{"refrec":{"BRefID":250067,"RR":"<b>Mojica, K.D.A.</b> (2015). Viral lysis of marine microbes in relation to vertical stratification. PhD Thesis. Universiteit van Amsterdam: Amsterdam. ISBN 978-94-91407-20-8. 247 pp. <a href=\"http://hdl.handle.net/11245/1.487499\" target=\"_blank\">hdl.handle.net/11245/1.487499</a>","BEntID":241767,"PublicFlag":1,"CheckedFlag":0,"wosflag":null,"vabbflag":null,"RefStringPartII":". PhD Thesis. Universiteit van Amsterdam: Amsterdam. ISBN 978-94-91407-20-8. 247 pp. <a href=\"http://hdl.handle.net/11245/1.487499\" target=\"_blank\">http://hdl.handle.net/11245/1.487499</a>","DocTypID":5,"DocType":"Book/Monograph","MarineFlag":1,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"Mojica, K.D.A.","OrigTitleTranslFlag":0,"Authorstringtrunc":"Mojica, K.D.A.","Englishabstract":"Marine microorganisms represent the largest reservoir of living organic carbon in the ocean and collectively manage the pools and fluxes of nutrients and energy. Climate-induced increases in sea surface temperature and associated modifications to vertical stratification are affecting the structure and production of autotrophic and heterotrophic microorganisms in ocean surface waters. However, little is known about how future alterations will affect the mortality of marine microbes. The various modes of mortality influence the cycling of biogeochemical elements very differently. This in turn affects the production to respiration ratio of the ocean and thus the efficiency with which photosynthetic organic carbon is transferred to higher trophic levels or exported to the deep ocean (via the biological pump). The Atlantic Ocean provides a meridional gradient in stratification, is essential to global circulation and acts as a major sink for anthropogenic carbon dioxide. The Northeast Atlantic thus provides an ideal model system for the current study which aims to investigate the influence that vertical stratification has on the source of mortality (i.e., viral lysis versus grazing).After a general introduction, this thesis begins by providing a comprehensive overview of what is currently known about how environmental factors in the marine environment affect virus-host interactions. Abiotic and biotic variables can influence the infectivity and survival of marine viruses, and regulate the physiology, production and distribution of the host. Ultimately, these aspects govern the efficiency with which viruses can replicate and thus propagate through the marine environment (Chapter 2). The review illustrates that at this moment in time, our ability to identify general ecologically functional patterns important in governing virus dynamics over broad oceanic scales is restricted by the availability of information regarding both the effect of individual environmental factors and by the scarcity of reported rates. In order to better understand the importance of vertical mixing and physicochemical features in structuring phytoplankton (unicellular algae) host populations, a high-resolution mesoscale description of the phytoplankton community along a meridional gradient in the Northeast Atlantic Ocean was conducted during the spring and summer (Chapter 3). Vertical stratification was identified as a key factor governing the distribution and separation of different phytoplankton taxa and size classes, indicating that incorporation of vertical turbulence structure of the water column will improve biogeochemical and ecological modeling studies. The data support predictions that climate-change induced increases in ocean surface temperature and expansion of oligotrophic (nutrient-limited) areas willincrease the contribution of pico-sized (< 2 µm) eukaryotic phytoplankton (while decreasing the abundance of cryptophytes and diatoms), and expand the geographic range of Prochlorococcus spp. northward (leading to alterations in phylogeography within unicellular cyanobacterial populations). This will likely result in large-scale biogeographical changes in virus distributions, including an expansion of the V3 viruses associated with picocyanobacterial hosts (Chapter 4). More importantly, simultaneous measurements of viral lysis and microzooplankton grazing rates conducted along the latitudinal transect during summer (Chapter 4) show that (i) viral lysis was responsible for half of the total mortality occurring in all phytoplankton groups, (ii) average virus-mediated lysis rates were higher for eukaryotic phytoplankton than for the prokaryotic cyanobacteria Prochlorococcus spp. and Synechococcus