Deltaproteobacteria also includes the genus Bdellovibrio , species of which are parasites of other gram-negative bacteria. The infection is lethal for the host cells. Another type of Deltaproteobacteria, myxobacteria , lives in the soil, scavenging inorganic compounds.
Motile and highly social, they interact with other bacteria within and outside their own group. Figure 9. Helicobacter pylori can cause chronic gastritis, which can lead to ulcers and stomach cancer. The smallest class of Proteobacteria is Epsilonproteobacteria , which are gram-negative microaerophilic bacteria meaning they only require small amounts of oxygen in their environment.
Two clinically relevant genera of Epsilonproteobacteria are Campylobacter and Helicobacter , both of which include human pathogens. Campylobacter can cause food poisoning that manifests as severe enteritis inflammation in the small intestine. This condition, caused by the species C.
Chickens often harbor C. Within the genus Helicobacter, the helical, flagellated bacterium H. Studies have also shown that H. It produces urease and other enzymes that modify its environment to make it less acidic. Table 5 summarizes the characteristics of the most clinically relevant genera of Epsilonproteobacteria. Skip to main content. Prokaryotic Diversity. Search for:. Proteobacteria Learning Objectives Describe the unique features of each class within the phylum Proteobacteria: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria Give an example of a bacterium in each class of Proteobacteria.
Think about It What characteristic do all Alphaproteobacteria share? Think about It What characteristic do all Betaproteobacteria share? Think about It List two families of Gammaproteobacteria. Think about It What type of Deltaproteobacteria forms fruiting bodies?
Think about It Name two Epsilonproteobacteria that cause gastrointestinal disorders. Key Concepts and Summary Proteobacteria is a phylum of gram-negative bacteria discovered by Carl Woese in the s based on nucleotide sequence homology.
Proteobacteria are further classified into the classes alpha-, beta-, gamma-, delta- and epsilonproteobacteria, each class having separate orders, families, genera, and species.
Alphaproteobacteria are oligotrophs. The taxa chlamydias and rickettsias are obligate intracellular pathogens, feeding on cells of host organisms; they are metabolically inactive outside of the host cell. Some Alphaproteobacteria can convert atmospheric nitrogen to nitrites, making nitrogen usable by other forms of life. Betaproteobacteria are eutrophs. They include human pathogens of the genus Neisseria and the species Bordetella pertussis.
Gammaproteobacteria are the largest and the most diverse group of Proteobacteria. Many are human pathogens that are aerobes or facultative anaerobes. Some Gammaproteobacteria are enteric bacteria that may be coliform or noncoliform. Escherichia coli , a member of Gammaproteobacteria, is perhaps the most studied bacterium. Deltaproteobacteria make up a small group able to reduce sulfate or elemental sulfur.
Some are scavengers and form myxospores, with multicellular fruiting bodies. Epsilonproteobacteria make up the smallest group of Proteobacteria. The genera Campylobacter and Helicobacter are human pathogens. Multiple Choice Which of the following describes Proteobacteria in domain Bacteria? Proteobacteria is a phylum within domain Bacteria. Show Answer Answer a. All Alphaproteobacteria are oligotrophs.
Show Answer Answer d. Campylobacter is not in class Betaproteobacteria. Show Answer Answer c. Haemophilus influenzae is a common cause of upper respiratory tract infections. Show Answer Rickettsias are obligate intracellular bacteria. Show Answer The species Helicobacter pylori , which belongs to Epsilonproteobacteria, causes peptic ulcers of the stomach and duodenum.
Show Answer The genus Salmonella belongs to the class Gammaproteobacteria and includes pathogens that cause salmonellosis and typhoid fever. Think about It What is the metabolic difference between coliforms and noncoliforms? Which category contains several species of intestinal pathogens? Why are Mycoplasma and Chlamydia classified as obligate intracellular pathogens? The cell shown is found in the human stomach and is now known to cause peptic ulcers.
What is the name of this bacterium? Suerbaum, P. Licenses and Attributions. These are often treated as classes. The alpha, beta, delta, epsilon sections are monophyletic, but the Gammaproteobacteria due to the Acidithiobacillus genus is paraphyletic to Betaproteobacteria, according to multigenome alignment studies, which if done correctly are more precise than 16S note that Mariprofundus ferrooxydans sole member of the Zetaproteobacteria was previously misclassified on NCBI taxonomy.
Acidithiobacillus contains 5 species and the sole genus in its order Acidithiobacillales. The divisions of the proteobacteria were once regarded as subclasses e.
