are diverse with five main classes. They're found everywhere, from soil to deep-sea vents. Some fix nitrogen for plants, while others cause diseases. Their varied metabolisms and structures make them crucial in ecosystems and human health.
These bacteria interact with humans in both good and bad ways. Some help clean up pollution or produce useful compounds. Others cause infections like E. coli or H. pylori. Understanding Proteobacteria is key for medicine, agriculture, and environmental science.
Characteristics and Significance of Proteobacteria Classes
Classes of Proteobacteria
are , aerobic or facultatively anaerobic bacteria with diverse metabolic capabilities including photoautotrophy (obtaining energy from light), chemoautotrophy (obtaining energy from chemical compounds), or chemoheterotrophy (obtaining energy from organic compounds) and includes important nitrogen-fixing bacteria that convert atmospheric nitrogen into bioavailable forms for plants ()
are Gram-negative, aerobic or facultatively anaerobic bacteria with chemoheterotrophic metabolism, some species capable of (reducing nitrate to nitrogen gas), and includes plant pathogens () and symbionts
are Gram-negative, aerobic or facultatively anaerobic bacteria with chemoheterotrophic metabolism, includes bioluminescent bacteria () and purple sulfur bacteria (Chromatium), and contains many human pathogens (, )
are Gram-negative, anaerobic bacteria that includes () and iron-reducing bacteria (), some species are predatory () or form ()
are Gram-negative, microaerophilic (require low oxygen levels) or anaerobic bacteria with chemoheterotrophic metabolism, includes human pathogens () and symbionts found in deep-sea hydrothermal vents ()
Representative Proteobacteria species
Alphaproteobacteria: forms symbiotic relationships with legumes (peas, beans) and fixes atmospheric nitrogen in , providing bioavailable nitrogen for the plant
Betaproteobacteria: cepacia is an opportunistic pathogen in cystic fibrosis patients and is capable of degrading various pollutants (pesticides, herbicides)
Gammaproteobacteria: is a model organism for molecular biology and genetics research, while some strains are pathogenic, causing intestinal (diarrhea) and extraintestinal infections (urinary tract infections)
Deltaproteobacteria: forms and exhibits , and produces bioactive compounds with potential pharmaceutical applications (antitumor, antibiotic properties)
Epsilonproteobacteria: pylori colonizes the human stomach and causes gastritis, peptic ulcers, and is a risk factor for gastric cancer
Proteobacteria-human interactions
Beneficial interactions:
by Rhizobium in legume root nodules provides bioavailable nitrogen for plants, reducing the need for synthetic fertilizers and improving soil fertility
Production of bioactive compounds with pharmaceutical potential by Myxococcus xanthus, offering new avenues for drug discovery and development
Bioremediation of pollutants by some Betaproteobacteria (Burkholderia, Comamonas) can aid in environmental cleanup and restoration
Pathogenic interactions:
Gastrointestinal infections caused by coli strains (EHEC, ETEC) leading to diarrhea, hemorrhagic colitis, and potentially life-threatening , and Helicobacter pylori causing gastritis, peptic ulcers, and increasing the risk of gastric cancer
Respiratory infections such as caused by (Betaproteobacteria) and Legionnaires' disease caused by pneumophila (Gammaproteobacteria), both leading to severe respiratory symptoms and complications
Urinary tract infections commonly caused by uropathogenic Escherichia coli (), resulting in painful and recurrent infections that can lead to kidney damage if untreated
Opportunistic infections in immunocompromised individuals, such as lung infections in cystic fibrosis patients caused by Burkholderia cepacia (Betaproteobacteria) and nosocomial infections in various body sites caused by aeruginosa (Gammaproteobacteria), both exploiting weakened immune systems to establish infection
Cellular structures and communication
Many Proteobacteria possess flagella, which are important for motility and (directed movement in response to chemical gradients)
The outer membrane of Gram-negative Proteobacteria contains , a complex molecule that contributes to pathogenicity and antibiotic resistance
Some species use , a cell-to-cell communication mechanism, to coordinate group behaviors such as biofilm formation and virulence factor production
Key Terms to Review (87)
Agrobacterium: Agrobacterium is a genus of Gram-negative bacteria known for its ability to transfer DNA to plants. It is commonly used in genetic engineering for creating transgenic plants.
Alphaproteobacteria: Alphaproteobacteria are a class of bacteria within the phylum Proteobacteria, known for their diverse metabolic capabilities and ecological roles. They include many agriculturally and medically important species.
Bacteria: Bacteria are single-celled, prokaryotic microorganisms that lack a nucleus and membrane-bound organelles. They can be found in nearly every habitat on Earth and have diverse metabolic capabilities.
