User:S4400077

Jolene Sim

Bench E

31 August 2016

Classification

Higher order taxa

Bacteria – Bacteria – Bacteroidetes – Bacteroidia – Bacteroidales – Porphyromonadaceae – Porphyromonas ¹

Species

Species name: Porphyromonas gingivalis

Type strain: W38 2 (consult LPSN http://www.bacterio.net/index.html for this information)

Description and significance

Porphyromonas gingivalis (P. gingivalis) is a non-motile, asaccharolytic, rod-shaped gram negative bacteria. 3 It is obligately anaerobic which requires iron for growth and forms black-pigmented colonies on blood agar plates. 3 P.gingivalis is significant in pathogenesis and progression of inflammations in periodontal diseases. 3 It is detected in 85.7% of subgingival plaque samples from chronic periodontal patients. 3 The disease initially occurs as acute inflammation of gingival tissue, and untreated infections progressively cause formation of teeth pockets and loss of teeth. 3 Habitat of P. gingivalis is subgingival sulcus of human oral cavity, and serves as secondary colonizer of dental plaques by attaching onto parimary colonizers such as Streptococcus gordonii and P. intermedia. 3 Its functional role is produce a variety of potential virulence factors as a significant pathogen in the progression of health to disease. 5 Besides gingival sulcular epithelial cells, P. gingivalis is able to attach onto human buccal epithelial cells in vitro. 6 Adding on, it is able to cause non-oral infections such as endocarditis and abscesses in lung, head, neck and abdominal area. 7 P.gingivalis has also been cultured to study its significance in attachment and invasion of host cells 4, as well as to study internalization within host cells. 8

Examples of citations ^[1], ^[2]

Genome structure

P. gingivalis strain W38 has a genome structure of 2,343,479 bp consisting of an average GC content of 48.3%. 9 It contains 4 ribosomal operons (5S-23S-tRNA Ala-tRNA Ile-tRNA 16S), 2 structural RNA genes, 53 tRNA genes coding for all 20 amino acids. 9 P. gingivalis genes encode 3 restriction system proteins (PG0971, PG0968, PG1469), hemagglutinin proteins B and C (Hag B, PG1972, Hag C, PG1975), various capsular synthesis proteins, 20 transposase genes and 2 large mobile elements (PG1473 to PG1480). 9

Cell structure and metabolism

Cell Wall

P.gingivalis uses its cell wall to attach and provide resistance to saliva flow, which is mediated by adhesins on surface of bacteria and by receptors on oral surfaces. These adhesins are associated with cell structures such as capsules and fimbriae of P.gingivalis. The cell wall consists of distal polysaccharide (O-antigen), a non-repeating core oligosaccharide and a hydrophobic domain known as lipid A (endotoxin). Lipid A, the inner-most part of cell wall, is the biological active site of lipopolysaccharide (LPS) that can cause deregulation of the mammalian innate immune system by interacting with both toll-like receptors 2 and 4. Lipid A has different acylation patterns that change according to microenvironmental conditions, affecting host immune signaling to facilitate bacterial survival in the host. LPS of gram-negative bacteria is significant in maintainance of cellular and structural integrity, as well as controlling entry of hydrophobic molecules and toxic chemicals. P. gingivalis LPS also inhibits osteoblastic differentitation and mineralization in periodontal ligament stem cells for periodontal tissue regeneration. 10

Motility

P. gingivalis is a non-motile bacterium.

Ecology

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

Major habitat of P. gingivalis is the subgingival sulcus of the human oral cavity. 3 It requires fermentation of amino acids for energy production needed for its survival in deep periodontal pocket, with low sugar availability. 11 P. gingivalis is usually found in periodontal pockets, but can be potentially found in supragingival plaque and oral mucosal surfaces, dorsum of the tongue, and pharynx. 12 P. gingivalis/host interaction is classified under amphibiosis, where the recent relationship between the host and microbe can change, which in this case P. gingivalis increases along with dental plaques. 13 Host physiological processes such as cell activation, proliferation, differentiation, metabolism and cellular motilities need cell-to-cell or cell-to-extracellular matrix (ECM) contacts. Cellular integrins function as ECM protein receptors for the linkage between the extracellular environment and intracellular cytoskeleton. 14 ECM proteins in periodontal pocket fluid include vitronectin and fibronectin. Vitronectin protects gingival epithelium, as well as connective tissues against periodontal damages (31). Fibronectin is significant in proliferation and chemotaxis of periodontal ligament cells. 15 P. gingivalis binds to ECM proteins through its fimbriae and outer membrane proteins, inhibiting the ECM proteins from functioning, therefore slowing the recovery processes caused by periodontal tissue destructions. P. gingivalis is able to bind to β2 integrin on mouse peritoneal macrophages, leading to expressions of interleukin (IL)-1β and tumor necrosis factor (TNF)-α genes. Arginine-specific protease (Arg-gingipain) complex of P. gingivalis disrupts fibronectin and its receptor to block the receptor-ligand interactions of human host fibroblasts. This leads to the inhibition of cellular signal transduction through ECM proteins and its receptors, enhancing tissue destruction. 15 P. gingivalis internalizes into host gingival epithelial 16 and endothelial cells through membrane ruffles. 17 These ruffles surround P. gingivalis, therefore internalizing it and exist as vacuoles 18 to replicate and persist within these cells. 19 The intracellular environment provides nutrients for P. gingivalis growth, and serves as a protection against host immune system. 15 P. gingivalis fimA genes have 5 variants (type I to V) which is classified based on the nucleotide sequences 20 Polymerase chain reaction (PCR) is used to detect these variants of P. gingivalis in saliva and dental plaque samples from periodontal patients. 21 It was shown that the majority of samples collected contained type II fimA, and followed by type IV. On the contrary, type I was found in healthy individuals. Type III and V were less prevalent in the samples. These findings illustrate the presence of disease and non-disease causations of P. gingivalis, where the fimbriae variations are associated with bacterial infections that affect disease development. Type II fimA was also observed to invade rapidly into host epithelial cells, promoting P. gingivalis invasion. 22

