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Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future
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Effects of Ocean Acidification on Trichodesmium IMS101 under Phosphorus Limited Condition
P-M5-11-S
Futing Zhang* , State Key Laboratory of Marine Environmental Science, Xiamen University
Haizheng Hong, State Key Laboratory of Marine Environmental Science, Xiamen University
Dalin Shi, State Key Laboratory of Marine Environmental Science, Xiamen University
Presenter Email: futing163479@stu.xmu.edu.cn |
| The filamentous diazotrophic cyanobacterium Trichodesmium introduces fixed nitrogen (N) to the N-depleted oligotrophic oceans where it inhabits. The growth and N2 fixation of Trichodesmium are often limited by the low availability of phosphorus (P) and/or iron in the vast regions of open oceans. Previous work mostly focus on the effect of ocean acidification on Trichodesmium under nutrient sufficient and iron-limited conditions. Here we used P-limited chemostats to show that the model strain Trichodesmium IMS101 contained less chlorophyll a, assimilated less carbon, and had lower nitrogen fixation rate per cell at high CO2. Consistently, the cellular particulate carbon (C) and N quota were significantly lower at high CO2. The particulate P quota, however, was slightly higher under acidified conditions due largely to the increase of inorganic polyphosphate (polyP), which likely plays an important role in cytosolic pH homeostasis. The resulting C:P and N:P ratios were significantly lower under high CO2 conditions, suggesting that Trichodesmium fixed less C and N per quota of P under P-limited conditions in response to increasing CO2. Comparative transcriptomic analysis showed that 189 genes are differentially expressed in response to acidification, including those involved in P acquisition and metabolism. For example, acidification led to up-regulatiuon of Tery_0365-68 a putative phosphonate or phosphite uptake system genes and down-regulation of Tery_1770 the inorganic polyphosphate/ATP-NAD kinase. Our study suggested that to cope with acidified conditions Trichodesmium increased P uptake but decreased NADP(H) utilization to maintain a high polyP content for maintaining cytosolic pH homeostasis. |
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