Bacteria

Domain Bacteria

Phylum Actinobacteria (High G+C Gram Positive Bacteria)

This group exhibits a large degree of pleomorphism.  Many are filamentous with numerous branches and resemble filamentous fungi in their morphology. 

Propionibacterium freudenreichii

These bacteria are non-motile, bacilli that are commonly found in dairy products as well as in the soil.  They are most notably known for their role in the manufacturing of Swiss cheese.  Here, their ability to ferment glucose or lactose into propionic acid is a main contributor to the cheeses' mild, nutty flavor.  Additionally, carbon dioxide, a bi-product of fermentation, is responsible for forming the characteristic, holey appearance of Swiss cheese.  During the cheese production process, the size of the holes are controlled by indirectly regulating the bacterial growth and metabolism.  This is done by changing the acidity, temperature, and curing time of the cheese.  Their growth and metabolism in cheese making is also dependent on the presence of Lactobacillus.  The Lactobacillus is involved in degrading the casein protein in cheese, thus providing free amino acids and peptides to feul P. freudenreichii.  Furthermore, research has shown that consuming P. freudenreichii cleanses the GI tract and is thought to lower the incidence of colon cancer.

Phylum Planctomycetes (Gram negative, budding bacteria)

Said to "blur the definition of what bacteria are," this group contains many organisms which  have similar characteristics, resembling those of the Archaea and Eukaryota domains.

Planctomyces maris

This obligate aerobe is primarily found in marine environments, growing optimally between 30-33 degrees Celsius. As chemoheterotrophs, they are capable of metabolizing numerous carbon sources. This species is uniquely distinguished by is morphological features and cell wall composition. They are spherical, containing a single, polar fibrillar structure. Distributed outside the cell are small crater-like structures which create divots along the cells surface. The most significant characteristic of this organism is the composition of their cell walls which lacks peptidoglycan. Contrarily, their cell walls consist of S-layer proteins which are stabilized by the protein sacculus and bound by disulfide bonds. P. maris also undergoes a dimorphic life cycle between a motile, daughter cell and a non-motile, parent cell. Before reproduction can occur, the daughter cell must first locate a substrate to which it can anchor itself and produce a stalk. Once the bacterium becomes attached, reproduction occurs through budding by which a small protuberance or bud develops at the reproductive pole and enlarges before separating from the parent cell.

Phylum Firmicutes (Low G+C Gram Positive Bacteria)

In addition to gram positive bacteria, this group also contains gram negative bacteria.  Important endospore-forming, lactic acid producing, and cell wall lacking species are included in this phylum.

 

Epulopiscium fishelsoni

As a gram positive bacterium, this species is found in nature as a gut symbiont of the Red Sea surgeonfish.  Originally thought to be a Protist, E. fishelsoni is known for its large size.  They can be over half a milimeter in length, large enough to be seen with the unaided eye.  They also exhibit extreme polypoidy in which they have up to 85,000 copies of at least one gene and has 25 times more DNA than the human cell.  Since this species does not rely on diffusion to disperse its nutrients throughout the cell, it is believed that the over-expression of genes is used to encode proteins to carry out this function.  To compensate for its large volume, the cell wall contains many external structures, similar to cilia, that increase its surface area.  Another unique characteristic of this bacteria is that it cannot undergo binary fission.  Instead, it undergoes a viviparous-like reproductive cycle in which multiple daughter cells are formed within one parent cell and are released into its environment as the parental cell is lysed open. 

Phylum Chlorobi (Green Sulfur Bacteria)

This group consists of gram negative, obligately anaerobic photoautotrophs; most included are non-motile.

Chlorobium tepidum 

This species of bacteria is found in anoxic environments such as hydrogen sulfide containing waters, muds, and sediments where they are able to grow with little light and form dense mats.  Their metabolism is driven by anoxygenic photosynthesis where oxygen is not one of the end products.  During this process, the initial electron donor, hydrogen sulfide, is oxidized to sulfur which is deposited within granules inside the cell.  Using electromagnetic energy, chlorosomes complexes, containing bacteriochlorophylls and carotenoids, are the primary "organelle" in which light energy is harvested and used to drive metabolic processes.  Additionally, C. tepidum can fix atmospheric nitrogen.  The ability to use sulfur containing compounds for photosynthesis and perform nitrogen fixation has made C. tepidum a prime model in using alternative sources of energy as well as to help us better understand the cycles of global nutrients. 

