The deep sea is completely devoid of sunlight, wind and
other inputs of energy from the cosmos, and must rely on the leftovers of the world
above it for energy and sustenance. These inputs are essential to life in this
harsh environment and arrive in the form of sunken wood, whale carcasses, kelp
and other debris soon forgotten or overlooked by sentient beings above.
When a piece of wood sinks to the deep ocean they form
hotspots of biodiversity which have a high sulphide concentration and high
reducing power, thus attracting chemoautotrophic bacteria. It is thought that
these hotspots of sunken debris acted as stepping stones for the spread of life
after its origin on hydrothermal vents through providing sulphide- and methane-
rich niches on which overspill from crowded hydrothermal vents could thrive.
This is an interesting concept and the study provides respectable evidence to
support it and addresses several inconsistencies.
The authors aim to address several questions in this study,
the most prominent of these being the question of how exactly the sulphic
habitats attract chemosynthetic bacteria and the effect of this on the
surrounding benthic communities. Ultimately this paper contributes to a better
understanding of microbial ecology and biogeochemistry of the unique ecosystem
created by falling wood and the role of these hotspots.
In order to study this, the authors deployed four replicate
wood falls of a similar size, depth, weighting and branches at different
distances to an active cold seep of the Central Nile deep-sea fan (Eastern
Mediterranean). The replicates were revisited one year after deployment and
smaller parts of the wood were enclosed for analysis. This method is
interesting as the surrounding water was captured and analysed for sulphide
levels, which is a good method, however laterally think it is easy to see that
the clumsy useage of remote vehicles to collect the sample could easily brush
off a significant proportion of the surface bacteria present and indeed, the
authors do state that “Due
to the sampling strategy on board, very small or rare organisms may have not
been captured”. Subsequent biochemical tests performed include bacteria
cell counts, DNA analysis and Automated RISA (ARISA) fingerprinting performed.
The results of these tests show that despite major
differences in community between the wood replicates, a core bacterial
community is observable; predominantly sulphur reducing bacteria, which facilitates
the development of
sulfidic niches, building stepping stones for chemosynthetic life at these
allochthonous habitats in the deep sea.
REF: Bienhold
C, Pop Ristova P, Wenzhöfer F, Dittmar T, Boetius A (2013) How Deep-Sea Wood
Falls Sustain Chemosynthetic Life. PLoS ONE 8(1): e53590.
doi:10.1371/journal.pone.0053590
Accessed From: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0053590
Hi Harri
ReplyDeleteGreat blog, To my understanding there are very few organisms that can actually digest wood due to the cellulose and lignin which causes specific enzymes to be required, so not many organisms are able to use its energy as a carbon source, also the degradation of wood under anoxic conditions is very slow. I noticed that this paper talks a lot about wood boring bivalves, did the authors mention anything about how the wood boring bivalves actually found there way to the samples?
The colonisation of wood boring bivalves seems to be as quick as the colonisation of bacterial communities and they also seem to play a important role in initial degradation of the wood and faecal matter surrounding the logs. The bivalves also provide colonisation surfaces for other organisms that are attracted to the wood, therefore I consider them a keystone species in wood fall habitats, as they seem transform the energy stored in the wood into nutrients that can be digested by other animals, either as feed for predators and scavengers or by their faeces which are used by detritus-feeders. Do you think this steals some of the limelight from the microbes?
Cheers James
... But I think the microbes give the limelight! Animals that digest wood depend on symbiotic bacteria in the gut. For example, this has been well studied in the shipworms (bivalves), where the activity of the bacteria in breaking down lingo cellulose and fixing nitrogen has been identified. here's an interesting new paper on this, published last week. http://www.pnas.org/content/110/4/E295/1.full
DeleteThanks Colin i will focus my next review on this
DeleteHi all,
ReplyDeleteI was a little confused by your comments on my blog James so I thought we could move the discussion to Harri’s blog.
So, as I said to Matt….
“Currently there is only speculation with regard to how organisms localise these ephemeral habitats, I suspect it will be some sort of chemotactic response. There is also very little known about the reproduction and life history/dispersal patterns. It is certain the wood-boring bivalves depend on these types of falling events to maintain their population. Which kind of links onto evolution… It appears the bivalves have evolved to be expert colonisers in the desert of the deep sea.
This paper has provided additional evidence for the stepping stone hypothesis. The deep sea is often described as a stable oligotrophic habitat, in which case it is likely many deep sea organisms have evolved under stabilising selection for a constant environment. In the case of vent and seep organisms however, it is difficult to comprehend the evolution of organisms adapted to ephemeral, nutrient rich, habitats present on a background desert of the deep sea. The evolutionary picture becomes even more complex when the symbiotic relationships of many of the organisms are considered. Not only do the organism’s larvae have to make use of the stepping stones, but also their symbiotic bacteria and the microbes required to create the sulphidic niches.”
With regards to the question about stealing the limelight, I have to say I agree with Colin, the microbes are the limelight! I’ve just written a blog on a genome/proteome publication of one sulfate reducers which isn’t exactly enlightening but provides the data needed for further work.
James I look forward to reading your blog on cellulose/lignin degradation. Bienhold et al. (2013) found that after one year the dominant genus was Demequina, of which isolates were shown to be closely related to Cellulomonas fermentans (cellulolytic bacteria), indicating that the Demequina genus could be of major importance for wood degradation, and hence carbon cycling, in the deep sea. So I think it would be useful to investigate this genus further if interested in cellulose degradation.
Thanks,
Vicky
Thanks but i am stilltorn both ways, Animals that digest wood depend on symbiotic bacteria in the gut. But the symbiotic bacteria depend on the animals for the habitat! i will put some more emphasis on both arguements in my next review next week
ReplyDeleteJames did you ever end up reviewing the paper suggested by Colin? I can't seem to find it on the blog...
Delete