The revelation of the essential interactions that stabilise our oceans

Through research at the University of Warwick it has been discovered that phototrophic and heterotrophic bacteria, two of the most abundant microorganisms in the ocean, work together in many of the nutrient cycles. This challenges the common belief that phototrophs and heterotrophs are in competition for nutrients that are scarce in the marine environment.

The interaction between these organisms balances the nutrient levels in the ocean, thus provides a base for a healthy marine ecosystem. Phototrophic bacteria fixes carbon dioxide from the air using light. This then converts to organic matter which heterotrophs consume and then release nutrients back into the ecosystem. This interaction was observed by the researchers through nutrient and molecular analyses, after growing cultures of each bacteria and putting them in natural seawater. Both microorganisms reached a stable state where both bacteria began to mutually benefit each other. This system works like an economy with nutrients acting as currency. If one of the partners takes too much and does not give back, they will suffer the consequences in the long term.

As half of the world’s primary production and oxygen we breathe relies on the interaction in this system to be efficient. The rate at which our oceans will continue to buffer against carbon dioxide in our atmosphere is determined by the speed at which nutrients are cycled through this process. These essential processes need to be understood more deeply, which will allow us to understand how to improve and conserve our waters. Through this predictions as to how the oceans will react to climate change can be made.   

Referenced paper: Joseph A. Christie-Oleza, Despoina Sousoni, Matthew Lloyd, Jean Armengaud, David J. Scanlan. Nutrient recycling facilitates long-term stability of marine microbial phototroph–heterotroph interactions. Nature Microbiology, 2017; 2: 17100 DOI: 10.1038/nmicrobiol.2017.100

Predatory Bacteria: The gate keepers of the holobiont?

This study assesses predatory bacteria, Halobacteriovorax, within the holobiont of three corals: Siderastrea siderea, Agaricia spp., and Porites spp. Within the microbiome there are various bacterial predators, Halobacteriovorax is one such predator and part of the Bdellovibionales group. These predators are thought to regulate the holobiont. Halobacteriovorax is a prevalent active predator on coral surfaces (Schoeffield and Williams, 1990). However, its role within the holobiont is poorly understood.

Interactions within the holobiont are important to coral health. In other systems, these interactions are regulated by predation. Although poorly understood, bacterial predation could influence microbial function by regulating community composition.

Delta-proteobacteria, such as Bdellovibionales and like organisms (BALOs), prey exclusively on other bacteria, including many known pathogens. In a small initial concentration, unlike viruses, BALOs can alter the bacterial composition of the host. Therefore, they have the potential to act as a microbial regulatory mechanism.

As Halobacteriovorax has a broad distribution range, it is a common and active predator with a biphasic life cycle, growth phase and attack phase. It was found in 79% of the samples taken across three genera, albeit with a low mean relative abundance. However, Siderastera and Agaricin accounted for the majority of BALOs interactions while Porites accounted for 8%, suggesting that its presence is not uniform across all hosts. Due to its high presence and predatory life style, it can be considered an important low-abundance member of the core microbiome.

By using the plaque assay technique, the study found that Halobacteriovorax predated Vibrio coralliiticus and Vibrio harveyii, known coral pathogens. It was also discovered that under laboratory conditions Halobacteriovorax preyed upon Vibrio fortis. V.fortis was isolated from a seemingly healthy Porites astreoides, which could be evidence that Halobacteriovorax maintained coral health by regulating the abundance of V.fortis.

Using taxonomic data from 16s rRNA sequencing, co-occurrence networks and networks for known drivers for holobiont shift were created, which were temperature and nutrient enrichment. The analysis showed that Halobacteriovorax interactions were influenced by temperature and nutrient supply. At the temperature extremes, the largest changes in interactions occurred. Other predatory bacteria, in this case Myxcoccales, were affected by temperature, implying there is a common response to microbial drivers. The nutrient response showed that three co-occurring taxa existed under nutrient enrichment conditions while only one occurred under control conditions. Only positive interactions were found in the analysis of the BALOS co-occurrence networks, displaying no mutual exclusions.

