by Elisha Wood Charlson and Nicole Webster
When you step back and look at the field of symbiosis research (see Mary Beth Saffo’s recent blog post for the ISS), one can see that the rapid growth and appreciation of our field is staggering. Perhaps we do not rival other research fields with respect to number of scientists per unit effort, but scientists and non-scientists alike are finally beginning to comprehend the true magnitude and importance of microbial symbiosis. A Grand Challenge Article (GCA) for the recently established journal Frontiers in Microbial Symbiosis highlighted how we are increasingly seeing the terms ‘holobiont’, ‘metaorganism’ and ‘microbiome’ used by researchers from a range of scientific disciplines. However, despite this recent progress in appreciating the importance and ubiquity of microbial symbioses, many scientists still tend to view symbiotic partners as separate individuals, thereby limiting our ability to assess interactive mechanisms (including synergism and pathogenesis) within these systems. As researchers we desperately need to overcome this perception of individualism to truly understand the ecology and evolution of microbial symbioses. And whilst Mary Beth highlighted the need for clarity and consistency regarding the definition of “symbiosis,” it is equally important to recognize that the concept of symbiosis needs to remain fluid. The subcategories of “symbiosis” (pathogenic, mutualistic and commensal) are ultimately just idealized interaction states; whereas the actualized state may wander across these defined boundaries depending on evolutionary processes, changes in environmental conditions and/or health state of the host/symbiont. For example, the cnidarian-algal mutualism, a partnership where most of the symbiont transmission is horizontal (and should therefore theoretically favour parasitism) highlights the complexity of symbiotic interactions. A study by Sachs and Wilcox (2006) used sequential horizontal transmission to demonstrate that after only a few forced horizontal transmissions, the Cassiopea–Symbiodinium partnership began to display parasitic rather than mutualistic characteristics.
The blurred lines between “mutualism” and “parasitism” get really interesting when we start to include the “new symbiont on the block” into our research questions – Viruses. Viruses are thought of as the nemesis to all cellular life since cells were formed, and there are many interesting theories with regards to the origin of cells and the role of viruses in the tree of life Moreira and Lopez-Garcia (2009) that are pertinent to symbiosis research , but how might viruses contribute to the future of symbiosis research? As coral and sponge ecologists from the Australian Institute of Marine Science, we have focused on microbial symbioses in corals and sponges for over a decade. However, through recent grants awarded by the Australian Research Council we are now starting to explore the potential role of viruses in coral and sponge symbioses including an assessment of whether they can enhance the adaptive capacity of their hosts during a rapidly changing climate. Whilst there are noticeably less virologists than bacteriologists in the field of environmental symbiosis, this may all be about to change. Attendance at a Symbiomics meeting in Valencia, Spain in February this year was noteworthy for just how many symbiosis researchers were discussing their plans to embark on research to understand the role of viruses in their own model symbiotic systems. Exciting times of discovery!
Viruses as the new frontier for symbiosis research?
In many ways, viruses may be the ultimate symbiont. They have been around since cellular life began. They are basically dormant, inert particles until they interact with an appropriate host where they spring to “life.” And some viruses, under the right conditions, confer adaptive benefit to their host cell, such as resistance to other viruses, niche expansion, and production of novel toxins for defence. In addition, viruses are veteran drivers of evolution, in a literal sense as agents of horizontal gene transfer, to a more biological sense by acting as a strong selection pressure for immunity. These little genetic reservoirs may also be a source of hope for rapid adaptation under the current projections of climate change.
As symbiosis researchers that have adopted viruses into our lives, we need to express a sense of caution to fellow symbiosis colleagues considering the jump. The data is not easy to come by, and the results are often mired in concerns about host contamination and determining what it is you are actually observing. Are we describing the whole viral assemblage or just those easy to “see” by standard techniques, such as flow cytometry, epifluroescent microscopy, or even extraction kits that were all designed to work with dsDNA from cellular organisms. In addition, viruses are not like anything you have ever worked with before. It may be relatively easy to switch from one type of invertebrate or plant symbiosis to another, but viruses require an entirely different skillset to work with. We recommend getting a nice cup of tea and settling in with the Marine Aquatic Viral Ecology (MAVE, ASLO publishing 2010) chapters, as they outline basic steps used to work with environmental viruses. Finally, find a new friend. The research community working with environmental viruses is enthusiastic and generally very open to collaboration and new ideas.
This may all sound a bit daunting but think about the novelty, the joy of exploring the unexplored. In many ways, that is why we were drawn to the field of symbiosis to begin with. So, are we ready for the new symbiont on the block?.
 Have a read through this initial paper, but don’t miss the 7 correspondence articles that follow!
Nicole Webster is well known as a sponge microbial ecologist, but she has recently ventured into the world of viruses with the award from the Australian Research Council. Her Future Fellowship looks at the role of viruses in sponge holobiont communities. (Add anything?) Nicole is a Senior Research Scientist at the Australian Institute of Marine Science and chief specialty editor for Frontiers in Microbial Symbiosis. Elisha Wood-Charlson came to work on viruses as symbionts in corals by initially working on the onset of coral-dinoflagellate symbioses, then open ocean marine cyanophages. The worlds collided when she took at postdoc at AIMS to work on another Future Fellowship grant (awarded to Madeleine van Oppen) to look at the potential role of viruses in corals - pathogens or mutualists? Together, Nicole and Elisha make up part of AIMS's " Team Virus", working to promote the recognition and consideration of viruses in all aspects of symbiosis and climate change research. Contact us at: email@example.com, firstname.lastname@example.org