These classes include: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria and Zetaproteobacteria. Alphaproteobacteria is a class of Proteobacteria; like all Proteobacteria, they are Gram-negative. Alphaproteobacteria is a class of Proteobacteria. Like all Proteobacteria, they are Gram-negative.
The Alphaproteobacteria comprise most phototrophic genera, but also several genera metabolising C1-compounds e. In addition, the precursors of the mitochondria of eukaryotic cells are thought to have originated from Rickettsia spp. See endosymbiotic theory. Because of their symbiotic properties, scientists often use Alphaproteobacteria of the genus Agrobacterium to transfer foreign DNA into plant genomes, and they also have many other biotechnological properties.
Alphaproteobacteria : Transmission electron micrograph of Wolbachia within an insect cell. The Class Alphaproteobacteria comprises ten orders viz. Magnetococcales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales, Caulobacterales, Kiloniellales, Kordiimonadales, Parvularculales and Sneathiellales. Comparative analyses of the sequenced genomes have also led to discovery of many conserved indels in widely distributed proteins and whole proteins i.
Rhizobiales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales and Caulobacterales and families viz. Rickettsiaceae, Anaplasmataceae, Rhodospirillaceae, Acetobacteraceae, Bradyrhiozobiaceae, Brucellaceae and Bartonellaceae. Phylogenetic analyses and conserved indels in large numbers of other proteins provide evidence that Alphaproteobacteria have branched off later than most other phyla and Classes of Bacteria with the exception of Betaproteobacteria and Gammaproteobacteria.
The Betaproteobacteria consist of several groups of aerobic or facultative bacteria that are often highly versatile in their degradation capacities, but also contain chemolithotrophic genera e. Nitrosomonas is a genus comprising rod shaped chemoautotrophic bacteria. This rare bacteria oxidizes ammonia into nitrite as a metabolic process.
Nitrosomonas are useful in treatment of industrial and sewage waste and in the process of bioremediation. They play an important role in the nitrogen cycle by increasing the availability of nitrogen to plants while limiting carbon dioxide fixation. Betaproteobacteria play a role in nitrogen fixation in various types of plants, oxidizing ammonium to produce nitrite- an important chemical for plant function.
Many of them are found in environmental samples, such as waste water or soil. Pathogenic species within this class are the Neisseriaceae gonorrhea and meningitis and species of the genus Burkholderia. Betaproteobacteria : Burkholderia pseudomallei colonies on a Blood agar plate. Burkholderia is a genus of proteobacteria probably best known for its pathogenic members: Burkholderia mallei , responsible for glanders, a disease that occurs mostly in horses and related animals; Burkholderia pseudomallei , causative agent of melioidosis ; and Burkholderia cepacia , an important pathogen of pulmonary infections in people with cystic fibrosis CF.
The two main groups of morphologically unusual proteobacteria include spirillum and prosthecate bacteria. Two main groups of morphologically unusual proteobacteria include spirillum and prosthecate bacteria. Spirillum in microbiology refers to a bacterium with a cell body that twists like a spiral. It is a genus comprising elongated forms with clusters of flagellae at both poles.
Spirillium usually live in stagnant water rich in organic matter. They are twisted and aerobic, and are highly flexible, like a spring. Spirillum : Spirillum in microbiology refers to a bacterium with a cell body that twists like a spiral.
Prosthecate bacteria are a non-phylogenetically related group of Gram-negative bacteria that possess appendages, termed prosthecae. These cellular appendages are neither pili nor flagella, as they are extensions of the cellular membrane and contain cytosol. Prosthecates are generally chemoorganotrophic aerobes that can grow in nutrient-poor habitats, being able to survive at nutrient levels on the order of parts-per-million — for which reason they are often found in aquatic habitats.
These bacteria will attach to surfaces with their prosthecae, allowing a greater surface area with which to take up nutrients and release waste products. Some prosthecates will grow in nutrient-poor soils as aerobic heterotrophs. One notable group of prosthecates is the genus Caulobacter crescentus, a Gram-negative, oligotrophic bacterium widely distributed in fresh water lakes and streams.
Caulobacter is an important model organism for studying the regulation of the cell cycle, asymmetric cell division, and cellular differentiation. Caulobacter daughter cells have two very different forms. Swarmer cells differentiate into stalked cells after a short period of motility. Chromosome replication and cell division only occurs in the stalked cell stage. The second word of its name crescentus refers to the fact that it forms a crescent shape; crescentin is a protein that imparts this shape.
Caulobacter crescentus : Caulobacter daughter cells have two very different forms. Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria. Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria, such as the Enterobacteriaceae Escherichia coli , Vibrionaceae and Pseudomonadaceae. Like all Proteobacteria, the Gammaproteobacteria are Gram-negative.
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