The Bdellovibionales increased with prey populations, suggesting that the presence of predatory bacteria is a method of microbial regulation. Since there were exclusively positive interactions, it suggests that the conditions are favourable to the co-occurring taxa and predators are removing the co-occurring taxa competitors. This would allow those taxa to increase their abundance, so this could be a method of microbial regulation within the holobiont and fits with the predator–prey model. As read depth and the ability to detect negative interactions were poorly corelated, it is likely the presence of the predator was beneficial to the co-occurring taxa. Some hosts displayed different interactions, such as Bdellovibionales co-occurring with Vibriionales on Angncia but not other hosts, this could be further evidence that BALOs in the holobiont are host specific.

This study showed that bacterial predators have an impact on microbiome dynamics and could be considered a regulatory tool of the holobiont. The highest level of interactions occurred at the temperature extremes, which could provide the host with a tolerance to environmental changes. In a review by Pernice et al. (2015), it was suggested that stressors increase the microbial diversity, potentially due to opportunistic pathogens invading the microbiome. Given that BALOs help defend against these invasions, further study could provide interesting opportunities regarding targeting conservation management.

References

McDevitt-Irwin, J.M., Baum, J.K., Garren, M. and Vega Thurber, R.L., 2017. Responses of coral-associated bacterial communities to local and global stressors. Frontiers in Marine Science, 4, p.262.

Schoeffield, A.J. and Williams, H.N., 1990. Efficiencies of recovery of bdellovibrios from brackish-water environments by using various bacterial species as prey. Applied and environmental microbiology, 56(1), pp.230-236.

Article Reviewed

Welsh, R.M., Zaneveld, J.R., Rosales, S.M., Payet, J.P., Burkepile, D.E. and Thurber, R.V., 2016. Bacterial predation in a marine host-associated microbiome. The ISME journal, 10(6), pp.1540-1544.

too hot for my biofilm?

Microorganisms in marine environments inhabit surfaces and form biofilms. The formation of biofilms involves adsorption of organic and inorganic molecules to submerged surfaces. The role of first colonisers is important as they enable the biofilm to stay intact or detach. Biofilms can be altered by biotic and abiotic factors.

Global warming is becoming an increasing concern and an Increase in temperatures could influence the structure and functions of biofilms in coral reef systems. Increases in sea temperature can alter the distribution, abundance, function and community dynamics in marine microbial systems both positively and negatively by affecting the biofilm recruitment and inductive capabilities of invertebrate larvae. As a biofilm grows it develops a complex architecture that contains different micro habitats which facilitates the growth of diverse microbial communities and the settlement and growth of invertebrate larvae. Previous studies have shown that living in biofilms can be advantageous. Biofilms can provide nutrients and protection against external factors such as toxins, heavy metals, dehydration and UV-radiation. Gamma-proteobacteria have been found to produce chemical cues that facilitate the induction of coral larvae. Crustose algae harbour or produce biofilms that can produce morphogens and crustose coralline algae precipitate calcium carbonate which is Important in reef building.

The Arabian Gulf, one of the hottest bodies of water on the earth, is characterised by the highest variability in annual temperatures. Corals suffer thermal stress when water temperatures exceed 32 °C or drop below 18 °C but corals in the Gulf can survive extreme temperature fluctuations of 35 °C in summer and below 11 °C in winter. The coral spawning season in the Arabian Gulf occurs between may and august when temperatures are highest.  Because microbial biofilms provide cues for larvae to settle and metamorphose it is important to know how biofilms develop at these temperature extremes.

The experiment was conducted in the inshore reef system of Qit'at Benayah, north of the Arabian Gulf.  Glass slides were used as a substratum for biofilm growth. Replicates were collected every 2 weeks from both sides of the glass slides. The physical and chemical properties of the seawater were checked onsite and showed a continuous increase in water temperature during the sampling period.

