1. General

To thrive, every organism needs a source of carbon, nitrogen, phosphorus, sulfur, mineral elements called trace elements, water and energy. These are sometimes required when bacterial metabolism is unable to synthesize them.

• Microorganisms are classified according to their carbon and energy requirements (table ).

  Most industrial processes involve heterotrophic micro-organisms, which use the cellular carbon of organic compounds in the environment and oxygen.

  A distinction is made between aerobic processes, which require the supply of dissolved oxygen to the cells, and anaerobic processes, where the cells draw oxygen from organic compounds.

  In contrast, autotrophic microorganisms derive their energy from light and use CO _2...