Program

The filamentous diazotrophic cyanobacterium Trichodesmium supplies 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 works reveal significant effects of ocean acidification on Trichodesmium under nutrient sufficient and iron-limited conditions. Few studies have examined the impacts of ocean acidification on Trichodesmium in batch culture with low P concentration. Here we used P-limited chemostat culture 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, while the particulate P quota was slightly higher. 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. In addition, comparative transcriptomic analysis showed that 189 genes are differentially expressed in response to acidification, which involved in urea metabolic process, kinase activity and transmembrane transport categories by Gene Ontology annotation analysis. Detailed data analysis is in progress to explore the underlying mechanisms of how Trichodesmium responds to elevated CO2 under P-limited conditions.