A New Highly Sensitive Method to Assess Respiration Rates and Kinetics of Natural Planktonic Communities by Use of the Switchable Trace Oxygen Sensor and Reduced Oxygen Concentrations

Oxygen respiration rates in pelagic environments are often difficult to quantify as the resolutions of our methods for O2 concentration determination are marginal for observing significant decreases during bottle incubations of less than 24 hours. Here we present the assessment of a new highly sensitive method, that combine Switchable Trace Oxygen (STOX) sensors and all-glass bottle incubations, where the O2 concentration was artificially lowered. The detection limit of respiration rate by this method is inversely proportional to the O2 concentration, down to <2 nmol L−1 h−1 for water with an initial O2 concentration of 500 nmol L−1. The method was tested in Danish coastal waters and in oceanic hypoxic waters. It proved to give precise measurements also with low oxygen consumption rates (∼7 nmol L−1 h−1), and to significantly decrease the time required for incubations (≤14 hours) compared to traditional methods. This method provides continuous real time measurements, allowing for a number of diverse possibilities, such as modeling the rate of oxygen decrease to obtain kinetic parameters. Our data revealed apparent half-saturation concentrations (Km values) one order of magnitude lower than previously reported for marine bacteria, varying between 66 and 234 nmol L−1 O2. Km values vary between different microbial planktonic communities, but our data show that it is possible to measure reliable respiration rates at concentrations ∼0.5–1 µmol L−1 O2 that are comparable to the ones measured at full air saturation.

海洋浮游环境中的氧气呼吸速率往往难以量化，因现有氧气浓度测定方法的分辨率不足以在小于24小时的瓶式培养过程中观测到显著的氧气浓度下降。本研究针对一种结合可切换痕量氧气（Switchable Trace Oxygen, STOX）传感器与全玻璃瓶式培养的新型高灵敏度方法展开评估，该方法可人为降低培养体系内的氧气浓度。该方法测得的呼吸速率检测限与氧气浓度呈反比，当初始氧气浓度为500 nmol L⁻¹时，检测限可低至<2 nmol L⁻¹ h⁻¹。该方法已在丹麦近岸海域及海洋低氧海域开展测试，结果表明其即便在低耗氧速率（约7 nmol L⁻¹ h⁻¹）下仍可获得精准测量结果，且相较于传统方法，培养所需时长可显著缩短至≤14小时。该方法可实现连续实时测量，可为诸多研究场景提供多样可能性，例如通过模拟氧气消耗速率以获取动力学参数。本研究数据显示，针对海洋细菌的表观半饱和浓度（Km值）较此前报道低一个数量级，其范围介于66至234 nmol L⁻¹ O₂。不同浮游微生物群落的Km值存在差异，但本研究数据表明，在约0.5–1 µmol L⁻¹ O₂的浓度下仍可测得可靠的呼吸速率，其结果与空气饱和浓度下测得的呼吸速率相当。