Question continued: In the laboratory these cultures are placed in such an environment (many times) together with a lit candle to get that extra CO2. Why is this extra CO2 needed? Which metabolic pathway is being used?

Answer by Tirumalai Kamala:

To culture anaerobic bacteria, we need to maintain reduced oxygen tension in the culture medium. There are two main approaches to create incubation conditions permissive for anaerobe growth, to either physically or chemically reduce the oxygen tension. The candle method physically reduces the oxygen tension. The story of the candle goes a while back, 1926 to be precise, when Parker and Hudson first described it, and it has nothing to do with metabolic pathways per se (Page on nih.gov). Burning the candle does two things:

  1. Increases the amount of CO2 in the atmosphere.
  2. Decreases the oxygen tension.

A candle extinction jar typically contains 2 to 3% CO2. Since 1926, a variety of comparisons suggest that both increasing the CO2 and decreasing the oxygen tension, as the candle extinction jar does,  are important for anaerobe growth (Page on europepmc.org;Page on asm.org).

Certain bacteria require an anaerobic environment in order to grow successfully. In the laboratory these cultures are placed in such an e…