中国东海二甲基巯基丙酸内盐(DMSP)合成与降解菌的水平和垂直分布

Horizontal and vertical distribution of dimethylsulfoniopropionate (DMSP) producing and catabolizing bacteria in the East China Sea

摘要:

[目的] 二甲基巯基丙酸内盐（dimethylsulfoniopropionate，DMSP）及其裂解产物二甲基硫（dimethyl sulfide，DMS）在海洋硫循环中发挥重要作用。目前关于DMSP降解细菌的分布已有部分报道，但其合成细菌的研究才刚刚起步。本文拟研究中国东海水体DMSP合成与降解菌及基因的水平和垂直分布（1000 m水深）差异，分析其对环境梯度变化的响应。[方法] 利用流式细胞仪计数海水样品中微微型浮游生物的数量，通过荧光定量PCR和高通量测序手段定量测定DMSP合成基因（dsyB和mmtN）及物种、DMSP降解基因（dddP和dmdA）及物种的丰度，分析其在东海海域水平及垂直方向上的分布差异。[结果] 在垂直方向上，聚球藻、原绿球藻、微微型真核生物和异养细菌丰度随着水深的增加而先增后减，最大值位于30-50 m附近。表层（4 m左右）水体的DMSP合成及降解基因丰度最高，DMSP合成菌（如Alteromonas、Phaeobacter和Pelagibaca等）丰度也最高；随着水深增加，表层以下水体中DMSP合成及降解基因和物种丰度先增加后降低，峰值均出现在100-150 m；100 m以下，DMSP降解基因丰度迅速下降，而合成基因丰度下降程度较低，而且接近底层（>500 m）时出现随水深逐渐增加的趋势。水平方向二者变化规律不明显。浅层水体（≤100 m）和深层水体（>100 m）细菌群落结构存在显著差异，前者拥有较高比例的黄杆菌纲、放线菌纲和蓝细菌纲细菌，后者α变形菌纲细菌丰度较高。[结论] 100 m及以浅和100 m以深的浮游细菌群落结构存在显著差异。表层水体中DMSP合成和降解细菌的丰度最高，100-150 m水体次之，但100-1022 m介导的DMSP合成和降解细菌丰度的变化趋势有较大差别。

Abstract:

[Objective] Dimethylsulfoniopropionate (DMSP) and its cleavage product dimethyl sulfide (DMS) play important roles in sulfur cycle of the marine environment. At present, some studies focus on the distribution of DMSP catabolizing bacteria, while studies on DMSP producing bacteria are just beginning. The objective of this study was to analyze the horizontal and vertical (1000 m depth) distribution of DMSP producing and catabolizing bacteria as well as genes in the East China Sea, and to study their responses to environmental parameters. [Methods] We quantified the abundance of microplankton by using flow cytometry. We measured the abundance of DMSP producing (dsyB and mmtN) and catabolising (dddP and dmdA including C/2 and D/1 subclade) genes and organisms by qPCR and high-throughput amplicon sequencing. [Results] The abundances of Synechococcus, Prochlorococcus, picoeukaryotes and heterotrophic bacteria increased and then decreased in the vertical profile with maximum located at 30-50 m depth. Surface water samples (~4 m) possessed the highest abundance of DMSP producing and catabolizing genes as well as the abundance of DMSP producers (Alteromonas, Phaeobacter and Pelagibaca). With increasing water depth, the abundances of DMSP producing and catabolizing genes and organisms increased and then decreased with peak values at the 100-150 m depth. The abundance of DMSP catabolizing genes decreased rapidly in the water below 100 m depth. However, the abundance of DMSP producing genes decreased slowly in the water below 100 m depth and even increased in the waters from 500 m to 1022 m depth. In contrast, the abundances of DMSP producing and catabolizing genes and organisms did not show apparent horizontal distribution patterns. The bacterial community composition showed significant difference between shallow water (≤100 m) and deep water (>100 m), and the relative abundance of the Flavobacteriia, Actinobacteria and Cyanobacteria in the shallow water were higher than that in the deep water, in contrast with an opposite trend for the Alphaproteobacteria in the deep water. [Conclusion] Bacterial communities differed significantly between waters below and above the 100 m depth. The surface water possessed the highest abundance of DMSP producing and catabolizing bacteria, followed by the 100-150 m water, with DMSP producing and catabolizing bacteria showing significantly different variation trends in the waters of 100-1022 m depth.