Response of Nodularia spumigena to pCO2 – Part 2: Exudation and extracellular enzyme activities

[摘要] The filamentous and diazotrophic cyanobacterium Nodulariaspumigena plays a major role in the productivity of the Baltic Seaas it forms extensive blooms regularly. Under phosphorus limiting conditionsNodularia spumigena have a high enzyme affinity fordissolved organic phosphorus (DOP) by production and release of alkalinephosphatase. Additionally, they are able to degrade proteinaceous compoundsby expressing the extracellular enzyme leucine aminopeptidase. As atmosphericCO₂ concentrations are increasing, we expect marine phytoplankton toexperience changes in several environmental parameters, including pH,temperature, and nutrient availability. The aim of this study was toinvestigate the combined effect of CO₂-induced changes in seawatercarbonate chemistry and of phosphate deficiency on the exudation of organicmatter, and its subsequent recycling by extracellular enzymes in aNodularia spumigena culture. Batch cultures ofNodularia spumigena were grown for 15 days under aerationwith low (180 μatm), medium (380 μatm), and high(780 μatm) CO₂ concentrations. Obtained pCO₂ levels inthe treatments were on median 315, 353, and 548 μatm CO₂,respectively. Extracellular enzyme activities as well as changes in organicand inorganic compound concentrations were monitored. CO₂treatment–related effects were identified for cyanobacterial growth, whichin turn influenced the concentration of mucinous substances and the recyclingof organic matter by extracellular enzymes. Biomass production was increasedby 56.5% and 90.7% in the medium and high pCO₂ treatment,respectively, compared to the low pCO₂ treatment. In total,significantly more mucinous substances accumulated in the high pCO₂treatment, reaching 363 μg Xeq L⁻¹ compared to269 μg Xeq L⁻¹ in the low pCO₂ treatment. However,cell-specific rates did not change. After phosphate depletion, theacquisition of P from DOP by alkaline phosphatase was significantly enhanced.Alkaline phosphatase activities were increased by factor 1.64 and 2.25,respectively, in the medium and high compared to the low pCO₂treatment. We hypothesise from our results that Nodulariaspumigena can grow faster under elevated pCO₂ by enhancingthe recycling of organic matter to acquire nutrients.

[学科分类] 地球化学与岩石