"St. Xavier’s College (Autonomous)Post graduate Department of MicrobiologyLiterature Review on“CONTRIBUTION OF LYSOGENIC PHAGESIN BACTERIAL INFECTIONS”ByMs. Ansari Sufiya Roll. No- 02UID- 158602Teacher In charge- Dr. Aparna TalekarDate of submission- 07/10/2015Contribution of Lysogenic phages in Bacterial infectionsINTRODUCTIONF. W. Twort (1915) and Felix d'Herelle (1917) independently discovered antagonistic microbesthat can infect and cause lysis of other bacteria- later they were known to be bacteriophages i.e. avirus that infects bacterium (H. Duckworth 1976). Phages are found to be present in all placeswhere their bacterial hosts are present(W. Hendrix et al.1999). Bacteriophage shows the presenceof lytic cycle and lysogeny cycle. In the lytic life cycle the phages rapidly infect and kill the hostcells whereas in lysogenic cycle no direct killing of the hosts is seen, instead the lysogenic phageintegrates with the host genome or stays as a plasmid within the host cell (Clokie et al. 2011). The lytic cycle involves adsorption of the phage to specific cell surface receptor of the host,delivery of the phage DNA in the hosts cytoplasm, transcription and replication of the phagegenome. The viral proteins are then assembled and progeny phages are released. Temperatephages also show the ability to carry out lytic cycle as virulent phages, but they have anadditional benefit of opting for a non lytic life i.e. lysogenic cycle. The decision to start either alytic or a lysogenic cycle is taken within minutes of DNA injection into the host cytoplasmdepending upon the metabolic state of the bacterial cell. The phage can integrate its DNA intothe host chromosome and stay as a “quiescent” prophage until favorable conditions forreactivation is acquired. The prophage DNA gets replicated along with the host chromosomeduring cell division. A bacterial host carrying one or more prophages is known as a lysogen.Lysogens are generally “immune” to infection by other phages of the same group. This capacityof temperate phages has great impact on the lifestyle, fitness as well as virulence of the lysogen(Forteir and Sekulovic O. 2013). Temperate phage contains genes that can affect the behavior and phenotype of their bacterialhosts by expression of phage encoded genes. These are extra genetic material i.e. foreign genesencoding for various toxins, antibiotic resistance, cell surface receptors for adhesion and invasionwhich helps in the pathogenesis of the bacterium. The Lysogenic state is very stable, although aswitch to lytic state by various mechanisms depending on the phage type can occur (Chung et al.2014). In this review we will discuss the various contributions of foreign genes of lysogenicphages on the pathogenesis of bacteria.ADHERENCE AND INVASION INTO THE HOSTA large variety of Pneumococcal phages are observed in nature, however their role inpathogenesis is not so frequently observed. An MM1 phage variant i.e. MM1-1998 isolated fromStreptococcus pneumonia serotype 24 was used to create three isogenic strain pairs (serotype 3, 4and 24). These isogenic strains differed by lysogenic presence of MM1-1998.Improvedadherence to inert surfaces and pharyngeal cells was observed with lysogeny as compared tocured variants. This improved adherence is due to the prophage association which helpsStreptococcus pneumonia to colonize the human nasopharynx contributing to the fitness andpersistence of the bacterium in human (Jutta M et al. 2006).A major pathogenesis of infective endocarditis is the binding of bacteria directly to platelets.Streptococcus mitis shows platelet binding activity due to the presence of lysogenicbacteriophage SM1 which encodes for lysin. Lysin interacts with fibrinogen present on theplatelet surface. The characterization of the fibrinogen binding domain of lysin revealed nosequence homology to other fibrinogen binding proteins that are known. Experiments showedthat lysin fibrinogen binding is mediated by specific phage proteins whose interaction was foundto be necessary for platelet binding and aggregation of S.mitis (Ho Seong et al.2011).A gram positive nosocomical infection causing pathogen E. faecalis establishes lysogeny with aphage V583. This prophage provides virulent factors or fitness benefits to the bacterium. Renataet al. showed the role of prophage V583 in pathogenecity. They also provided a correlationbetween lysogeny of E. faecalis and use of antibiotic fluoriquinolone. The antibiotic leads to therelease of prophages and promotes gene dissemination amongst the isolates. Three prophagesparticipate to E. faecalis V583 adhesion to human platelets. This is the first step in thedevelopment of infective endocarditis (2013).Bacteriophage P22 encodes tailspike proteins (TSPs), a trimeric ß-helical protein which isimportant organelle for infection. On infection these TSPs of P22 binds and cleaves O-antigen oflipopolysaccharide (LPS) of the host (Salmonella). P22TSP is an endorhamnosidase i.e. a phageencoded protein that can recognize and depolymerize repetitive carbohydrate structure of O- antigen