Like humans and other animals, bacteria need to breathe. In some cases, bacteria use oxygen to respire, as humans do. In other situations, bacteria use one or more different molecules as a final electron acceptor for respiration. The purpose of respiration is to provide the cell with the appropriate molecules for creating energy in the form of adenosine triphosphate, ATP. ATP is the energy currency of cells, allowing important cellular processes to proceed.
Bacterial respiration begins with a step, glycolysis, that is primarily concerned with the breakdown of sugar to create ATP and important byproducts. In glycolysis, an organic molecule known as pyruvate supplies energy to the Kreb's cycle and is broken down into two molecules of acetyl-CoA. Acetyl-CoA is the main source of carbon that enters the Kreb’s cycle for energy production. The Kreb's cycle uses these molecules to create a small amount of ATP, and a large amount of NADH+ and FADH2. NADH+ and FADH2 have great importance in donating protons to the membrane potential around the electron transport chain, which further drives production of ATP.
The Proton Gradient
NADH+ and FADH2 act as transports for protons. These molecules move from the Kreb’s cycle to the electron transport chain and carry protons. In the electron transport chain, NADH+ and FADH2 donate protons and increase the proton gradient on the outside of the cell. Once enough protons relocate outside the cell membrane, the cell is ready to begin producing adenosine triphosphate.
Electron Transport Chain
In addition to oxygen, bacteria can respire with many different inorganic and organic molecules. According to the Ohio State University, anaerobic bacteria use inorganic molecules like nitrate, sulfate and carbonate as final electron acceptors in the place of oxygen. These molecules sit at the end of the electron transport chain. The electron transport chain in bacteria uses the products of glycolysis, a process that breaks down sugars, to create a proton gradient across the outside of the cell membrane. These protons then cross back across the cell membrane, driving the addition of a phosphate group to adenosine diphosphate, an adenosine molecule with only 2 phosphate groups, to make adenosine triphosphate.
Mutations in genes in the electron transport chain causes decreased function in the chain, which can result in the cell not producing enough energy to live. Often mutations in the electron transport chain are deleterious; they cause cell death. Cellular processes simply can’t proceed without the energy produced from the electron transport chain.
The electron transport chain can be blocked through the use of poisons. Rat poison works by blocking one of the first steps in the electron transport chain. Other poisons like cyanide and carbon monoxide block steps further down in the chain. Use of poisons is typically not recommended for controlling a problematic bacterial population, as the poisons do not distinguish between human and bacterial electron transport chains.
- Ohio State University: Cellular Respiration
- "Microbiology: 6th Edition"; Lansing Prescott, John Harley and Donald Klein; 2005