Cycle Under Laboratory Condition

  1. Lag Phase

  2. Log Phase

  3. Stationary Phase

  4. Death or Decline Phase
• Lag Phase


  • No cell division
  • Cell synthesizes metabolites, enzymes, coenzymes, ribosomes and transport proteins needed for growth under prevailing conditions
• Log Phase


  • Bacteria grow exponentially
  • Different species vary in terms of generation time or doubling time
  • Environmental conditions like temperature, pH and oxygen (for aerobes) have major influence for bacterial growth
• As temperature increases


  Growth rate increases
• Stationary Phase


  • No growth
  • Nutrient is exhausted; toxic by-products accumulate
  • Cells entering stationary phase undergo changes like synthesis of new starvation-specific proteins for survival
• Death or Decline Phase


  • Cells die in greater number than the dividing cells as the culture medium accumulates toxic waste and nutrients are exhausted
• Viable but not culturable (VBNC)

  Bacterial cells that are alive but cannot be detected by standard culturing techniques
• VBNC state of marine bacteria are very much affected by the amount of nutrients in the environment, temperature, pH, salinity and pressure
• Macronutrients needed for bacterial growth

  • Carbon
  • Oxygen
  • Nitrogen
  • Sulfur
  • Phosphorus
• Micronutrients and trace elements needed for bacterial growth

  • Potassium
  • Calcium
  • Magnesium
  • Iron
  • Manganese
  • Cobalt
  • Zinc
  • Molybdenum
  • Copper
  • Nickel
• Most marine bacteria also require small amounts of preformed amino acids, pyrimidines, purines and vitamins because they lack the biochemical pathways to synthesize these micronutrients
• Sodium requirement of marine bacteria and archaea

  Most marine prokaryotes optimally grow at a concentration of NaCl similar to seawater (about 3.0 – 3.5% NaCl)
• Psychrophilic (cold-loving) prokaryotes


  • Optimum growth temperature less than 15°C, max of 20°C and min of 0°C or less
• Psychrotolerant bacteria


  • Can grow as low as 0°C but have an optimum of 20-35°C
• Thermophilic prokaryotes


  • Can grow at 60°C
• Hyperthermophiles


  • Can grow above 80°C, majority belong to Archaea domain
• Barotolerant organisms


  • Can grow from 1-400 atm but have low metabolic and growth rate
• Obligate or extreme barophiles

  • Can grow above 400 atm
• Types of organisms based on oxygen requirement

  • Obligate aerobes
  • Obligate anaerobes
  • Facultative anaerobes
  • Facultative aerobes
• UV-screening products in bacteria

  • Mycosporine-like amino acids
  • Scytonemin (a complex aromatic compound in cyanobacterial sheaths)
• Mechanisms of UV resistance in some coral-associated bacteria

  • Enhanced activity of NAD(P)H quinone oxidoreductase, a powerful antioxidative enzyme
• Extreme halophiles


  • Several genera of Archaea that can grow at very high NaCl concentrations (15–35%)
• Extreme halophilicity


  Rare in Bacteria, but Salinibacter rubrum is an exception
• Major divisions of the ocean

  • Pelagic (water column)
  • Benthic (bottom)
• Pelagic provinces


  • Neritic (low tide line to shelf break)
  • Oceanic (open ocean)
• Ocean zones


  • Epipelagic (0-200 m)
  • Mesopelagic (200-1000 m)
  • Bathypelagic (1000-4000 m)
  • Abyssopelagic (4000-6000 m)
  • Hadopelagic (6000 m and below)
• Marine snow


  A continuous shower of organic material falling from upper waters to the deep ocean, composed of a variety of organic matter, protists, fecal matter, sand and other inorganic dust
• Levels of marine microbes in marine snow are typically 100-10000 fold higher than in the bulk water column
• Deep-sea organisms rely heavily on marine snow as an energy source
• Biofilms


  A collection of microbes bound to a surface
• Matter, sand and other inorganic dust

  • Can form through abiotic processes (i.e. extrapolymeric substances made by phytoplankton and bacteria)
• Aggregates


  • Contain active complex assemblages of bacteria and bacterivorous protists
  • Levels of marine microbes in marine snow are typically 100-10000 fold higher than in the bulk water column
  • Grow over time and may reach several centimeters in diameter, traveling for weeks before reaching the ocean floor
• Marine sediments


  • Derived from continental transport and sedimentation of biological products
  • Provide important habitats for microorganisms
• Other types of sediment that provide special habitats for microbes include those in salt marshes, mangroves and coral reefs
• Biofilms


  • Consist of a collection of microbes bound to a solid surface by their extracellular polymeric substances (EPS) which trap organic and inorganic components
  • Often called as "cities of microbes"
  • Found in both living or non-living surfaces