When the going gets hot the dinoflagellates (sometimes) get going, how viruses might affect coral symbionts

Corals represent more than meets the eye, they host intricate and interesting communities composed of dinoflagellates (also referred to as zooxanthellae), and a suite of microbes that include bacteria, archaea, fungi, protists, and viruses. One such dinoflagellate that often shares a symbiotic relationship with coral is Symbiodinium.

Image courtesy of wikicommons

Image courtesy of wikimedia commons

These algal symbionts are essential to overall reef function and are present in incredible numbers, a healthy coral reef could harbor more than 1010 algal symbionts per meter squared (!!!). These organisms are essential and understanding their role and unique relationship to coral is important, as it can be screwed up by heat stress, ultimately leading to bleaching (eg. when Symbiodinum cells get the heck out of Dodge and the coral then looks completely white).

Simbiodinium fitti. Image: Todd C. LaJeunesse, Penn State University

Simbiodinium fitti. Image: Todd C. LaJeunesse, Penn State University

However, the mechanism triggered by heat stress that leads to bleaching isn’t completely understood. While it was previously suggested that viruses might somehow play a part in such events, a recent short communication published last week in the ISME Journal presented interesting evidence from Levin and colleagues that it is likely that viral infections lead to thermal sensitivity in Symbiodinium and, ultimately, bleaching.

 

In a previous study, two Symbiodinium populations were cultured from Acropora tenuis at two sites on the Great Barrier Reef. The population from South Molle (SM) Island was thermosensitive and didn’t grow well at 32ºC, while the “thermotolerant” population from Magnetic Island (MI) was cool as a sea cucumber at this elevated temperature. Replicates of both populations (SM and MI) were then maintained at 27ºC or 32ºC and the transcriptomes (sequences of all of the mRNA extracted from the population) were obtained.

Our study exemplifies how RNA-Seq can be used to gain valuable insight into resident viruses.

Levin and colleagues found that only in the thermosensitive population (SM) were incredibly high expression levels of a new RNA virus observed at 27ºC, while at 32ºC anti-viral transcripts increased. At the same time, there was basically no change in the low level of virus RNA expressed in the thermotolerant MI population.

    Thus, we conclude TR74740|c13_g1_i1 to be the RNA genome of a novel +ssRNAV, making this the first discovered genome of any virus infecting Symbiodinium

This study is cool because it presents the FIRST genome of a Symbiodinium virus, and provides a possible explanation for thermal sensitivity in coral symbionts that can lead to bleaching events. Understanding the intricate relationships that underlie coral reef function is important as we deal with climate change and attempt to protect such incredibly essential, not to mention beautiful, ecosystems.

References

Baker, A.C., 2003. Flexibility and specificity in coral-algal symbiosis: diversity, ecology, and biogeography of Symbiodinium. Annual Review of Ecology, Evolution, and Systematics, pp.661-689.

Levin, R.A., Voolstra, C.R., Weynberg, K.D. and van Oppen, M.J.H., 2016. Evidence for a role of viruses in the thermal sensitivity of coral photosymbionts. The ISME Journal.

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Friday Action Item: Get involved with a scientific society

In the wake of the recent U.S. election, we at The Molecular Ecologist wanted to better use the site to help organize our community’s support for scientific inquiry and science education under an administration that may be quite unfriendly to them. One small thing we thought we could do is highlight “action items” every week. Look for these “Friday Action Item” posts for ideas about specific things you can do to support science — from calling Congress to helping crowd-fund a cool new research project. Got a suggestion for a future Action Item? E-mail and tell us all about it!

This week’s action item: get involved with a scientific society. Even in the days of science blogs (ahem) and preprints, scientific societies are the glue that holds together communities of experts on topics as broad as all of science, or as narrow as a single taxon. Societies provide research and travel funds for graduate students and early career scientists, organize training and conferences, and generally help us be, well, social. In many cases, they’re also advocates for scientific work in their respective fields — lobbying (yep) government for research support, and offering expertise where it connects to specific policy.

Probably most of our readers are members of at least one society — good fits for molecular ecologists can include the hyper-generalist American Association for the Advancement of Science, or more societies more focused on ecology, evolution and genetics, like

(These are, obviously, a list drawn from the TME team’s personal interests … please feel free to nominate some more in the comments!)

