The study was performed by deploying free drifting sediment traps at 150, 200m, 300m and 500m in the North Pacific subtropical gyre. One set of these cylinders contained only sterile seawater, deemed "live", and the other was "poisoned" with a solution that inhibited further growth and preserved the DNA of micro-organisms that fell into it. Once collected, the sediments were analysed with epifluorescence and confocal microscopy. DNA from the sediments was also collected and analysed.
The most abundant bacterial genera differed between "live" and "poisoned" traps: Alteromonadales (e.g. Alteromonas and Pseudoalteromonas) in the live traps and Vibrios in the poisoned traps. The paper does not discuss this difference but considering the poisoned traps inhibited any further growth, it is possible the particles trapped were preserved at an earlier stage of succession whereas "live" populations were able to grow and become more complex. This is reinforced by the data that showed poison traps populations collected at 500m were more balanced and not so dominated by Vibrios; it is possible that Vibrios are part of the colonising population on marine snow and as it sinks, the population becomes more diverse.
The study showed that live trap assemblages had a high
bacterial genetic diversity such as genes for motility, vitamin synthesis and
metabolism of carbohydrates and amino acids such as those from algae and
diatoms. The bacterial genes from the poison traps coded largely for
siderophores and iron acquisition, which according to the paper are linked with
lifestyles associated to eukaryotes. Virulence factors and quorum sensing genes
were also enriched in the “poison” traps; all of which were associated with Vibrios. “Poison” trap bacteria were
also associated with eukaryotic surfaces and anaerobic intestinal tracts as
pathogens, saprophytes or symbionts.
Genes for chitin attachment and degradation were expressed in both traps, but of different bacterial origin.
I think this is a nice study, marine snow is a major import of nutrients into the ocean depths and carbon cycling. This study- understandably- only sampled relatively shallow particles; I would be interested in see how populations and metabolisms further progress at even greater depths along with the degradation state of the POM itself so we get a better understanding of the nutrients that sink into the deep sea.
Fontanez, K.M. Eppley, J.M. Samo, T.J. Karl, D.M. and
DeLong, E.F. (2015) Microbial community structure and function on sinking
particles in the North Pacific Subtropical Gyre. Frontiers
in Microbiology, 6, article 469
A very interesting study, could be used for further investigation into mapping the diversity as you go deeper, and build up a microbial diversity profile and how the different generas interlink in terms of processes and pathways. Testing the other microbes found (not just bacteria) such as algae/diatoms could show the links between all these genes coding for pathways. Just a question about the method - am I right in thinking that the difference between the sediment trap being 'live' and 'poisoned' was that the live one stayed exposed to the outside factors such as the temperature changing etc. on it's way back up from the selected depth? Or were they contained? And also was the poisoned one essentially 'frozen' in time so could not develop further?
ReplyDeleteHey Joss,
ReplyDeletesince it is unusually warm and snow is nowhere to be seen, thanks a lot for providing some christmassy atmosphere to the blog. In most of the previous discussions about Vibrios, temperature played a key role in the distribution of Vibrio species. It would be interesting to look closer at the Vibrio distribution at species level in colder depth. Take samples and identify down to the species level and so on. They should be a clear shift in the abundance of single Vibrio species...just guessing.
Hi Nuri, that's a good thought. It might not be that the populations progress as the marine snow sinks, rather that the Vibrios are not actually present in the deeper waters. That's confounded a little by a paper I read a long time ago about a Vibrio being isolated from a deep sea hydrothermal vent, however, as you say, it would be warmer around the vent. Though it might be that a Vibrio was seeded there by marine snow, it's more likely it was associated with a host.
DeleteHi Caroline, thanks for your comments and questions. This paper does briefly mention eukaryote microbes caught in the traps, but not much past what they were. As for the method, they use a method from another paper that I'm not able to access, it's called "Fluxes of particulate carbon, nitrogen, and phosphorus in the upper water column of the northeast Pacific" by Knauer et al., 1979. So whilst I can't comment on their method, I would at least hope the both traps were closed off before they were brought up. Whilst deployed though, they were both exposed to ambient environmental conditions.
ReplyDeleteAs for the "poison" trap, that's right. It's a compound called RNALater, that stops the microbes growing and preserves their DNA, essentially 'freezing' their function.
Hi Joss, this looks like a really nice study I just wish they had gone deeper! It’s really interesting that assemblages appear to change more with time rather than depth. Does this paper discuss any other changes with depth; for example was more sediment collected at 150m compared to 500m? I think it would be useful to quantify how much POM is being metabolised to approximate how much is reaching the seabed.
ReplyDeleteIt would be interesting to see if there are specific or further population shifts deeper as Nuri suggested. Further work could investigate if the amount of sediment or assemblage changes in different areas, for example closer to the North Pacific Giant Garbage Patch, perhaps species found cold have bio-applications in clearing up the oceans.