Pursuit of chlorovirus genetic transformation and CRISPR/Cas9-mediated gene editing

Genetic and molecular modifications of the large dsDNA chloroviruses, with genomes of 290 to 370 kb, would expedite studies to elucidate the functions of both identified and unidentified virus-encoded proteins. These plaque-forming viruses replicate in certain unicellular, eukaryotic chlorella-like green algae. However, to date, only a few of these algal species and virtually none of their viruses have been genetically manipulated due to lack of practical methods for genetic transformation and genome editing. Attempts at using Agrobacterium-mediated transfection of chlorovirus host Chlorella variabilis NC64A with a specially-designed binary vector resulted in successful transgenic cell selection based on expression of a hygromycin-resistance gene, initial expression of a green fluorescence gene and demonstration of integration of Agrobacterium T-DNA. However, expression of the integrated genes was soon lost. To develop gene editing tools for modifying specific chlorovirus CA-4B genes using preassembled Cas9 protein-sgRNA ribonucleoproteins (RNPs), we tested multiple methods for delivery of Cas9/sgRNA RNP complexes into infected cells including cell wall-degrading enzymes, electroporation, silicon carbide (SiC) whiskers, and cell-penetrating peptides (CPPs). In one experiment two independent virus mutants were isolated from macerozyme-treated NC64A cells incubated with Cas9/sgRNA RNPs targeting virus CA-4B-encoded gene 034r, which encodes a glycosyltransferase. Analysis of DNA sequences from the two mutant viruses showed highly targeted nucleotide sequence modifications in the 034r gene of each virus that were fully consistent with Cas9/RNP-directed gene editing. However, in ten subsequent experiments, we were unable to duplicate these results and therefore unable to achieve a reliable system to genetically edit chloroviruses. Nonetheless, these observations provide strong initial suggestions that Cas9/RNPs may function to promote editing of the chlorovirus genome, and that further experimentation is warranted and worthwhile.

Modification of Low-Density Slag Cementing Slurry with SiC Whiskers at High Temperature

The aim of this study was to improve the mechanical properties of a slag solidified body at high temperatures. Composite materials with different contents of SiC whiskers were prepared and characterized using techniques such as mechanical testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR). When the SiC whisker addition is 1% mass percentage, the compressive and tensile strength of the slag solidified body after hydration for 7 days increased by 10.2% and 39.3%, respectively, and Young’s modulus decreased by 16.8%. The results show that the addition of SiC whiskers can enhance the mechanical properties of solidified slag bodies at high temperatures. According to the test results, the hydration products of the slag solidified body mainly consist of honeycomb tobermorite (C-S-H) gel at high temperatures in addition to a small number of spherical products. The spheres are connected to form a dense structure; however, noticeable cracks were present. The addition of SiC whiskers effectively inhibited the initiation and further development of microcracks and improved the bearing capacity of the slag solidified body.

Pursuit of chlorovirus genetic transformation and CRISPR/Cas9-mediated gene editing

The ability to carry out genetic and molecular modifications of the large dsDNA chloroviruses, with genomes of 290 to 370 kb, would expedite studies to elucidate the functions of both identified and unidentified virus-encoded proteins. These plaque-forming viruses replicate in certain unicellular, eukaryotic chlorella-like green algae and are present in freshwater environments throughout the world. However, to date, only a few of these algal species and virtually none of their viruses have been genetically manipulated due to lack of practical methods for genetic transformation and genome editing. In an effort to develop gene editing tools for modifying specific chlorovirus CA-4B genes using preassembled Cas9 protein-sgRNA ribonucleoproteins (RNPs), we first tested multiple methods for delivery of Cas9/sgRNA RNP complexes into infected cells including cell wall-degrading enzymes, electroporation, silicon carbide (SiC) whiskers, and cell-penetrating peptides (CPPs). Agrobacterium -mediated transfection of chlorovirus host Chlorella variabilis NC64A with a binary vector containing a chlorovirus-encoded glycosyltransferase mutant gene was also examined. Attempts at developing a reliable chlorovirus transformation system were unsuccessful. However, in one experiment two independent virus mutants were isolated from macerozyme-treated NC64A cells incubated with Cas9/sgRNA RNPs targeting CA-4B-encoded gene 034r , which encodes a putative glycosyltransferase. Selection of these mutants using antibodies was dependent on a specific change in the pattern of glycans attached to the virus’ major capsid protein (MCP). Analysis of DNA sequences from the two mutant viruses showed highly targeted nucleotide sequence modifications in the 034r gene of each virus that were fully consistent with Cas9/RNP-directed gene editing. However, we were unable to duplicate these results and therefore unable to achieve a reliable system to genetically edit chloroviruses. Nonetheless, these observations provide strong initial suggestions that Cas9/RNPs may function to promote editing of the chlorovirus genome, and that further experimentation is warranted and worthwhile.