in the LPS. Enzymatic cleavage of LPS polysaccharide allows access to the membraneand specific receptors. The carbohydrate binding ability inferred to the host by phage P22 helpsthe bacterial attachment to the host cell (Andres et al. 2010a).Subsequent invasion into the host cell is also mediated by phage P22. For DNA ejection thetailspike positions the phage particles on the outer membrane surface, the gp26 (central needle)and the phage plug protein (phage tail) are forced by tailspike through the oligosaccharide coreinto the hydrophobic portion of the outermembrane. This leads to refolding of gp26 lazo-domain,releasing the plug and subsequent ejecting the DNA and pilot proteins (Andres et al. 2010b).Interaction of tailspike proteins of both the short-tailed podovirus P22 as well as the long-tailedsiphovirus 9NA with LPS provided a signal for release of DNA from the capsid initiating theinfection process i.e. the tail morphology proves to be important factor for release of DNA(Andres et al. 2010c).Phages have played an important role in generating a vast diversity of Salmonella strains. Phageencoded virulent proteins of Salmonella has led to the emergence of new epidemic strains.Salmonella enteric is known to use type III secretion system for delivery of effector proteins intohost cell. These effector proteins manipulate the host cell signaling cascade. Salmonella infectedwith phage SopE? is more invasive in nature. The phage bacterium integrate produces amembrane associated effector protein SopE. SopE is a guanine nucleotide exchange factor thatactivates Rho GTPases. This activation causes membrane ruffling and enhances invasion ofSalmonella (Humphreys et al. 2012). BIOFILM FORMATIONVarious microorganisms use biofilm formation as a mode of their survival. Biofilm is a complexadherent surface of bacteria held together by an extracellular matrix. The etiological agent forsevere diarrhoeal disease, Vibrio cholerae forms biofilm and persists in aquatic ecosystems. Forthis process the pathogen uses extracellular DNA (foreign genes) and two extracellular nucleasesXds and Dns (Seper et al. 2011).Gram negative bacterial pathogens Bordetella pertussis and Bordetella bronchiseptica colonizein the respiratory tract of mammals. This colonization is favored by biofilm formation. Onanalysis the matrix of this biofilm was shown to consist of various polysaccharides, proteins aswell as extracellular DNA. Studies also revealed the crucial role of extracellular DNA in thestructural matrix both in vitro and in vivo (Conover et al. 2011).An upper respiratory tract infection causing pathogen, S. pneumonia uses biofilm formation forcolonization and infection purpose. Margarida et al. demonstrated the ability of lysogenic andnon lysogenic pneumococcal strains to form biofilm. It was observed that lysogenic strainsformed prominent biofilm. Studies also revealed that a fraction of bacterium undergoes phagemediated host lysis. This is due to spontaneous phage induction, which contributes as a majorsource of extracellular DNA for the formation of biofilm matrix of S. pneumonia. This phagemediated host lysis of a fraction of bacterial population releasing extracellular DNA favorsbiofilm formation by the remaining bacterial population (2015).PHAGE ENCODED VIRULENT PROTEINS Bacteriocins are proteins used by bacteria as a competitive factor in microbial ecosystems.ColicinIb (ColIb) imparts important fitness benefits to its host Salmonella entericaserovar Typhimurium (S. Tm) against commensal gut Escherichia coli. S.Tm releases ColIb a pore forming bacteriocin into the environment causing killing of itssusceptible competitors. After a long time researchers were able to find a link between release ofColIb and presence of temperate phages and its lysis genes (Nedialkova et al. 2015).PHAGE ENCODED TOXINSClostridium difficle is an emerging nosocomical pathogen that produces two large proteinexotoxins- TcdA and TcdB. These toxins are responsible for cellular damage and form animportant virulent factor of the bacterium. The genes for these toxins are located on apathogenecity locus (PaLoc) which is known to be inherited from a phage. Studies revealed thattoxin production is enhanced on introduction of fCD38-2 into a Clostridium difficile NAP1/027isolate (Ognjen et al. 2011).Hargreaves et al. documented a phage phiCDHM1 that infects the nosocomical infection causingpathogenic bacterium Clostridium difficile. This phage showed the presence of novel genes thatare not commonly found in phage genome.It included three homologs of bacterial genes fromquorum sensing systems i.e. the accessory gene regulator (agr). The phiCDHM1 phage might be eliciting some response in the host to enhance toxin or spore production thereby contributing tohost fitness. Using AgrA mutants, increased toxin A production have been reported in C.difficile,regulating the fitness of the bacterium (2014).BACTERIOPHAGE AS MEDICAL TOOLPseudomonas aeruginosa strains associated with cystic fibrosis forms an exopolysaccharidelayer of alginate which protects the bacterium from