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CRISPR-Cas9 has been demonstrated as a transformative genome engineering tool for many eukaryotic organisms; however, its utilization in bacteria remains limited and ineffective. Here we explored Streptococcus pyogenes CRISPR-Cas9 for genome editing in Clostridium beijerinckii (industrially significant but notorious for being difficult to metabolically engineer) as a representative attempt to explore CRISPR-Cas9 for genome editing in microorganisms that previously lacked sufficient genetic tools. By combining inducible expression of Cas9 and plasmid-borne editing templates, we successfully achieved gene deletion and integration with high efficiency in single steps. We further achieved single nucleotide modification by applying innovative two-step approaches, which do not rely on availability of Protospacer Adjacent Motif sequences. Severe vector integration events were observed during the genome engineering process, which is likely difficult to avoid but has never been reported by other researchers for the bacterial genome engineering based on homologous recombination with plasmid-borne editing templates. We then further successfully employed CRISPR-Cas9 as an efficient tool for selecting desirable "clean" mutants in this study. The approaches we developed are broadly applicable and will open the way for precise genome editing in diverse microorganisms.

The anaerobic spore-forming, gram-positive, solventogenic clostridia are notorious for being difficult to genetically engineer. Based on CRISPR/Cas9 assisted homologous recombination, we demonstrated that clean markerless gene deletion from the chromosome can be easily achieved with a high efficiency through a single-step transformation in Clostridium beijerinckii NCIMB 8052, one of the most prominent strains for acetone, butanol and ethanol (ABE) production. This highly efficient genome engineering system can be further explored for multiplex genome engineering purposes. The protocols and principles developed in this study provided valuable references for genome engineering in other microorganisms lacking developed genetic engineering tools.

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Global climate change caused by the emission of anthropogenic greenhouse gases (GHGs) is a grand challenge to humanity. To alleviate the trend, the consumption of fossil fuels needs to be largely reduced and alternative energy technologies capable of controlling GHG emissions are anticipated. In this study, we introduced a synthetic reductive pentose phosphate pathway (rPPP) into a xylose-fermenting Saccharomyces cerevisiae strain SR8 to achieve simultaneous lignocellulosic bioethanol production and carbon dioxide recycling. Specifically, ribulose-1,5-bisphosphate carboxylase/oxygenase from Rhodospirillum rubrum and phosphoribulokinase from Spinacia oleracea were introduced into the SR8 strain. The resulting strain with the synthetic rPPP was able to exhibit a higher yield of ethanol and lower yields of byproducts (xylitol and glycerol) than a control strain. In addition, the reduced release of carbon dioxide by the engineered strain was observed during xylose fermentation, suggesting that the carbon dioxide generated by pyruvate decarboxylase was partially reassimilated through the synthetic rPPP. These results demonstrated that recycling of carbon dioxide from the ethanol fermentation pathway in yeast can be achieved during lignocellulosic bioethanol production through a synthetic carbon conservative metabolic pathway. This strategy has a great potential to alleviate GHG emissions during the production of second-generation ethanol.

The Ion AmpliSeq™ HID single nucleotide polymorphism (SNP) panel, a primer pool of 103 autosomal SNPs and 33 Y-SNPs, was evaluated using the Ion 314™ Chip on the Ion PGM™ Sequencer with four DNA samples. The study focused on the sequencing of DNA at three different initial target quantities, related interpretation issues, and concordance of results with another sequencing platform, i.e., Genome Analyzer IIx. With 10 ng of template DNA, all genotypes at the 136 SNPs were detected. With 1 ng of DNA, all SNPs were detected and one SNP locus in one sample showed extreme heterozygote imbalance on allele coverage. With 100 pg of DNA, an average of 1.6 SNP loci were not detected, and an average of 4.3 SNPs showed heterozygote imbalance. The average sequence coverage was 945-600× at autosomal SNPs and 465-209× at Y-SNPs for 10 ng-100 pg of DNA. The average heterozygote allele coverage ratio was 89.6-61.8 % for 10 ng-100 pg of DNA. At 10 ng of DNA, all genotypes of the 95 SNPs shared between the two different sequencing platforms were concordant except for one SNP, rs1029047. The error was due to the misalignment of a flanking homopolymer. Overall, the data support that genotyping a large battery of SNPs is feasible with massively parallel sequencing. With barcode systems, better allele balance, and specifically designed alignment software, a more comprehensive rapid genotyping and more cost-effective results may be obtained from multiple samples in one analysis than are possible with current typing and capillary electrophoresis systems.

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