Climate change, chemistry, and community composition – can microbes save our oceans?

Some things are certain in life... like climate change! Climate change is happening and there is increasing atmospheric CO2 concentration from prior stable levels at ~280μatm pCO2(atm) to present-day levels at >400μatm and predicted to reach >750μatm mid-late century.  Dissolved CO2 decreases seawater pH; this leads to a decrease in seawater carbonate, ion concentrations, and lower saturation state for calcium carbonate minerals. But what about the microbes... 

Benthic microbial communities are directly influenced by seawater chemistry. Changes in pCO2 shall likely influence microbial community composition and their key functions in biogeochemical cycles, particularly for nitrification processes. However, microbial community compositions are so complex that sometimes, it may be difficult to accurately predict future community shifts in short-term experiments. Long-term experiments allow results to include factors of microbial acclimatization, evolutionary adaptations, complex feedbacks, and indirect effects. Natural CO2 venting systems can be used to study microbial sediment communities when exposed to pCO2 levels after a long time period.  

The study by Raulf et al. (2015) investigated microbial community composition (bacteria and archaea) in oxic sandy sediments across a natural CO2 gradient at a volcanic vent system in Papua New Guinea. Although volcanic systems are different to ‘general’ surface-sediment systems, the Authors explain how some confounding effects from nearby volcanic activity are negligible. Samples were taken from the oxic zone (<3cm surface sediment) of sandy sediments in shallow waters (1-4m water depth). Samples were analysed by the molecular fingerprinting technique ARISA using a triplicate PCR electrophoresis approach. This was combined with the MPTS technique for deeper diversity analysis and taxonomic identification of key microbial indicators.  

Results showed that as pCO2 increases, bacterial and archaeal richness increases. Additionally, as pCO2 increased, there was an increase of rare members for both bacteria and archaea. The microbial communities from sites with low/present day pCO2 concentrations were structured different than for sites with elevated pCO2. Sites with high pCO2 had communities that selected different dominant microbial types. As pCO2 increased, sequences related to bacterial nitrifying organisms like Nitrosococcus and Nitrospirales decreased. Subsequently, as pCO2 increased, there was an increase in sequences related to archaeal ammonia-oxidizing organisms like Nitrosopumilus maritimus (Phyla: Thaumarchaeota).  

So, the study predicts that as more CO2 dissolves into oceans, microbial community composition shall change; meanwhile, community richness/evenness shall increase. But why? 

Firstly, there could be direct pCO2 effects on specific cellular processes via enzyme kinetics or cell homeostasis. Additionally, increased pCO2 leads to higher nutrient availability and increased benthic cover of primary producers. So, as expected, results found an increase in biomass turnover and an increase in organic matter degrading bacterial groups like Flavobacteriaceae and Rhodobacteraceae. 

Results also found a change in the sequences related to nitrifying organisms. Nitrification is one of the biogeochemical processes most sensitive to pH change, due to decline in the availability of ammonia for nitrifying organisms. Rising oceanic pCO2 may have disadvantages for ammonia-oxidising bacteria because ammonia-oxidising archaea may be better adapted and be better competitors under acidifying conditions and limited resources. However, it’s difficult to predict how the nitrification cycle will change because biogeochemical cycles are complex, and each component has a knock-on effect to the next part of the nitrification cycle.  

Authors explain that, ecologically speaking, the observed increase in microbial diversity and larger proportion of rare microbial types at high pCO2 sites may potentially have a stabilising effect on local biological processes. A richer community of rare types might provide an increase of interchangeable biochemical functions which could replace those that may be lost or weakened... but this uncertain. So, microbial composition is sensitive to change of seawater chemistry and there shall be an impact on ecosystem functions, but maybe there’s hope in microbes! 

Referenced material: 

Raulf, F.F., Fabricius, K., Uthicke, S., de Beer, D., Abed, R.M. and Ramette, A., 2015. Changes in microbial communities in coastal sediments along natural CO2 gradients at a volcanic vent in Papua New Guinea. Environmental microbiology, 17(10), pp.3678-3691.

