User:S4352142
Rochelle Overton
Bench E
31082016 [1]
Capnocytophaga gingivalis
Classification
Higher order taxa
| Kingdom | Bacteria |
|---|---|
| Domain | Bacteroidetes |
| Phylum | Bacteriodetes |
| Class | Flavobacteriia |
| Order | Flavobacteriales |
| Family | Flavobacteriaceae |
| Genus | Capnocytophaga |
Species
Capnocytophaga gingivalis ATCC 33624
Description and significance
Capnocytophaga gingivalis are a class of Flavobacteriia that inhabit the oral cavity of the mouth (kagermeier), making up a large component of subgingival plaque (spratt). Microscopy has revealed that C. gingivalis are straight rod-shaped bacteria with a fusiform morphology, having a granulated outer surface. Capnocytophaga gingivalis are a motile facultative anaerobe, meaning that it can create ATP through aerobic respiration if oxygen is present(London), but is also to use fermentation in instances where oxygen is poor/absent (kagermeier, newman). Gram staining produced a purple, gram negative cell, which was is also able to be successfully cultured in laboratories with a preference from environments with high carbon dioxide levels (London).
Whilst present in natural microbiome of the mouth, C. gingivalis can become pathogenic under certain conditions. Dental ailments such as periodontal infections, loss of teeth and supporting tissues as well as alveolar bone loss can occur. In severe cases, C. gingivalis has also spread to the eyes, brain, lungs, digestive tract, heart or muscular skeletal system and causing disease. Although these diseases are treatable with antibiotics, there have been reports of resistant strains occurring since the mid 1980's, making it an important bacterium to study.
Discovered (when/where):
Examples of citations [1], [2]
Genome structure
Capnocytophaga gingivalis strain ATCC 33624 contains approximately 5,000bp in its genome and 2,641 recorded genes (JGI IMG/M)(BioCyc). This microaerophilic organism contain a newly discovered bacterial Pnkp1-Rnl-Hen1 RNA repair mechanism(NCBI WANG). Studies have linked these heterohexamer proteins to the restoration of RNA and overall immunity. This can be seen as an adaptive defense mechanism against toxins as the organism is able to successfully excise ribotoxins, preventing infection and increasing longevity. In order for this process to occur, Hen1 must first methylate the RNA, marking the RNA for cleavage. Pnkp1 then attaches to the damaged RNA ends, followed by Rnl1 that ligates it, restoring the RNAs function. Once this process has been carried out, that strand of RNA will contain a form of immunity to that specific ribotoxin.
Cell structure and metabolism
Being a gram negative bacteria, the crystal violet stain used in gram staining does not stick to C. gingivalis as its cell wall contains a very small amount of peptidoglycan. The cell walls of gram negative bacteria are composed of a nuclear envelope, a thin layer of peptidoglycan and an outer membrane. Due to the presence of peptidoglycan in their cell walls, gram negative bacteria are still susceptible to lysozyme which catalyzes hydrolysis of the cell by weakening the glycosidic bonds, although often used in conjunction with ethylenediaminetetraacetic acid (Ianco)(Voss).
A biofilm is the clustered formation of a thin layer of microorganisms which cling together to adhere to a hard surface, such as the tooth. It begins with the pellicle (saliva) containing large quantities of absorbed macromolecules directly to the teeth (sakaguchi). Free-floating bacteria will then attach themselves to the saliva-coated tooth in order to feed, being the primary colonizers. Then the secondary colonizers, Capnocytophaga gingivalis, bind to the primary colonizers creating a second layer, proving increased strength and structure to the biofilm. When left over long periods of time, this can create instances of plaque which if left unchecked can result in periodontal infections. Throughout this micro-colony, each microorganism is exposed to different environmental conditions such as; physical proximity, oxygen and glucose requirements. This is why each C. gingivitis will exhibit different phenotype throughout the oral cavity (hosohama-saito).
Capnocytophaga gingivalis are motile organisms, despite lacking both flagella and flagellates. They create longitudinal movement in a gliding motion. Although the exact mechanisms which control this form of movement are still unknown, it is hypothesized that the front of the bacteria extends and attaches to the surface before detaching at the rear creating a gliding motion (balows).
Aerobic metabolism is the preferred method of respiration used by Capnocytophaga gingivalis, although it is capable of reverting to fermentation if oxygen is absent. To aerobically respire, the bacteria will go through the process of glycolysis whereby the cell will uptake glucose, and oxidize it. This breaks the glucose apart into two pyruvates and two NAD molecules which are then put through the citric acid cycle. In this process the pyruvates are broken down into carbon dioxide and FADH molecules. The NAD becomes NADH which goes on to stimulate the production of ATP in the electron transport chain, performed by complexes I-IV. The oxidation of NADH and FADH2 are carried out in complexes I-II, creating the proton gradient. Capnocytophaga gingivalis is a flavobacteria, meaning that the electron transfer carrier will be either a cytochrome, electron-transfer quinone, or flavoprotein in the electron transport chain, using oxygen as the terminal acceptor. In cases of anaerobic respiration, the terminal acceptor can contain a variety of organic or inorganic compounds (BIOCYC.org).
