Sulphur cycle

Sulphur cycle

Sulphur cycle

  • Sulphur is found in living organisms in the form of compounds such as amino acids, coenzymes and vitamins.
  • It can be utilised by different types of organisms in several forms.
  • In its elemental form, sulphur is unavailable to most organisms.
  • However, certain bacteria such as Acidithiobacillus are able to oxidise it to sulphate, a form that can be utilised by an organisms.

bacteria oxidise it to sulphate

  • Sulphate-reducing bacteria convert the sulphate to hydrogen sulphide gas using either an organic compound or hydrogen gas as electron donor:

sulphate to hydrogen sulphide gas

sulphur cycle

  • These bacteria are obligate anaerobes, and the process is termed dissimilatory sulphate reduction.
  • Plants are also able to utilise sulphate, incorporating it into cellular constituents such as the amino acids methionine and cysteine.
  • Plants and bacteria incorporate sulfates to become part of sulfur-containing amino acids for humans and other animals.
  • When the plants die, these compounds are broken down, again with the release of hydrogen sulphide.
  • Green and purple photosynthetic bacteria and some chemoautotrophs use hydrogen sulphide as an electron donor in the reduction of carbon dioxide, producing elemental sulphur and thus completing the cycle.

Sulphur cycle





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