Biofilms were removed from the glass slides and placed into petri dishes. Biofilms were divided into two and either used to measure the abundances of phototroughs and heterotroughs or used in molecular analysis.

The abundances of heterotroughs and phototroughs were investigated using total and viable count techniques using epifluorescence microscopy. Developed biofilms were plated onto marine agar to determine the culturable bacterial abundance and developed bacterial colonies were subcultured to purify them. PCR was then used with 16s r/RNA to identify the isolates.

Four Vibrio isolates, Vibrio harveyi, Vibrio owensii, Vibrio ponticus and Vibrio sinaloensis, were inoculated on a marine agar to assess the ability of vVbrio to precipitate calcium carbonate. Calcium carbonate crystals were removed and examined under an emission scanning microscope to assess size and number of crystals.

The results showed a linear increase in the number of heterotrophs on both sides of the glass slides as the age and temperature of the biofilm increased. Biofilms kept at 33 °C for longer times saw heterotroph numbers start to decrease. Phototroph numbers fluctuated overtime along with levels of phototroughs detected in seawater samples.

The study found that biofilms were similar in the diversity of microbes but were found grouped together by age. Biofilms of a younger age were seen to cluster together and remained separate from mature biofilms no matter which side of the substrata they were growing on suggesting the age groups had different bacterial communities.

Light microscopy was used to examine the diversity of phototrophs in the biofilms. Phototrophs which have the potential to produce substances involved in coral larvae settlement and metamorphosis was found colonizing the substrata. Bacillariophyceae (diatom) and Cyanobacteria dominated the biofilms. Bacillariophyceae dominated young biofilms but decreased in number with age whilst cyanobacterial abundance increased with age and dominated later.

For all biofilm age groups Gamma-Proteobacteria dominated with vibrio being the most dominant genus of that group. Invertebrate Larvae were found in 6-week-old biofilms suggesting that this may be the age the biofilm becomes mature. 

There were 20 Vibrio species isolated from the biofilm samples 4 of which could precipitate calcium. This calcification is important in providing stability for the biofilm, the Vibrio produced larger sized crystals at 30°C than at 23°C and there were more of them.

In conclusion, the study found that bio-films grown on glass substrata over 14 weeks contained bacterial and algal species capable of producing morphogens and stabilising biofilms through calcification. Natural elevations of prolonged temperature at 33°C did not affect structural diversity of the bacterial communities within the biofilm. The study found that the microbial community shifted as the bio-film aged with mature biofilms containing key species such as Vibrio important in calcification and the production of morphogens. During the study invertebrate larvae were found in 6-week-old bio-films but no coral larvae were found despite the experiment being carried out during coral spawning.

The paper stated that it may have no found coral larvae due to the method of removing the biofilms. They said they could have looked under a microscope to see if they were there but it would have meant they couldn’t have used other methods to assess the biofilm diversity. I feel that because this paper was based on corals they could have assigned extra slides just for looking at coral larvae settlement so they could see if they do settle or not and at what point which could have improved our knowledge on how these corals persist at higher temperatures.

 https://ac.els-cdn.com/S0025326X15301041/1-s2.0-S0025326X15301041-main.pdf?_tid=4d0fe71a-cfcf-11e7-a00b-00000aab0f6b&acdnat=1511387672_0b3a9a067e4c65089de9374bce95d315

Mahmoud (2015) ‘Variations in the abundance and structural diversity of microbes forming biofilms in a thermally stressed coral reef system’, Marine Pollution Bulletin 100, 710–718. doi.org/10.1016/j.marpolbul.2015.10.030

how microbes can prevent invasive success

Invasive species can cause dramatic changes to environments by out competing native species. A lack of understanding of the processes that allow species to invade successfully makes it difficult to manage their establishment and their spread. There is some understanding on the mechanisms underpinning the establishment of invasive terrestrial plants but these tend to focus on the direct effects on above ground processes. There is growing evidence to show that soil microbes have some part in controlling invasive success in terrestrial ecosystems, but this is yet to be tested in marine ecosystems.