Relationship between vitamins and iron limitation in diatoms

Biosynthesised molecules such as B vitamins are irreplaceable co-factors in enzymes helping cellular metabolism. They can be growth limiting for those unable to synthesise or acquire from the environment, possibly influencing microbial community composition, where in bloom events seawater may be depleted or enriched. B7 is required in carboxylation enzymes involved in fatty acid synthesis. Four genes are involved in the biosynthetic pathway and all genes are found in algae except for dethiobiotin synthase (BIOD). Diatoms in culture are able to grow with B7 suggesting there is a BIOD homologue present. It is iron dependant so it is hypothesised that iron limitation in marine diatoms could alter production, function and activity.

In yeast saccharomyces cerevisiae iron limitation causes a decrease in B7 synthesis and activates a transporter that functions in the acquisition of external sources of B7. if the same happens in diatoms it would allow intracellular iron in short supply to redistribute towards other necessary iron dependant processes. B12 plays a major role in methionine synthesis  and some plankton possess B12 independent of METE, there being a strong correlation between absence of METE and B12 auxotrophy.

Iron, and B12 co limitation on phytoplankton has been documented in the southern ocean. It has been previously seen in studies such as those by Bertrandt et al 2011 who looked at the Ross sea, which has been shown to be iron limited and B12 colimited in the summer. B12 was limiting only when bacterial abundance was low with iron addition enhancing bacterial growth. Iron additions enhanced B12 uptake in phytoplankton maybe due to it increasing bacterial growth and consequently B12 production.

Cohen et al 2017 looked into the iron and vitamin interactions further with marine diatoms. Exploring the dynamics between iron and vitamins can lead to better understanding of how iron fertilisation events could influence B vitamin production and consumption. The influence of iron status on B7 production, B12 utilisation and METE activity in diatom isolates in the Pacific ocean was studied. They quantified the transcriptional response of BIOB under variable iron and B7 growth conditions through gene expression in the diatom P. granii . The expression of METH and METE in Grammonema cf islandica with B12 requirement was also measured in response to the variables.

P. granii in iron replete cultures grew at a rate higher than those in iron limiting conditions, there being a 65% reduction in growth rate. There was no significance in growth rate between cultures with or without B7 in both iron conditions. P. granii had a reduced growth rate of 50% when iron limited with B12. G. cf islandica under the same conditions of either iron or none with B12 experienced 67% reduction in growth rate when iron limited. B12 absence would decrease growth rate by 35% and the combination of both variables limited reduced growth rate and METH expression by 3 fold. Diatom populations when incubated with iron increased appreciably 40 fold higher in density, the highest abundance being exhibited when this was combined with B12. Vitamin B7 metabolism was affected by iron addition increasing 2 fold in iron treatments. Laboratory studies with G. islandica under iron/B12 conditions demonstrate METE gene expression is primarily regulated by B12 status. Any increase in METE following iron addition is due to B12 concentrations becoming limiting, so there is insufficient acquisition of B12 from the environment causing METE possessing diatoms to produce B12 independently.

It is probable that iron limitations reduced the amount of diatom produced vitamin B7 available to other auxotrophs. Following iron enrichment emergence of METE containing diatoms provide evidence for B12 limitation. Iron limited diatoms produce fewer vitamin synthesis transcripts compared to cells enriched with iron either they require less vitamins when growing or they lack essential resources for fuel production. Cohen et al 2017 concluded that subarctic North East ocean diatom community examined was driven into B12 limitation following the iron addition.

paper reviewed: Cohen, N., A. Ellis, K., Burns, W., Lampe, R., Schuback, N., Johnson, Z., Sañudo-Wilhelmy, S. and Marchetti, A. (2017). Iron and vitamin interactions in marine diatom isolates and natural assemblages of the Northeast Pacific Ocean. Limnology and Oceanography, 62(5), pp.2076-2096.

reference: Bertrand, E., Saito, M., Lee, P., Dunbar, R., Sedwick, P. and DiTullio, G. (2011). Iron Limitation of a Springtime Bacterial and Phytoplankton Community in the Ross Sea: Implications for Vitamin B12 Nutrition. Frontiers in Microbiology, 2.

New Year, New Prospects for Bioactive Metabolites in Fungi!