Phylum Cyanobacteria (Blue-green Bacteria)
Cyanobacteria are gram negative bacteria and have a characteristic blue-green pigmentation.  They play a major role in increasing the global oxygen content through oxygenic photosynthesis.

Anabaena circinalis

A. circinalis are found in fresh water bodies all over the world and occur in large, blue-green blooms. They are photoautotrophs which carry out oxygenic photosynthesis similar to plants and algae in that water is used as the initial electron source. This species is also capable of producing several neurotoxins, one of which is paralytic shellfish poison (PSP). In their vegetative state, they grow in long filamentous, coccoid chains, acting as a multicellular unit. Under low nitrogen conditions, about one in every ten vegetative cells transform to become heterocysts. These cells' function specifically to aquire nitrogen through nitrogen fixation as needed. The heterocysts contain the nitrogen fixing enzyme, nitrogenase, which can only function properly in low oxygen conditions. To keep the cell anoxic, and thus, the nitrogenase functioning at its optimum level, these cells eliminate photosystem II and form a thickened envelope around the cell. Without photosystem II, photosynthesis can no longer be performed in these cells. Therefore, the vegetative cells provide the heterocysts with the energy needed for nitrogen fixation.  

Phylum Proteobacteria

This phylum is the largest taxonomic group and includes the majority of the chemoheterotrophic gram negative species.  They vary greatly in their environment, metabolism, and functions.

Class Alphaproteobacteria

Most species in this group are able to grow with very little nutrients.  It includes some with unusual morphology as well as nitrogen fixers symbionts that are agriculturally important.

Acetobacter diazotrophicus

This species is a rod-shaped, plant symbiont and endophyte, promoting growth in the internal tissues of sugarcane, coffee plants, fruits, grasses, and potatoes.  They are unique in that they can convert ethanol to acetic acid when in the presence of oxygen.  This process is used in the production of vinegar.  A. diazotrophicus is also a nitrogen-fixing bacteria, using atmospheric nitrogen to sustain its metabolic processes.  As a plant symbiont, the bacteria excretes approximately half the fixed nitrogen to benefit their plant host.  During nitrogen fixation, atmospheric nitrogen is converted to ammonia using the nitrogenase enzyme and normally can only function under anoxic conditions.  However, A. diazotrophicus is an obligate anaerobe and can only perform its metabolic prossess in the presence of oxygen.  

Class Betaproteobacteria

The Betaproteobacteria are highly versatile in their degradation capabilities.  Many use inorganic materials in their metabolic processes.

Sphaerotilus natans

S. natans are rod-shaped cells that cling together forming many branching filaments.  This bacteria is enclosed in a thin, hollow, tubular sheath which provides protection and also aids in the accumulation of nutrients.  Such bacterial colonies are common among iron rich waters where the iron is oxidized by their sheath and encrusts around the cell.  S. natans are chemoheterotrophs that are capable of growing in environments with relatively low amounts of oxygen.  They are commonly found in fresh waters or in sewage plants where they are known to clog pipes.  This problem occurs due to the bacteria's tendency to settle on solid substrates and attach using adhesive basal elements from their filamentous sheath.

Class Deltaproteobacteria

This class contains most of the known sulfate and sulfur reducing bacteria, as well as some that form fruiting bodies.

Stigmatella aurantiaca

S. aurantiaca is commonly found in rotting wood or bark where they occur in large swarms.  In nature, they help to decompose otherwise insoluble biological debris and are capable of breaking down a large variety of carbohydrates, including peptidoglycans, polysaccharides, proteins, and other cellular detritus.  The development and life cycle of this species is very complex and is composed of a  vegetative state or a myxospore form.  Vegetative cells are characterized by their ability to move in a gliding motion, leaving behind a slime or biofilm trail.  In unfavorable conditions, vegetative cells secrete a chemical message, signaling the surrounding cells to aggregate and form fruiting bodies.  During this transformation, individual cells change physically and metabolically as the fruiting bodies begin to act as a multi-cellular organism, capable of communicating to one another through chemical signals.