The latest craze over phage WO, the bacterial virus that
infects
Wolbachia, has been both
exciting and overwhelming. The press is great at communicating the science in a digestible
format, but it can sometimes become sensationalized and misleading. When one
press release builds upon the hype of a previous release, the end result is
much like the game of telephone. As an author of “
Eukaryotic association module in phage
WO genomes from Wolbachia”, I want to
make sure that the science in the public's eye is not over-represented and that we are providing a
realistic view of the data.
Let’s first talk about what the paper is not, though headlines have claimed otherwise.
·
Phage WO
does not encode the entire black widow venom (latrotoxin) gene. In fact, as
we present in the paper, it contains DNA that is similar to just the C-terminal
domain. This particular region of the gene is associated with the protoxin that
is hypothesized to be involved in lysis of the spider’s secretion cells.
·
The phage
did not necessarily “steal” the DNA from the spider. Yes, viruses hijack
DNA from their hosts and this has been shown in both bacterial viruses and
animal viruses. Viruses are incredible, rapidly evolving entities. Due to the
level of divergence between the sequences in this particular study, the genetic
transfer, if it did happen, occurred long, long ago. We can’t definitively say
if the spider transferred to phage or phage to spider, but in our opinion both
would be equally exciting. The current data leans towards spider to virus,
possibly via a yet-to-be-discovered intermediary (see the paper for more
discussion). We also can’t definitively say that it was even a legitimate transfer
event. It could have been the result of convergent evolution. This is when
different organisms independently evolve similar traits. Given the fact that
widow spiders are often infected with Wolbachia,
and Wolbachia are often infected with
phage WO, there is an ecological niche that would provide opportunity for
genetic transfer. Plus, we present other examples in the paper that support genetic
transfer from animal to virus. Beyond that, many other research groups have
reported the transfer of DNA between Wolbachia
and their animal hosts, so the transfer between the phages and the animal is
not a huge stretch.
With that said, this is what the paper is:
·
To our knowledge, this is the first report of animal-like DNA found in a bacterial virus.
Is this a completely absurd, mind-blowing discovery? Not really. Bacterial
viruses are known to exchange DNA with their bacterial hosts and animal viruses
with animals. However, we don’t really know much about how viruses of bacteria
might interact with animals. This field is really in its infancy.
·
Phage WO
harbors a eukaryotic association module. About half of WO’s genome is
devoted to structural genes (such as capsid, tail, baseplate) and other common
phage elements. However, it also devotes a large percentage of its genome to
unique genes that putatively encode functions relevant to animal interaction. Like
some other viruses, phage WO appears to take different chunks of DNA from
different sources and mix and match the chunks to create unique genes. What do
these genes do? Do they retain the same functions as they did in the original
donor? These are all still mysteries to be solved; so many questions left to be
answered! I can tell you that some of the genes in the eukaryotic association
module quickly grabbed our attention and we look forward to expanding the story
of phage WO and Wolbachia in the
months to come. Stay tuned…
·
Phage WO
integrates into the Wolbachia genome
via specific attachment (att) sites.
Why does this matter? Wolbachia is an
obligate intracellular endosymbiont. That means, it is dependent on its animal
host for survival and cannot be cultured outside of the animal cell (as you
would with standard free-living microbes such as E. coli). This makes it very hard for scientists to test functions
of specific genes and fully understand its biology. We are particularly
interested in Wolbachia because it
infects over 40% of all arthropods as well as some nematodes of human health
relevance and crustaceans. The identification of WO’s att sites offers a potential method of accessing the Wolbachia chromosome in order to unlock
its secrets. Using the phage may or may not work, but it’s the best chance we
have to-date.
On a personal note, I want to thank journalists such as Ed
Yong (The Atlantic -
link) and Jacqueline Howard (CNN -
link) for directly reaching out to
us, the scientists, and making sure that they understood the complexity of the
system rather than simply promoting catchy phrases. When it comes to science,
words matter. I agree that this is a fun system to explore, but I hope that the
science can stand on its own without adding falsehoods and making incorrect
conclusions.
Please don’t hesitate to reach out to scientists (including
me) if you have questions about our research and possibly don’t believe or
understand what you read in the news. We are honored to share this journey with
you and are particularly delighted to hear from the next generation of
researchers. Viruses are incredibly fascinating and, in my opinion, phage WO
tops the charts. We are just beginning to explore the landscape of viruses
infecting intracellular bacteria and I can’t wait to see what comes next.