Bartonella: Bartonella is a genus of gram-negative bacteria that are intracellular pathogens primarily transmitted by vectors such as fleas, lice, and ticks. They are known to cause a variety of diseases in humans, including cat scratch disease and trench fever.
Bdellovibrio: Bdellovibrio is a genus of predatory bacteria known for preying on other Gram-negative bacteria. It displays a unique life cycle that involves invading and replicating within the periplasm of its prey.
Beggiatoa: Beggiatoa is a genus of colorless, filamentous sulfur bacteria found in both freshwater and marine environments. They play a role in the sulfur cycle by oxidizing hydrogen sulfide to sulfate.
Betaproteobacteria: Betaproteobacteria are a class of Gram-negative bacteria within the phylum Proteobacteria, characterized by their metabolic diversity. They play significant roles in nitrogen fixation and are commonly found in soil and water environments.
Bioluminescence: Bioluminescence is the production and emission of light by living organisms, typically as a result of biochemical reactions. In microbiology, it is often observed in certain species of bacteria, including some proteobacteria.
Bordetella: Bordetella is a genus of Gram-negative, obligate aerobic bacteria known for causing respiratory illnesses in mammals, including humans. The most notable species is Bordetella pertussis, the causative agent of whooping cough.
Bordetella pertussis: Bordetella pertussis is a Gram-negative, aerobic coccobacillus that causes whooping cough, a highly contagious respiratory disease. It primarily infects the trachea and bronchi by producing toxins that paralyze the respiratory cilia.
Brucella: Brucella is a genus of Gram-negative bacteria that are pathogenic and cause brucellosis in various animals and humans. These bacteria are primarily intracellular and affect the circulatory and lymphatic systems.
Burkholderia: Burkholderia is a genus of Proteobacteria known for its metabolic diversity and environmental versatility. These bacteria are often found in soil and water, some species being pathogenic to humans and plants.
Burkholderiales: Burkholderiales is an order of Gram-negative Proteobacteria known for their metabolic diversity and environmental adaptability. They are commonly found in soil, water, and as plant and animal pathogens.
Caulobacter: Caulobacter is a genus of gram-negative bacteria within the class Alphaproteobacteria, known for its unique life cycle characterized by asymmetric cell division. It is commonly found in freshwater environments and plays a role in nutrient cycling.
Chancroid: Chancroid is a bacterial infection caused by Haemophilus ducreyi, characterized by painful genital ulcers and swollen lymph nodes. It is a sexually transmitted infection (STI) that primarily affects the urogenital system.
Chemotaxis: Chemotaxis is the directed movement of an organism or cell in response to a chemical stimulus. It is a fundamental process that allows organisms to navigate their environment and respond to various chemical signals, such as those involved in finding food, avoiding threats, or locating a suitable host or habitat.
Coliforms: Coliforms are a group of Gram-negative, non-spore-forming bacteria that are commonly found in the environment and in the feces of warm-blooded animals. They are often used as indicator organisms to assess water quality and potential contamination.
Coxiella: Coxiella is a genus of bacteria that includes the pathogenic species Coxiella burnetii, which causes Q fever in humans. It is an obligate intracellular pathogen, meaning it can only replicate within host cells.
Deltaproteobacteria: Deltaproteobacteria are a class of Proteobacteria known for their diverse metabolic capabilities, including sulfur reduction and predatory behavior. They are often found in aquatic environments and soil.
Denitrification: Denitrification is a microbial respiratory process in which nitrate (NO3-) is reduced to gaseous nitrogen compounds, such as nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2), which are then released into the atmosphere. This process is particularly important in the biogeochemical cycling of nitrogen within various ecosystems, including soils and aquatic environments.
Desulfovibrio: Desulfovibrio is a genus of Gram-negative, sulfate-reducing bacteria commonly found in anaerobic environments. These bacteria play a significant role in the sulfur cycle by reducing sulfate to hydrogen sulfide.
Ehrlichia: Ehrlichia is a genus of obligate intracellular bacteria that are transmitted by ticks and can cause the disease ehrlichiosis in humans and animals. These bacteria primarily infect white blood cells, leading to various clinical symptoms.
Enteric: Enteric refers to anything related to or affecting the intestines. In microbiology, it often pertains to bacteria that inhabit the gastrointestinal tract.
Enterobacteriaceae: Enterobacteriaceae is a large family of Gram-negative bacteria that includes many pathogenic genera such as Escherichia, Salmonella, and Klebsiella. These bacteria are commonly found in the intestinal tract of humans and animals.
