Aspergillus sydowii causing aspergillosis in corals-not such a fun-gi

Coral reefs have long been subject to threats from a wide range of sources, such as pollution and overfishing. However, they are also very much at threat from a variety of diseases. One of these diseases is that of Aspergillosis, caused by the fungus Aspergillus sydowii. The taxa of Gorgonian corals, found in the Carribean, are the corals that are most afflicted by this disease. The disease is well studied, but aspects such as origin, transmission and mechanisms of pathogenicity are still unknown. As a result, modes of controlling and preventing the disease are hampered (Rypien et al., 2008).

Rypien et al., (2008) looked into the generic structure of a global sample of A.sydowii and used them to look at any patterns of genetic diversity and relatedness between environmental isolates and disease causing isolates of the fungi. The samples came from diseased corals, infected humans and environmental sources and were characterized using microsatellite and polymorphic markers. Colony growth and microscopic structure were also recorded in order to distinguish between samples (Rypien et al., 2008). Therefore, the study used both molecular and morphological measurements to assess relatedness and diversity, giving far more detail and accuracy to the results compared to if only one of these measurements was taken. Single isolates were analysed as a single population, showing whether or not disease causing and environmental isolates differ. Results will allow knowledge of broader patterns of emergent diseases in a broader range of ecosystems. (Rypien et al., 2008)

They found a lack of evidence of any recent bottlenecks and isolation by distance, so infer that a single introduction of the disease was unlikely. They also found that diseased sea fans were interspersed with environmental isolates, therefore suggesting that the disease has had multiple introductions from terrestrial and marine environments. The differentiation between environmental and disease causing isolates was found to be very low. This presents a big problem, particularly in bioremediation and management of the disease. With the isolates being so similar genetically, it should therefore be assumed that any isolate of the fungi could cause disease. Rypien et al., (2008) describe A.sydowii as an opportunist, with a diversity of isolates that can cause disease. They conclude that the variation in disease prevalence is likely a result of environmental factors and host resistance.

This study raises points that show definite challenges to the management of this disease. With such similarity, distinguishing between disease causing isolates and environmental isolates is very hard, raising the issue that direct control and targeting of the disease causing fungi is equally difficult. As a result, in order to manage and reduce the effects and spread of the disease, the best form of control possible is to reduce the impact of environmental stressors. These include managing pollution, temperature etc, which are linked with increased variation in disease prevalence (Rypien et al., 2008) The study gives strong evidence further supporting the fragility of corals in a changing environment, and extends the evidence for the need to control the threats that are presented to them.

Rypien, K., Andras, J., and Harvell, C. (2008). Globally panmictic population structure in the opportunistic fungal pathogen Aspergillus sydowii. Molecular Ecology. 18, 4068-4078.   

I am Maximus (Bacillus licheniformis) – The saviour of Rome (Aquaculture)

Please note: This article has been reviewed by Bekki already, but as I have already written it, I thought it would be a waste not to post it. 

Vibrio and Pseudomonas are both well-known aquaculture pathogens and have been previously associated with major diseases of aquatic organisms. Vibrio and Vibrio harveyi are primary pathogens of marine fish and crustaceans, and bacteria belonging to the genus Pseudomonas are affiliated with black spot bacterial necrosis in prawns. As a greater number of pathogens continuously develop antibiotic resistance, one of the major challenges in aquacultures these days is to prevent bacterial diseases.

Biofilms are generally important for the survival, virulence and stress resistance of bacteria and can act as reservoirs for pathogens allowing recurrent infections. Hamza et al. (2015) tested the anti-biofilm potential of a cell free supernatants (CFS) of a tropical marine epibiotic bacterium Bacillus licheniformis D1 isolate to prevent or disrupt, aquaculture associated biofilms. This may be potential for a natural way to deal with the problems described above. The marine epibiotic bacterium B. licheniformis was isolated from the surface of green mussel, Perna viridis, collected from near shore regions of Kovalam, Tamil Nadu, India. The ability of CFS to inhibit biofilm formation of test cultures (V. harveyi and P. aeruginosa) and to disrupt biofilms of V. harveyi and P. aeruginosa that have been allowed to form in advance, were both tested in this study. The biofilm growth of V. harveyi and P. aeruginosa was inhibited up to 80.46 and 77.51% respectively, when co-incubated with CFS of B. licheniformis. CFS also disrupted pre-formed biofilms of both the test cultures with comparable efficiency. Latter was determined by performing ONPG assays, where the results revealed that the CFS effectively disrupted cytoplasmic membranes, leading to the leakage of cytoplasm and finally to death of the bacterial cells.

