Phylogenetic Tree

Breakdown of Phylogenetic Tree

Gammaproteobacteria Breakdown


This subgroup contains bacteria of rods, curved rods, spirals, coccobacilli, and pleomorphic morphologies. 


Rickettsias- can only grow and reproduce while within the living cells of their host.

Rhizobia: These bacteria live in a mutualistic relationship with the roots of legumes where they are able to "fix" nitrogen (N2) in the air into compounds that can be used by living things.


This subgroup consists of gram-negative bacteria that can live in environments having low nutrient levels.

Chemoautotrophic sulfur bacteria secure needed energy by oxidizing a reduced substance in their environment, and the free energy released is harassed to the manufacture of food. For example, some of these types of bacteria oxidize H2S in their surroundings to produce energy and then later use it to reduce carbon dioxide to carbohydrate. 

Also in this subgroup are iron bacteria. These chemoautotrophs are responsible for the brownish scale that forms inside the tanks of flush toilets. They complete the oxidation of partially oxidized iron compounds and are able to couple the energy produced to the synthesis of carbohydrate.

An additional part of this subgroup are Nitrosomonas. This chemoautotroph oxidizes NH(produced from proteins by decay bacteria) to nitrites (NO2). This provides the energy to drive their anabolic reactions. The nitrites are then converted (by other nitrifying bacteria) into nitrates (NO3), which supply the nitrogen needs of plants.

There are three important human pathogens included in this subgroup:

1. Neisseria meningitidis: Causes meningococcal meningitis, an extremely serious infection of the meninges that   occasionally occurs in very young children and in military camps. There is a vaccine that is effective against several strains but unfortunately not the most dangerous one.

2. Neisseria gonorrhoeae: Causes gonorrhea, one of the most common sexually-transmitted diseases (STDs): over 300,000 cases were reported in the U.S. in 2009. In males, the bacterium invades the urethra causing a discharge of pus and often establishes itself in the prostate gland and epididymis. In females, it spreads from the vagina to the cervix and fallopian tubes. If the infection is untreated (penicillin is usually effective although strains resistant to it are now being encountered), the resulting damage to the fallopian tubes may obstruct the passage of eggs and thus cause sterility.

3. Bordetella pertussis: the cause of "whooping cough".


The Phylum Proteobacteria is a major phylum in bacteria. All proteobacteria are gram-negative bacteria that contain an outer membrane mostly made up of lipopolysaccharides.This phylum is divided into six different classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria, and Zetaproteobacteria. Proteobacteria include a wide variety of pathogens such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera. There are others that are free-living and include many of the bacteria responsible for nitrogen fixation. Many Proteobacteria move about using flagella, however some are nonmotile or rely on bacterial gliding. The metabolism of this bacterial phylum ranges as well. Most members are facultatively or obligately anaerobic, chemoautotrophs, and heterotrophic, however there are also exceptions. There are even a variety of genera that are not closely related to each other that convert energy from light through photosynthesis. 

Carl Woese developed this bacterial collection in 1987 and called it the “purple bacteria and their relatives.”  Proteobacteria was named after Proteus, a Greek god of the sea, due to the great diversity of forms found in this group and that they are capable of assuming many different shapes.

Gram-Negative Cell Wall


This subgroup is the largest and most diverse one of the Proteobacteria Phylum. 


1. Escherichia coil: The most thoroughly-studied of all creatures (possibly excepting ourselves). Its entire genome has been determined down to the last nucleotide: 4,639,221 base pairs of DNA encoding 4,377 genes. Lives in the human colon, usually harmlessly. However, water or undercooked food contaminated with the O157:H7 strain has caused severe, occasionally fatal, infections.

2. Salmonella enterica: Two major human pathogens:

-Salmonella enterica var Typhi. Causes typhoid fever, a serious systemic infection occurring only in humans. This microbe is also known as Salmonella typhi

-Salmonella enterica var Typhimurium. Confined to the intestine, it is a frequent cause of human gastrointestinal upsets but is also found in many other animals (that are often the source of the human infection). Also known as Salmonella typhimurium. 

3. Vibrio cholerae: Causes cholera, one of the most devastating of the intestinal diseases. The bacteria liberate a toxin that causes massive diarrhea (10–15 liters per day) and loss of salts. Unless the water and salts are replaced quickly, the victim may die (of shock) in a few hours. Like other intestinal diseases, cholera is contracted by ingestion of food or, more often, water that is contaminated with the bacteria.

4. Pseudomonas aeruginosa: A common inhabitant of soil and water, it can cause serious illness in humans with defective immune systems, serious burns, and cystic fibrosis.

5. Yersinia pestis: This bacillus causes bubonic plague. It is usually transmitted to humans by the bite of an infected flea. As it spreads into the lymph nodes, it causes them to become greatly swollen, hence the name "bubonic" (bubo — swelling of a lymph node) plague. Once in the lungs, however, the bacteria can spread through the air causing the rapidly lethal (2–3 days) "pneumonic" plague. Untreated, ~30% of the cases of bubonic plague are fatal, and the figure for the pneumonic form reaches 100%.

6. Francisella tularensis: causes tularemia.This is primarily a disease of small mammals, but about 100 people become infected each year in the United States. Most cases occur in south-central states (KS, MO, OK, AR). However, the import of infected rabbits by game clubs has introduced the disease to Cape Cod and Martha's Vineyard in Massachusetts. In the summer of 2000, 15 people became ill (one died) on the island. All seem to have acquired their infection as they used lawn mowers and brush cutters that presumably stirred up the organism from the carcasses of infected animals.

7. Haemophilus influenzae: was once thought to cause influenza. It does not, but it can cause bacterial meningitis and middle ear infections in children and pneumonia in adults — especially those whose resistance is lowered by other diseases (e.g., AIDS). There is now an effective vaccine against the most dangerous strains. The complete genome of Haemophilus influenzae is known: 1,830,138 bp of DNA encoding 1,743 genes.

8. Purple Sulfur Bacteria: photosynthetic bacteria. They use the sunlight energy to reduce carbon dioxide to carbohydrate. However, they do not use water as a source for electrons like plants do, but instead use hydrogen sulfide in order to synthesize NADPH and ATP. During this process, they produce elemental sulfur. 


This group contains the myxobacteria which are a group of bacteria that predominately live in the soil and feed on insoluble organic substances. These bacteria have a defined "fruiting body" structure. 

Myxobacteria: Deltaproteobacteria


There are two members of this group that are pathogenic to humans:

1. Helicobacter pylori: the main cause of stomach ulcers.

2. Campylobacter jejuni: the bacterium most frequently implicated in gastrointestinal upsets.

Energy Metabolic Pathways

Pathogenic E. Coli

Helicobacter Pylori Causing Stomach Ulcers

Rhizobium bacteria infecting root nodule-Symbiosis for N2 Fixation

Adaptation of Ps. Aeruginosa Colonization and Infection in the CF Airway

Vibrio and Salmonella Infections

Additional Articles

Want to know more about the Phylum Proteobacteria? Check out these articles below for some additional information:

1. Phylogenomics and signature proteins for the alpha Proteobacteria and its main groups: