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Louise Chan Bench E 31082016

Classification

Higher order taxa

Bacteria – Bacteroidetes – Bacteroidia– Bacteroidales – Porphyromonadaceae – Porphyromonas

Species

Species: P. gingivalis

Type Strain: strain 2561 = ATCC 33277= CCUG 25893 = CCUG 25928 = CIP 103683 = DSM 20709 = JCM 12257 = NCTC 11834

Description and significance

P. gingivalis was originally discovered and classified as Bacteroides melaninogenicus in 1977 by J.Slots at State University of New York, Buffalo [ref]. Slot’s strain 2561 (ATCC 33277) was isolated from a human gingival sulcus during a study of eight patients aged between 34-48 years with advanced periodontitis. In the same year, Finegold and Barnes [ref] refined this classification after their studies revealed that several strains within B. melaninogenicus differed according to their carbohydrate metabolism (asaccharolytic v.s. saccharolytic) and their G + C composition[ref]. In 1980, Coykendall et al. proposed a further reclassification of human oral strains of B. asaccharolyticus to B. gingivalis due to its differences from non oral strains in its base composition, serology and its unique ability to produce phenylacetic acid [ref]. The classification of this microorganism as "P. gingivalis did not occur until 1988 when Shah and Collins proposed the reclassification of B. assacharolyticus, B. gingivalis and B. endodontalis in a new genus, Porphyromonas after the discovery that these three species differed markedly from the type species of Bacteroides, B. fragilis, in many biochemical and chemical properties [ref].

Give a general description of the species (e.g. where/when was it first discovered, where is it commonly found, has it been cultured, functional role, type of bacterium [Gram+/-], morphology, etc.) and explain why it is important to study this microorganism. Examples of citations ^[1], ^[2]

Genome structure

Strain ATCC 33277 is the type strain of P. gingivalis. It has a single circular chromosome of 2,354,886 bp and an average G + C content of 48.4%. At this point, no plasmids have been identified in ATCC 33277 [ref]. A large proportion of the genome contains coding sequences. A total of 2090 CDSs have been identified in the genome of ATCC 33277, making up 86.1% of the genome. The genome has 53 tRNA genes that provide the specificity for producing all necessary amino acids and 4 RNA operons.

ATCC 33277 has a total of 93 Insertion Sequence (IS) elements that have the ability to independently transpose, and 48 miniature inverted-repeat transposable elements (MITES) that are dependent on IS element transposase. The genome also has an abundance of other mobile genetic elements including novel conjugative transposons (CTns) encoding Na⁺-driven multi-drug efflux pumps and composite transposons (Tns) encoding tetR family transcriptional regulators, proteases and ABC transporter ATP-binding proteins. It has previously been proposed that P. gingivalis is assaccharolytic due to a nonsense mutation in the glucose kinase-encoding gene (glk) [ref]. An insertion of MITE239 was identified in the glk gene of ATCC 33277, however, no nonsense mutation was identified. Nonsense mutations were not identified in the glk gene of five other strains of P. gingivalis, suggesting that glk may not be the only determinant of assaccharolysis.

Genes from lateral gene transfer from other bacterial species have been identified. These genes have been proposed to have similarities to genes in other bacteria such as Bacteroides fragilis, the type strain of Bacteroides, and B. thetaiotaomicron, an enteric commensal [ref]. ATCC 33277 is a less virulent strain of P. gingivalis and has been useful in genomic comparative studies for identifying virulence genes in other strains. Many of these virulence genes are located on pathogenicity islands and have been introduced through lateral gene transfer. A comparison of the ATCC 33277 genome to the virulent strain W83 revealed the absence of a cluster of ORFS in ATCC 332277 that are involved in the synthesis of capsular polysaccharide [ref].

Select a strain for which genome information (e.g. size, plasmids, distinct genes, etc.) is available.

Cell structure and metabolism

Cell wall, biofilm formation, motility, metabolic functions.

Ecology

Aerobe/anaerobe, habitat (location in the oral cavity, potential other environments) and microbe/host interactions.

P. gingivalis is an obligate anaerobe that is most commonly associated with the human oral cavity. Although present at low levels in the healthy human oral microbiome, it is most prevalent within subjects with periodontal disease. As such, its main nice within the oral cavity is on and within the periodontum (tissues damaged by periodontal disease) [ref.]. It has also been shown to survive and replicate within the environmental amoeba Acanthamoeba castellani, suggesting a possible environmental reservoir [ref.].

To aid in its survival within the oral cavity, P. gingivalis can invade the epithelial cells lining the host gingival tissues [ref]. Gingival epithelial cells are typically the first cells to be colonised. These cells are an important first line of defence in the gingival innate immune system. They exhibit the purinergic receptor P2X7, which is responsive to ATP-induced apoptosis [ref.]. However, P. gingivalis has evolved to circumvent this by consuming the ATP signal, thus preventing cell apoptosis [ref.]. Furthermore, it can replicate and disseminate to surrounding cells without rupturing the cell. These features enable P. gingivalis to effectively shield itself from the host immune system.

Pathology

Do these microorganisms cause disease in the oral cavity or elsewhere?

Application to biotechnology

Bioengineering, biotechnologically relevant enzyme/compound production, drug targets,…

Current research

Summarise some of the most recent discoveries regarding this species.

References

References examples

1. Sahm, K., MacGregor, B.J., Jørgensen, B.B., and Stahl, D.A. (1999) Sulphate reduction and vertical distribution of sulphate-reducing bacteria quantified by rRNA slotblot hybridization in a coastal marine sediment. Environ Microbiol 1: 65-74.

2. Human Oral Microbiome

This page is written by Louise Chan for the MICR3004 course, Semester 2, 2016