Microbial metabolism is the series of biochemical reactions needed for life. It includes catabolism, which is how these organisms obtain energy, and amabilism, that we'll encounter towards the end of this chapter, which allows them to build their macromolecules. Most organisms employ only one type of metabolism, but some can use different energy sources depending on their environmental conditions. Now we're going to look at the energy sources to start with, and those can be defined as either a chemical energy source or light, in particular, photon energy source. We're just going to call it light to be more simple.
Chemical energy sources, otherwise known as chemotrophs, trophy meaning to nourish. can be further defined based on the type of chemical. So we have organic chemicals like glucose, and these are referred to as chemo-organotrophs. So we have this word, but now we're also inserting a definition to tell us a little bit more detail about it. And a great example of these organisms is E.
coli. We also have those that use inorganic chemicals as their energy source, for example, hydrogen gas. and these are our chemolithotrophs, litho meaning stone-like. Example here that you've probably never heard of, theobacillus theo-oxidans, and these will use these to make ATP and other molecules for energy. Now if we look back at light or our phototrophs, these contain pigments that allow them to use photons as an energy source.
For example, Rhodobacter capsulatus is a great example. Now in addition to energy, cells also require carbon. So these are the definitions over here for carbon. So heterotrophs obtain carbon from organic sources. So this is from organic sources and autotrophs use carbon dioxide as a carbon source.
So these are inorganic forms of carbon. And so we can join some of these together. So we can have, for example, chemolithotrophs, but we can now add chemolithoautotrophs because most chemolithotrophs and most phototrophs are autotrophs. In addition, most chemoorganotrophs are heterotrophs.
So we can add that into our definition as well, chemoorganoheterotroph.