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, requiring 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 Disease initially occurs as acute inflammation of gingival tissue, untreated infections progressively cause formation of teeth pockets and loss of teeth. 3 Habitat of P. gingivalis is subgingival sulcus of human oral cavity, serving as secondary colonizer of dental plaques by attaching onto primary colonizers such as Streptococcus gordonii and P. intermedia. 3 It functions to produce a variety of potential virulence factors as significant pathogen in 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 causes 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, and 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, mediated by adhesins on surface of bacteria and receptors on oral surfaces. These adhesins are associated with cell structures such as capsules and fimbriae of P.gingivalis. Cell wall consists of distal polysaccharide (O-antigen), a non-repeating core oligosaccharide and a hydrophobic domain known as lipid A (endotoxin). Lipid A is the biological active site of lipopolysaccharide (LPS) that causes deregulation of 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 hosts. LPS of gram-negative bacteria is significant in maintaining 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

Major habitat of P. gingivalis is subgingival sulcus of human oral cavity. 3 It requires amino acid fermentation to produce energy needed for surviving 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 tongue, and pharynx. 12 P. gingivalis/host interaction is amphibiosis, where recent relationship between 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-extracellular matrix (ECM) contacts. Cellular integrins function as ECM protein receptors for linkages between extracellular environment and intracellular cytoskeleton. 14 ECM proteins in periodontal pocket fluid include vitronectin and fibronectin. Vitronectin protects gingival epithelium and connective tissues against periodontal damages (31). Fibronectin is significant in proliferation and chemotaxis of periodontal ligament cells. 15 P. gingivalis binds ECM proteins through its fimbriae and outer membrane proteins, inhibiting ECM proteins from functioning, therefore slowing recovery processes caused by periodontal tissue destructions. P. gingivalis binds 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, blocking receptor-ligand interactions of human host fibroblasts. This leads to inhibition of cellular signal transduction, 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 Intracellular environment provides nutrients for P. gingivalis growth, and serves as protection against host immune system. 15 P. gingivalis fimA genes have 5 variants (type I to V), classified based on nucleotide sequences. 20 Polymerase chain reaction (PCR) is used to detect P. gingivalis variants in saliva and periodontal samples. 21 It was shown that 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 illustrate presence of disease and non-disease causations of P. gingivalis, where fimbriae variations are associated with bacterial infections, affecting disease development. Type II fimA was also observed to invade rapidly into host epithelial cells, promoting P. gingivalis invasion. 22

Pathology

The bacteria has also been identified as risk factor for coronary heart disease, pulmonary infections and pre-term, low birth weight deliveries. 23 P. gingivalis produces variety of virulence factors 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,causing damage in hosts. To survive and multiply in hosts, P. gingivalis has to overcome host external protective barrier before finding suitable environment for colonization, occuring 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 first attach onto teeth or mucosal surfaces through adhesins, which is essential in resisting saliva flow. 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 less virulent strains, such as W376. Encapsulated strains are more virulent than non-encapsulated strains. Encapsulated strains could 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 by macrophages and dendritic cells. Capsule was shown to promote virulence by reducing phagocytosis, thereby increasing bacterial survival within hosts, and ultimately a chronic inflammatory response. However, invasion efficiency is affected by capsule, making it less efficient to invade gingival fibroblast compared to non-capsular strains. Regulatory mechanisms in capsule synthesis is known as tyrosine phosphatase (Ltp1) encoded by PG1641, 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)

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 of LPS 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

Ability of P. gingivalis to secrete numerous hydrolytic, proteolytic and lipolytic enzymes with toxic metabolites allows it 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, and are commonly known as gingipains (gingipain R and K that cleave after arginine and lysine respectively). They account for 85% 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, and extracellular matrix proteins (collagen) degradation, 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; outer membrane (OM) and inner membrane (IM), of which both have different composition and structure. 3 IM is a phospholipid bilayer containing many integral IM proteins 23 however OM is an asymmetrical bilayer containing phospholipids and lipopolysaccharide in inner and outer leaflet respectively. 3 Bacterial cell membrane acts as a selective barrier, protecting and allowing 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, 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

Periodontal tissue engineering involves repairing of alveolar bone, tooth-associated cementum and periodontal ligament (PDL). 26 Regeneration of periodontal tissues depends on appropriate signals, cells, blood supply and scaffold necessary for targeting tissue defects. Appropriate signals such as growth factors, regulate cellular activities, providing signals for cell differentiation and produce matrix for developing tissues. Cells serve as machinery for new tissue growths and differentiation. Scaffolds serves as structural template for processes in periodontal tissue regeneration. Studies have shown that enamel matrix derivative (EMD),a bioactive molecule, can promote periodontal wound repairing by regenerating periodontal tissues. 27

Biotechnologically relevant enzyme/compound production

Major arginine-specific cysteine proteinase of P. gingivalis, RGP-1 can be generated as polypeptides to function as erythrocyte-binding protein through various adhesion domains at the carboxyl terminus. 28

Drug Targets

Nasal immunization with hemin-binding protein and cholera toxin exhibit immune response against P. gingivalis in young and aged mice, and preventing atherosclerosis. 29 Nasal delivery of OM protein can be a potential vaccine strategy in providing protective immunity to human to prevent periodontitis. Plant-derived bioactive compunds as therapeutic roles to regulate interactions between microorganisms have been widely used and is non-toxic towards human cells. 3 An anthraquinone from rhubarb roots, Rhein, shows antibacterial synergistic effect when used together with other polyphenols. It downregulates rgpA and Kgp proteases genes associated with inactivation of host defense. 30 Main polyphenols in black tea, theaflavins, inhibit P. gingivalis proteinase activities based on dosages. 31 KYT-41, a synthetic dual protease inhibitor, inhibiting Rgp and Kgp of P. gingivalis. Also, it displays anti-inflammatory activity, which can be a potential treatment for gingivitis. 32

Current research

Inhibitory effect of grape seed proanthocyanidin extracts can inhibit P. gingivalis LPS. 33 Roles of α-tocopherol in countering damaging effect of LPS decreased inflammatory cytokines, increasing β-defensins, promoting gingival fibroblast growth and migration. 34 Tormentic acid inhibits LPS-induced inflammatory response in human gingival fibroblasts. 35 Differences in LPS profile of P.gingivalis affects colony morphology and polymyxin B resistance. Unlike healthy individuals, periodontal isolates were resistant to polymyxin b with low aggregation ability. This resistance highly relates to variation in LPS profiles as LPS from healthy individuals lack high molecular weight O-antigen moieties and anionic polysaccharide, whereas P. gingivalis isolates from periodontal subjects produce modified lipid-A molecules. 36 P. gingivalis fimbriae activate human gingival epithelial cells, spleen cells, and peripheral blood monocytes to release interleukins and TNF-α, and these molecular interactions between P. gingivalis and human hosts are currently being investigated. 22

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