Phosphorus storage and utilization strategies of two bloom-forming freshwater cyanobacteria

The inter-relationships between cellular phosphorus (P) storage, dissolved inorganic P (DIP) uptake affinity, alkaline phosphatase activity (APA), and dissolved inorganic nitrogen (DIN) concentrations were studied in two ubiquitous diazotrophic freshwater cyanobacteria, Raphidiopsis raciborskii (six strains) and Chrysosporum ovalisporum (two strains). DIP uptake kinetics were measured using rates of incorporation of the radio-isotope, 33P, and APA as a proxy for DOP-ester utilization. The study showed that DIP uptake of individual strains followed Michaelis-Menten kinetics (modified in our study to incorporate cellular P quotas), but differed with DIN and P availability, and between growth stages. High-affinity DIP uptake and APA were activated below a P quota threshold of ~0.01 µg P µg-1 C across the species and strains. C. ovalisporum had significantly higher APA and P quotas (per unit C and cell) but lower uptake affinity than R. raciborskii. Demand for DIP by C.ovalisporum increased..., We collected all the data from laboratory culture experiments on two diazotrophic cyanobacteria, Raphidiopsis raciborskii (six strains) and Chrysosporum ovalisporum (two strains), in response to different DIN and P availabilities. Dissolved inorganic P (DIP) uptake affinity, alkaline phosphatase activity (APA), photosynthetic yield, optical density at 750 nm wavelength (OD750), cell count (cell volume, number), cellular nutrient concentrations (carbon, N, and P), dissolved inorganic N and P (ammonium, nitrite/nitrate, phosphate) were measured over the duration of the experiments. We used R package “segmented” to run segment regression analysis to determine the threshold of cellular P quotas where there was an abrupt change in DIP uptake affinity and APA. We used MATLAB and high performancing computer (HPC) to run Monte Carlo simulations to determine the best fit of uptake kinetics, i.e., maximum uptake rates and half saturation constant of DIP uptake, in response to a given external DIP..., Codes are written in R and Matlab. Input files can be .csv files for the R codes, and .xlsx files for Matlab.本研究针对两种广布性固氮淡水蓝细菌——拉氏拟柱孢藻（Raphidiopsis raciborskii，共6株）与卵形孢囊藻（Chrysosporum ovalisporum，共2株），探究了细胞磷（P）储存、溶解性无机磷（DIP）摄取亲和力、碱性磷酸酶活性（APA）与溶解性无机氮（DIN）浓度之间的相互关系。研究通过放射性同位素³³P的掺入速率测定DIP摄取动力学，并以APA作为溶解性有机磷酯（DOP-ester）利用的替代表征。结果显示，各菌株的DIP摄取均符合米氏动力学（本研究对其进行修正，纳入细胞磷配额参数），且其摄取效率随DIN与P的可利用性以及生长阶段的不同而存在差异。在所有供试物种与菌株中，当细胞磷配额低于约0.01 μg P·μg⁻¹ C的阈值时，高亲和力DIP摄取与APA即被激活。卵形孢囊藻的APA与细胞磷配额（以单位碳与单个细胞计）均显著高于拉氏拟柱孢藻，但其DIP摄取亲和力则更低。卵形孢囊藻对DIP的需求随……提升。本研究收集了两种固氮淡水蓝细菌（拉氏拟柱孢藻6株、卵形孢囊藻2株）在不同DIN与P可利用性条件下的实验室培养实验数据。实验周期内测定的指标包括：DIP摄取亲和力、APA、光合产率、750 nm波长下的光密度（OD750）、细胞计数（细胞体积与数量）、细胞营养盐浓度（碳、氮、磷）以及溶解性无机氮与磷（铵态氮、亚硝态氮/硝态氮、磷酸盐）。本研究使用R语言"segmented"包开展分段回归分析，以确定DIP摄取亲和力与APA发生突变时的细胞磷配额阈值。本研究使用MATLAB与高性能计算机（HPC）开展蒙特卡洛模拟，以确定在给定外源DIP条件下摄取动力学的最优拟合参数，即DIP摄取的最大速率与半饱和常数……。相关代码使用R与MATLAB编写：R代码的输入文件格式为.csv文件，MATLAB代码的输入文件格式为.xlsx文件。