Hamza et al. (2015) and several previous studies revealed the potential of marine bacteria dealing with bacterial biofilms. The protein BLDZ1, derived from the same bacterium, for instance was found to be effective in disrupting biofilms of other microorganisms. It seems that B.licheniformis may have a great potential in helping to deal with diseases found in aquacultures. However, it should be noted, that V. harveyi biofilm formation was especially found in low salinity (NaCl = 1%), and P. aeruginosa in media that lacked NaCl. The effectiveness of B. licheniformis tested in the present study therefore mainly accounts for aquacultures in fresh-water or estuarine habitats. Further investigations are needed for the marine sector.

Hopefully we can find some more of these “heroes” of aquaculture. Wouldn`t it be great if we were able to cram fish and other farmed animals into even smaller space, not having to worry about diseases? I am sure this would just solve all the problems associated with intense aquaculture…

Hamza F, Kumar AR, Zinjarde S (2015) Antibiofilm potential of a tropical marine Bacillus licheniformis isolate: role in disruption of aquaculture associated biofilms. Aquaculture Research 1-9, doi:10.1111/are.12716

Algal toxins... you may take our lives, but you’ll never take our freedom! (Okay... very politically incorrect - apologies).

Harmful algal blooms have increased dramatically since the 1980s and considered a major contributor in marine mammal mortalities worldwide. Dinoflagellates from the genus Alexandrium and the diatoms from the genus Pseudo-nitzschia are two of the most important toxin-producing species in Scottish waters and have the ability to produce marine toxins such as domoic acid (DA; Pseudo-nitzschia) and saxitoxins (STX; Alexandrium).

In Scotland, there has been regular monitoring for DA in shellfish since 1998 and it has been detected in shellfish above the regulatory limit (20 mg DA/kg of shellfish meat) on many occasions. It can also be toxic to humans and is known as amnesic shellfish poisoning (ASP), which can cause neuronal degeneration and necrosis in specific parts of the brain. A case study of DA exposed California sea lions (Zalophus californianus) highlighted neurological signs such as ataxia, head weaving, seizures or coma (this has also been reported for bottlenose dolphins (Tursiops truncatus) in the northern Gulf of Mexico). Studies have suggested that pregnant Z. californianus may be greater exposed due to toxins in the amniotic fluid and that DA causes reproductive failure.

Paralytic Shellfish Poisoning (PSP) toxins (STX) pose the greatest concern for seals in Scotland and due to a lack of information on chronic PSP toxicity data; the European Food and Safety Authority established an oral acute reference dose of 0.5 µg STX equivalents/kg body weight in humans. Canids (thought to be evolutionarily and physiologically similar to seals) have an acute oral LD₅₀ dose of 180-200 µg STX/kg, and whilst humans have a minimum oral dose of 7-16 µg of STX/kg, there have been cases where human mortalities have been observed at oral doses reaching 500-12,400 µg STX/kg. PSP toxins bind to the voltage-gated sodium channels in the brain blocking the flow of ions across the cell membrane. This can inhibit nerve and muscle cells to send electrical signals, which prevents normal cellular function, and ultimately lead to paralysis. Respiratory arrest is the most severe symptom of PSP exposure and can be rapidly be followed by death. Many case studies in the past has indicated evidence of STX exposure; the North Atlantic right whale (Eubalaena glacialis) in 2001 where the population was failing to recover from decline, the Mediterranean monk seal (Monachus monachus) off western Sahara in 1997 and humpback whales (Megaptera novaeangliae) off Cape Cod Bay, USA in 2001.

