Applications of Biotechnological Processes

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Applications of Biotechnological Processes

• Enhancing Nitrogen Fixing

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Nitrogen fixation Revision

• Nitrogen is an element required for the amino
  groups of proteins.
• Nitrogen is taken up by plants in the form of
  ammonium or nitrate. These supplies of nitrogen
  are usually limiting.
• Nitrogen fixing bacteria convert atmospheric
  nitrogen into ammonia.
• Nitrogen fixing bacteria can be free living e.g.
  Azotobacter or be in symbiosis with plants (root
  nodules) e.g. Rhizobium.

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• Enzyme nitrogenase is responsible for the
  conversion of nitrogen to ammonia.
• Nitrogenase operates in anaerobic conditions but
  nitrogen fixation is an ATP demanding reaction
  (aerobic respiration is therefore necessary).
• Leghaemoglobin in root nodules binds to oxygen to
  prevent it disabling nitrogenase activity.
  Leghaemoglobin releases oxygen slowly for aerobic
  respiration to take place.

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Rhizobia

• Contain a set of nif genes that are responsible
  for the coding of nitrogenase.
• However the expression of nif genes alone is not
  sufficient for nitrogen fixation to take place.
• Scientists have attempted to transfer nif genes
  to other bacteria e.g. E.coli and directly into
  plant cells. However nitrogenise expression has
  not been successful

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Enhancing nitrogen fixing

• Farmers can add Rhizobia inoculum cultures to
  their legume fields (this reduces the need for
  artificial fertiliser and increases crop yield).

• Mutant Rhizobia have been engineered so that the
  nif genes are never switched off. The effector
  complex which binds to the nif genes to prevent
  expression in high nitrogen environments, is
  prevented from binding

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• There are many species of Rhizobia. A single
  species will form a symbiosis with only certain
  legumes (there is a degree of specificity between
  plant and bacteria).
• This specificity is due to the type of plasmid
  carried by the Rhizobia. The plasmid produces
  enzymes that are responsible for producing signal
  molecules that are detected by the plant.
• It is possible to transfer the plasmid of one
  Rhizobia species to another Rhizobia.

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The plasmid from (a) is transferred to Rhizobium
(b), to create (c) that can infect pea and carry
out good fixation.

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An ideal inoculum will

• Have a large number of bacteria
• Have been mutated to ensure that nif genes are
  permanently switched on
• Have the correct plasmid for the target plant
  species
• Past Paper Questions
• 2004 Q1(ii)