Ecology
Capnocytophaga gingivalis is present in a standard human microbiome. Individuals with plaque were discovered to have a higher prevalence of the bacteria with children having a higher risk. When compared with physical ailments results concluded that patients diagnosed with leukemia and oral diseases had 57% and 71% increase in the amount of C. gingivalis found in their oral microbiome respectively (Jolivet-gougeon).
When grown on Trypticase-soy-blood agar, Capnocytophaga gingivalis show consistent irregular colonization, staying isolated from other microorganisms (Poirier). Due to their ability to translocate via gliding, the bacteria are confined by their surrounding cells and start clumping into mounds, creating halo zones. Their irregular populations comprise of smooth cell surfaces with small pioneer colonies on the outer edges of halo zones. This is in contrast to bacteria found within the human microbiome as it is forced to co-aggregate with other microorganisms in order to gain survival advantages such as adhesion (Kolenbrander). This agglutination of neighboring cells forms the basis for biofilms and in turn, dental plaque. Co-aggregation reacts to lectin-carbohydrate molecules which are recognized by each cell. Experiments conducted in alternate ecosystems concluded that this process was unique to the oral cavity, as predation or nutritional instability were common occurrences when grown elsewhere. This is definitive proof that C. gingivalis are opportunistic pathogens when they are in an environment where they can dominate, they will become predatory and pathogenic.
Although C. gingivalis can be considered a commensalist within the oral cavity of humans, when they move into other substrates of the body it can soon become pathogenic. Capnocytophaga gingivalis has been shown to yield a much higher biomass when grown on rich brain-heart extracts (newman) (Spratt1999)(spratt 1995). As a results of its preference for these high protein substrates, C. gingivalis have been known to invade and attack human tissues pertaining to the gums, brain, eyes, lungs, heart, and gastrointestinal tract under certain circumstances. Its ability to grow in such a vast array of environments stems from its ability to respirate both aerobically and anaerobically through fermentation.
Pathology
Despite being commensalisms found in the plaque on our teeth, Capnocytophaga gingivalis can invade and attack the host tissue when the body's natural lines of defense are compromised. If given the opportunity, C. gingivalis will invade the oropharyngeal tract through cuts, abrasions, ulcers or other trauma in the oral cavity, spreading to induce infection (poirier)(joulivet). Supragingival plaque, present above the gum line is constantly exposed to glycoproteins contained within the pellicle. If left untended for extended periods of time, the plaque can start to creep below the surface of the gum creating gingivitis. The subgingival plaque, located below the gum line, will then become exposed to gingival crevicular fluid (GCF) (kolenbrander). This inflammatory exudate is full of antibodies in order to keep the pathogen contained and prevent it from invading further down the tooth. This immune response creates inflammation of the gums, furthering the gingivitis as it becomes a periodontal infection. This invasion of bacteria below the gum lines can be enough to cause an imbalance in the microbiome of the oral cavity as the C. gingivalis proceeds to cause damage to the gums and surrounding teeth. If left unchecked this could result destruction of the cementum, bones and periodontal ligaments as well as creating large periodontal pockets caused by the bacteria eating away at the gum tissue (dental health services victoria).
Studies have shown that in some cases C. gingivalis have been associated with numerous diseases throughout the body. Bronchoscopy of patients with pneumonia discovered high levels of C. gingivalis present in the lungs (Geisler). When treated with beta-lactam antibodies, patients began showing signs of improvement over the first 24 hours of treatments, with the pneumonia settling down significantly over the next week. It was hypothesized that C. gingivalis could be the causality for the inflammation in the lungs, or leaving the patient immuno-compromised making it easier for another bacterium to infect the patient. Blood pathology examinations have also discovered the presence of Capnocytophaga gingivalis in the blood, also known as bacteraemia (elpis)
Application to biotechnology
It is through C. gingivalis' exposure to gingival crevicular fluid over long periods of time that is thought to have brought about the bacteria's antibiotic resistance. Another hypothesis predicts its resistance arose though horizontal gene transfer from genetically similar families of prevotella or bacteroides (joulivet). Typically, C. gingivalis is susceptible to beta-lactam, but its antibiotic resistant strains contain plasma or chromosomal encoded beta-lactamase.
Bioengineering, biotechnologically relevant enzyme/compound production, drug targets,…
Current research
Summarise some of the most recent discoveries regarding this species.
References
References examples
- ↑ MICR3004
This page is written by Rochelle Overton for the MICR3004 course, Semester 2, 2016
