A novel cohabitation between two diazotrophic cyanobacteria in the oligotrophic ocean
A novel cohabitation between two diazotrophic cyanobacteria in the oligotrophic ocean
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DOI：
10.1038/ismej.2014.186
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发表时间：
2015-04-01
期刊：
影响因子：
11
通讯作者：
Webb, Eric A.
中科院分区：
文献类型：
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作者：
Momper, Lily M.;Reese, Brandi Kiel;Webb, Eric A.
蓝藻属 Trichodesmium 具有重要的生物地球化学意义，因为它在寡营养海洋中具有固氮和固碳的双重作用。毛藻物种形成的菌落可以很容易地从水柱中富集，并用于船上速率测量，以估计它们对海洋碳和氮预算的贡献。 2010 年 7 月，在夏威夷群岛附近贫营养的北太平洋副热带环流中，在落射荧光显微镜下检查了毛毛藻泡状菌落的特定形态，发现其中含有菌落内生物，形态学上鉴定为异囊固氮蓝细菌 Calothrix。利用从这次航行中获得的单藻富集，我们表明这些类似Caothrix的异囊蓝生物（hetDA为“与Trichodesmium相关的异囊固氮生物”）在昼夜周期中固氮（最大程度在光周期中间，在黑暗中可检测到最小值）。对富集的 nifH 进行基因测序表明，该属可能无法使用当前描述的定量 PCR (qPCR) 引物进行定量。在分离株序列的指导下，设计了新的 hetDA 特异性引物，随后对环境样品进行 qPCR 检测，从地表水到 150 m 深处检测到了这种固氮菌，达到的密度高达类似于 9 x 10(3) l(-1)。根据nifH和16S rRNA基因序列的系统发育相关性，预测这种蓝藻生物的分布不仅限于北太平洋亚热带，还可能到达南太平洋和大西洋。因此，这种以前未被认识到的共生现象，如果它超出了贫营养的北太平洋，可能会影响世界海洋中来自毛藻的固氮预算。
The cyanobacterial genus Trichodesmium is biogeochemically significant because of its dual role in nitrogen and carbon fixation in the oligotrophic ocean. Trichodesmium species form colonies that can be easily enriched from the water column and used for shipboard rate measurements to estimate their contribution to oceanic carbon and nitrogen budgets. During a July 2010 cruise near the Hawaiian Islands in the oligotrophic North Pacific Subtropical Gyre, a specific morphology of Trichodesmium puff-form colonies were examined under epifluorescent microscopy and found to harbor a colonial endobiont, morphologically identified as the heterocystous diazotrophic cyanobacterium Calothrix. Using unialgal enrichments obtained from this cruise, we show that these Calothrix-like heterocystous cyanobionts (hetDA for 'Trichodesmium-associated heterocystous diazotroph') fix nitrogen on a diurnal cycle (maximally in the middle of the light cycle with a detectable minimum in the dark). Gene sequencing of nifH from the enrichments revealed that this genus was likely not quantified using currently described quantitative PCR (qPCR) primers. Guided by the sequence from the isolate, new hetDA-specific primers were designed and subsequent qPCR of environmental samples detected this diazotroph from surface water to a depth of 150 m, reaching densities up to similar to 9 x 10(3) l(-1). Based on phylogenetic relatedness of nifH and 16S rRNA gene sequences, it is predicted that the distribution of this cyanobiont is not limited to subtropical North Pacific but likely reaches to the South Pacific and Atlantic Oceans. Therefore, this previously unrecognized cohabitation, if it reaches beyond the oligotrophic North Pacific, could potentially influence Trichodesmium-derived nitrogen fixation budgets in the world ocean.