南海F-冷泉和冲绳海槽热液区可培养二甲基巯基丙酸内盐合成与降解细菌的分离鉴定及其多样性

Isolation, identification, and diversity analysis of culturable DMSP-synthesizing and-degrading bacteria in F-cold seep of the South China Sea and hydrothermal fields of the Okinawa Trough

摘要:

【目的】 冷泉和热液是海洋中典型的化能生态系统，其独特的理化特征孕育了特殊的微生物类群。二甲基巯基丙酸内盐(dimethylsulfoniopropionate, DMSP)是地球上最丰富的有机硫化合物之一，多种海洋细菌能够合成与降解DMSP，在驱动海洋碳、硫元素循环过程中发挥重要作用。本研究对南海F-冷泉和冲绳海槽热液区的DMSP合成与降解细菌进行了分离鉴定，分析其多样性与分布，拓展了对海洋中DMSP代谢细菌的认识。【方法】 选取南海F-冷泉和冲绳海槽Yaeyama Knoll热液区不同深度水体、沉积物和动物为研究对象，利用3种富集培养基(甲硫氨酸添加、高盐低氮条件用于富集DMSP合成细菌，DMSP添加用于富集DMSP降解细菌)和2216E分离培养基进行细菌的富集与分离培养。通过16S rRNA基因测序确定菌株分类地位，并检测代表菌株的DMSP合成与降解能力。【结果】 本研究共获得874株可培养细菌，其中γ-变形菌纲(Gammaproteobacteria)为3种培养基中获得的优势纲；海杆菌属(Marinobacter)为优势属。经富集后冷泉样品的可培养菌株数量和多样性均高于热液样品。冷泉来源的14株DMSP合成细菌分属于7个属，其中5株属于近海螺旋菌属(Thalassospira)且含有DMSP合成基因mmtN，2株属于假栖大洋菌属(Pseudooceanicola)并含有dsyB。冷泉来源的130株DMSP降解细菌分属于39个属，谷氨酸杆菌属(Glutamicibacter)为最优势属(24株)且不含已知DMSP降解基因。热液区来源的DMSP合成细菌仅1株，降解细菌18株，均远少于冷泉样品。具有DMSP裂解途径的菌株占降解细菌总数(148株)的98.6%，其中55株裂解活性较强且以放线菌纲(Actinobacteria)为主。在40株不同种且DMSP降解能力较强的菌株中，9株含有已知的裂解基因，3株含有已知的脱甲基基因。【结论】 南海F-冷泉和冲绳海槽热液区存在丰富的DMSP合成与降解细菌，包括多种含有潜在新型DMSP合成/降解基因的细菌类群。本研究为进一步深入理解化能生态系统中微生物驱动的有机硫循环提供了基础。

关键词:二甲基巯基丙酸内盐;合成与降解;冷泉;热液区;细菌多样性

Abstract:

[Objective] Cold seeps and hydrothermal fields are typical chemosynthetic ecosystems in the ocean. With distinctive physicochemical properties, they harbor unique microbial communities. Dimethylsulfoniopropionate (DMSP), one of the most abundant organic sulfur-containing compounds on Earth, is synthesized and degraded by a variety of marine bacteria, which plays an important role in driving carbon and sulfur cycles in the ocean. In this study, we isolated and identified DMSP-synthesizing and degrading bacteria from the F-cold seep of the South China Sea and hydrothermal fields of the Okinawa Trough and analyzed their diversity and distribution, aiming to expand the understanding of these bacteria in the ocean. [Methods] Water, sediment, and animal samples were collected at different depths from both the F-cold seep of the South China Sea and the Yaeyama Knoll hydrothermal field of the Okinawa Trough. Three enrichment media (l-methionine addition and high salinity and low nitrogen for DMSP-synthesizing bacteria; DMSP addition for DMSP-degrading bacteria) and the 2216E medium were used for the enrichment and isolation of bacteria. The taxonomic status of strains was determined by 16S rRNA gene sequencing, and the abilities of representative strains to synthesize or degrade DMSP were assessed. [Results] A total of 874 culturable strains were obtained. Gammaproteobacteria emerged as the dominant class in the three media, and Marinobacter was the most abundant genus. The number and diversity of culturable strains obtained from cold seep samples after enrichment were higher than those from the hydrothermal field. The 14 strains of DMSP-synthesizing bacteria from the cold seep belonged to 7 genera, including 5 Thalassospira strains carrying the DMSP synthesis gene mmtN and 2 Pseudooceanicola strains carrying dsyB. A total of 130 DMSP-degrading bacterial strains were obtained from the cold seep, belonging to 39 genera, among which Glutamicibacter was the most abundant genus (24 strains) without known genes associated with DMSP degradation. There was only 1 strain of DMSP-synthetizing bacteria and 18 strains of DMSP-degrading bacteria from the hydrothermal field, both were much fewer than those from the cold seep. The strains with DMSP cleavage pathway accounted for 98.6% of the total DMSP-degrading strains (148), among which 55 strains had strong cleavage activity and were mainly Actinobacteria. Among the 40 strains with strong DMSP-degrading activity, 9 strains contained known cleavage genes and 3 strains contained known demethylation genes. [Conclusion] Abundant DMSP-synthesizing and -degrading bacteria exist in F-cold seep of the South China Sea and hydrothermal fields of the Okinawa Trough, including a variety of bacterial groups carrying potential novel DMSP synthesis/degradation genes. This study provides a basis for further understanding the microbial-driven organosulfur cycling in chemosynthetic ecosystems.

Key words:dimethylsulfoniopropionate;synthesis and degradation;cold seep;hydrothermal field;bacterial diversity