Application of synechocystis in removal of cadmium ions

Abstract

The invention relates to application of synechocystis in removal of cadmium ions and a method for reducing cadmium ions in an environment, and the method comprises a step of culturing synechocystis in the environment. By means of the method, the concentration of free-state cadmium ions in the environment can be reduced to about 10 micrograms / L, and cadmium in the environment is greatly reduced after cadmium particles outside microalgae and cells are removed. Although the concentration of cadmium ions which can be treated by the method provided by the invention is relatively low and is 1mg / L or below, the concentration of the cadmium ions in the supernatant can be finally reduced to a very low value, so that the method can be used for further cadmium removal after primary cadmium removal of a water sample, and extremely low cadmium emission is realized.

Description

Technical Field

[0001] The present invention relates to the field of microalgae and environmental protection, and more particularly to the application of Synechocystis in removing cadmium ions. Background Art

[0002] Cadmium is a widely recognized non-essential heavy metal element that is extremely toxic and dangerous. Cadmium easily accumulates in organisms, causing significant acute and chronic toxic effects on biological health and the ecological environment, and is considered one of the most dangerous heavy metal pollutants. Cadmium and its compounds have been identified as Class I carcinogens by the internationally authoritative International Agency for Research on Cancer (IARC).

[0003] Long-term intake of cadmium-containing food or water can cause cadmium to accumulate in the human body, leading to a variety of health problems. The main symptoms of cadmium poisoning include kidney damage, manifested as proteinuria and renal failure; bone diseases, such as osteomalacia and osteoporosis, because cadmium replaces calcium in the bones, causing fragile bones; respiratory diseases, such as emphysema and chronic obstructive pulmonary disease; and reproductive system problems, such as male infertility and female miscarriage. Children and pregnant women are more sensitive to cadmium. Long-term exposure to cadmium-contaminated environments may affect children's growth and intellectual development, and may increase the risk of premature birth and low birth weight for pregnant women.

[0004] In addition, cadmium pollution has many impacts on the environment. In the soil, cadmium can be tightly bound to soil particles and is not easily washed away by rainwater, resulting in its long-term accumulation in the soil. This accumulation not only reduces the fertility of the soil, but also affects the growth of crops, and in turn affects the health of other organisms in the food chain. In water bodies, the presence of cadmium can hinder the growth and development of aquatic organisms and destroy the balance of aquatic ecosystems.

[0005] Therefore, the control of cadmium pollution is a very important issue in the fields of agriculture and environment.

[0006] Microalgae-mediated morphological transformation is an effective remediation method to reduce the bioavailability, water solubility and toxicity of heavy metals, but current studies have found that the efficiency of microalgae in transforming heavy metals is not high. Summary of the invention

[0007] During our research, we found that Synechocystis can internalize part of the cadmium ions in the environment into its cells and fix the other part into cadmium sulfide particles, thereby reducing the concentration of free cadmium ions to about 10μg / L.

[0008] Based on the above research, the present invention provides the use of Synechocystis in removing cadmium ions.

[0009] The present invention also provides a method for reducing cadmium ions in an environment, comprising the step of culturing Synechocystis in the environment.

[0010] In a specific embodiment, the environment is a water environment, and the cadmium ion concentration does not exceed 1 mg / L.

[0011] In a specific embodiment, the environment contains sulfate ions.

[0012] In a specific embodiment, the initial sulfate ion concentration in the environment is not less than 0.3 mM, and the culture time is not shorter than 4 days.

[0013] In a specific embodiment, the initial sulfate ion concentration in the environment is 0.075-0.3 mM, but sulfate ions are supplemented during the culture process, and the culture time is not shorter than 4 days.

[0014] In a specific embodiment, the Synechocystis sp. is Synechocystis sp. PCC 6803.

[0015] The present invention also provides a method for removing cadmium in the environment. After reducing the cadmium ions in the environment by the above method, the method further comprises the step of removing Synechocystis and cadmium particles.

[0016] By using the method of the present invention, the free cadmium ion concentration in the environment can be reduced to about 10 μg / L. After removing the microalgae and the extracellular cadmium particles, the cadmium in the environment is greatly reduced. Although the cadmium ion concentration that can be treated by the method provided by the present invention is relatively low, 1 mg / L or less, since the cadmium ion concentration in the supernatant can be reduced to a very low value in the end, it can be used for further cadmium removal after the initial cadmium removal of the water sample to achieve extremely low cadmium emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the growth curve of Synechocystis PCC 6803 under different cadmium concentrations.

[0018] Figure 2 The adsorption and accumulation process of algal cells exposed to 0.5 ppm Cd(II) and the removal rate of cadmium (a), as well as the percentage of cadmium in the cell, outside the cell and in the adsorbed state (b).

[0019] Figure 3 The cadmium accumulation in the cells of Synechocystis PCC 6803. Among them, ac: cadmium-exposed algae cells under TEM characterization; d: lattice fringes and diffraction gratings in particles; e: EDS energy spectrum of Cd and S elements; f: EDS energy spectrum of Cd and S elements; g: SEC-ICP-MS peak diagram.

[0020] Figure 4 The reactive oxygen species in each experimental condition.

[0021] Figure 5The distribution of cadmium in ionic, particulate and adsorbed states under low sulfur (a), medium sulfur (b) and high sulfur (c) conditions.

[0022] Figure 6 Peak diagrams of intracellular (a) and extracellular (b) CdS particles detected by SEC-ICP-MS.