Microbial communities can have positive and negative effects on invasive success. 

Microorganisms in marine sediments can exert strong control over ecological processes by controlling things like nutrient availability and sediment chemistry which in turn effects marine macrophytes. These processes differ between interacting invasive and native species.

Caulerpa taxifolia is an invasive green alga that forms high density beds in sediments outside sea grass beds and has severe impacts on native fauna within the sediments. It can outperform native sea grasses and it is thought its success comes from the alga’s ability to modify chemical and physiological sediment properties. C. taxifolia grows amongst seagrass and is often dense immediately next to it. Zostera capricorni commonly occurs as meadows in mud and sand.

Sediments were collected from Coral Bay, Austrailia. Samples were taken from sites with 100% cover of Zostera capricorni, 100% cover of Caulerpa taxifolia and taken from sediments with o% alga cover as a control. Each of these samples were then split in half with half being autoclaved to create an inactive microbe free sediment type. Commercially available sediment was also purchased and used as an inactive control to account for any modification autoclaving could have on the sediment. Detrus samples from each site were ground into a paste and added to the sediment samples. Fragments of each species were placed into each experimental condition; the biomass of each fragment was used to measure fragment growth. To assess microbe activity in the sediments 16s rRNA was amplified using PCR and Operational taxonomic units (OTU) were created using MOTHUR.

The study found that each sediment type was characterised by the same OTU’s but with contrasting abundance. The most abundant being Gamma and Delta-proteobacteria. Phylum Bacteroidetes and phylum Chlorofexi were also abundant, these bacteria are common in estuarine and marine sediments and carry out aerobic and anaerobic nutrient cycling including nitrogen, sulfur and iron. C. taxifolia sediments were found to contain bacteria associated with the reduction of sulfate, sulphite, thiosulfate and sulfur in anaerobic environments. Z.capricorni sediments had bacteria accosciated with the oxidation of sulfur in aerobic environments producing sulfates.

Z. Capricorni sea grass sediments likely have bacterial communites that are delicately balanced between aerobic and anaerobic sulfur cycling which may provide an unfavourable environment for C. taxifolia. C. taxifolia may be able to take hold on declining sea beds due decaying detrus making the sediments anaerobic, the absence of Z. capricorni rhizoids may also lead to a decrease of oxygen being put into the sediments. This lack of oxygen would be favourable to sulfate reducing bacteria already present in the sediments which would cause an increase in sulphides. This would make the environment favourable for C. taxifolia. The invasion of C. taxifolia in disturbed sea beds accelerates the decline of seagrasses by modifying the sediments and increasing sulphide levels. C. taxifolia can only invade sea beds where there is already a microbial community present as results showed that C. taxifolia fragment growth decreased in sediments absent of microbes.

In conclusion. Z. capricorni and C. taxifolia has similar bacterial communities but in varying levels of density. Z. capricorni has rhizoids which provide oxygen for aerobic sulfur cycling. C. taxifolia is associated with microbes that use anaerobic sulfur cycling. These differences in sediment chemistry prevent C. taxifolia from invading. However, if the Z. capricorni seagrass bed is damaged, the breakdown of detrus along with the absence of rhizoids causes the sediment to become anaerobic. This allows anaerobic sulfur reducing bacteria to increase making the sediments inhabitable for C. taxifolia. The more C. taxifolia invades the more it changes the sediments and Z. capricorni declines. C. taxifolia can only invade where microbial communities are already established.