Epidemic typhus: Epidemic typhus is a bacterial infection caused by Rickettsia prowazekii, primarily transmitted through the body louse. Characterized by high fever, rash, and severe headache, it can be fatal if untreated.
Epsilonproteobacteria: Epsilonproteobacteria are a class of Proteobacteria, known for being microaerophilic, often found in extreme environments. They include important genera such as Helicobacter and Campylobacter, which are notable pathogens.
Erwinia: Erwinia is a genus of Gram-negative bacteria belonging to the family Enterobacteriaceae. They are known for causing plant diseases such as soft rot and fire blight.
Escherichia: Escherichia is a genus of Gram-negative, rod-shaped bacteria commonly found in the intestines of warm-blooded organisms. The most well-known species is Escherichia coli (E. coli), which can be both a harmless gut bacterium and a pathogen.
Escherichia coli: Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacterium commonly found in the intestines of warm-blooded organisms. While most strains are harmless, some can cause serious food poisoning and infections.
Fruiting bodies: Fruiting bodies are multicellular structures produced by certain microorganisms, particularly some bacteria and fungi, for the purpose of spore dispersal. They play a critical role in the reproductive cycle of these organisms.
Fruiting Bodies: Fruiting bodies are the reproductive structures produced by certain types of microorganisms, particularly fungi. They serve as the means for these organisms to disperse their spores and propagate to new environments.
Gammaproteobacteria: Gammaproteobacteria are a class of diverse, Gram-negative bacteria that include many well-known human pathogens. They are characterized by their metabolic diversity and ability to thrive in various environments.
Geobacter: Geobacter is a genus of anaerobic, metal-reducing bacteria that play a crucial role in the biogeochemical cycling of various elements, particularly in subsurface environments. These bacteria are known for their ability to use a wide range of organic compounds as electron donors and solid metal oxides as electron acceptors, making them important players in the transformation and remediation of environmental contaminants.
Gliding Motility: Gliding motility is a unique form of bacterial movement that does not involve flagella or other appendages. Instead, bacteria with gliding motility are able to propel themselves across surfaces or through liquids using a smooth, sliding motion.
Gram-negative: Gram-negative refers to a classification of bacteria based on their cell wall structure and response to the Gram staining technique. Gram-negative bacteria have a unique cell wall composition that distinguishes them from Gram-positive bacteria, with important implications for their characteristics and behavior.
Gram-negative bacteria: Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining method. They have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides.
Helicobacter: Helicobacter is a genus of Gram-negative, microaerophilic bacteria known for colonizing the stomach lining and causing chronic gastritis and peptic ulcers. It includes species like Helicobacter pylori, which is linked to stomach cancer.
Helicobacter pylori: Helicobacter pylori is a gram-negative, spiral-shaped bacterium that colonizes the human stomach lining. It is associated with various gastrointestinal diseases, including peptic ulcers and gastric cancer.
Hemolytic Uremic Syndrome: Hemolytic uremic syndrome (HUS) is a rare and life-threatening condition characterized by the sudden destruction of red blood cells (hemolytic anemia), the sudden failure of the kidneys (uremia), and a low platelet count (thrombocytopenia). It is often triggered by a bacterial infection, typically involving the Shiga toxin-producing Escherichia coli (STEC) bacteria, and can lead to severe complications if not promptly treated.
Hemophilus: Hemophilus is a genus of Gram-negative, facultatively anaerobic bacteria that are part of the Proteobacteria phylum. Notable for its role in respiratory tract infections, it includes species like Hemophilus influenzae.
Hyphomicrobium: Hyphomicrobium is a genus of Proteobacteria known for its unique budding reproduction and methylotrophic metabolism. These bacteria are commonly found in aquatic environments and soil.
Legionella: Legionella is a genus of pathogenic Gram-negative bacteria that includes the species L. pneumophila, responsible for causing Legionnaires' disease. These bacteria thrive in aquatic environments and can infect humans through inhalation of contaminated water droplets.
Legionnaires disease: Legionnaires' disease is a severe form of pneumonia caused by the bacterium Legionella pneumophila. It primarily affects the lungs and can be fatal if not treated promptly.
Leptothrix: Leptothrix is a genus of filamentous, iron-oxidizing bacteria commonly found in aquatic environments. They are known for their ability to create sheaths encrusted with iron and manganese oxides.
Lipopolysaccharide: Lipopolysaccharide (LPS) is a complex molecule found in the outer membrane of Gram-negative bacteria. It is a key component of the bacterial cell wall and plays a crucial role in various aspects of microbiology, immunology, and pathogenesis.
Meningitis: Meningitis is an inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. It can be caused by bacterial, viral, fungal, or parasitic infections.