Marine fungi produce a wide range of bioactive secondary metabolites; an area of promising research, especially in medical circles, as many show antibacterial activity. This has recently piqued the interest of aquaculture organisations, as a large proportion of stock and hence profit is lost to bacterial diseases every year. With the global awareness of antibiotic resistance increasing, the overuse of antibiotics is now a more pressing issue to be solved. Vibrio species are particularly prolific pathogens worldwide, especially in shrimp culturing. More recently it has caused an increased mortality in these populations due to its role  in acute hepatopancreatic disease (AHPND) during early mortality syndrome (EMS). The AHPND-causing bacteria colonise the shrimp stomach cuticle, forming biofilms that release damaging toxins. Preventing the biofilm formation could therefore mitigate the negative effects of this pathogen. Consequently, in 2019, Soowannayan et al.investigated whether protection for the shrimp could be induced through reduction in biofilm formative ability in Vibrio, using bioactive isolates from marine fungi: a property previously shown in such compounds. This would reduce the risk of selection for resistant bacteria such as with antibiotics. 

7 different isolates of Vibrio parahaemolyticus and Vibrio harveyi were obtained from a variety of AHPND-affected, EMS-affected and unaffected shrimp pods in Thailand and continuously cultured. 39 known obligate marine fungal isolates were taken from a culture collection, originally sourced from decayed mangrove woods in intertidal zones. These were used to create a cell-free culture broth (CF-CB) containing secondary metabolites. This was first used to test for inhibition of Vibrio growth: CF-CB was added to Vibrio cultures and left to grow overnight. The optical density was compared between Vibrio cultures and negative controls and used to quantify the mean percentage of relative inhibition. The effect of the CF-CB on biofilm formation was assessed and quantified in a similar way. 

CF-CB from 25 isolates of marine fungi were capable of inhibiting biofilm formation in 7 different Vibrio isolates. The main Vibrio isolate of interest was one involved in AHPND, for which 11 fungal isolates inhibited biofilm formation, while mostly stimulating growth in the Vibrio. This is seen as a positive effect by the authors, who suggest that an increase in growth coupled with biofilm inhibition could drive selection towards reduced biofilm production and therefore reduced pathogenicity.  

The results of these assays were used to inform the choice of the four most successful inhibitory isolates; these were then used to supplement the feed of Panaeus vanname, a popular aquaculture species. The addition of fungal isolate to the food, in the form of CF-CB, was continued for 8 days, after which the specimens were immersed in a culture of V. parahaemolyticus for 24h. Only one isolate protected these shrimp from AHPND. The authors speculated that there was something in the test system that neutralised the activity of other isolate inhibitors. No mechanism for the effects has been investigated yet, but perhaps a mechanism that impacts quorum sensing is likely, as interruption of this has previously been reported to protect shrimp against vibriosis (Defoirdt et al., 2006). Further investigation into this would be valuable, as the implications of these results could have significant bearing on how we continue more sustainable aquaculture in the future, as well as potentially further informing how we treat pathogenic diseases in humans and other organisms. 

One interesting aspect mentioned previously in “Marine fungi – not so much fun for pathogens! Marine fungi show antibacterial activity for pathogens in fish aquaculture” is the influence of co-culture and competition on metabolite production and function (Özkaya et al. 2017). It would be interesting to compare the products and effects of co-culture of fungi and Vibrios in this study; this may initiate more active production of bacteria-interferring metabolites, or conversely stimulate an aggressive toxin-based response. Either outcome would be valuable to look into further.

Finally, given the communal nature of many saprotrophic assemblages, it follows that the secondary metabolites produced may be different in quantity and nature when fungi are grown in co-culture with many fungal strains, rather than mono-culture such as the ones in this study. This is yet another avenue which could illicit some interesting results and useful compounds. 

Reviewed paper:

Soowannayan, C., Teja, D.N.C., Yatip, P., Mazumder, F.Y., Krataitong, K., Unagul, P., Suetrong, S., Preedanon, S., Klaysuban, A., Sakayaroj, J. and Sangtiean, T., (2019). Vibrio biofilm inhibitors screened from marine fungi protect shrimp against acute hepatopancreatic necrosis disease (AHPND). Aquaculture, 499, pp.1-8.

References:

Defoirdt, T., Crab, R., Wood, T. K., Sorgeloos, P., Verstraete, W., Bossier P., (2006).

Quorum Sensing-Disrupting Brominated Furanones Protect the Gnotobiotic Brine Shrimp Artemia franciscanafrom Pathogenic Vibrio harveyi,Vibrio campbellii, and Vibrio parahaemolyticus Isolates.Applications of Environmental Microbiology,72 (9)6419-6423

from Marine fungi – not so much fun for pathogens! Marine fungi show antibacterial activity for pathogens in fish aquaculture:

Özkaya, F.C., Peker, Z., Camas, M., Sazak Camas, A. and Altunok, M., (2017). Marine Fungi Against Aquaculture Pathogens and Induction of the Activity via Co‐Culture. CLEAN–Soil, Air, Water, 45(8), p.1700238.

