Physarum polycephalum macroplasmodium exhibits countermeasures against TiO2 nanoparticle toxicity: A physiological, biochemical, transcriptional, and metabolic perspective.

Concerns about the environmental and human health implications of TiO2 nanoparticles (nTiO2) are growing with their increased use in consumer and industrial products. Investigations of the underlying molecular mechanisms of nTiO2 tolerance in organisms will assist in countering nTiO2 toxicity. In this study, the countermeasures exhibited by the slime mold Physarum polycephalum macroplasmodium against nTiO2 toxicity were investigated from a physiological, transcriptional, and metabolic perspective. The results suggested that the countermeasures against nTiO2 exposure include gene-associated metabolic rearrangements in cellular pathways involved in amino acid, carbohydrate, and nucleic acid metabolism. Gene-associated nonmetabolic rearrangements involve processes such as DNA repair, DNA replication, and the cell cycle, and occur mainly when macroplasmodia are exposed to inhibitory doses of nTiO2. Interestingly, the growth of macroplasmodia and mammal cells was significantly restored by supplementation with a combination of responsive metabolites identified by metabolome analysis. Taken together, we report a novel model organism for the study of nTiO2 tolerance and provide insights into countermeasures taken by macroplasmodia in response to nTiO2 toxicity. Furthermore, we also present an approach to mitigate the effects of nTiO2 toxicity in cells by metabolic intervention.

Construction of a directional T vector for cloning PCR products and expression in Escherichia coli.

In order to clone PCR products and express them effectively in Escherichia coli, a directional cloning system was constructed by generating a T vector based on pQE-30Xa. The vector was prepared by inserting an XcmI cassette containing an endonuclease XcmI site, a kanamycin selective marker, a multiple-cloning-site (MCS) region and an opposite endonuclease XcmI site into the vector pQE-30Xa. The T vector pQE-T with single overhanging dT residues at both 3' ends was obtained by digesting with the restriction enzyme XcmI. For directional cloning, a BamHI site was introduced to the ends of the PCR products. A BamHI site was also located on the multiple cloning site of pQE-T. The PCR products were ligated with pQE-T. The directionally inserted recombinants were distinguished by using BamHI to digest the recombinants because there are two BamHI sites located on the both sides of PCR fragment. In order to identify the T-vector functions, the 14-3-3-ZsGreen and hRBP genes were amplified and a BamHI site was added to the ends of the genes to confirm this vector by ligation with pQE-T. Results showed that the 14-3-3-ZsGreen and hRBP were cloned to the vector pQE-T directly and corresponding proteins were successfully produced. It was here demonstrated that this directional vector is capable of gene cloning and is used to manipulate gene expression very easily. The methodology proposed here involves easy incorporation of the construct into other vectors in various hosts.