Background

Arsenic in nature is widely present in groundwater, atmosphere, soil and other environments. Hundreds of millions of people in more than 70 countries around the world face the threat of high arsenic groundwater. Long term drinking of high arsenic groundwater will lead to chronic Arsenic poisoning, cancer and serious harm to health^[1] .

Fig. 1 Spatial distribution of arsenic concentration (in ppb) in the Jianghan Plain^[2]

We come from Hubei province. In our local community, Jianghan Plain, people are literately suffering from high arsenic ground water. More than 73,500 inhabitants have been exposed to contaminated ground water, which has caused some arsenic poisoning incidents^[3]. The first event of As poisoning (six people had arsenical keratosis) in Jianghan Plain was reported in 2005, which found that the several villages with As concentrations in drinking water exceeding 0.05 mg/L constitute 43% (35 villages) of 81 villages in Xiantao City. Therefore, performing the health risk assessment regarding drinking and dermal contacting high As-contaminated groundwater in Jianghan Plain and understanding the potential threat for residents due to As intake from groundwater are indispensable^[8]. The detection and monitoring of arsenic in the environment has become a hot research direction in recent years.

Current Solution

Many methods have been reported to detect arsenic at low concentrations, such as chemiluminescent immunoassay, inductively coupled plasma optical emission spectrometry (ICP-OES), and atomic absorption spectrometry (AAS)^[4]. However, these methods often require complicated and expensive instruments and trained professionals to pretreat and analyze samples, making them hard to use in-situ. To overcome these limitations, biosensors using enzymes, antibodies, and microorganism cells have garnered interest for use in the detection of arsenic in drinking water. Especially, whole-cell biosensors (WCBs) have been studied for the specific and sensitive detection of toxic heavy metal ions^[5].

Our Project

In 2023, the CUG-China team is preparing to develop an arsenic biosensor with a electrochemically active biofilms (EABs) based biosensor. EABs are formed by electroactive bacteria capable of exchanging electrons with electrodes. The self-immobilization, self-sustainability, and high robustness of EABs make EAB-enabled biosensors show promise in environmental applications, such as water quality monitoring. This year, our team utilized the electroactive microorganism Shewanella oneidensis MR-1 as the chassis cell to construct an EAB-based biosensor for sensitive and specific detection of arsenic in the Microbial fuel cells (MFC)^[6].

Fig. 2 EAB-based biosensors^[7]

To achieve the goal of arsenic detection, we engineered the biofilm of S. oneidensis MR-1 by knocking out its ptpA gene that is associated with the biosynthesis of extracellular polysaccharides, resulting in a more conductive S. oneidensis MR-1 biofilm formed on the anode of MFCs. The enhanced conductivity of S. oneidensis MR-1 biofilm improved the sensitivity of EAB-based biosensor for arsenic detection.

Besides, we designed a arsenic specific sensing gene circuit to improve the specificity of out biosensor. By transferring this gene circuit into double deletion strains ΔptpAmtrC or ΔptpAcymA, the presence of arsenic can be converted to increased electrical signals, as arsenic can promote the expression of cymA or mtrC to recover the ability of EET in S. oneidensis MR-1.

To further optimize the biosensor, we construct a self-amplifier system that does not rely on exogenous inducers by modifing the LuxR protein from Vibrio fischeri. We combined this self-amplifier system with the arsenic sensing circuit to enhance the sensitivity and specificity of the biosensor.

Reference