Enhancing high-efficient cadmium biosorption of Escherichia coli via cell surface displaying metallothionien CUP1

Cadmium (Cd) is one of the common heavy metal pollutants in soil, which can induce various diseases and pose a serious threat to human health. Metallothioneins (MTs) are well-known for their excellent metal binding ability due to a high content of cysteine, which has great potential for heavy metal chelation. In this study, we used the Escherichia coli (E. coli) surface display system LPP-OmpA to construct a recombinant plasmid pBSD-LCF encoding LPP-OmpA-CUP1-Flag fusion protein. Then we displayed the metallothionein CUP1 from Saccharomyces cerevisiae on E. coli DH5α surface for Cd removing. The feasibility of surface display of metallothionein CUP1 in recombinant E. coli DH5α (pBSD-LCF) by Lpp-OmpA system was proved by flow cytometry and western blot analysis, and the specificity of the fusion protein in the recombinant strain was also verified. The results showed that the Cd2+ resistance capacity of DH5α (pBSD-LCF) was highly enhanced by about 200%. Fourier-transform infrared spectroscopy showed that sulfhydryl and sulfonyl groups were involved in Cd2+ binding to cell surface of DH5α (pBSD-LCF). Meanwhile, Cd removal rate by DH5α (pBSD-LCF) was promoted to 95.2%. Thus, the recombinant strain E. coli DH5α (pBSD-LCF) can effectively chelate environmental metals, and the cell surface expression of metallothionein on E. coli can provide new ideas and directions for heavy metals remediation.

Synthetic biology toolkits and applications in Saccharomyces cerevisiae

Synthetic biologists construct biological components and systems to look into biological phenomena and drive a myriad of practical applications that aim to tackle current global challenges in energy, healthcare and the environment. While most tools have been established in bacteria, particularly Escherichia coli, recent years have seen parallel developments in the model yeast strain Saccharomyces cerevisiae, one of the most well-understood eukaryotic biological system. Here, we outline the latest advances in yeast synthetic biology tools based on a framework of abstraction hierarchies of parts, circuits and genomes. In brief, the creation and characterization of biological parts are explored at the transcriptional, translational and post-translational levels. Using characterized parts as building block units, the designing of functional circuits is elaborated with examples. In addition, the status and potential applications of synthetic genomes as a genome level platform for biological system construction are also discussed. In addition to the development of a toolkit, we describe how those tools have been applied in the areas of drug production and screening, study of disease mechanisms, pollutant sensing and bioremediation. Finally, we provide a future outlook of yeast as a workhorse of eukaryotic genetics and a chosen chassis in this field.

The cadmium tolerance in Saccharomyces cerevisiae depends on inorganic polyphosphate

The sensitivity to cadmium (Cd(II)), an important environmental pollutant, was studied in the cells of Saccharomyces cerevisiae strains with genetically altered polyphosphate metabolism. The strains overproducing polyphosphatases PPX1 or PPN1 were more sensitive to Cd(II) than the parent strain. The half maximal inhibitory concentrations were 0.02 and 0.05 mM for the transformants and the parent strain, respectively. Transformant strains cultivated in the presence of Cd(II) show a decrease in the content of short-chained cytosolic acid soluble polyphosphate. The role of this polyphosphate fraction in detoxification of heavy metal ions is discussed.