GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

6. MICROBIAL GROWTH

6.3. MICROBIAL NUTRITION

6.3.4. Growth and non-growth substrates

If a carbon compound is utilized by a microorganism as the sole source of carbon, energy, and electrons, this is a classic example illustrating METABOLISM/2.html">THE CONCEPT OF a growth substrate. In this context, we will focus exclusively on carbon compounds as growth factors, without detailing sources of nitrogen, phosphorus, and other elements essential for Microbial growth.

It is also well known that the carbon and Energy Sources are not always the same compound. For most autotrophic microorganisms, carbon dioxide serves as the carbon source, while energy may be derived from an organic or inorganic compound, or light, with electrons donated by either an organic or inorganic compound. In such cases, the growth substrate consists of two or three distinct compounds that supply The Cell with energy and electrons. Obviously, none of these components individually can support microbial growth. For instance, According to the Classification and data presented in Table 6.5, autotrophic organisms such as cyanobacteria and purple sulfur Bacteria exhibit a photolithotrophic mode of Nutrition (energy source: light; electron donor: Inorganic Compounds). Autotrophs such as nitrifying bacteria, hydrogen bacteria, methanogens, and iron-reducing/iron-oxidizing bacteria are chemolithotrophs (energy source: an inorganic compound; electron donor: also an inorganic compound). In the latter case, the growth substrate comprises three different compounds.

A non-growth substrate is a substance (compound) that is not utilized by a microorganism as a sole source of carbon and energy.