hosts defense mechanism as well asantimicrobial agents. This helps the pathogen to establish chronic infections in patients sufferingfrom cystic fibrosis. Bacteriophages that can target the alginate exopolysaccharide using alginatedepolymerase enzyme can improve the health of these patients by increased phagocytosis of thebacterium due to destruction of their protective coat (Glonti et al. 2010).CONCLUSION Along the years, bacteria have learnt and evolved to adapt to various environmental and growthconditions for their survival. Integration of a bacterial chromosome with a phage forming aprophage is one of the survival strategies of bacteria. Important virulent features are obtainedfrom lysogeny. Apart from bacterial pathogenesis, lysogeny also plays a role in evolution andorigin of several bacterial strains.Various steps for a bacterium to establish an infection are: attachment or adhesion to target cell,invasion of the host cell and release of toxins or other virulent proteins. Various temperatephages modify the virulence, fitness and evolution of their bacterial host in a variety of manner.A large contribution of lysogeny is seen in the pathogenesis of various bacteria. The mostimportant pathogenic contribution involves the acquisition of potent toxins earlier. Biofilmdevelopment helps the bacteria to colonize and also provides fitness benefit. Bacterium in abiofilm can survive in the presence of high antibiotic concentrations and other harshenvironmental conditions that are normally not tolerated by a single bacterium leading to afailure in treatment.Research about various phage-host interactions in different species of bacteria have led to thediscovery of other novel virulence characters that a bacterial host can acquire by a prophage suchas adhesion to host tissues, invasion and production of various virulent proteins.Use ofbacteriophages which are natural bacterial pathogens is a well known concept to treat bacterialinfections. Previously lytic phages were customized and used, however recently researchers alsotried using temperate phages for our benefit. Increased development in molecular biology andgenomic sequencing have provided great scope for development of customized engineered phageas well as phage derived proteins.Better understanding of the phage biology, genomicsequencing and detailed study about the various pathogenic properties obtained from phagesneed to be carried out so that it can be exploited to our benefit.REFERENCESAndres D, Baxa U, Hanke C, Seckler R, Barbirz S. 2010a. Carbohydrate Binding ofSalmonella Phage P22 Tailspike Protein and Its Role during Host Cell Infection.Biochem SocTrans. 38(5): 1386–89Andres D, Hanke C, Baxa U, Seul A, Barbirz S, Seckler R. 2010b. Tailspike Interactionswith Lipopolysaccharide Effect DNA Ejection from Phage P22 Particles in Vitro. J Biol Chem.285(47): 36768–75Andres D, Roske Y, Doering C, Heinemann U, Seckler R, Barbirz S. 2010c. TailMorphology Controls DNA Release in Two Salmonella Phages with One LipopolysaccharideReceptor Recognition System. Mol. Microbiol.83(6): 1244–53Chung IY, Jang HJ, Bae HW, Cho YH. 2014. A Phage Protein That Inhibits the BacterialATPase Required for Type IV Pilus Assembly.Proc Natl Acad Sci U S A. 111: 11503–8Clokie MR, Millard AD, Letarov AV, Heaphy S. 2011. Phages in Nature. Bacteriophage.1(1): 31–45Conover MS, Mishra M, Deora R. 2011. Extracellular DNA Is Essential for MaintainingBordetella Biofilm Integrity on Abiotic Surfaces and in the Upper Respiratory Tract of Mice.PLuS One. 6(2):1-10Fortier LC, Sekulovic O. 2013. Importance of Prophages to Evolution and Virulence ofBacterial Pathogens. Virulence.4(5): 354–65Glonti T, Chanishvili N, Taylor PW. 2010. Bacteriophage-Derived Enzyme ThatDepolymerizes the Alginic Acid Capsule Associated with Cystic Fibrosis Isolates ofPseudomonas Aeruginosa. J Appl Microbiol.108(2): 695–702 Hargreaves KR, Kropinski AM, Clokie MR. 2014. What Does the Talking? QuorumSensing Signalling Genes Discovered in a Bacteriophage Genome.PLos ONE. 9(1)H. Duckworth. 1976. Who Discovered Bacteriophage?Bacteriological Reviews. 40(4):793–802Ho Seong, Sullam PM. 2011. Characterization of the Fibrinogen Binding Domain ofBacteriophage Lysin from Streptococcus Mitis. Infect. Immun. 79(9): 3518–26Humphreys D, Davidson A, Hume PJ, Koronakis V. 2012. Salmonella Virulence EffectorSopE and Host GEF ARNO Cooperate to Recruit and Activate WAVE to Trigger BacterialInvasion. Cell Host Microbe. 11(2): 129–39Jutta M, Fischetti VA. 2006. Lysogeny of Streptococcus Pneumoniae with MM1 Phage:Improved Adherence and Other Phenotypic Changes. Infect. Immun. 74(8): 4486–95Margarida Carrolo, Maria João Frias, Francisco Rodrigues Pinto, José Melo-Cristino,Mário Ramirez.2010. Prophage Spontaneous Activation Promotes DNA Release EnhancingBiofilm Formation in Streptococcus pneumonia. PLoS One. 5(12): e15678.Nedialkova LP, Sidstedt M, Koeppel MB, Spriewald S, Ring D, Gerlach RG, Bossi L,Stecher B. 2015. Temperate Phages Promote Colicin-Dependent Fitness of Salmonella EntericaserovarTyphimurium.Envirom Microbiol. 1462–2920 "