A review of: Beltran Rodriguez-Brito et al. (2010). Viral and microbial community dynamics in four aquatic environments. The ISME Journal. 4, 739-751.
In the past decade our understanding of diversity and abundance of marine microorganisms have increased drastically, we are now aware that viruses are the most abundant in the oceans with approximately ten for every one Bacteria or Archaea. Understanding the diversity and abundance of any organism is important but understanding the function or dynamics of that organism within an ecosystem can be just as important.
In this paper the authors try to monitor microbial communities with the use of metagenomics and four distinctive aquatic environments. The four environments were controlled and stabilized by humans, the first of which was a freshwater aquaculture system and the other three being of different saline properties (low, medium & high) with the water samples were taken over the period of one year. The authors used many methods to analyse the microbial communities including, metagenome to metagenome comparisons, metabolic potential, phage and microbial taxonomy. They also introduced a new statistical analysis to assess the similarities between microbiomes called Taxiɸ. Once they had all of their data they used the model proposed by Thingstad (1997,2000) called Lotka-Volterra which is commonly known as Kill-the-winner. This model predicts that viruses will rapidly and drastically reduce the population of the most abundant microbial species, thus preventing the best microbial competitors from building up a high biomass.
Their results seemed to support the author’s hypothesis that different environments have characteristic metagenomics signatures. They investigated this hypothesis further with a more detailed survey of the 16S rDNA in the microbiomes. The results also indicated that microbial communities seem to remain constant in their diversity but that the abundance rapidly changed throughout the year.
The paper concludes that their data combined with other literature strongly suggests that Viral predation is a major, and possibly the dominant, factor shaping microbial communities based on the model used.
This paper does seem to prove their hypothesis but they only used human controlled environments which mean that the community conditions are fairly stable, if the conditions alter like In the natural world, we may see a shift in which viral microbes dominate and then consequently a possible shift in the abundance and diversity of the marine microbes throughout the year. This is a good base for testing microbial community dynamics but further tests in more natural conditions could show different findings.
3 comments:
Dan - thanks for a nice post showing operation of KTW hypothesis in nature. Just one point of clarification - the KTW hypothesis is based on earlier Lotka-Volterra predator-prey relationships. It is based on an idealized food web and the "winner" is the most active population of bacteria or or other viral hosts (it often is, but may not always be, the most abundant). Se txtbook p.167 for more discussion.
Hi Dan
I think it is very interesting the point you make about microbial communities being shaped so much by viruses. In the paper I just reviewed it talks about dissolved organic material (DOM) being a major energy source for microbes and that most DOM comes from viral lysis of other microbes, most importantly primary producers. I know that a lot of gene transfer takes place within a population via viral transduction but it appears that they have many more important roles to play, like shaping microbial communities as discussed in your paper. You would naturally think that something that kills marine microbes could only have a negative impact but that clearly is not the case.
My blog above on Phylodynamics of viruses is also on a paper that says virus abundances change rapidly but not just throughout the year also over thousands of years! Are the fluctuations because the microbes they infect grow in abundance with seasonal changes / climate change or is it like a bacterial community that grows exponentially until all the nutrients, in this case hosts, are gone? I suppose it depends on if the viruses lyse their hosts or bud off. The papers agree that the viruses are predators and are important for controlling the microbial and algal population. Therefore to understand microbial dynamics and processes we must recognise the crucial influence viruses have.
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