In this study, high-throughput promoter screening was employed to optimize the heterologous expression of Mesorhizobium loti carbonic anhydrase (MlCA) in order to reduce the costs associated with carbon capture and storage (CCS). To simplify the complexity of traditional vectors, a fusion protein expression system was constructed using superfolder green fluorescent protein (sfGFP) and MlCA. The synthetic promoter library in Escherichia coli was utilized for efficient one-step screening. Based on fluorescence intensity on agar plates, a total of 143 monoclonal colonies were identified, forming a library with varying expression levels. The top four recombinants with the highest fluorescence intensity were selected, among which MlCA driven by the promoter 342042/+ exhibited the highest enzymatic activity, with a specific activity of the 34.6 Wilbur-Anderson units (WAU)/mg. Optimization experiments revealed that MlCA exhibited the best performance when cultured for 4 days under pH 7.0 and 40 ℃ conditions. The Michaelis constant (K_m·hdy) and maximum reaction rate (V_max·hdy) for CO₂ hydration were determined to be 62.46 mmol/L and 0.164 mmol/(s·L), respectively. For esterase hydrolysis, MlCA showed the K_m and V_max of 639.8 mmol/L and 0.035 mmol/(s·L), respectively. MlCA accelerated the CO₂ hydration process, promoting CO₂ mineralized into CaCO₃ within 9 min at low pH and room temperature conditions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses confirmed that the precipitated product was calcite. This study provides a low-cost and environmentally friendly alternative for future CCS applications.
Carbonic Anhydrases/biosynthesis* ; Promoter Regions, Genetic/genetics* ; Escherichia coli/metabolism* ; Carbon Sequestration ; Carbon Dioxide/metabolism* ; Green Fluorescent Proteins/metabolism*

Objective To investigate the effect of metformin on the growth of human anaplastic thyroid cancer cell HTh74Rdox which is doxorubicin resistant. Methods The HTh74Rdox was treated with different concentrations of metformin for 48 h. Cell morphology was observed by microscope, cell viability was tested by methylthiazoletetrazolium (MTT), cell apoptosis by annexin Ⅴ and propidium iodide double staining, the anti-oncogenic miRNA was assayed by realtime fluorescence quantitative PCR (RT-PCR), and the adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling pathway tested by western blot. Furthermore, the anti-oncogenic miRNAs were knockdown by miRNA inhibitors (miR-34a, miR-101, miR-125b, and miR-138 inhibitors) and the cells were treated by metformin for 48 h, after that, cell apoptosis was detected by annexin Ⅴ and propidium iodide double staining, the expression of protein related to AMPK/mTOR signaling pathway was detected by western blot. Results Metformin inhibited the growth of human anaplastic thyroid cancer cell HTh74Rdox in a concentration-dependent manner, the cell apoptosis was induced by metformin, and there was a significantly lower expression of miR-34a, miR-101, miR-125b, and miR-138 in the HTh74Rdox. However, the four above miRNAs were upregulated by metformin, and AMPK/mTOR pathway was also activated by metformin. When these miRNAs were suppressed by miR-inhibitors (miR-34a, miR-101, miR-125b, miR-138 inhibitors), the stimulating effect of apoptosis and AMPK/mTOR pathway by metformin were reversed. Conclusion Metformin significantly suppresses cell viability of human anaplastic thyroid cancer cell HTh74Rdox, and stimulates AMPK/mTOR pathway and apoptosis by upregulating the expressions of miR-34a, miR-101, miR-125b, miR-138 in HTh74Rdox cell.