Coupling CRISPR/Cas9 and Lambda Red Recombineering System for Genome Editing of Salmonella Gallinarum and the Effect of ssaU Knock-Out Mutant on the Virulence of Bacteria

CRISPR-Cas9-assisted genome editing in E. coli elevates the frequency of unintended mutations

Cas-assisted lambda Red recombineering techniques have rapidly become a mainstay of bacterial genome editing. Such techniques have been used to construct both individual mutants and massive libraries to assess the effects of genomic changes. We have found that a commonly used Cas9-assisted editing method results in unintended mutations elsewhere in the genome in 26% of edited clones. The unintended mutations are frequently found over 200 kb from the intended edit site and even over 10 kb from potential off-target sites. We attribute the high frequency of unintended mutations to error-prone polymerases expressed in response to dsDNA breaks introduced at the edit site. Most unintended mutations occur in regulatory or coding regions and thus may have phenotypic effects. Our findings highlight the risks associated with genome editing techniques involving dsDNA breaks in E. coli and likely other bacteria and emphasize the importance of sequencing the genomes of edited cells to ensure the absence of unintended mutations.

Vaccines to Control Salmonella in Poultry

This review is focused on describing and analyzing means by which Salmonella enterica serotype strains have been genetically modified with the purpose of developing safe, efficacious vaccines to present Salmonella-induced disease in poultry and to prevent Salmonella colonization of poultry to reduce transmission through the food chain in and on eggs and poultry meat. Emphasis is on use of recently developed means to generate defined deletion mutations to eliminate genetic sequences conferring antimicrobial resistance or residual elements that might lead to genetic instability. Problems associated with prior means to develop vaccines are discussed with presentation of various means by which these problems have been lessened, if not eliminated. Practical considerations are also discussed in hope of facilitating means to move lab-proven successful vaccination procedures and vaccine candidates to the marketplace to benefit the poultry industry.