To study the biological characteristics and gene function of Ligilactobacillus salivarius CICC23174 strain,a strain isolated from chicken intestines.The next generation sequencing plat-form HiSeq2000 was used for sequencing,and bioinformatics software was employed to assemble and optimize the raw data.Functional annotation,bacteriocin and signal peptide,gene collinearity comparison,and phylogenetic analysis were performed on its gene information.Our results indica-ted that the linear genome of Ligilactobacillus salivarius CICC23174 was 203 542 bp in length,with a GC content of 32.84％,encoding 1 890 genes,containing 3 bacteriocins,and 50 signal pep-tides.Importantly,the Ligilactobacillus salivarius CICC23174 included into 27 unique genes,forming four systems:the Type Ⅰ CRISPR Cas defense system,the Type Ⅱ toxin antitoxin system,the tumor escaped inhibitory gene,and the protein secretion pathway.Moreover,collinearity analy-sis showed that CICC23174 strain was most similar to the Ligilactobacillus salivarius UCC118,but 16S rRNA phylogenetic analysis indicted that CICC23174 strain was genetically close to FZJTZ9M6 strain.The results of this study lay the foundation for enriching the species evolution-ary library of Lactobacillus salivarius and exploring the potential probiotic functions of Lactoba-cillus salivarius.

Severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)is the main pathogen that causes COVID-19,which is fast-mutating and highly transmissible.The infection has led to a global epidemic.As the main preventive and control measure,vaccination plays a critical role in fighting a-gainst COVID-19.Although a large number of epitope-based and mucosal vaccines have been stud-ied,few peptide epitope vaccines targeting the mucosa and their functional evaluation have been re-ported.In this study,we used SARS-CoV-2 structural protein M peptide epitope predicted by the IEDB database as an antigenic target to design the MS-3S gene containing 3 050 and 1 229 signal peptides and DCpep optimized for insertion into MS2 phage coat proteins.The expression plasmid pSIP:MS-3S was constructed by cloning the PCR fragments seamlessly and was transformed into Lactiplantibacillus plantarum 18 to obtain the recombinant bacterium LP18:MS-3S.Expression conditions such as induction time,inducer concentration,rotational speed and initial pH were opti-mized.The intranasal immunization experiments were performed to examine the vaccine efficacy.The results showed that the 916 bp-long target gene MS-3S modified and optimized was amplified and used to successfully construct the recombinant bacterial strain LP18:MS-3S.The optimal con-ditions for recombinant protein expression were obtained and verified by Western blot,flow cy-tometry,immunofluorescence and other detection methods.The optimal expression conditions were determined as follows:induction time was 4 h with 100 pg/L of SppIP as the optimal induction concentration.Antibody-specific for the epitope was verified by ELISA experiments in serum,alve-olar lavage fluid and fecal dilutions of mice.In summary,a recombinant bacterial strain expressing the epitope antigen of the SARS-CoV-2 M protein peptide was constructed.The obtained protein can induce the body to produce humoral and mucosal immunity,which lays the foundation for the development of a vaccine candidate for the mucosal immunity of COVID-19.