Centre for Ecology and Evolution in Microbial Model Systems (EEMiS), Linnaeus University, Kalmar, Sweden.
Present address: Department of Biology/Aquatic ecology, Lund University, Sölvesgatan 37, 223 62, Lund, Sweden.
Microbiome. 2017 Aug 9;5(1):96. doi: 10.1186/s40168-017-0311-5.
A key characteristic of eutrophication in coastal seas is the expansion of hypoxic bottom waters, often referred to as 'dead zones'. One proposed remediation strategy for coastal dead zones in the Baltic Sea is to mix the water column using pump stations, circulating oxygenated water to the sea bottom. Although microbial metabolism in the sediment surface is recognized as key in regulating bulk chemical fluxes, it remains unknown how the microbial community and its metabolic processes are influenced by shifts in oxygen availability. Here, coastal Baltic Sea sediments sampled from oxic and anoxic sites, plus an intermediate area subjected to episodic oxygenation, were experimentally exposed to oxygen shifts. Chemical, 16S rRNA gene, metagenomic, and metatranscriptomic analyses were conducted to investigate changes in chemistry fluxes, microbial community structure, and metabolic functions in the sediment surface.
Compared to anoxic controls, oxygenation of anoxic sediment resulted in a proliferation of bacterial populations in the facultative anaerobic genus Sulfurovum that are capable of oxidizing toxic sulfide. Furthermore, the oxygenated sediment had higher amounts of RNA transcripts annotated as sqr, fccB, and dsrA involved in sulfide oxidation. In addition, the importance of cryptic sulfur cycling was highlighted by the oxidative genes listed above as well as dsvA, ttrB, dmsA, and ddhAB that encode reductive processes being identified in anoxic and intermediate sediments turned oxic. In particular, the intermediate site sediments responded differently upon oxygenation compared to the anoxic and oxic site sediments. This included a microbial community composition with more habitat generalists, lower amounts of RNA transcripts attributed to methane oxidation, and a reduced rate of organic matter degradation.
These novel data emphasize that genetic expression analyses has the power to identify key molecular mechanisms that regulate microbial community responses upon oxygenation of dead zones. Moreover, these results highlight that microbial responses, and therefore ultimately remediation efforts, depend largely on the oxygenation history of sites. Furthermore, it was shown that re-oxygenation efforts to remediate dead zones could ultimately be facilitated by in situ microbial molecular mechanisms involved in removal of toxic HS and the potent greenhouse gas methane.
沿海海域富营养化的一个关键特征是缺氧底层水的扩张，通常称为“死亡区”。波罗的海沿海死亡区的一种拟议修复策略是使用泵站混合水柱，将充氧水循环到海底。尽管人们认识到沉积物表面的微生物代谢是调节整体化学通量的关键，但微生物群落及其代谢过程如何受到氧气供应变化的影响仍不清楚。在这里，从含氧和缺氧地点以及间歇性充氧的中间区域采集了波罗的海沿海沉积物样本，进行了实验性氧气变化暴露。进行了化学、16S rRNA 基因、宏基因组和宏转录组分析，以研究沉积物表面化学通量、微生物群落结构和代谢功能的变化。
与缺氧对照相比，缺氧沉积物的氧气化导致能够氧化有毒硫化物的兼性厌氧属 Sulfurovum 的细菌种群增殖。此外，充氧沉积物中具有更多数量的 RNA 转录本被注释为参与硫化物氧化的 sqr、fccB 和 dsrA。此外，通过上述氧化基因以及编码还原过程的 dsvA、ttrB、dmsA 和 ddhAB 确定了在缺氧和中间沉积物中识别出的隐蔽硫循环的重要性，强调了隐蔽硫循环的重要性。特别是，中间位置的沉积物在氧气化时的反应与缺氧和含氧位置的沉积物不同。这包括具有更多栖息地通才的微生物群落组成、归因于甲烷氧化的 RNA 转录本数量减少，以及有机物降解率降低。
这些新数据强调了基因表达分析具有识别调节微生物群落对死区氧气化反应的关键分子机制的能力。此外，这些结果表明，微生物反应，因此最终的修复努力，在很大程度上取决于地点的氧气化历史。此外，事实证明，通过参与去除有毒 HS 和潜在温室气体甲烷的原位微生物分子机制，可以最终促进死区的再充氧修复工作。
