A culture medium must contain a balanced mixture of the required nutrients, at concentrations sufficient to allow a good growth rate. If a nutrient is in excess, it can inhibit growth or even be toxic. Often one nutrient is present in limiting quantities, to allow adequate growth while preventing the microorganisms from multiplying at their maximum rate. By moderately slowing down the growth rate, the microorganisms are kept healthy. Usually a mineral base is made, containing all the possible nutrients in inorganic form. To this can be added a carbon source, energy source, nitrogen source and growth factors, to suit the organism being cultured. A medium composed entirely of chemically defined nutrients is called a synthetic medium. A medium which contains some ingredients of unknown chemical composition, such as malt extract, is called a complex medium.
No comments:
Post a Comment