Epsilonproteobacteria represent a diverse group of microorganisms. This class of bacteria plays multifaceted roles in both natural ecosystems and, in some instances, impacts human health.
Understanding Epsilonproteobacteria
Epsilonproteobacteria are classified as a class within the phylum Proteobacteria, a collection of Gram-negative bacteria. This class includes notable genera such as Campylobacter and Helicobacter, recognized for their specific shapes and metabolic capabilities.
Many Epsilonproteobacteria appear as curved rods, spiral, or helical shapes. They are microaerophilic, meaning they thrive in environments with low oxygen concentrations, but not entirely oxygen-free conditions. Their metabolic diversity is notable, with some species being chemoheterotrophs, obtaining energy from organic compounds, while others are chemolithoautotrophs, deriving energy from inorganic chemical reactions and fixing carbon dioxide.
Diverse Habitats of Epsilonproteobacteria
These bacteria inhabit a range of environments. They are found in extreme marine settings, such as deep-sea hydrothermal vents and cold seeps, where they thrive despite high temperatures, extreme pressures, and unusual chemical compositions. In these deep-sea environments, they colonize the periphery of vents where hot, chemically rich water mixes with cooler ocean water.
Beyond these extreme aquatic habitats, Epsilonproteobacteria also exist in more common environments. They are found in marine sediments and terrestrial soils. Additionally, many species inhabit the digestive tracts of various animals, including both marine and terrestrial mammals, serving as either beneficial symbionts or pathogens.
Ecological Contributions and Symbiotic Relationships
Epsilonproteobacteria contribute to various biogeochemical cycles. They are active in the sulfur cycle, with many species capable of sulfur reduction or oxidation, which is a significant process in marine and terrestrial ecosystems. They also participate in the nitrogen cycle, performing processes like denitrification, which helps regulate nitrogen availability in environments such as deep-sea cold seeps.
In deep-sea hydrothermal vents and cold seeps, Epsilonproteobacteria often form symbiotic relationships with marine invertebrates. These bacteria act as primary producers, converting reduced chemical compounds from the Earth’s interior into energy. For example, some Epsilonproteobacteria live as endosymbionts within the gills of deep-water sea snails, providing nutrients to their hosts in nutrient-poor deep-sea environments. This chemosynthetic activity forms the base of the food web in these unique ecosystems.
Epsilonproteobacteria and Human Health
Some species within the Epsilonproteobacteria class are significant human pathogens, with Campylobacter and Helicobacter being the most well-known examples. Campylobacter jejuni is a leading cause of foodborne illness worldwide, causing a condition called campylobacteriosis. This bacterium commonly resides in the intestinal tracts of animals, especially poultry, and is transmitted to humans primarily through consumption of undercooked poultry, unpasteurized dairy products, or contaminated water.
Symptoms of Campylobacter jejuni infection typically appear two to five days after exposure and include diarrhea, which can be watery or bloody, abdominal pain, cramping, fever, and nausea. While most cases are mild and resolve within about a week, some individuals, particularly young children, the elderly, or those with weakened immune systems, may develop more severe illness. Rarely, Campylobacter infections can lead to complications such as Guillain-Barré syndrome, a serious neurological disorder, or reactive arthritis.
Another prominent pathogen is Helicobacter pylori, a spiral-shaped bacterium that infects the stomach lining. H. pylori is a major cause of peptic ulcers, which are sores in the lining of the stomach or small intestine, and chronic inflammation of the stomach lining known as gastritis. The infection is often acquired during childhood, and while many infected individuals remain without symptoms, it can lead to long-term damage.
Helicobacter pylori infection also increases the risk of stomach cancer, accounting for a significant percentage of cases globally. Transmission of H. pylori primarily occurs through direct person-to-person contact, such as sharing food or utensils, or through exposure to contaminated vomit or stool. The bacteria’s ability to survive in the stomach’s acidic environment by producing enzymes that neutralize acid allows it to establish chronic infections, silently altering the stomach environment and increasing cancer risk over time.