This paper has shown that microbial communities have an important role in sediment function like terrestrial ecosystems. Microorganisms appear to indirectly modify the establishment and growth of invasive macrophytes in marine sediments. This is an important step to understanding how marine sediments can provide biotic resistance to invasive species it also improves our knowledge of how coastal ecosystem pressures could allow invasive species to take hold. Further study could allow us to identify the importance of microorganisms in identifying the risk to native species by invasive species. There could also be other terrestrial studies which could be applied to marine environments. I think that this was a good paper apart from the layout which I feel affects the flow of how you read it.

https://www.nature.com/articles/s41598-017-10231-2.pdf

Gribben et al., (2017) ‘Microbial communities in marine sediments modify success of an invasive macrophyte’, Scientific Reports 7: 9845. DOI:10.1038/s41598-017-10231-2

The potentially non-stick SAR11 clade

This paper proposes that some free living bacteria species have adapted to have a non-stick surface in order to evade predation from filter feeders. This however is a trade of as many marine bacteria thrive in their environment through their ability to stick to nutrient rich organic particles.  The SAR11 clade which includes the species studied, Pelagibacter ubique, are the most ubiquitous in the upper ocean, it has been suggested that they may comprise between 15-60% of the total bacteria. 

Grazing in the marine environment is one of the most prominent mortality factors for bacteria. The microbial composition of the ocean is controlled by the grazing by filter feeders. Adaptation to evade this threat may be one of the reasons that the SAR11 clade is highly abundant. It is thought that they are able to slip through the mucous nets of benthic and pelagic tunicates. This study tested this theory through experiments using the pelagic relatives of the ascidians, the appendicularians. This pelagic species was used as it is unlikely that benthic bacterivory would have any significant effect on the distribution and abundance of pelagic bacterial population. Appendicularians only dominate open ocean bacterivory during temporary population blooms, yet are very important pico-planktivores. They play a central role in role in pelagic food webs as they can remove more than half of the microbial populations in a few days.

This study suggested that, Pelagibacter ubique can slip through the mucous nets of common filter feeders. This trade-off may help to explain the SAR11 clade’s success in the ocean. The biochemical, physiological and ecological roles that this adaptation has for oligotrophic bacteria would require further study. Bacterial recognition and mucociliary mechanisms are effective defence mechanisms against pathogens. A better understanding of the bacterial cell wall structure and how these mucous filters interact could have benefits beyond marine biology, making this study highly important and providing evidence that this area of study needs to be investigated more. The future importance of this study makes it incredibly interesting, further study is needed into how this adaptation may have evolved and how it may have enabled the proliferation of the species.

Referenced paper: Dadon-Pilosof, A., Conley, K.R., Jacobi, Y., Haber, M., Lombard, F., Sutherland, K.R., Steindler, L., Tikochinski, Y., Richter, M., Glöckner, F.O. and Suzuki, M.T., 2017. Surface properties of SAR11 bacteria facilitate grazing avoidance. Nature microbiology, p.1.

Persistent Vibrios – evidence why they won’t leave us alone

Gram-negative marine bacteria, pathogenic Vibrio species, are common and abundant in estuaries and coastal habitats. Species densities correlate with environmental seasonality. Increasing during spring and summer months when temperatures are 20-30°C and salinities 10-20ppt (DePaola et al., 2003), as well as occurring more consistently within harmful algal blooms of Ostreopsis (Bellés-Garulera et al., 2016). During these periods, an increased risk of human infection occurs both directly and indirectly by V. parahaemolyticus and V. vulnificus which cause gastroenteritis and septicaemia by foodborne pathogens in shellfish. These bacteria are found in sediments, plankton and water and its recovery during the seasonal re-emergence in shellfish is of great interest in health and aquaculture.

Givens et al., (2014) collected 10 common estuarine fish species and 6 oysters, along with sediment and water samples, from Dauphin Island Bay, Albama at 12 points during March 17-May 02, 2011. Measuring water temperature and salinity using a YSI 85 metre. The contents of the mid- to hind-gut regions of the fish digestive tracts were pooled and a control of alkaline peptone water culture of V. cholera was added overnight, quantifying ctx gene recovery using qPCR, a culture-independent method. Various DNA extraction kits were used for; 1.0g of fish gut substrate, 0.5g of pooled, blended Oyster meats and liquids and 100ml water sample filtered through a 0.22µmol l-1 nitrocellulose filter. Secondly, the culture-dependent method, 100µl of each homogenised sample was spread-plated on V. vulnificus and T₁N₃ agars, with addition of 0.1g homogenised Oyster and 10ml of water spread-plated onto VVA and T₁N₃ agars, 35ºC incubated overnight. Developed bacterial colonies were hybridized using DNA probes targeting V. vulnificus vvhA and V. parahaemolyticus tlh genes, using 16 rRNA in PCR. Virulence potential was gained by spread-plating on agar plates. Quantified in PCR but found low virulence genotypes. Their novel methods were detailed, however, it would have been useful if pH, nutrients and trace metals were also included to see if these factors had an influence on the densities as well.