Harbour seals (Phoca vitulina) are exposed to these neurotoxins via the food web, consuming contaminated prey such as fish or squid and having a direct effect on health and survival rates. Jensen et al., (2015) hypothesised that a possible factor for the rapid decline of P. vitulina since 2000 is the effect of marine toxins have on the seals. Jensen et al., (2015) investigated the exposure and health effects of DA and STXs in P. vitulina and examined accumulated toxin levels in different prey species to explore possible links between toxin concentrations and degree of exposure between the declining and stable harbour seal populations.

Urine, faeces and blood samples were collected from live-captured harbour seals between 2008 and 2013, from three different regions, the Northern Isles (including the north coast of mainland Scotland), the west coast and the east coast; with the aim to detect and quantify DA and PSP toxins. As well as live capture, faecal and urine samples were collected from dead stranded harbour seals and were stored until needed. Fish otoliths present in faeces were removed and identified, if possible, to species level. Fish were collected from local fishermen in the summer and autumn of 2012 and throughout the calendar year of 2013 (except Jan, Feb and Apr). To investigate the presence of DA, extracted samples were used directly for the ASP Enzyme-Linked Immunosorbent Assay method (ELISA; for overview and protocol see http://www.biosense.com/comweb.asp?articleno=192&segment=3). The ELISA assay has no cross-reactivity to non-toxic, structural analogues like kainic acid (a natural marine acid present in some seaweeds). Results were confirmed using an ultra-high performance liquid chromatography-tandem mass spectrometry method (see Braña-Magdalena et al., 2014), with results from both methods correlating well. Analysis of PSP toxins in extracts was carried out using High Performance Liquid Chromatography with post-column oxidation and fluorescence detection with white blood cells counted. For the quantification of cortisol (stress response hormone) in the plasma samples, a commercially available solid phase enzyme-linked immunosorbent assay (ELISA) kit was used. Generalised linear models were used to select the models that best fitted the data with toxin concentration (in urine or faeces) as the dependent factor and sex and region as the independent factors.

Results for DA exposure in P. vitulina revealed a temporal change before and after 2012; urine samples collected between 2008 and 2010 contained quantifiable amounts of DA, whilst in 2012 and 2013 only 43.6 % had DA levels above limit of quantification (0.025 µg/g). This was complimented with faecal samples from both live captured harbour seals and anonymous faecal samples for which during 2008-2010 revealed the highest levels of DA. This shift in DA contamination of harbour seals relates to the annual variability in Pseudo-nitzschia spp. blooms in Scotland from 2006 to 2013 (two major blooms occurred in 2008 and one in 2010). Harbour seals on the east coast of Scotland had over three times higher DA concentrations compared to those from the Northern Isles and the west coast.

Results for PSP toxification was less clear, highlighting a likely chronic rather than acute exposure, where long-term effects are not yet fully understood. Despite the fact that the east coast is the region with the greatest population decline, over half of the live captured harbour seals found exposed to PSP toxins (55.6 %) were captured on the west coast (May 2013). Active screening of PSP toxins in the live captured harbour seals first started in 2012; however, both 2012 and 2013 were years where harbour seals were found exposed to PSP toxins, suggesting PSP toxins could constitute a potential risk for the health of this species in Scotland. Only acute effects of PSP toxins have been reported in mammals such as seals, long term exposure to non-lethal doses of STX may in fact make them potentially become less susceptible to the effects through their consumption of contaminated fish prey such as plaice, dab, long rough dab, whiting, and cod.

The authors highlighted that there were many variables in this study that need to be looked into further; i.e., there is little information on how widespread Pseudo-nitzschia blooms are due to the limited phytoplankton-monitoring network. Furthermore, light microscopy identification cannot differentiate between toxic and non-toxic species of Pseudo-nitzschia.

Jensen, S.K., Lacaze, J.P., Hermann, G., Kershaw, J., Brownlow, A., Turner, A., & Hall, A. (2015) 'Detection and effects of harmful algal toxins in Scottish harbour seals and potential links to population decline' Toxicon. 97, 1-14.

