Diversity of bacterial DMSP degradation genes in surface seawater of Arctic Kongsfjorden

Dimethylsulfoniopropionate (DMSP) is a readily produced source of organic sulphur and is abundant in all oceanic bodies of water plus many of the smaller bodies of water like inland seas in fjords. DMSP is usually produced by many phytoplankton. As the phytoplankton continuously produce this chemical it leaches out of the cells into the water column where it is rapidly degraded by bacteria using either the cleavage method to produce dimethylsulfide (DMS) or by demethylation to produce 3-methylmercaptopropionate (MMPA). Different bacterial genes code for each of these different processes.

In this study three of the genes encoding for the degradation of DMSP were measured dmdA coding for bacterial demethylation and both dddL and dddP coding for DMS production. The dmdA genes where found to be confined to bacteria within the Roseobacter clade and the dddL gene was confined more specifically to the genus Sulfitobacter. The dddP gene again was mainly found within the Roseobacter clade but there were a few genes found associated with both Alphaproteobacter and Gammaproteobacter. The prokaryotic community that is found in Kongsfjorden is dominated by bacteria with much lower levels of archaea in the survey areas.

3 sites placed around Kongsfjorden where sampled with only the surface water being sampled as this is the main area of DMSP production and where you are most likely to find any bacterial genes associated with DMSP breakdown. The researchers found that the highest amounts of bacteria present in the surface waters occurred during the months of May and July. The further up the fjord the sample sites went the detected levels of dddP and dddL dropped; to zero in the case of dddP. This shows that in shallower coastal waters the major route of DSMP degradation is by the demethylation process which in turn suggests the majority of the DMSP sulphur is assimilated by the bacteria.

This paper slightly alters the accepted view that most DMSP is degraded into DMS instead it shows that in shallower coastal waters most DMSP is demethylated into MMPA instead which would have the effect of reducing the amount of sulphate entering the atmosphere. Further studies would be needed to test whether this happens in all shallow coastal waters or whether it just occurs in Fjords and other semi-enclosed bodies of water and it could also test how deep into the water column that DMSP degradation genes are found.

Paper Reviewed

Zeng, Y. X., Qiao, Z. Y., Yu, Y., Li, H. R., & Luo, W. (2016). Diversity of bacterial dimethylsulfoniopropionate degradation genes in surface seawater of Arctic Kongsfjorden. Scientific Reports, 6. http://www.nature.com/articles/srep33031