北极王湾夏季海水中DMSP降解基因的丰度及分布调查

ABUNDANCE AND DISTRIBUTION OF DIMETHYLSULFONIOPROPIONATE-DEGRADING GENES IN KONGSFJORDEN IN THE ARCTIC IN SUMMER

作为海洋中最丰富的有机含硫化合物之一,二甲基巯基丙酸内盐(DMSP)不仅在浮游植物细胞内具有重要的生理生化及生态功能,同时也是海洋微生物的重要营养物,其分解产物二甲基硫(DMS)还是海洋中最重要的还原态挥发性生源有机硫化物,因此DMSP的代谢在全球硫循环中扮演着重要角色。细菌可通过脱甲基与裂解这两条途径降解海水中的DMSP,从而决定硫元素是以含硫蛋白形式进入微生物食物网还是以DMS形式进入大气。截至目前,在高纬度北极海域开展的有关细菌降解DMSP的相关研究报道很少。本文采用荧光定量PCR技术,首次对北极王湾夏季(2015及2016年)海水中涉及细菌降解DMSP的两条主要代谢途径中的脱甲基酶基因dmdA及裂解酶基因dddP的丰度及分布进行了检测。结果显示,2015-2016年海水中DMSP降解酶基因(dmdA、dddP)与细菌16S rRNA基因的丰度比值的平均值分别为0.25%±0.31%、0.32%±0.58%。2015年水样中,除K5站位的dddP基因之外,表层水中dmdA及dddP的丰度相对值从湾口至湾内均呈递增趋势。但2016年的结果却显示出很大差异:湾口附近dmdA基因丰度相对值总体高于湾内;表层水中的dddP基因丰度相对值变化趋势不明显,而深层水中dddP基因丰度相对值从湾口到湾内总体呈递减趋势。本次研究的结果初步表明,含有DMSP降解基因的浮游细菌在王湾夏季水体中丰度很低,而且参与不同代谢途径的DMSP降解菌在海水中的时空分布存在很大变化。对于王湾水域中细菌参与DMSP分解代谢及其在当地硫元素循环中的生态地位的进一步认识,尚待后续研究工作的深入开展。

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.