Selection markers are essential tools in gene editing, the utility of such systems is inherently constrained by species-specific limitations, governed by divergent host genetic backgrounds and metabolic compatibility. To address this limitation, we leveraged the CRISPR/Cas9 system to develop a universal counter-selection tool. We designed and introduced an sgRNA expression cassettes as counter-selection markers, which directs the Cas9 protein to target and cleave genomic DNA, allowing for the selection of the strains where the sgRNA expression cassette has been replaced. Optimized to target multiple copy sites with sgRNA, this system significantly enhances cell lethality, boosting counter-selection efficiency to over 85.00%. This counter-selection tool is not limited to single strains and is suitable for various scenarios, including multi-copy plasmid assembly and plasmid editing, demonstrating broad application potential.
CRISPR-Cas Systems/genetics* ; Gene Editing/methods* ; RNA, Guide, CRISPR-Cas Systems/genetics* ; Plasmids/genetics*

Objective To explore the association between low blood lead exposure and nervous system symptoms among the workers exposed to oil paint.Methods Through cluster sampling,workers with occupational oil paint exposure in 2 factories were selected to conduct a questionnaire survey,biochemical detection and health examination.x2 test and unconditional logistic regression analysis were performed for the determinants analysis.Results A total of 525 oil paint workers completed the survey,in whom,55 (10.5％) were blood lead positive,the mean of blood lead concentration was (0.088 4 ± 0.053 9) mg/L,278 (52.95％) had nervous system like symptoms and 69 (13.14％) had peripheral neuropathy symptoms.Multinomial logistic regression analysis showed that working age (OR=1.827),drinking (OR=1.607),health status (OR=3.862),blood lead (OR=1.983) were risk factors for nervous system like symptoms.Working age (OR=2.282),and drinking (OR=2.704) were risk factors for peripheral neuropathy.Conclusion Low blood lead exposure might be associated with nervous system like symptoms.