Nitric Oxide Synthesis Protects Against Oxidative Stress

close up microscopic image of bacteria in a petri dish

Biological Strategy

Bacteria

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Chemically Generate Flow of Electrons (Redox)

Electron flows, or electron transport, is a critical step in numerous biochemical pathways. For example, the flow of electrons along the electron transport chain between membrane-bound proteins of mitochondria during cellular respiration or the chloroplast during photosynthesis triggers a flow of protons across the same membrane. This flow provides the energy for cellular processes similar to the flow of water across a hydroelectric dam.

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Modify Electron Transport

Electron transport is essential for helping organisms to produce energy and survive. Several species can modify the movement of electrons in different ways, allowing them to survive in a variety of conditions.

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Modify Oxidation State

Oxidation state refers to the degree to which an element has gained or lost electrons–it can have a significant impact on the characteristics of that element. For example, hexavalent chromium with an oxidation number of +6, is a known carcinogen whereas the less oxidized (i.e., “reduced”) trivalent form, with an oxidation number of +3, is less toxic. The bacterium, Acidiphilium cryptum, can enzymatically convert chromium from the hexavalent to the trivalent form.

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Modify Free Radical Reactivity

Free radicals are molecules react very easily with other molecules, which can cause them to breakdown or cease to function in the same way. They are natural by-products of many biochemical reactions in the body, including metabolism and immune responses. Different organisms have adapted to modify or control free radical activity, in order to maintain the integrity of their biochemical processes and improve their fitness.

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Chemically Break Down Inorganic Compounds

The vast majority of biochemical assembly and breakdown processes–even by the most complex organisms–occur within cells. In fact, cells are able to perform hundreds, even thousands of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). For example, inorganic pyrophosphate is hydrolyzed to form two phosphate groups in the cellular degradation pathway of fatty acids.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Bacillus subtilis defends itself against the damaging effects of oxidative free-radicals by synthesizing nitric oxide.

Immune cells like macrophages release free radicals when they encounter foreign microbes. Free radicals can cause oxidative stress including damage to DNA and cellular materials leading to cell death. Some bacteria, like Bacillus subtilis utilize a nitric oxide (NO) mediated system to rapidly respond to oxidative stress and minimize its effects. When reactive oxygen species (ROS) like hydrogen peroxide are detected by a bacterium, NO is quickly synthesized enzymatically. The NO counteracts the effects of the ROSs by two means. It activates a class of enzymes called catalases that break down hydrogen peroxide, or it starves the cell of the reduced form of iron needed by hydrogen peroxide to cause cell damage. This process increases bacterial resistance to hydrogen peroxide 100 fold in only 5 seconds. Although other processes like the synthesis of specialized proteins are responsible for long term resistance to ROSs, NO represents a critical rapid response chemical that confers immediate protection to the cell.

Last Updated August 23, 2016

References

Journal article

Bacterial Nitric Oxide Synthases

Annu. Rev. Biochem. | 09/06/2010 | Brian R. Crane, Jawahar Sudhamsu, Bhumit A. Patel

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Reference

Journal article

NO-mediated cytoprotection: Instant adaptation to oxidative stress in bacteria

Proceedings of the National Academy of Sciences | 20/09/2005 | I. Gusarov, E. Nudler

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