If you’re a member of any societies, your action item for the week is to find out how to be more useful to that society, and do that. Maybe just take the time to vote in the leadership election instead of letting reminder e-mails pile up. (Hey, it’s a chance to vote on something where every candidate has the necessary expertise.) Maybe add your name to the list of potential volunteers for conference organizing or governance work. Maybe donate a membership to a graduate student who needs an extra push, or has more urgent priorities for their TA stipend.

If you’re not a member of a society, then your action item for the week is to pick one and join it. You’ll probably earn discounted, or free, publication fees in a journal relevant to your interests and preferential rates for at least one conference you should be attending anyway — and you’ll be supporting the broader scientific effort of your closest colleagues.

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Friday Action Item: Support science teaching through Donors Choose

In the wake of the recent U.S. election, we at The Molecular Ecologist wanted to better use the site to help organize our community’s support for scientific inquiry and science education under an administration that may be quite unfriendly to them. One small thing we thought we could do is highlight “action items” every week. Look for these “Friday Action Item” posts for ideas about specific things you can do to support science — from calling Congress to helping crowd-fund a cool new research project. Got a suggestion for a future Action Item? E-mail and tell us all about it!

Public school classrooms are the point of entry into science for the vast majority of children in the United States, yet public schools are dramatically variable in the resources they have to offer. This is in large part because nationwide, public education is supported by local property taxes, which converts economic inequality into inequality of opportunity. One small way to help fix this is provided by Donors Choose, a kind of Kickstarter for classroom supplies. The Donors Choose website lets K-12 teachers propose projects, activities, or supply purchases with set budgets, and lets donors choose which to support — you can search proposals by subject matter, grade level, supply type, geography, and economic need. Here’s a few examples that are particularly apt for molecular ecologists:

Many of the proposed project budgets are heartbreakingly modest, and some have donation matching offers from Donors Choose sponsors — a donation of $20 can make a big difference. So that’s your Action Item this week: help fund science education at the earliest stage.

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Diving into chilly California waters, understanding genomic differentiation and the role of gene transfer in marine cyanophages

At this point, it’s clear: microbes are everywhere, there are a lot of them, and they are important. In fact, they are more abundant, more diverse and older than any other organism we have on this planet. In particular, cyanobacteria are pretty amazing, and contribute to the majority of the oxygen we breathe (2 of every 3 breaths).

Gregory et al., (2016) Figure 1.The most abundant marine cyanobacteria are Synechococcus and Prochlorococcus, the main representatives of oceanic phytoplankton, which contribute to about half of the world’s primary production. The forces driving population structure and ecotype differentiation in Synechococcus and Prochlorococcus are diverse (including light, temperature, nutrients) as well as cyanophages.

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The road ahead

(Flickr: Allison Meier)

Since Election Day, people have been posting their thoughts and fears about the future on the walls of the New York City subway. (Flickr: Allison Meier)

It’s been almost two weeks since we woke up to the reality that Donald Trump — the failed casino mogul, the virtuoso tax-dodger, the reality-show star, the self-described serial sexual assailant, the Ku Klux Klan endorsee and darling of white supremacists, and, yes, the short-fingered vulgarian — will be the next President of the United States. It was a shock on the night of November 8th, and it is no less disorienting a fortnight later. Every aspect of U.S. society as we’ve known it faces an uncertain future after Inauguration Day, and scientific research and education is at the top of that crowded list.

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Posted in citizen science, community, funding, NIH, NSF, politics, United States | 3 Comments

Fungi and the quest for old polyploids

Polyploidy, that curious increase in a species’ number of genomes, is now a well recognized force in the evolutionary history of plants and animals. Those extra genomes are often much more than just extra: having a spare genome or four may help lineages radiate into unexplored niches and colonize harsh environments previously uninhabitable by parental species.

Importantly, transitions to polyploidy aren’t just a recent phenomenon. Ancient polyploidization events can be found across the eukaryotic tree of life, from the appearance of angiosperms to the origin of vertebrates:

Figure 1 from Campbell et al.

Figure 1 from Campbell et al. (2016) — starbursts indicate well-characterized (red), partially-supported (grey), and proposed (blue) instances of polyploidization among eukaryotes.

It doesn’t take long to see something weird about this annotated tree. What is up with Fungi? The fungal Kingdom is old and diverse, yet it displays a lack of ancient polyploidization events that are common across other eukaryotes. In a recent volume of The American Naturalist, Matthew Campbell and colleagues lay out the case for the missing ancient polyploids.