Methylocystis: Methylocystis is a genus of Gram-negative, methane-oxidizing bacteria belonging to the class Alphaproteobacteria. These bacteria play an essential role in the biogeochemical cycling of carbon by converting methane into methanol.
Methylomonas: Methylomonas is a genus of Gram-negative, rod-shaped bacteria that are part of the gammaproteobacteria class. These bacteria are known for their ability to oxidize methane as their source of carbon and energy.
Myxobacteria: Myxobacteria are a group of Gram-negative, rod-shaped bacteria within the class Deltaproteobacteria known for their complex life cycle and social behaviors. They exhibit unique gliding motility and form multicellular fruiting bodies under nutrient-limited conditions.
Myxobacterium: Myxobacterium are a type of gram-negative, rod-shaped bacteria known for their complex social behavior and ability to form fruiting bodies. They belong to the class Deltaproteobacteria and are found in soil and decaying organic matter.
Myxococcus: Myxococcus is a genus of Gram-negative, aerobic, myxobacteria that are known for their complex social behaviors and unique life cycle. These bacteria are commonly found in soil and play a significant role in the Proteobacteria class.
Myxococcus xanthus: Myxococcus xanthus is a species of Gram-negative, aerobic bacteria that belongs to the Proteobacteria phylum. It is known for its unique social behavior, complex life cycle, and ability to produce a wide range of secondary metabolites.
Myxospores: Myxospores are specialized, dormant cells formed by certain myxobacteria within fruiting bodies. They are resistant to desiccation and can survive harsh environmental conditions until favorable conditions return.
Nitrogen Fixation: Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into ammonia (NH3) or other organic compounds, making it available for biological processes. This is a crucial step in the nitrogen cycle that allows nitrogen to be utilized by living organisms.
Noncoliforms: Noncoliforms are a diverse group of bacteria that do not ferment lactose within 48 hours at 35°C. They are typically found in various environments including soil, water, and the intestines of animals.
Obligate intracellular pathogen: An obligate intracellular pathogen is a microorganism that can only replicate and survive within the cells of a host organism. They rely on the host's cellular machinery for energy production and reproduction.
Oligotroph: Oligotrophs are organisms that thrive in environments with very low nutrient concentrations. These microbes have adapted to survive and grow slowly under nutrient-limited conditions.
Pasteurellaceae: Pasteurellaceae is a family of Gram-negative, facultatively anaerobic bacteria within the class Gammaproteobacteria. Members of this family are often pathogenic and can infect both animals and humans.
Pertussis: Pertussis, also known as whooping cough, is a highly contagious respiratory disease caused by the bacterium Bordetella pertussis. It is characterized by severe coughing fits that can last for weeks.
Proteobacteria: Proteobacteria are a major phylum of Gram-negative bacteria that includes a wide variety of pathogenic and non-pathogenic species. They are characterized by their diverse metabolic capabilities and roles in various environments.
Pseudomonas: Pseudomonas is a genus of Gram-negative, rod-shaped bacteria known for their metabolic diversity and ability to thrive in various environments. They are often opportunistic pathogens, particularly Pseudomonas aeruginosa, which can cause infections in humans.
Quorum Sensing: Quorum sensing is a communication mechanism used by bacteria to coordinate gene expression and behavior in response to changes in cell population density. It allows bacteria to sense and respond to the presence of other bacteria, enabling them to act in a coordinated manner as a community rather than as individual cells.
R. rickettsii: Rickettsia rickettsii is a gram-negative, intracellular bacterium that causes Rocky Mountain spotted fever. It primarily infects endothelial cells and is transmitted to humans through tick bites.
Ralstonia solanacearum: Ralstonia solanacearum is a Gram-negative, aerobic, rod-shaped bacterium that is known as the causative agent of bacterial wilt, a devastating plant disease that affects a wide range of economically important crops. This bacterium is classified within the Proteobacteria phylum, specifically in the Betaproteobacteria class.
Rhizobium: Rhizobium is a genus of gram-negative soil bacteria that fix nitrogen after becoming established inside the root nodules of legumes. They play a crucial role in the nitrogen cycle by converting atmospheric nitrogen into ammonia, which plants can use.
Rhizobium leguminosarum: Rhizobium leguminosarum is a species of nitrogen-fixing bacteria that form symbiotic relationships with leguminous plants, such as peas, beans, and alfalfa. These bacteria are able to convert atmospheric nitrogen into a form that can be readily absorbed and utilized by the host plant, making them an important component of the nitrogen cycle.