Reference for liquid chromatography-tandem mass spectrometry method

Braña-Magdalena, A., Leāo-Martins, J.M., Glauner, T., & Gago-Martínez, A. (2014) 'Intralaboratory validation of a fast and sensitive UHPLC/MS/MS method with fast polarity switching for the analysis of lipophilic shellfish toxins' J. AOAC. Int. 97(2), 285-292.

Plankton’s Perspective in Trophic Mismatching

This blog is set out slightly differently than the usual post. The paper I’m basing this off is a review and is written in three distinct blocks so I have imitated this in my post. Enjoy!

Plankton is one of the many groups of species which base their seasonal cycles on changes in their environment. These phenological changes could cause disruption in the local ecosystems due to the increasing temperatures especially if the species with changing timings are relied upon or rely on a different species. Climate change driven phenological changes in both Phytoplankton and zooplankton’s population has been reported in freshwater and marine ecosystems. This paper looks at the evidence, reviews what these changes could mean for the plankton communities and suggests what future studies should focus on.

What is the current evidence for the trophic mismatching in the plankton?

 The authors looked at a very specific collection of papers by searching through ISI Web of Knowledge. By only looking at the papers studying holoplankton, and no transient life cycles, the number of papers reviewed reduced significantly. The authors then reduced the number studies further by removing those which did not show a significant difference  between the two levels and the measures of species performance or abundance must be directly linked to the degree of synchrony between trophic levels. Many of these papers focused on the spring phytoplankton peak and zooplankton grazers (mostly represented as diatoms or estimates of the phytoplankton biomass). They found that the number of studies has not provided for trophic mismatching, and so does not support trophic mismatch within plankton.

 There was very little field evidence and it was biased towards the spring events and phytoplankton grazers, especially Daphnia. There are also few studies directly matching abundance or performance to phonological mismatching. The authors suggest a more specific and dedicated research to measure the importance, identifying the conditions that may promote/negate the effects and to demonstrate a link between mismatching and population/ ecosystem effects.

What does trophic mismatching mean for the plankton?

 Current understanding of plankton seasonal succession states that there’s feedback between the zooplankton and phytoplankton, any factor influencing the rates of population affects the balance between these two populations. The plankton-cladoceran interaction forms the basis of many studies which increase rapidly in response to the seasonal increase of phytoplankton. Rapid seasonal increases in population size/ and fecundity has been observed, in response to seasonal increases in response to the available phytoplankton recourse. This suggests that to some extent the seasonal timing of the zooplankton population development will be dependent on food recourses. For the grazer’s population increase, the phytoplankton’s abundance needs to exceed the threshold amount, which is the point at which there is enough food to allow the zooplankton to reproduce. In extreme cases resource driven increases in grazer populations could feed-back on to their resources and suppress the phytoplankton populations, and lead to the collapse bloom. Modellign studies  suggest that if the temperature continues to change, the consumer-resource cycle could alter, and thus influencing replication, development and grazing.

Future priorities for studies of trophic mismatch in plankton:

The phenology of resource limitation: there are a couple of assumptions there are that resource limitation prevents reproduction this needs evidence. Food threshold needs to be found, laboratory studies are critical for this There are currently discrepancies in the data between about whether Daphina as the herbivore is the only factor affecting the populations, or it has been suggested that the Daphnia population growth may also be partly supported by grazing. Important to state what food resources are and are used.

Food chains to food webs:  the studies reviewed adopted the linear food chain paradigm. However, to understand the consequences mismatching future studies should adopt a wider view of the community, adopt more of a food web based approach.  For example, the seasonal period of abundance of the phytoplankton consumed by cyclopoid nauplii might be affected by strong grazing pressure from co-existing Daphnia.

The complexity of copepods: very few studies directly examine the potential mismatching between copepods and their food resources.  To truly understand mismatching in copepods, it would be necessary to define multiple developmental stage-dependent food resource windows and examine shifts in their seasonality over the longer term. As a further complexity, the life cycles of copepods may also be interrupted by quiescence and diapause, which may cause lags between resource availability and copepod development.