Pathology

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

The bacteria has also been identified as a risk factor for coronary heart disease, pulmonary infections and pre-term, low birth weight deliveries. 23 P. gingivalis produces a variety of virulence factor to penetrate gingivae and causes tissue destruction directly or indirectly, by inducing inflammation. These virulence factors are constituents or metabolites important in different stages of life cycle and can cause damage to the host. To survive and multiply in a host, P. gingivalis has to overcome host external protective barrier before finding a suitable environment for colonization, which occurs only in presence of virulence factors such as fimbriae, capsules, lipopolysaccharide (LPS), lipoteichoic acids, haemagglutinins, gingipains, outer membrane proteins and outer membrane vesicles. Expression of viulence factors is regulated in response to external environment changes of peridontopathogen. 3

Capsules

Bacteria must first attach onto teeth or mucosal surfaces through adhesins, which is essential in resisting saliva flow. The capsule component is found to be involved in perturbation of gingival epithelial cells. Increased encapsulation leads to increased resistance to phagocytosis, serum resistance, and decreased induction of polymorphonuclear leukocyte chemiluminescence. Virulent W83 and W50 strains have thicker capsules that decreases leukocytes production than those strains which are less virulent, such as W376. It was shown that encapsulated strains are more virulent than non-encapsulated strains. Encapsulated strains was able to modulate host response to bacteria by decreasing cytokine production interleukin-1 (IL-1), IL-6, IL-8 by fibroblasts. Non-encapsulated strains are more prone to phagocytosis, or killed quickly by macrophages and dendritic cells. Capsule was shown to promote virulence using mouse abscess model by reducing phagocytosis and thereby increasing bacterial survival within hosts, and ultimately a chronic inflammatory response However, the invasion efficiency is affected by the capsule which makes it less efficient to invade gingival fibroblast compared to non-capsular strains. The regulatory mechanisms in capsule synthesis is known as tyrosine phosphatase (Ltp1) encoded by PG1641 (controls expression of a number of genes encoding proteins involved in surface polysaccharides synthesis), DNABII protein HU β-subunit (PG0121). 3

Fimbriae

Fimbriae are thin, proteinaceous surface appendages that protrude out of outer membrane of bacterial cell. 3

Lipopolysaccharide (LPS)

The LPS of P. gingivalis is a large molecule with at least 10kDa in size, and is an important component of bacterial outer membrane. Lipid A is the hydrophobic domain on LPS, and deregulates mammalian innate immune system by interacting with toll-like receptors 2 and 4. For gram-negative bacteria, LPS is important in maintaining cellular and structural integrity, controlling entry of hydrophobic molecules and toxic chemicals. Folding and insertion of outer membrane proteins take place in presence of LPS only. LPS disrupts host gingival epithelial cells in secreting chemokineinterleukin 8 (IL-8), affecting activation of neutrophils, eosinophils and basophils. This phenomenon is known as chemokine paralysis, leading to resistance in oxidative burst-killing by polymorphonuclear neutrophils. With decreased efficiency of innate host immune system, periodontal bacteria can multiply to huge numbers. LPS also stimulates thrombospondin-1 production, an extracellular matrix protein secreted by human monocytic cells to cause macrophage migration and modulates host inflammatory response. These responses are mediated by plasminogen activator inhibitor type I (PAI-1) mRNA-binding protein that is upregulated during gingival inflammation induced by P. gingivalis.

Proteases

The ability of P. gingivalis to secrete numerous hydrolytic, proteolytic and lipolytic enzymes with toxic metabolites allows the bacteria to survive in oral cavity. There are 2 distinct families of proteases; trypsin-like enzyme and serine proteinase. Trypsin-like enzymes cleave polypeptides at C-terminal after arginine/lysine residue. These proteinases are commonly known as gingipains (gingipain R and K that cleave after arginine and lysine respectively). They account for 85% of extracellular proteolytic activity of P. gingivalis at site of infection. There are 2 types of gingipain R (RgpA and RgpB), 1 type pf gingipain K (Kgp). Gingipain R degrades extracellular matrix components including integrin-fibronectin-binding, cytokine, immunoglobulin and complement factors. It is also important for processing and maturation of FimA. P. gingivalis proteases aids in colonization of periodontal pocket which leads to destruction of supporting periodontal tissue, as well as degradation of extracellular matrix proteins (collagen), activation of host matrix metalloproteinases, inactivation of plasma proteinase inhibitors, cleavage of cell surface receptors and deregulation of inflammatory. 3

Outer Membrane Protein

Cell wall of gram negative bacteria is made up of two cell membranes; the outer membrane (OM) and the inner membrane (IM), of which both have different composition and structure. 3 IM is a phospholipid bilayer containing many integral IM proteins 23 however the OM is an asymmetrical bilayer containing phospholipids and lipopolysaccharide in inner and outer leaflet respectively. 3 Bacterial cell membrane acts as a selective barrier that protects and allow various molecules to enter/exit through OM porin proteins. 24 There are two OM proteins; OM lipoproteins anchored to OM by N-terminal lipid tail, and another OM integral protein consisting membrane-spanning regions. 25 OM proteins mediate interaction between periodontal microflora, which is associated to forming and maintaining periodontal biofilms. 23 LptO, an OM protein (PG0027) is important for O-deacylation of LPS of P.gingivalis, and this structural formation is hypothesized to be crucial in providing attachment onto host cells. 24

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 Jolene Sim for the MICR3004 course, Semester 2, 2016