spp., (iii) overall the total phytoplankton mortality rate (viral lysis plus microzooplankton grazing) was comparable to phytoplankton gross growth rate, signifying high turnover rates of marine phytoplankton populations, and finally (iv) viral lysis rates were reduced in the north (> 58°N), resulting in grazing-dominated phytoplankton mortality. A method optimization for the enumeration of samples with low viral abundance (pH modification of the TE-buffer used for the dilutions) substantially improved total virus counts in North Atlantic samples compared to those obtained using the standard method (Chapter 5). This method was applied to enumerate field samples which utilized a virus reduction approach to investigate the viral life strategy and magnitude of infection in heterotrophic prokaryotic populations (Chapter 6). Compared to grazing, viruses were the dominant mortality factor regulating prokaryotic losses in the surface waters of the Northeast Atlantic Ocean during summer. Lytic infection (virus replication and host lysis proceeds immediately after infection) was the favored life strategy in the surface mixed layer, while lysogeny (virus incorporated into host genome where it remains until triggered into lytic cycle upon stimulation by an environmental factor) was only relevant within the deep chlorophyll maximum layer of oligotrophic southern stations. The data revealed a close to steady state situation and rapid turnover in the south and net heterotrophic production in the north, suggesting that alterations in stratification will also affect heterotrophic prokaryote production.Implementing measured production and loss rates of autotrophic (Chapter 4) and heterotrophic (Chapter 6) organisms into a steady state carbon-flux model demonstrates that 80% of the photosynthetically fixed carbon flowed through the viral shunt in the oligotrophic south, which is more than 2-fold higher than thenorthern region. These results illustrate that viruses play a more prominent role in stratified (steady state) marine ecosystems than thought previously. Overall, this thesis reveals that viral lysis is an important factor regulating the biomass and productivity of marine microbial populations during summer stratification in the Northeast Atlantic Ocean. Moreover, the data support the hypothesis laid out in this thesis that alterations in microbial communities due to global warming-induced changes in vertical stratification will affect mortality processes and the distribution of predators (e.g. mortality agents). The partitioning of photosynthetic carbon through the separate mortality pathways has important implications for ecosystem functioning as each pathway affects the structure and activity of the pelagic food web in different ways. Grazing transfers biomass to higher trophic levels, thus increases the overall efficiency and carrying capacity of the ecosystem. On the other hand, viral activity stimulates recycling via heterotrophic prokaryotes by shunting biomass to the dissolved organic matter pool, and therefore enhances the availability of inorganic nutrients in the oligotrophic surface waters of the ocean. In conclusion, the data presented in this thesis indicate that climate change-induced alterations in the timing and strength of seasonal stratification at the higher latitudes will shift the ecosystem towards a more viral-lysis dominated system. A more prominent future role of viral lysis in the northern region of the North Atlantic Ocean would thus markedly reduce biological carbon export into the ocean’s interior in one of the key areas of global carbon sequestration, reducing the potential for the ocean to serve as a long-term sink for anthropogenic carbon dioxide.","AbstractOtherLang":"Mariene micro-organismen vertegenwoordigen het grootste reservoir van organische koolstof in de oceaan en hebben een sturende rol in de kringloop van nutriënten en de stromingen van materie en energie. Klimaatverandering leidt tot opwarming van de bovenste waterlagen (oppervlaktewateren) in zeeën en oceanen, waarbij de resulterende veranderingen in verticale gelaagdheid (stratificatie) van de bovenste waterlaag de structuur en productie van auto- en heterotrofe micro-organismen beïnvloeden. Er is nog maar weinig bekend over de wijze waarop deze toekomstige veranderingen de sterfte (mortaliteit) van mariene micro-organismen beïnvloeden. De verschillende modi van sterfte werken anders door op de cycli van biochemische elementen. Dit heeft weer gevolgen voor de verhouding tussen de productie en