Conclusions

The authors summarised that although trophic mismatch has been proposed as a mechanism in which climate change could affect, there is currently limited evidence for this occurrence and its impacts on ecosystems. Since the evidence is also biased towards spring blooms and a small number of organism groups, further studies should address this.   The authors believe that by recognising and incorporating the that exist between population development at different trophic levels and the context in which the changes occur.  I, however, believe that a wider range of papers needs to be examined.
 

Thackeray, Stephen J. "Mismatch revisited: what is trophic mismatching from the perspective of the plankton?." Journal of plankton research 34.12 (2012): 1001-1010.

 http://plankt.oxfordjournals.org/content/34/12/1001.short

P.australis: Don’t you know that you’re toxic? (sorry for the really bad Britney Spears line)

Harmful Algal Blooms (HAB’s) are a risk to the health of humans and marine organisms, costing the economy millions of pounds. During 1998, 400 Californian sea lions (Zalophus californianus), were found dead along the Central California coast, whilst numerous others exhibited signs of neurological dysfunction. At this same time observations of a toxic diatom Pseudo-nitzshia australis, known for the production of domoic acid (DA) were made in the area. DA had been detected in planktivorous fish and within the body fluids of sea lions in the surrounding area, leading to the theory of domoic acid moving through the trophic web.

Within the study by Scholin et al., (2000) a diatom bloom of P.nitzschia was examined to determine its effect on the marine organisms of the Central Californian Coast. During early spring of 1998 diatom communities observed in Monteray Bay were mainly comprised of Chaetoceros spp. with a clear absence of P.nitzschia sp., additionally tests at this time provided no trace of DA activity. In the beginning of May there began a transfer of dominant diatom species to P.australis, which coincided with the presence of DA. This was followed in June with transfer of dominant diatom species from the P.australis to Pseudo pseudodelicatissima, the level of DA decreased in correlation with the end of the P.australis bloom. Through the use of several assays, performed using surface seawater samples of the time, a fluctuation of nutrients could be observed. Immediately before the P.australis bloom occurred, an increase of NO₃^-, HPO₄^-2 and H₂SiO₃ was detected, possibly stimulating the growth of the toxic diatoms.    

During the bloom of P.australis the stomachs of small fish within the area were examined, species investigated included anchovies and sardines. The results of the examinations show the level of DA in the fish rose and fell with the appearance and disappearance of P.australis. In addition to the DA level, species of diatom which had been ingested were also assessed. Where high levels of DA were observed the ingestion of P.australis was also noted, in comparison, when low levels of DA were observed the ingestion of other P.nitzschia strains were noted, whilst P.australis was absent. During the P.australis bloom, an increase in marine mammal and bird carcases were observed along the Central California Coast. Although this supports the effect of DA causing marine organism death, no official surveys had been conducted on the number of marine animal deaths, and their specific causes.

Of the 400 Z. californianus deaths, 70 were cared for by the Marine Mammal Centre (TMMC), of which 48 died. Tissues from the 48 Z. californianus which died were examined, and displayed unique brain and heart lesions, which have previously been identified in studies of animals exposed to DA. Reports of sick sea lions along the coast reduced in June at the same time the P.australis bloom declined, stopping completely by the end of June. To assess the P.australis bloom for toxicity and its effects, DA receptor binding assays and DNA probes were used. Liquid Chromatography –tandem mass spectroscopy (LC-MS/MS) confirmed the presence of DA in plankton, anchovies and sea lions; which had died during the bloom. The urine, serum and faeces of the 48 examined sea lions was analysed, DA was identified in the faeces along with P.australis, therefore ingestion of the toxin appears to occur at the same time as the P.australis ingestion. As anchovies feed on P.australis and are a main food source of sea lions, there appears to be a trophic transfer of the DA through the marine food web. This would explain the deaths of higher trophic feeders opposed to those lower down the food web. As the period of P.australis bloom only lasted for around a month, it is clear to see the amount of damage caused can be vast, within a short period of time.     