The Ocean's Thin Slice: Drivers of the Community Composition of the Sea Surface Microlayer

The sea surface microlayer (SML) is defined as the top 1 mm of the ocean’s surface and is biologically and chemically distinct from the underlying water (UW) beneath. The SML is primarily composed of dissolved organic carbon and transparent exopolymer particles (TEP), a gelatinous mix of polysaccharides derived from phytoplankton. This concoction of carbon supports high amounts of biomass in the SML, with the inhabitants of this thin slice of the sea (known as the neuston) often found associated with TEP. However, the communities of bacterioneuston in the SML can be altered depending on abiotic factors for example temperature and wind speed, or biotic factors such as nutrient availability. The study presented here aimed to better understand the bacterioneuston communities and the mechanisms that controlled these communities off the Peruvian coast.

SML samples and UW samples were collected from 11 stations during the SO243 cruise to a Peruvian upwelling. Various abiotic and biotic parameters were measured during the cruise, such as wind speed, temperature, salinity, the concentration of TEP and available nutrients (phosphate, nitrate, silicate, and carbohydrates). The bacteria from both depths (SML and UL) at each station were identified by Illumina high-throughput sequencing of 16S rRNA sequences and total bacterial abundances were determined by flow cytometry. Finally, the most abundant families were tested for enrichment or depletion in the SML.

Twenty-four families that made up over 1% of the communities were found across the 11 stations, none of which were found to be significantly depleted in the SML. Of the 24 families, 4 (unknown Flavobacteriales, Flavobacteriaceae, Crymorphaceae, and unknown Bacteroidetes) were significantly enriched in the SML but their abundances were similar at both depths. Overall, the community compositions and bacterial abundances were similar between both depths within a station but more different between stations. Negative correlations of the enriched families were found for temperature and wind speed as this can cause disruption of the SML and prevent enrichment. The enriched families did show positive correlations with nutrient concentrations and TEP, suggesting that the increases in abundance were likely found at upwelling stations. This is not surprising as the upwelling will bring nutrients up from deeper waters that the bacteria can utilise and aid with the transport of TEP and TEP associated bacteria, like the Flavobacteriales, to the surface.

However, the authors suggest that TEP has a limited influence on the community structure of the SML, given that TEP concentrations and community structures were similar at the SML and UL. This was quite surprising to me, as it was my understanding that TEP was the major player in determining SML communities. However, from this study, it is difficult to determine if TEP enhances the growth of bacterioneuston or, is simply a vehicle for some bacteria to float to the surface. It may be that the availability of nutrients (nitrate, phosphate, silicate) coupled with a favourable external environment with low wind speed and suitable temperature could be more important to the enrichment of SML communities.

Paper reviewed:

Zäncker, B., Cunliffe, M., & Engel, A. (2018). Bacterial community composition in the sea surface microlayer off the Peruvian coast. Frontiers in Microbiology, 9, 1-11.

Mutation, Mutation, Mutation: Roseobacter needed a lifestyle change

Rapid adaptation of organisms in stressful environments is vital for survival, especially with today’s warming climate. Marine bacteria have shown that they can quickly adapt to such adverse conditions; given their intrinsic function in global biogeochemical cycling, it is important to understand any ramifications of such adaptations on the physiology and lifestyle of these organisms. 

Kent et al. (2018) used experimental evolution to assess the rapid adaptation in physiology and lifestyle of a member of the abundant marine bacterial clade Roseobacter, under chronic high temperature conditions (33˚C). Roseovarius sp. TM1035 were isolated from a Chesapeake Bay dinoflagellate culture and propagated for 500 generations under optimal (25˚C) and high (33˚C) temperature regimes.

Through genomic and physiological assessment, they found that High Temperature-adapted Lines (HTLs) of Roseobacter had a higher number of gene mutations. A restriction enzyme assay was used to quantify these changes in sequence and allele frequency in the final colonies, compared to the initial ancestor isolated, and calculate the selection rate constant. Mutations found included alterations in genes controlling gas transfer, growth rate, exopolysaccharide secretion and quorum sensing. 

