Abstract:

As one of the most abundant organic sulfur compounds in the oceans, dimethylsulfoniopropionate (DMSP) has important physiological and ecological functions in phytoplankton cells and is also an important nutrient for marine microorganisms. Dimethyl sulfide (DMS) is produced during DMSP decomposition, and is also the most important source of volatile organic sulfide in a reduced state in the oceans. Therefore, the metabolism of DMSP plays an important role in the global sulfur cycle. Bacteria can degrade DMSP in seawater through demethylation and cleavage pathways, thus determining whether sulfur elements enter the microbial food web in the form of sulfur-containing proteins or enter the atmosphere as DMS. To date, there have been few reports on bacterial degradation of DMSP in high-latitude Arctic waters. Demethylase gene dmdA and lyase gene dddP are involved in the two major pathways of DMSP degradation. We examined abundance and distribution of these two genes in the waters of Kongsfjorden in the Arctic in summer 2015 and 2016 using quantitative polymerase chain reaction (qPCR). Average abundance ratios of DMSP-degrading enzyme genes (dmdA and dddP) to 16S rRNA genes in seawater were 0.25%±0.31%, 0.32%±0.58%, respectively. Measurements along transects from the outer to the inner fjord indicate that relative abundances of dmdA and dddP in surface waters were lower in the outer fjord and increased towards the inner fjord in 2015, with the exception of the dddP gene at the K5 site. However, in 2016, there was no obvious trend of relative abundance of dddP gene in surface waters in the fjord; relative abundance of dddP gene in deep waters was higher in the outer fjord and decreased towards the inner fjord. Abundance of bacterioplankton containing DMSP degradation genes was very low in Kongsfjorden in summer. There were large spatial and temporal variations in the distribution of DMSP-degrading bacteria that are involved in different DMSP catabolism pathways. Further studies are needed to improve our understanding of bacterial DMSP degradation in Kongsfjorden and the ecological role of these bacteria in the local sulfur cycle.

Key words: quantitative fluorescence PCR, Arctic Kongsfjorden, dmdA, dddP