respiratie van de oceaan en daarmee dus de efficiëntie waarmee fotosynthetisch vastgelegd organisch koolstof naar hogere trofische niveaus (plek in de voedselketen), of naar de diepzee wordt getransporteerd. De Atlantische Oceaan heeft een noord-zuid gradiënt in stratificatie, is essentieel voor de wereldwijde oceaan circulatie en dient als voornaamste afvoer voor antropogeen koolstofdioxide. Het noordoostelijk deel van de Atlantische Oceaan vormt daarom een ideaal modelsysteem voor de huidige studie, die als doel heeft om de invloed van verticale stratificatie op de sterfte (virale lysis of begrazing) en de onderlinge verhouding van de verschillende wijzen van mortaliteit te onderzoeken. Het onderzoek in dit proefschrift begint met een uitgebreid overzicht van de huidige kennis van omgevingsfactoren die virus-gastheer interacties in het mariene milieu beïnvloeden. Abiotische en biotische variabelen kunnen invloed uitoefenen op en overleving van mariene virussen en kunnen de fysiologie, productie en de (geografische) verspreiding van de gastheer reguleren. Uiteindelijk reguleren deze aspecten het succes waarmee virussen zich repliceren en verspreiden in het mariene milieu (Hoofdstuk 2). Het review artikel maakt duidelijk dat op dit moment ons vermogen om algemene ecologisch functionele patronen te herkennen die belangrijk zijn in het aansturen van de virus populatiedynamiek op oceanische schaal, wordt belet door de schaarste aan informatie betreffende de individuele omgevingsfactoren en de intensiteit van hun effect.Om beter te begrijpen wat het belang is van verticale menging en de fysisch-chemische eigenschappen van het zeewater op het structureren van eencellige algen (fytoplankton) gastheerpopulaties, werd over een noord-zuid transect en met hoge resolutie de fytoplanktongemeenschap in de Noordoost Atlantische Oceaan tijdens de lente en zomer in kaart gebracht (Hoofdstuk 3). Verticale stratificatie werd geïdentificeerd als een belangrijke factor die de vertikale en geografischeverspreidingvan verschillende fytoplankton taxa en grootteklassen bepaalt, wat aangeeft dat toevoeging van de verticale turbulentiestructuur van de waterkolom de biochemische en ecologische modelstudies zal verbeteren. De data ondersteunen de voorspellingen dat (1) klimaatverandering-gerelateerde toename in temperatuur en de uitbreiding van oligotrofe (nutrient-gelimiteerde) gebieden in de oceaan de bijdrage van eukaryote picofytoplankton (<2 µm diameter) vergroot, terwijl het aantal cryptofyten en diatomeeën afneemt; en (2) dat het verspreidingsgebied van Prochlorococcus spp. noordelijk uitbreid (wat leidt tot veranderingen in de geografische verspreiding van de verschillende populaties van deze eencellige cyanobacteriën). Dit zal waarschijnlijk resulteren in biogeografische veranderingen in virusverspreiding op grote schaal, inclusief een expansie van de V3-virussen die geassocieerd zijn met eencellige cyanobacterie gastheren (Hoofdstuk 4). Belangrijker nog, simultane metingen van sterftesnelheden door virale lysis en microzoöplankton begrazing, uitgevoerd langs een noord-zuid transect gedurende de zomer (Hoofdstuk 4), laten zien dat (i) virale lysis verantwoordelijk was voor de helft van de mortaliteit in alle fytoplankton groepen, (ii) de gemiddelde sterftesnelheid door virale lysis hoger was voor eukaryote fytoplankton dan voor de prokaryote cyanobacteriën Prochlorococcus spp. en Synechococcus spp., (iii) omzettingssnelheden van fytoplankton populaties hoog zijn aangezien algeheel de totale sterftesnelheid voor fytoplankton (virale lysis plus begrazing) vergelijkbaar was met de bruto groeisnelheid, en tot slot (iv) de afgenomen virale lysis snelheden in het noorden (58°N) resulteerden in begrazing-gedomineerde algensterfte. Deze resultaten impliceren dat door het opwarmen van de oceaan het ecosysteem op hogere breedtegraden kan verschuiven naar een systeem waarin virale lysis domineert. Door een methode te optimaliseren voor monsters met kleine concentraties virussen (bijstellen van de pH van de TE-buffer in de verdunningen) verbeterde het aantal getelde virussen in monsters in de Noord-Atlantische Oceaan aanzienlijk in vergelijking met de standaard methode (Hoofdstuk 5). Deze methode was ontwikkeld om virale lysis van de heterotrofe prokaryoten beter te kunnen bestuderen (Hoofdstuk 6). In vergelijking met begrazing was virale lysis de overwegende sterftefactor voor heterotrofe prokaryoten in de oppervlaktewateren van de Noordoost Atlantische Oceaan gedurende de zomer. Lytische infectie (virus