These mutations corresponded to the increased production of biofilm at high temperatures at the water’s surface. This was quantified between experimental lines, with the aid of a crystal violet stain and a spectrophotometer. These results are particularly interesting as an increase in biofilm formation could alter the community structure and composition of the sea-surface microlayer: a vital component particularly of the open ocean ecosystem. It is intrinsic in governing gas exchange, aerosolization and production of Cloud-condensation nuclei, affecting many important ocean processes. If the results of this paper are applicable to a real-world scenario of ocean warming, the precise nature of the sea-surface microlayer may be destabilised. However, some may argue that high temperature events in the ocean are likely to be short term; temperature would fluctuate over 500 generations in a more natural system, potentially yielding different results than seen in this highly controlled experiment.

In addition to increased biofilm formation, some colonies also displayed wrinkly morphotypes, and both these observations were almost entirely confined to the HTLs. Furthermore, the HTL wrinkly morphotypes were experimentally competed against the ancestor and Low Temperature-adapted Lines (LTL) and this was used to independently calculate the selection rate constant. The results yielded from this were consistent to those from the restriction enzyme assay.

The changes in physiology and lifestyle were linked to the thermally-driven decline in oxygen tension. This was assessed in a secondary investigation, in which the HTLs grew relatively better under conditions of low gas transfer compared to the LTLs and ancestor lines. Increased biofilm production may facilitate access to oxygen, sequestering it into a relatively stable matrix, therefore allowing the Roseobacter to grow more efficiently in the thermally-limited low oxygen conditions. HTLs were also shown to have an increased selection rate constant under low oxygen tension, suggesting that this stress induced directional selection: a means for quick adaptation. Kent et al. highlight that the warming climate presents multi-faceted challenges, and indirect effects of adaptation may initiate significant modification to lifestyle and ecosystem function of ubiquitous and crucial marine microorganisms; understanding this is the key to more accurately predicting the effect of warming on our microbial seas. The rapid nature of the adaptations observed here are simultaneously comforting and alarming. While it seems that the survival of a major biogeochemical powerhouse is not at risk, the significant modification of its lifestyle could have severe implications for the delicately balanced sea-surface micro layer: yet another facet of ocean warming to be considered.

Definitions:

Quorum sensing: The ability of organisms to sense and respond to nearby cell density; this can include the alteration of phenotype expression according to the density of the local population. In turn it can inform biofilm formation along with virulence factor expression, motility and many more processes.

Reference:

Kent, A. G., Garcia, C. A., & Martiny, A. C. (2018). Increased biofilm formation due to high-temperature adaptation in marine Roseobacter. Nature microbiology, 3(9), 989.

Microplastics in the SML of estuarines

The pollution by industrial contaminants or plastic debris is an example of anthropogenic changes affecting marine ecosystems. Microplastics (MPs), defined as particles of plastic in the size range of 0.05 to 4.5 mm, are of major interest in present studies. Most recent findings suggest that MPs impact the marine environments in a great extend which is not fully understood. Therefore it is highly necessary to gain more data about the effect of plastic debris of all sizes. Usually MPs have a lower density than the surrounding seawater and depending on their composition and the state of biofouling they tend to float near or at the sea surface. Previous studies on coastal ecosystems or on the open ocean suggest a high presence of MPs in the sea surface microlayer (SML). The SML is characterized by a high microbial activity and the presence of marine microgels. It is already known that the accumulation of MPs in the SML can have an effect on the physical and chemical conditions altering the environment of inhabiting organisms.

This study (Anderson et al., 2018) focused on the accumulation of MPs in the SML of estuarine systems. Estuaries play a major component in the transfer of MPs originated of land-based sources to the open ocean. These highly productive ecosystems are being more and more urbanised and industrialised. A rapid increase of fishing and shipping industries has occurred since a few decades. As a result contamination by sewage, urban run-offs and MPs can be observed. Interestingly this study compared two differing estuarine systems, the Hamble estuary and the Beaulieu estuary. Both of a similar size are very close to each other and located in the southern part of the UK but vary in their stage of development. Hamble is a highly industrialised estuarine, the Beaulieu system is more pristine.

Samples where taken on two days using a multiplicity of methods allowing the extraction of sea surface water or sub surface water samples. The main aims were to evaluate the relatively novel dipped glass plate method for the characterization of the SML and to compare these to sub surface samples regarding the content in MPs. The glass-based method is very applicable for the characterization of the SML; this technique allows taking samples from a depth of 100 to 200 µm representing the SML precisely.

