Microbe classification according to ecotype
Additional to a genetic classification into species, qualities like type of energy and type of nutrients and physicochemical living conditions like temperature, pH and salinity are useful characteristics of an organism since these environmental factors determine whether an organism will survive, grow or die.
Energy is used to maintain chemical disequilibrium, a criterion of life. Organisms have different energy sources:
- Light is used by phototrophs
- Chemical compounds are used by chemotrophs
Nutrients are needed to build cell mass.
Carbon is the most abundant macronutrient in the cell. Organisms have different sources of carbon:
After carbon, nitrogen is the next most abundant element in the cell
- Inorganic nitrogen (N2) - Nitrogen fixaters
- Organic nitrogen – Special name?
Combining energy and carbon source
A fuller description of microbes typically refers to both energy and carbon source. Combinations:
- Lithotrophic autotroph = chemolithotroph
- Chemoorganotrophs are always heterotrophs. Organotrophic heterotrophs. (For example humans. Most known bacteria and archaea are chemoorganotrophs, as are all animals, fungi, and many protists.)
- Phototroph + autotroph = photoautotroph
- Phototroph + heterotroph = photoheterotroph
In addition to sources for energy and nutrients, the environmental factors must be favourable in order for an organism to survive and thrive:
- Psychrophiles grow at 0-20 °C. Optimum growth 15°C or lower
- Thermophiles Optimum growth 45-80°C
- Hyperthermophiles Optimum growth 80°C or higher
- Halophiles – manage high Na-concentrations