Rickettsia: Rickettsia are a genus of obligate intracellular bacteria that cause various diseases, including typhus and Rocky Mountain spotted fever. They are transmitted primarily through arthropod vectors like ticks, fleas, and lice.
Rocky Mountain spotted fever: Rocky Mountain spotted fever (RMSF) is a bacterial infection caused by Rickettsia rickettsii, transmitted primarily through tick bites. It is characterized by fever, rash, and potentially severe complications if untreated.
Root Nodules: Root nodules are specialized structures that form on the roots of certain plants, particularly legumes, as a result of a symbiotic relationship with nitrogen-fixing bacteria. These nodules serve as a hub for the exchange of nutrients and the fixation of atmospheric nitrogen, which is crucial for plant growth and development.
Salmonella: Salmonella is a genus of rod-shaped, Gram-negative bacteria that cause gastrointestinal infections in humans and animals. These bacteria are known for their ability to cause foodborne illness through the ingestion of contaminated food or water.
Salmonellosis: Salmonellosis is an infection caused by Salmonella bacteria, often resulting in gastrointestinal illness. It is commonly transmitted through contaminated food or water.
Serotypes: Serotypes are distinct variations within a species of bacteria or viruses, classified based on their surface antigens. Different serotypes can elicit unique immune responses and may vary in virulence and resistance to treatments.
Serovars: Serovars are distinct variations within a species of bacteria or viruses, identified by differences in their surface antigens. They are used to classify microorganisms for epidemiological studies and disease tracking.
Serratia: Serratia is a genus of Gram-negative, rod-shaped bacteria often found in soil, water, and the human intestine. Serratia marcescens is the most studied species due to its association with hospital-acquired infections.
Shigella: Shigella is a genus of Gram-negative bacteria known for causing shigellosis, a severe form of dysentery. It primarily affects the gastrointestinal tract by invading and destroying the epithelial cells lining the intestines.
Sulfate-reducing bacteria: Sulfate-reducing bacteria (SRB) are a group of microorganisms that can obtain energy by oxidizing organic compounds or molecular hydrogen while reducing sulfate to hydrogen sulfide. They play a crucial role in the sulfur cycle and are commonly found in anaerobic environments.
Sulfurovum: Sulfurovum is a genus of chemolithoautotrophic bacteria within the Proteobacteria class. These bacteria are capable of oxidizing reduced sulfur compounds, such as sulfide, to obtain energy for growth and are commonly found in marine environments.
Thiobacillus: Thiobacillus is a genus of Gram-negative bacteria known for its role in the sulfur cycle. These bacteria are chemolithoautotrophs, meaning they obtain energy by oxidizing inorganic sulfur compounds.
Typhoid fever: Typhoid fever is a serious bacterial infection caused by the protoebacterium Salmonella enterica serotype Typhi. It spreads through contaminated food and water, leading to high fever, abdominal pain, and other systemic symptoms.
UPEC: UPEC, or Uropathogenic Escherichia coli, is a pathogenic strain of the Gram-negative bacterium Escherichia coli that is a leading cause of urinary tract infections (UTIs). UPEC is a member of the Proteobacteria phylum and has evolved specialized virulence factors that allow it to successfully colonize and infect the human urinary tract.
Vibrio: Vibrio is a genus of Gram-negative bacteria, several species of which can cause foodborne infections. These bacteria are typically found in marine environments and are associated with gastroenteritis in humans.
Vibrio fischeri: Vibrio fischeri is a bioluminescent marine bacterium that engages in symbiotic relationships with various marine organisms, including the Hawaiian bobtail squid. It is a Gram-negative, curved rod-shaped bacterium that is part of the Proteobacteria phylum and is known for its ability to produce light through a process called quorum sensing.
Vibrionales: Vibrionales is an order of Proteobacteria, characterized by a curved rod shape and commonly found in aquatic environments. Many species within this order are known for their pathogenicity in humans and marine life.
Whooping cough: Whooping cough, also known as pertussis, is a highly contagious bacterial infection of the respiratory tract caused by Bordetella pertussis. It is characterized by severe coughing fits followed by a high-pitched 'whoop' sound during inhalation.
Woese: Carl Woese was an American microbiologist who revolutionized the understanding of life's diversity by discovering the domain Archaea. His work on ribosomal RNA led to a new phylogenetic tree that includes Bacteria, Archaea, and Eukarya.
Xenobiotics: Xenobiotics are compounds that are foreign to a biological system. These can include drugs, pollutants, and synthetic chemicals that are not naturally found in an organism.
Yersinia: Yersinia is a genus of Gram-negative bacteria belonging to the family Enterobacteriaceae. Some species are pathogenic to humans, causing diseases such as plague and gastroenteritis.