The authors focus on three hypotheses:

(1) Ancient fungal polyploids are actually rare (a.k.a. “The Null”)

For some interesting biological reason, maybe polyploidy just doesn’t happen that often in fungi. However, this is fairly straightforward to reject. Polyploidy is found in a wide swath of diverse fungi and can be initiated in the laboratory by crossing species. Additionally, chromosome-based sex determination — one of the major roadblocks for polyploidy in animals — doesn’t appear among fungi.

(2) Fungal polyploids don’t last for the evolutionary long haul.

One of the major talking points in the discussion on the evolutionary significance of polyploidy is the trend for most polyploid lineages to be relatively young. The higher extinction rate of polyploids might be overemphasized in fungi, making extant polyploids that emerged far in the past unlikely. The problem here is that polyploidy is often tied to asexuality in many taxa, and asexual reproduction is a more established cause for evolutionary dead ends. Currently recognized fungal polyploids, such as Saccharomyces yeasts, are in fact sexual polyploids, which suggests that fungi can produce sexual polyploid lineages similar to those seen in plants and animals.

(3) Ancient cases of polyploidization are hard to detect.

Finally, ancient fungal polyploids might be out there right now, happily stretching their little hyphae after a rain, but are just difficult for scientists to identify. Some of the most fundamental work recognizing plant/animal polyploids is via karyotyping, which is a mighty task when looking at the small, condensed, and membranous chromosomes of fungi. Modern approaches to identifying polyploidization use genomic signatures (synteny-based methods for example), but fungi also display significant genome restructuring over short time frames that could confound the search for ancient signals of polyploidization.

Saccharomyces cerevisiae, the stuff of bread, beer, and undergraduate microbiology midterms.

Saccharomyces cerevisiae, the polyploid origin of bread, beer, and undergraduate microbiology midterms.

Given what we know about Fungi, hypothesis 3 is the most likely explanation for the lack of ancient fungal polyploids. Campbell et al. go on to provide a succinct review of the current genomic methods to evaluate polyploidization and their applicability to fungal biology, including Ks calculations, gene/species tree concepts, and the identification of conserved gene clusters in fungi.

Together, this perspective piece is a call to action for genomics and polyploid researchers: there is polyploid treasure somewhere in the fungal kingdom, now go find it.

 

Cited

Campbell, M. A., Ganley, A. R., Gabaldón, T., & Cox, M. P. (2016). The Case of the Missing Ancient Fungal Polyploids. The American Naturalist, 188(6), DOI: 10.1086/688763

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The importance of culturing the uncultured, delving into the microbial consortia in the human gut

Rappe (2013). Figure 1. Direct sequencing and cultivation efforts are both integral aspects of molecular ecology.

Rappe (2013). Figure 1. Direct sequencing and cultivation efforts are both integral aspects of molecular ecology.

The molecular side of ecology has grown by leaps and bounds in recent decades. The review we covered not too long ago, did a nice job of summarizing many key aspects highlighting the importance of this relatively new molecular view of the world. In particular, fancy high throughput sequencing has allowed us to explore the difficult to visualize world of microbes – we can identify things that are there without actually growing cultures in the laboratory.

It wasn’t until the mid 80’s that microbial diversity was examined using molecular tools, and eventually standard methods were developed for identification of bacterial isolates (namely, often sequencing the 16S rRNA gene). Metagenomics has been a game changer: from allowing us to explore the bacteria in a drop of seawater to identifying the key players affecting human health. In fact, once we were able to sequence environmental samples, we realized that only a small fraction of what is out there has been grown in a laboratory. Often the microbes that aren’t cultured are referred to as the “uncultivated microbial majority”.

Marine microbial ecology has benefitted greatly from all of the metagenomics, transcriptomics and (generally) genomics-based studies. Many of the most abundant microbes that play major roles in biogeochemical cycling worldwide are difficult to obtain in culture. It wasn’t until relatively recently that specific high throughput culturing approaches were applied to isolate some of the most abundant lineages inhabiting the oceans. However, this challenge is not unique to environmental microbiology and also must be considered when studying systems such as the human gut.

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Posted in community ecology, genomics, medicine, metagenomics, microbiology | Tagged , , | 1 Comment