Results of qPCR found highest densities of V. vulnificus than V. parahaemolyticus within the fish intestines when co-occurring. Overall, Bacteria abundance is 1.7ml^-1 greater than Oysters, 0.6ml^-1 than sediment and 3.2ml^-1 than water, with Vibrios being 3.7ml^-1 greater than Oyster, 4.2ml^-1 than sediment and 5.9ml^-1 than water. The authors results contradict and back up previous studies. They found similar sample density results to DePaola et al., (1994), however, Jones et al, (2013) detected higher densities for V. parahaemolyticus than V. vulnificus in fish intestines. All three studies varied in season of samples taken, thus, temperature influences Vibrio species densities occurring. Vibrios correlate to environmental conditions in this study. Water temperature ranged from 20-25ºC and salinity from 3.7-19ppt therefore, higher densities as its more favourable environments. The low salinity, cooler temperature samples were less favourable for V. vulnificus, qPCR could not detect the low abundances, and V. parahaemolyticus only detected in fish. Therefore, a higher resolution culture-dependent-method (colony hybridisations) was used, resulting in both species detected but, at lower densities. The author suggests this higher density prevalence in the intestine niche during the limiting conditions, causes the re-emergence of the pathogenic Vibrios in Oysters.

This interested me as Vibrios affect a broad range of habitats and species and climate change could intensify its persistence and dominance in more species and areas than found today. A novel study as it is the first to conduct and compare two culture methods, by comparing results were more defined as each method was limiting in some way, but similar trends were seen. Future study for Vibrios in different species has future importance as it defines not just environmental factors causing Vibrio species to bloom, but also in which species it may keep re-occurring. This narrows the knowledge gap, leading to further infection prevention, helping decrease coastal human infections by sectioning off habitats and aquaculture prevention.

Reviewed Article

Givens, C. E., Bowers, J. C., DePaola, A., Hollibaugh, J. T., & Jones, J. L. (2014). Occurrence and distribution of Vibrio vulnificus and Vibrio parahaemolyticus – potential roles for fish, oyster, sediment and water. Letters in Applied Microbiology, 58, 503-510 http://onlinelibrary.wiley.com/doi/10.1111/lam.12226/full

Further Reading

Bellés-Garulera, J., Vila, M., Borrull, E., Riobó, P., Franco, J. M., & Sala, M. M. (2016). Variability of planktonic and epiphytic Vibrios in a coastal environment affected by Ostreopsis blooms. Scientia Marina, 80(S1) http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/viewArticle/1661/2144

DePaola, A., Nordstrom, J. L., Bowers, J. C., Wells, J. G., & Cook, D. W. (2003). Seasonal Abundance of Total and Pathogenic Vibrio parahaemolyticus in Albama Oysters. Applied and Environmental Microbiology, 69(3), 1521-1526                         http://aem.asm.org/content/69/3/1521.full

Viruses rule the waves: a 2017 review of our knowledge thus far

Viruses are the most abundant biological entity in the marine environment (averaging 10⁸ viruses ml^-1). They infect everything from animals to unicellular organisms and in the last decade have been revealed as key players in marine ecosystems; driving bacterial and algal mortality and influence biogeochemical cycles. Authors Middelboe and Brussaard (2017) have produced a review of our viral knowledge thus far (2017) and their function and regulation of aquatic ecosystems.