[0023] Figure 7 This is the distribution of ionic cadmium and particulate cadmium inside and outside cells after sodium sulfate supplementation during the culture process. DETAILED DESCRIPTION

[0024] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0025] 1. Removal of cadmium by Synechocystis PCC 6803

[0026] Synechocystis PCC 6803 was inoculated in culture medium with different cadmium concentrations and cultured. Growth curves were drawn. The results are shown in Figure 1 As shown in the figure, when the cadmium ion concentration exceeds 5 mg / L, the growth of Synechocystis PCC 6803 is significantly affected, but when the cadmium ion concentration is 0.5-1 mg / L, the growth of Synechocystis PCC 6803 is good. It can be seen that Synechocystis PCC 6803 can well tolerate cadmium ion concentrations of 1 mg / L and below.

[0027] In further experiments, algae cells were exposed to 0.5 ppm Cd(II) to detect the adsorption and accumulation of cadmium, as well as the removal rate of cadmium. Figure 2 As shown, the cadmium-sensitive Synechocystis PCC 6803 can continuously accumulate cadmium in cells and has a high removal rate of cadmium in the culture environment.

[0028] 2. Characteristics of algal cells under cadmium exposure

[0029] Transmission electron microscopy was used to observe the algae cells exposed to cadmium. The cell morphology and internal subcellular structure were Figure 3 Under cadmium exposure, cadmium particles accumulated in algal cells. HRTEM-EDS results confirmed that Synechocystis PCC 6803 was able to convert cadmium ions into CdS in cells. SEC-I CP-MS showed that particle peaks appeared in cells one day after cadmium exposure, indicating that algal cells could quickly convert them into CdS particles.

[0030] Further studies showed that as the exposure time increased, the amount of intracellular CdS particles gradually increased and the particle size changed. In the early stage of exposure, no obvious CdS particles were found outside the cells. As the exposure time increased, the amount of CdS particles in the supernatant gradually increased.

[0031] 3. Effects of different sodium sulfate concentrations on cadmium internalization in algal cells

[0032] The magnesium sulfate in the culture medium was replaced with magnesium chloride of the same molar concentration, and then different concentrations of sodium sulfate were added to adjust the sulfate concentration in the culture medium. Cadmium exposure was performed in 20 ml of the culture system under low sulfur (1.5 μmol, i.e., sulfate concentration was 0.075 mM), medium sulfur (6 μmol, i.e., the molar concentration of magnesium sulfate in the original BG11 culture medium was 0.3 mM), and high sulfur (60 μmol, i.e., sulfate concentration was 3 mM). The results are shown in Figure 2. Figure 4 As shown in the figure, under low sulfur and cadmium stress conditions, the reactive oxygen species increased significantly, while under high sulfur and cadmium stress conditions, the ROS content decreased significantly. It can be seen that sulfate ions are beneficial for algal cells to resist cadmium stress.

[0033] Further experimental research was conducted to investigate the effect of sulfur concentration on the absorption and conversion of cadmium ions by algae cells. Figure 5 As shown in the figure, under medium and high sulfur conditions, the cadmium ions in the culture medium gradually decreased over time, while the particulate cadmium gradually increased. Especially under high sulfur conditions, the particulate cadmium was significantly higher than that under the other two conditions, while under low sulfur conditions, the cadmium ions in the culture medium showed a trend of first decreasing and then increasing. The particulate cadmium increased first and then decreased. This indicates that in the late exposure period, the lack of sulfur may cause the sulfur in the particulate cadmium to be released for reuse.

[0034] SEC-I CP-MS detected the effect of different sodium sulfate concentrations on the internalization of cadmium in algae cells. The results are as follows Figure 6 As shown, after 7 days of cadmium exposure, the peak time of intracellular CdS particles under medium and high sulfur conditions was earlier than that under low sulfur conditions, indicating that the CdS nanoparticles were larger ( Figure 6 a); The particle size of extracellular CdS nanoparticles is not affected by sulfur concentration ( Figure 6 b) The cadmium particles formed under high sulfur conditions are larger, which improves their stability.

[0035] The above experiments show that Synechocystis PCC 6803 can utilize the sulfur in the sulfate ions in the culture medium to react with Cd 2+ Combining into CdS particles and increasing the concentration of sulfate is beneficial for algal cells to remove cadmium ions in the environment and promote the conversion of cadmium ions into particulate cadmium, reducing the cadmium ion concentration in the environment to 10μg / L.

[0036] 4. The content of particulate cadmium increased significantly after sulfur supplementation during low-sulfur culture

[0037] After 7 days of low-sulfur culture, 1.5 μmol sodium sulfate was added. Figure 7As shown, the intracellular particle concentration increased by 274% after 14 days. The particle concentration in the supernatant increased by 86.4%. It can be seen that after supplementing with sulfate, the cells restored the ability to continuously convert cadmium ions into cadmium nanoparticles.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of Synechocystis in removing cadmium ions.

2. A method for reducing cadmium ions in an environment, characterized in that, The method comprises the step of culturing Synechocystis in the environment.

3. The method according to claim 2, characterized in that The environment is a water environment, and the cadmium ion concentration does not exceed 1 mg / L.

4. The method according to claim 3, characterized in that The environment contains sulfate ions.

5. The method according to claim 4, characterized in that The initial sulfate ion concentration in the environment is not less than 0.3 mM, and the culture time is not shorter than 4 days.

6. The method according to claim 4, characterized in that The initial sulfate ion concentration in the environment is 0.075-0.3 mM, but sulfate ions are added during the culture process, and the culture time is not shorter than 4 days.

7. The method according to any one of claims 2 to 6, characterized in that the Synechocystis sp. is Synechocystis sp. PCC 6803.

8. A method for removing cadmium from the environment, characterized in that: After reducing the cadmium ions in the environment by the method according to any one of claims 2 to 7, the method further comprises the step of removing Synechocystis and cadmium particles.

Images