The study provides a great deal of evidence from investigations; which support the presence of P.australis when DA levels are high. Repeated DA and diatom species presence studies within the same location would offer either supporting evidence to this study, or even add to the species of diatoms which produce DA to marine systems. Due to the nature of HAB’s this area of study is of great importance, due to its effect on the health of humans and marine animals, along with the negative impact it can have on fisheries and tourist economies.   

http://www.nature.com.plymouth.idm.oclc.org/nature/journal/v403/n6765/full/403080a0.html

Scholin, C.A., Gulland, F., Doucette, G.J., Benson, S., Busman, M., Chavez, F.P., Cordarok, J., Delong, R., De Vogelaere, A., Harvey, J., Haulena, M., Lefebvrel, K., Lipscomb, T., Loscutoff, S., Lowenstine, L.J., Marin III, R., Miller, E. M., McLellan, W.A., Moeller, P.D.R., Powell C.L., Rowleeskk, T., Silvagni, P., Silverl, M., Spraker, T., Trainer, V and Van Dolah, F.M. (2000) Mortality of sea lions along the central California coast linked to a toxic diatom bloom. Nature 403 pp. 80-83.

Dishing the dirt on shrimp burrows and nitrogen cycling

Macrofauna such as thalassinidean shrimps living within sediments can have a large impact on the benthic microbial communities. These active decapods live in marine sediments in large numbers and create vast burrow systems. The shrimps oxygenate their burrows by beating their pleopods (walking legs) to flush water through these networks. This burrowing activity is known to affect the structure and diversity of the microbial communities within the sediments. Previous work has shown enhanced nitrification in the burrow walls, higher rates of denitrification in the sediment surrounding the burrows and increased loss of dissolved inorganic nitrogen from the sediment. As a result, the activities of these bioturbating organisms may augment many of the microbial metabolic processes. There may also be seasonal patterns in the abundance of these microbial communities within shrimp burrow sediments.

Laverock et al., (2014) looked at the effects of a burrowing mud shrimp Upogebia deltaura on the temporal changes of certain bacterial and archaeal genes that represented the main nitrogen (N)-cycling guilds in the sediment. To determine whether there was any temporal variation in the abundance of N—cycling bacterial and archaeal genes, the study utilised quantitative polymerase chain reaction (q-PCR) to analyse sediment samples taken from the burrow walls of U. deltaura and from surface sediments in Plymouth Sound. The q-PCR counted the bacterial and archaeal 16S rRNA genes (to gauge overall numbers of bacteria and archaea), as well as genes that represented betaproteobacteria and archaeal ammonia oxidizers (amoA), bacterial denitrifiers (nirS) and bacteria that undertook the anammox process. These specific phyloptypes that other studies had previously identified in marine sediments were targeted with particular primers.

Bioturbation did appear to affect the temporal variation of certain N-cycling genes and these effects differed between the ammonia oxidising bacteria (AOB) and the ammonia oxidising archaea (AOA). There were seasonal variations in the guilds of AOB in burrow sediments compared to surface sediments and these variations were believed to be affected by bioturbation activity. These included genes represented by bacterial guilds that remove nitrogen (NO₃^-, NO₂^-, and NH₄⁺) from marine sediments by denitrification (nirS) and anammox. During the summer, shrimp increase bioturbation and aeration of their burrows, bringing a greater oxygen influx into these systems. This has an impact on oxygen-sensitive processes such as denitrification and anammox.

Although the abundances of AOA genes did vary over time, these changes were not as a result of bioturbation and appeared to be controlled by independent abiotic factors. These range from the increased availability of ammonium over the winter months to the dissolved oxygen levels in the water and salinity gradients. In addition, archaeal amoA genes were four times as abundant as betaproteobacterial amoA genes during the year but it is still unclear whether it is AOA or AOB that make the greatest contribution to ammonia oxidation rates in marine sediments.

The authors acknowledged that certain phylotypes were targeted in this study and this could have introduced an inherent bias. The primer sets used may have missed gammaproteobacterial amoA genes and denitrifying nirK genes, both of which represent important bacterial guilds in marine sediments and oxygen minimum zones. In addition, no primers yet exist to target archaeal nirS genes.

