Bacteroidetes

The phylum Bacteroidetes is a large, diverse group of bacteria composed of three large classes that are found across every habitat on Earth including in soil, in sediments, sea water and in the guts and on the skin of animals. The group is composed of around 7000 sub-groups split into six catagories: Bacteroidia, Chitinophagia, Flavobacteria, Sphingobacteria, Saprospiria and Cytophagia.
Bacteroidetes have many roles but primarily breakdown large organic matter such as proteins and complex sugars into smaller molecules. Members of Bacteroidetes can be both helpful and unhelpful to humans to humans and plants. Some members are involved in metabolism and breaking down food. On the other hand, some members are pathogenic, they cause disease in humans. Members of the genus Bacteroides are opportunistic pathogens. Rarely are members of the other two classes pathogenic to humans.
Bacteroidetes in humans
The gastrointestinal tract in humans is made up of the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. This is the path that food enters the body and waste matter leaves the body. The majority of microbes in the human body live in this gastrointestinal tract . Bacteroidetes can be found in all of the different parts of the gastrointestinal tract, even though the conditions in each part can be very different from each other.
Bacteroidetes have many functions in humans but their main role is breaking down molecules of food in the small intestine. They break down strong molecules like plant cell walls that human cells find hard to digest. The products of this breakdown reaction are absorbed through the intestine and are used by humans as a source of energy. Bacteroidetes help humans to get energy from strong material and are important for gut health.
The number of Bacteroidetes can be used to indicate the health of the gut. Low numbers can be associated with obesity. Higher numbers are associated with irritable bowel syndrome and diabetes.
Bacteroidetes as pathogens in humans
Although many members of Bacteroidetes are needed for a healthy gut in humans, some can act as pathogens to humans. Members of the Bacteroides group are useful bacteria that live in the gut. However, if there is a tear in the intestine, they are able to escape and can cause infections in the body. Bacteroides can cause infections in the gastrointestinal tract and the appendix.
Bacteroides are tolerant to many antibiotics and can share this tolerance with other dangerous bacteria. It can be treated with certain antibiotics but the problem of tolerance is of real concern.
Bacteroidetes in soil
Members of Bacteroidetes are also found in soil such as members of the Flavobacteria and Sphingobacteria classes. They have been found in many different types of soil including farm soil, greenhouse soil and untouched soil.
Bacteroidetes is one of the most common bacteria found in the rhizosphere, this is the area surrounding a plant's roots. They can also be found on the surface of leaves.
Bacteroidetes have a similar role in plants. They break down organic matter, such as proteins, surrounding the roots of a plant into simpler forms that can be taken up by the plant and used as energy.
Like in humans, Bacteroidetes can also cause disease in plants. Flavobacterium johnsoniae is a member of Bacteroidetes which causes decay of plants and vegetables. Some strains of Flavobacterium cause disease in red plants and algae. Bacteroidetes can also break down cell walls damaging plants.
Bacteroidetes in water
Bacteroidetes can also be found in marine environments such as seas , oceans and lakes. They are the third most common bacteria found in the ocean. They are found on surfaces (living and non-living), rocks and minerals, corals and algae. They are an important part of floating bacterial life (bacterioplankton) in marine environments. Bacterioplankton are involved in the recycling of essential elements in marine ecosystems. Bacteroidetes breakdown large organic matter in marine environments.
References
Gram-negative bacteria