With the use of these methods MPs could be extracted from different water layers. Afterwards a characterization of the MPs took place regarding their colour, length and surface texture using a standard light microscope and a scanning electron microscope (SEM). Mainly fibres of MPs were identified during the two sampling days, as it is the most common type of microplastic in those estuaries. Reading the study I wondered for what reason the colour and size of the fibres were of importance if it doesn’t allow predicating the original source of contamination? In another study on microplastics researchers used Raman spectroscopy in order to determine the composition of plastic (Imhof et al., 2012), possibly leading to the source identification.

Using the dipped glass plate method the highest concentration of MPs was sampled at the Hamble site, which supports the hypothesis that in the SML MPs accumulate. But generally both sites had significant microplastic concentrations highlighting the ubiquitous existence of plastic particles in relatively pristine aquatic environments.

Generally the study provides a first insight in the accumulation of MPs in the SML in estuarine systems but an adequate comparison between estuaries and sampling days was not possible due to very small number of samples. Much more data would be needed to allow any comparisons or even any biological interpretations.

However this study approved the dipped glass method as a highly suitable SML sampling method.

Article Reviewed

Anderson, Z. T., Cundy, A. B., Croudace, I. W., Warwick, P. E., Celis-Hernandez, O., & Stead, J. L. (2018). A rapid method for assessing the accumulation of microplastics in the sea surface microlayer (SML) of estuarine systems. Scientific reports, 8(1), 9428.

References

Imhof, H. K., Schmid, J., Niessner, R., Ivleva, N. P., & Laforsch, C. (2012). A novel, highly efficient method for the separation and quantification of plastic particles in sediments of aquatic environments. Limnology and oceanography: methods, 10(7), 524-537.

Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics.

Polar marine ecosystems are very sensitive to effects of warming and temperature change because of the significant influence of sea ice on ecosystem dynamics. Rapid warming in the highly productive area of the Western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels ranging from ecosystem foundational microbes to high-level consumers such as krill and penguins. Microorganisms, especially in these locations are known to play significant roles in polar ecosystem changes and the abundance of key microorganisms are suggested to predict carbon cycling and climate feed backs on global-scale models. However, viruses are also known to play a substantial role in marine ecosystems through their alteration of microbial communities by causing bacterial mortality through viral infection and altering the biogeochemical cycling through the release of cellular contents via lysis. Recently published studies from a global-scale analysis of viromes suggest that viral diversity in this region is lower than that observed at lower-latitude locations. (Brum et al., 2015).

Despite the role these organism play, viral influences on microbial processes and ecosystem function remain highly unstudied in the Southern Ocean compared to other marine environments. Most studies focus on the spatial and temporal variability of community viral abundance via microscopy.

Quantitative examinations of these viral roles in nature is challenging, however, recent methodological advances through optimized sample-to-sequence pipeline are being used to generate quantitative double-stranded DNA (dsDNA) viral metagenomes (viromes). These new methods increase the knowledge of viral genomic diversity, niche differentiation and ecological drivers of variability.

Viral infections can either be lytic, where viral takeover of cellular machinery results in new viral progeny and lysis of the host or may involve a lysogenic stage in the case of temperate viruses where in viral DNA is maintained within the host as a prophage until induced to replicate lytically. Viruses in polar systems are thought to have diverse replication strategies that aid in the survival of the species in low temperature environments. The current paradigm based on cultivated temperate virus-host systems, is that they primarily utilise lysogeny when bacterial production is low (such as winter conditions) and switch to lytic replication when bacterial production increases (such as spring phytoplankton blooms), therefore temperate viral dominance offers a mechanism for survival in harsh winter conditions.

The data from this study compliments the long-term ecological research in the WAP (Ducklow et al, 2012) suggesting that temperate viruses play a very important role in modulating microbial driven processes in the biogeochemical cycle for this region.

Brum JR, Ignacio-Espinoza JC, Roux S, Doulcier G, Acinas SG, Alberti A et al. (2015). Patterns and ecological drivers of ocean viral communities. Science 348: 1261498.

Brum, J., Hurwitz, B. l., Schofield, O., Ducklow, H.W. & Sullivan, M.B (2016). Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics. The International Society for Microbiology Journal. 10, 437-449.