The effects of burrowing shrimp clearly have an impact on microbial processes and communities. Any changes in the abundances of nitrogen-cycling microbes could therefore impact the fluxes of nitrogen across the sediment interface. Further work should focus on whether the presence of these genes is in fact associated with the relevant biogeochemical processes or not.

Reference:

Laverock, B., Tait, K., Gilbert, J.A., Osborn, A.M., and Widdicombe, S. (2014) Impacts of bioturbation on temporal variation in bacterial and archaeal nitrogen-cycling gene abundance in coastal sediments, Environmental Microbiology Reports, 6, (1), 113-121.

http://onlinelibrary.wiley.com.plymouth.idm.oclc.org/doi/10.1111/1758-2229.12115/abstract

 

Rhabdoviridae to the Rescue?

As noted in my last post, Lepeophtherius salmonis is a serious problem for Atlantic salmon aquaculture and is getting progressively worse. In Norway, use of neurotoxins has led to the development of strains of multi-resistant super lice unaffected by the standard neurotoxins used to keep them under control. Given that other methods such as cleaner wrasse are relatively ineffective this is clearly a cause for concern. Viruses offer an alternative and are thought to have a significant negative impact on lice. However, substantial work is required to develop them as a realistic option. Okland et al. (2014) took the first steps by describing the genomes, target tissues and virion morphology of two (RNA) rhabdoviruses infecting L. salmonis.

Lice were collected from five farming sites in Norway. Sections for T.E.M (transition electron microscopy) were taken from abnormal areas of the cephalothorax in infected lice. This revealed large number of bascilliform or enveloped and rod-shaped virus particles budding from cellular membranes. The glandular tissues the particles were found infesting also showed necrosis and disintegration. Illumina sequencing of the RNA from the infected lice was then carried out to generate the (almost) complete genomes of two rhabdoviruses. These were named Lepeophtherius salmonis rhabdovirus No9 (LSRV-No9) and L. samonis rhabdovirus No127 (LSRV-No127). Their genomes consisted of five structural protein-encoding genes and phylogenies were generated using the sequence for the proteins L and N. These revealed the two viruses were closely related and separate from other rhabdovirus viruses suggesting they were distinct species in their own genus. Interestingly, the N-sequence of No9 sat closely with a sequence also obtained from lice in the Canadian Pacific.

Sequencing of the genomes allowed the development of primers facilitating further investigation of the prevalence of the viruses in lice but also salmon tissue. RT-PCR revealed that all lice developmental stages were positive for the viruses but the highest levels occurred in the adults. In situ hybridisation of the tissue showed the presence of both viral mRNA and DNA in the lice with all lice being positive for at least one virus. However, ovaries and eggs only contained the viral mRNA. In comparison, the viruses were absent or only occurred only at low levels in most fish tissues. In contrast high levels of e viruses occurred at the lice attachment sites. Indicating that the lice maybe injecting the virus into the salmon. The authors postulated the lice could doing this on purpose. By using the viruses in some manner to suppress the rejection of the attached parasite by the host. However, the viruses were unable to replicate in fish cell lines and are genetically distant from rhabdoviruses that can. On balance, it seems more likely the viruses just happens to circulate into the host as it reaches high levels in the lice.

Overall, I found this publication extremely interesting. I was however disappointed they did not discuss the bio-control potential of the viruses further. Clearly, a number of questions need to be asked next. Firstly, how deadly are these viruses? Secondly, how specific are they and do they hit non-target crustacean species? Most importantly, the potential role of the virus as an immunosuppressant must be investigated to rule out any danger to the fish themselves. In conclusion, lice are on the rise and viruses could play an important role in preventing an aquaculture apocalypse.

Reference: Økland, A.L., Nylund, A., Øvergard, A-C., Blindheim, S., Watanabe, K., Grotmol, S., Arnesen, C-E. and Plarre, H. (2014). Genomic Characterisation and Phylogenetic Position of Two New Species in Rhabdoviridae infecting the Parasitic Copepod, Salmon Louse (Lepeophtheirus salmonis). PLOS One, 9(11), e112517.