vermenigvuldiging en lysis gastheer vindt plaats direct na infectie) was de preferente levensstrategie in de gemixte oppervlakte laag, terwijl lysogenische infectie (uitgestelde lysis door inbouw in gastheer genoom) alleen relevant was inhet chlorofyl-maximum (diepere laag in zuidelijke oligotrofe stations). De data laten een noord-zuid gradiënt zien met een nagenoeg stabiel evenwicht (steady state) met hoge omzetting in het zuiden en netto heterotrofe productie in het noorden. Dit impliceert dat veranderingen in stratificatie dus ook effect zullen hebben op de heterotrofe prokaryote productie. Het implementeren van de gemeten productie- en verliessnelheden van autotrofe (Hoofdstuk 4) en heterotrofe (Hoofdstuk 5) organismen in een steady-state koolstofmodel laat zien dat in het oligotrofe zuiden 80% van de door fotosynthese vastgelegde koolstof via de virale route (‘viral shunt’) stroomt, wat meer dan twee keer zoveel is dan in de noordelijke regio. Deze resultaten tonen aan dat virussen een prominentere rol spelen in gestratificeerde (steady-state) mariene ecosystemen dan eerder gedacht. Algeheel laat dit proefschrift zien dat sterfte door virale lysis een belangrijke factor is in het reguleren van biomassa en productiviteit van mariene microbiële populaties gedurende stratificatie in de zomer in de Noordoost Atlantische Oceaan. Bovendien ondersteunen de data de hypothese die was uiteengezet in dit proefschrift, namelijk dat aanpassingen in microbiële gemeenschappen door veranderingen in verticale stratificatie ten gevolge van wereldwijde opwarming effect hebben op de sterfteprocessen en verspreiding van virussen en predatoren. De verdeling van de vastgelegde koolstof via de verschillende routes van sterfte heeft belangrijke implicaties voor het functioneren van het ecosysteem, omdat elke route de structuur en activiteit van het pelagisch voedselweb op verschillende wijze beïnvloedt. Begrazing transporteert biomassa naar hogere trofische niveauswaarbij als zodanig de algehele efficiëntie en draagkracht van het ecosysteem wordt verhoogd. Anderzijds stimuleert virale activiteit recycling door biomassa naar het reservoir van opgelost organisch koolstof te transporteren alwaar omzetting hiervan door heterotrofe prokaryoten de beschikbaarheid van anorganische nutriënten in oligotrofe oppervlaktewateren van de oceaan vergroot. Ter afsluiting, de data in dit proefschrift tonen aan dat deviaties in de timing en de sterkte van seizoensstratificatie door klimaatverandering het ecosysteem op hogere breedtegraden zal verschuiven naar een systeem waarin lysis door virussen de dominante verliesfactor is. Een toekomstig prominentere rol van sterfte door virale lysis in de noordelijke regio van de Noord Atlantische Oceaan zou dus de export van biologisch koolstof naar de diepzee aanzienlijk verminderen en daarbij zal ook het potentieel van dit belangrijke gebied voor koolstofopslag als langdurige put voor antropogeen koolstofdioxide afnemen.","BibLvlCode":"M","StandardTitle":"Viral lysis of marine microbes in relation to vertical stratification","OrigTitleLangCode":"en","OrigTitleLangCodeExtended":"eng","OrigTitleLangID":15,"DateLastModified":{"date":"2024-12-10 01:33:17.368041","timezone_type":1,"timezone":"+01:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":null,"OtherDescriptors":null,"Notes":null,"AnaPub":null,"MonPub":2015,"DateUpdate":"2019-05-27","DateCreate":"2015-09-25","SecASFANote":null,"ConfID":null,"PeerRev":0,"VlizCoreFlag":1,"WoScode":null,"VABBcode":null,"OpenAcc":1,"Handle":"11245/1.487499"},"refs":null,"anarec":null,"monrec":{"MonID":250067,"ISBN":"978-94-91407-20-8","PubliDate":2015,"IssueDate":null,"Volume":null,"Issue":null,"Pagination":"247","Place":"Amsterdam","Edition":null,"BRefXtra":null,"BRefXtraRR":null,"SerID":null,"SerRR":null,"Ser2BRefID":null,"Ser2RR":null,"StandardTitleSer":null,"ISSN":null,"AbbrevSer":null,"Degree":"PhD","ThesisID":250067,"InsID":null,"Acronym":null,"FullStandardName":null,"ToPubliDate":null,"SerNotes":null,"eISBN":null,"Pages":247},"serrec":null,"relations":null,"relationsRev":null,"addrec":null,"othpubs":null,"ownerships":null,"authors":[{"AutName":"Mojica","Firstname":"Kristina","Initials":"K.D.A.","Affiliation":null,"Discriminator":null,"CorporateFlag":0,"BEntID":241767,"AutID":247997,"OrderNr":1,"DegrID":null,"EditorFlag":0,"CorrespFlag":0,"IllustratorFlag":0,"ReviserFlag":0,"TranslatorFlag":0,"InsAcronym":"MMB","InsFSN":"Koninklijk Nederlands Instituut voor Onderzoek der Zee; 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