Backgroud

Arsenic (As) is a highly toxic, metalloid element widely present in the environment. It possesses typical chara cteristics of heavy metals, such as persistence and non-biodegradability, and is normally classified and managed as a heavy metal. Among arsenic's four valence states (−3, 0, +3, and +5), arsenite (As(III)) and arsenate (As(V)) are the most common environmental species (with trivalent arsenic being more toxic). These forms can naturally convert into each other or undergo microbial-catalyzed transformations in the environment. Once concentrations exceed safety standards (Table 1, take rice as an example), they pose serious threats to both aquatic ecosystems and human health. The hazards of arsenic contamination to human health are significant; therefore, excessive intake of arsenic-containing foods can lead to arsenic poisoning. Initial symptoms include dermatitis, physical weakness, lethargy, anorexia, nausea, vomiting, and diarrhea. As poisoning progresses, acute diarrhea, edema, skin pigmentation, arsenic-induced melanosis, hyperkeratosis, hepatomegaly, and cancers of the respiratory system and skin may develop. Concurrently, the U.S. Environmental Protection Agency (EPA) has classified arsenic as a potential human carcinogen.

Arsenic Contamination Risk Screening Values for Rice Soils at Different pH Ranges

The primary sources of arsenic pollution include the widespread use of arsenic-containing pesticides and impacts from specific mining areas and industrial activities. The secondary sources include natural phenomena such as volcanic eruptions and forest fires. Arsenic-contaminated soil near mining areas, industrial pollution zones, volcanic deposits, and forest fire sites can be washed into rivers and groundwater by rainfall. Its distribution is also quite extensive, as shown in Figure 1.

Below are two primary ways arsenic may harm us. ① Drinking water sources. When groundwater or rivers contaminated by arsenic are used as drinking water sources, human consumption of water containing excessive arsenic levels poses health risks. ② Transmission through the food chain. When crops are irrigated with water contaminated with arsenic, this toxic substance is transferred to humans through the food chain. For instance, rice exhibits strong adsorption and accumulation of arsenic, particularly in its sprouts and grains. This characteristic leads to arsenic enrichment in rice grains. Consuming rice with arsenic levels exceeding 0.2 mg/kg can cause arsenic poisoning. Certain livestock feed grown in arsenic-contaminated soil transfers accumulated arsenic to animals. When humans subsequently consume these animals, arsenic accumulates in our bodies, posing a threat. Simultaneously, marine foods like seafood also accumulate arsenic through the food chain, ultimately concentrating in human bodies. We also can see the picture below in Figure 2.

Our previous research on the endophytic bacterium Cupriavidus metallidurans CML2 in rice revealed its tolerance to multiple heavy metals, including the metalloid arsenic. Given the current state of arsenic pollution, we envision designing an arsenic biosensor to facilitate convenient and rapid detection of arsenic exceeding safe levels.

brief Introduction

To address the threats posed by arsenic ions (As³⁺) to the environment and human health, we have launched an innovative project based on synthetic biology. Our goal is to develop a new-type and high-efficiency biosensor that can accurately detect arsenic ions in water and convert concentration signals into intuitive fluorescent signals.

We present the "Rice Endophyte Arsenic Biosensor". This project utilizes a newly discovered rice endophyte species—Cupriavidus sp. CML2, and its unique ArsR protein serves as the arsenic ion-sensing element. We couple the ArsR protein with a green fluorescent protein (GFP) reporting system, enabling it to specifically recognize arsenic ions and convert the concentration signals of arsenic ions into quantifiable green fluorescent signals.

To further enhance the sensor's sensitivity and signal stability, we have designed a brand-new sfGFP self-assembly module. This module can reduce the expression of background signals, thereby significantly improving the signal-to-noise ratio. This ensures that the sensor can provide clear and reliable detection results even in environments with low arsenic concentrations.

Our project aims to create a rapid, low-cost, and easy-to-operate arsenic biosensor, providing a promising solution for environmental monitoring and drinking water safety. This sensor not only leverages the unique advantages of the new species but also improves sensing performance through innovative module design, laying a foundation for future research on bioremediation and environmental monitoring.

References