1. Energy Source:
* Phototrophs: These bacteria get energy from light. They use pigments like chlorophyll to capture sunlight and convert it into chemical energy. Examples include cyanobacteria.
* Chemotrophs: These bacteria get energy from the oxidation of chemical compounds. This includes:
* Chemoorganotrophs: They break down organic compounds like sugars, proteins, or fats.
* Chemolithotrophs: They break down inorganic compounds like hydrogen sulfide, ammonia, or ferrous iron.
2. Electron Source:
* Organotrophs: They obtain electrons from organic compounds.
* Lithotrophs: They obtain electrons from inorganic compounds.
3. Carbon Source:
* Autotrophs: They fix carbon dioxide (CO2) from the atmosphere to build organic compounds.
* Heterotrophs: They obtain carbon from pre-existing organic molecules.
Metabolic Pathways:
Bacteria employ various metabolic pathways to extract energy from their sources. Some key pathways include:
* Glycolysis: A common pathway used by many bacteria to break down glucose and produce ATP (energy currency).
* Krebs Cycle: This pathway generates additional ATP and electron carriers used in the electron transport chain.
* Electron Transport Chain: This chain of proteins uses the energy from electron carriers to pump protons across a membrane, generating a proton gradient. The flow of protons back across the membrane drives ATP synthesis.
* Fermentation: Some bacteria use this pathway to produce energy in the absence of oxygen. This process involves breaking down organic molecules without using an electron transport chain.
Examples:
* E. coli: A chemoheterotrophic bacterium that obtains energy from glucose through glycolysis and the Krebs Cycle.
* Nitrifying bacteria: Chemolithotrophs that obtain energy from the oxidation of ammonia to nitrite and nitrite to nitrate.
* Cyanobacteria: Photoautotrophs that use photosynthesis to produce energy from sunlight and carbon dioxide.
In summary:
Bacteria are diverse in their metabolic strategies, allowing them to thrive in a wide range of environments. They obtain energy by breaking down chemical compounds and use various metabolic pathways to harness this energy for growth and other processes.
