ABSTRACT

The concentration of nitrate (NO³⁻) in Narragansett Bay has been shown to undergo considerable temporal and spatial variation. However, the dynamics of this flux has never been monitored on a fine-scale (<100 m, < 1 d) or in real-time. Whole-cell bio-reporters are promising candidates for low cost environmental sensing of bioavailable nutrients. Yet difficulties remain in creating sensors for long term deployment in the marine environment. This paper describes the creation and validation of a low-cost sensor using a self-bioluminescent strain of the cyanobacteria Synechococcus elongatus pcc 7942 for the direct measurement of bioavailable nitrate. Nitrate bioavailability was measured by monitoring light emission from a luxAB based promotor fusion to glnA using a light to frequency sensor and single board microcontroller. Sensor designs are presented in this manuscript with specific focus on storage, cell viability, and compatibility with the marine environment. Sensors were able to consistently assess nitrate standards as low as 1 ppm (16.3 μM). Using a wavelet denoising approach to reduce white noise and hardware noise, nitrate detection of standards as low as 0.037 ppm (0.65 μM) was achieved. Good sensitivity and low cost make these sensors ideal candidates for continuous monitoring of biological nitrates in estuarine systems.

摘要

^{Narragansett 湾的硝酸盐 (NO 3-} )浓度已被证明经历了相当大的时间和空间变化。然而，这种通量的动态从未在精细尺度（<100 m，< 1 d）或实时监测。全细胞生物报告器是生物可利用营养素的低成本环境传感的有希望的候选者。然而，在制造用于在海洋环境中长期部署的传感器方面仍然存在困难。本文介绍了使用蓝藻细长聚球藻 pcc的自发光菌株创建和验证低成本传感器7942 用于直接测量生物可利用的硝酸盐。通过使用光频率传感器和单板微控制器监测从基于 luxAB 的启动子融合到 glnA 的光发射来测量硝酸盐生物利用度。本手稿中介绍了传感器设计，特别关注存储、细胞活力和与海洋环境的兼容性。传感器能够持续评估低至 1 ppm (16.3 μM) 的硝酸盐标准。使用小波去噪方法来降低白噪声和硬件噪声，实现了低至 0.037 ppm (0.65 μM) 标准的硝酸盐检测。良好的灵敏度和低成本使这些传感器成为连续监测河口系统中生物硝酸盐的理想选择。