Microbiology Revision

    Temperature/pH: Temperature monitor and control to maintain the optimum conditions, water jackets remove excess heat due to respiration, commercial and sophisticated monitors improve the control of temperature and pH, add acid/alkali/buffer to maintain optimum pH.

    Culture/ medium: Pure culture is needed for pure product (only one microorganism), vessel and medium should be sterilised and mixing of the culture to improve contact with nutrients.

    Aeration/mixing: Sterile air produced by a filter, not needed by bacteria/fungi if anaerobic, in commercial machines air inlets use spargers and other devices to improve aeration, forced aeration may be needed for maximum growth of aerobes, mixing can be improved by a seperate mixer, provide oxygen for aerobes, improves contact with nutrients and prevent sedimentation (bacteria/fungi sink to the bottom)

    Product: Batch fermentation - nutrients added at the start and nothing added in the fermentation processs, products harvested at the end. Continuous fermentation - nutrients and products are harvested throughout the process.

- the vessel should be sterilised beforehand and an appropriate sterile medium used. During use the vessel openings must be protected from contamination by filters, aseptic conditions and handiling are required to maintain purity.                                                                                          

- Primary metabolites are involved in normal growth and metabolism of cells. The production of primary metabolites matches the growth rate of the population e.g. ethanol produced by the fermentation of yeast cells. Normally continuous fermentation. 

- Secondary metabolites are used to reduce competition and kill bacteria around itself. The production of secondary metabolites reach a maximum level after the exponential growth phase, they may be secreted by cells e.g. the antibiotic penicillin produced by the fermentation of the Penicillium notatum. Usually batch fermentation. 

For the commercial production of penicillin the fungus Penicillium notatum is grown in batch culture. The antibiotic produced after the growth phase, when glucose is depleted (secondary metabolite). This reflects the need of the organism, when free living, to reduce competition when food supplies are running out.

1) Fermenter is inoculated with a culture of Penicillin notatum, which grows under optimum conditions provided in the fermenter

30 hours later

2) The penicillin is secreted by the fungus and accumulates in the medium, there's a delay in the process due to penicillin being a secondary metabolite

6 days later

3) Culture fluid mixture is filtered and the penicillin is extracted and purified. Culture medium, after filtering is retained and processed. 

Disadvantage of method: the fermenter has to be emptied, cleaned and sterilised ready for the next batch.