theme 7(4)Nitrifiers

• Nitrifiers:

  • Grow chemolithotrophically at expense of reduced inorganic N compounds (NH3)
  • obligate anaerobes (can also grow autotrophically).
  • fix CO2 by Calvin cycle.
• Physiology:

  • Ammonia oxidisers (NH3 to NO2-)
  • genus: Nitroso(in soil and water )
  • bacteria found near high [NH3] (sewage treatments)
  • archaea found near low [NH3] (Ocean)
• • Nitrite oxidisers (NO2- to NO3-)
  • genus:
  • Nitro- Nitrospira grow autotrophically
  • lack extensive internal membranes
  • can do both
• Denitrifiers:

  Grow by aerobic respiration of inorganic N (NO3/2-) to gaseous NO, N2O, N2

  Facultative aerobes and chemoorganotrophs (use organic C for e- donor)
• Denitrifiers:

  • Genera: Paracoccus, Pseudomonas
  • NB in agricultural soils, cause loss of N fertilizers
  • Diverse - Genes for denitrification are widespread via horizontal gene exchange)
  • many nitrate reducers only have part of the pathway