Dimethylsulfoniopropionate (DMSP) is an organic sulfur molecule known for its role in climate regulation. Previous studies have shown that zooxanthellae (genus Symbiodinium) abundance found in cnidarian species are correlated to DMSP concentrations among the host, which are further available for coral-associated bacteria that metabolize it into dimethylsulfide (DMS) – the gas implicated in climate regulation. Two DMSP degradation pathways may occur, one involving phytoplankton or bacteria using enzymes (DMSP lyases) and the other involving only bacteria which carry out an initial demethylation of DMSP to methylmercaptopropionate (MMPA). This initial step involves a single gene, DMSP demethylase (dmdA). DMSP has been thought to act as an antioxidant towards marine algae, helping corals survive periods of thermal stress. Mucus-associated microbes have also been seen to play an important role in protecting the host coral against pathogens. The surface mucus is also subjected to high levels of DMSP which leaks from coral tissues. Furthermore, there is a possibility for DMSP degradation to take place in the surface mucus layer in corals, where coral associated DMSP-demethylating microbial communities perform this.
This study by Frade
et al. (2015) looks at the link between coral DMSP availability and the
community dynamics of DMSP-demethylating bacteria found in the surface mucus of
corals. This was done by first determining in situ DMSP concentrations in the
tissue of three common reef-building coral species (Meandrina meandrites, Porites
astreoides and Siderastrea sidereal)
in relation to solar radiation intensity and desiccation stress (exposure to
air). Genetic analysis was used to investigate taxonomic affiliation and
relative abundance of mucus-associated bacterial assemblages harboring the gene
dmdA.
The results showed that DMSP varied with host
species-specific traits such as zooxanthellae cell abundance. It was mostly
seen that the occurrence of higher symbiont cell abundance as a cause for
increased amounts of DMSP in the tissue. Exposure to air caused a doubling of
their DMSP concentration, suggesting rapid de novo production of DMSP by the
coral symbiont, either by the zooxanthellae or the coral host itself, possibly
due to oxidative stress from thermal stress which further suggests the
molecules role as an antioxidant. A higher availability of DMSP corresponded to
a lower relative abundance of the dmdA
gene, however this was not seen throughout all host species suggesting distinct
DMSP microbial niches exist.
Overall, this study is the first to provide quantification
of dmdA gene assemblages in corals
and link it to changes in community dynamics of DMSP-degrading bacteria to DMSP
availability. It shows that DMSP is important in establishing links between
coral hosts and associated bacterial communities, with the possibility of
shifts in these communities and growth rates to depend on DMSP availability.
Further study should be done into correcting the assumptions (such as whether
changes in the relative abundance of dmdA
genes relate to the degree of adaptation) which may allow a more definitive
answer behind this study.
Frade, P. R. et al., 2015. Dimethylsulfoniopropionate
in corals and its interrelations with bacterial assemblages in coral surface
mucus. Environmental Chemistry, pp. A-K.
Given what we discussed from today's seminar (17th), do you think that the increased production of DMSP may be due to the increased chances of Vibrios and other opportunistic pathogens infecting the coral, as well as a response to thermal stress? Were any pathogens discussed in this paper?
ReplyDeleteThe conclusion of this paper states that DMSP mediates the regulation of microbes by the coral host, which goes against obviously what we talked about in the seminar on the 17th, how increased DMSP may lead to increased Vibrios. They did not talk about Pathogens in the paper, they only mentioned the phylogenetic affiliation of bacterial dmdA gene (Demethylase gene) assemblages, which showed that the gene was affiliated to Alphaproteobacteria closely. Because they only looked at bacteria associated with this gene and it's role in demethylising DMSP, I do believe further study should be taken in looking at including the coral holobiont. Relying solely on looking at this gene dmdA only provides one side of answers, rather than what other consequences of increase DMSP could lead to.
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