Viruses are not homogeneously spread throughout the ocean. Availability of inorganic limiting nutrients are important predictors of host and consequently of viral abundance and thus virus-host ratios across temporal and spatial scales.  Also, trophic interactions (e.g host predation) in the microbial food web are now known to influence viral and prokaryote community structure. Understanding these interactions/ environmental influence is key to understanding/ mapping viral distribution.

A key feature of this review is that the authors provide a schematic diagram which gives a breakdown of virus-host interactions. I will summarise it here:

1)    Bacteria defend against phage infection by mutating their surface receptors or enzymatic degradation of incoming phage DNA.

2)    Aggregation/ biofilm life can act as phage defence.

3)    Phage DNA can integrate in to hosts DNA, residing as prophage and can prevent. further infection by similar phages.

4)    Prophage induction may stimulate biofilm production.

5)    Phages can manipulate host gene expression to improve infection efficiency.

6)    Phages interact with their bacterial hosts contribute to shaping the gut microbiome and thus affect symbiotic relationship between gut microbes and their host.

7)    Some coccolithophore (e.g. Emilinania huxleyi) diploid cells undergo viral lysis OR re-emerge as viral resistant haploid cells containing viral RNA (reforming in to diploid via karyogamy).

8)    Giant viruses (NCLDV) infect a large range of photosynthetic protists, thus effecting mortality and diversity of phytoplankton. Influencing the entire marine food web.

Viruses have been shown to shift in response to seasonal variation in host diversity, however persistence of viral genotypes across a 3-year study suggest virus-host co-existence. Investigation of current theories of viral-host interactions are dynamic and current understanding is constantly being challenged. Host defences have always been thought as being costly, creating a trade-off between resistance and fitness. However, recent studies using phytoplankton Prymnesium parvum (Heath et al., 2017) and Emilinania huxleyi (Ruiz et al., 2017) showed no direct cost of resistance, highlighting the complexity of interplay between virus-host co-evolution. Climate change is also predicted to impact viral-host interactions, thus far elevated pCO₂ levels have been shown to impact diversity of E. huxleyi viruses (EhV) (see Highfield et al., 2017) and Maat et al. (2017) demonstrated temperature sensitivity in virus infectivity related to Arctic picophytoplankter Micromonas polaris.

This review paper provides an excellent brief summary for recent advances in our knowledge of viruses and their influence on marine ecosystems, especially in regard to their impacts on primary productivity. This review details many topics, far too many to summarise in 500 words, therefore I have created a small reference list below of the key studies from this review.  

Reference of this paper:

Middelboe, M. and Brussaard, C. (2017). Marine Viruses: Key Players in Marine Ecosystems. Viruses, 9(10), p.302.

Reference’s from particularly interesting points in this review:

Highfield, A.; Joint, I.; Gilbert, J.A.; Crawfurd, K.J. (2017) ; Schroeder, D.C. Change in Emiliania huxleyi virus assemblage diversity but not in host genetic composition during an ocean acidification mesocosm experiment. Viruses, 9. 


Maat, D.S.; Biggs, T.; Evans, C.; van Bleijswijk, J.D.L. (2007); van Der Wel, N.N.; Dutilh, B.E.; Brussaard, C.P.D. Characterization and temperature dependence of arctic micromonas polaris viruses. Viruses, 9, 6–9. 


Haatveit, H.M.; Wessel, Ø.; Markussen, T.; Lund, M.; Thiede, B.; Nyman, I.B.; Braaen, S.; Dahle, M.K.; Rimstad, E. (2017) Viral protein kinetics of piscine orthoreovirus infection in atlantic salmon blood cells. Viruses, 9. 


Middelboe, M.; Glud, R.N. (2006). Viral activity along a trophic gradient in continental margin sediments off central Chile. Mar. Biol. Res., 2, 41–51. 


Rohwer, F.; Thurber, R.V. (2009). Viruses manipulate the marine environment. Nature, 459, 207–212.