Since Koch provided an early description of pathogens many
scientist have focused on the idea that a single pathogen is the cause of a
particular disease, however as we have begun to understand microbial ecology
and interactions between host and microbes views are beginning to change. Ideas
are beginning to shift from correlating specific groups of bacteria to disease instead
a more holobiont approach may be more appropriate.
A paper by Egan and Gardiner (2016), looks at the finding of
research conducted in the field of medicine which has found that many diseases
are not caused by a single pathogen but by a microbial imbalance known as dysbiosis
they conclude that many of the disease in the marine environment are likely the
result of this dysbiosis and opportunistic pathogens. The paper puts forward
some interesting ideas and urges us to rethink the tradition views of how
pathogens cause disease.
The incidence of disease is predicted to increase with
climate change and increased anthropogenic pressures and so it is becoming even
more important to understand the causes and ways disease are mitigated. Understanding
the causes of disease in the marine environment is also important because it
does not just effect the host population but may also result in an
ecosystem-wide impact for example due to the loss of muscle beds or a coral
reefs.
There are a number of possible explanations to explain the uncertainty
over the cause of diseases in the marine environment.
- Firstly It is often difficult to distinguish between pathogens from other non-harmful bacteria that may be present on a diseased or decaying host.
- Secondly disease may not be the result of a single microbial agent this is well documented for the black band disease in corals where a complex number of microbes are found to play distinct role in the formation of the disease. Black band disease can be seen as a polymicobial disease.
- It is likely that under stressful conditions the host’s native microbiome can switch from commensal to a pathogenic lifestyle this makes it hard to apply Koch’s postulates as its does not follow the assumption that the causative agent is always associated with disease while being absent from a healthy host.
- Finally environmental pressure may lead to the invasion of opportunistic pathogens.
Compared to the research into humans, the concept of
dybiosis in the marine environment is still very new however research has
provided a number of cases for example Microbial dysbiosis allows the emergence
of opportunistic pathogens such as Aqunimarina ssp. Which are linked to shell diseases in lobsters.
Exposure to stressful conditions is also shown to cause a shift in the microbial
community that can be detected before any physical signs of disease in coral.
This shifts have in some cases been found to have an increase in pathogenic
bacteria such as Vibro species The understanding of disease as the result of
stress and the increases susceptibly to opportunistic pathogens can help to explain
inconsistences in laboratory infections.
One limitation is that although studies of dybiosis in the
medical field can provide a framework to understanding diseases in the marine environment
the complex nature of the marine environment and the difference between humans
and marine organisms such as the lack of immune system in coral means that some
factors will be hard to apply entirely to disease in the marine environment
I like how this paper found a way around the limitations of
studying dybiosis in the marine environment due to the limitations in research effort
and funding by using information that can be transferred from the medical field
of course it is also important for dysbiosis to be studied specifically in the
marine environment to acquire a more in depth understanding and take into
account factors such as difference in life histories between terrestrial and
marine species and recruitment in the open marine environment . This paper
provides a good foundation and explains why a paradigm shift which takes into
account dybiosis, opportunistic pathogens and polymicobial diseases is
important in order to more fully understanding disease in the marine environment.
References
Egan, S. and Gardiner, M. (2016). Microbial Dysbiosis:
Rethinking Disease in Marine Ecosystems. Front. Microbiol., 7.
Hi Alisha,
ReplyDeleteGreat read! Very interesting how the author brought up some points about human dysbiosis as I had never heard of it occurring outside of mammals before.
The way we treat it in mammals is often through pro/prebiotics to try and correct the imbalance of microbes. I know you mentioned that this may not be a suitable way to cure coral but did you come across any other methods that could be used?
Thanks for your time,
Stefan
Hi Stefan, I agree with you I found it interesting that the potential shift/imbalance of microbes within marine species has been observed to lead to disease. I think the idea of dysbiosis is a concept that has very much been focused within mammals, however as this paper shows recently we have begun to apply this concept to the marine environment
ReplyDeleteIn response to your question I think its important to take into account the environments in which dysbioisis occur in each case, treating mammals by the use of pro/prebiotics is much more straight forward it is a lot simpler to administrate probiotics to terrestrial organisms using probiotics to cure coral would most likely inviolve needing to distribute the probiotic within the water column and it would be hard to say how this could impact other organsims in the ecosystem. In the case of coral this dysbiosis seems to be triggeres by environmental stressors such as increased temperature and so of course the ideal solution would be to prevent this increase in tempature which would prevent this change in microbal community however of course this is much eaiser said then done and with climate change something that we are not able to prevent its not really a likely solution.
As for treating coral already effected I haven’t currently come across any suggested methods the study of dysbiosis in the marine system is something that still requires a lot more study and there is little information currently available this was something brought up in the paper they found that in the last 10 years 1020 articles have been published on microbial dysbiosis in humans alone however they only found 3 publications for dybiosis in marine organisms
Recently we have been discussing the use of phages and their have been a few post about how phages might be used to cure disesae I think when applied to the idea of dybiosis being the cause of the diease due to the change in the community structure. Which as mentioned previously is often linked to environmental change, which can lead to the proliferation of opportunism pathogens and the loss of the native microbes one possible way to treat the coral may be the use of phages I’m not aware of any studies that have done this and in my opinion I don’t think it would be as effective as we would hope I think even if we could use phages to remove the opportunic pathogen the loss of the original microbiota may not be able to return to how it was previously