The beneficial effects of lactic acid bacteria are well known and recognized as functional foods that are health benefits for companion animals. This study, for the first time, reports the probiotic properties, safety, and whole-genome sequence of Pediococcus acidilactici GLP06 isolated from feces of beagles. In this study, candidate probiotic bacteria P. acidilactici GLP02 and GLP06 were morphologically characterized and tested for their antimicrobial capacity, tolerance to different conditions (low pH, bile salts, an artificial gastrointestinal model, and high temperature), antibiotic sensitivity, hemolytic activity, cell surface hydrophobicity, autoaggregation activity, and adhesion to Caco-2 cells. P. acidilactici GLP06 showed better probiotic potential. Therefore, P. acidilactici GLP06 was evaluated for in vivo safety in mice and whole-genome sequencing. The results showed, that the supplemented MG06 group (1010 cfu/mL), GLP06 was not only nontoxic to mice, but also promoted the development of the immune system, improved resistance to oxidative stress, and increased the diversity of intestinal microorganisms and the abundance of Lactobacillus. Whole-genome sequencing showed that P. acidilactici GLP06 was 2,014,515 bp and contained 1,976 coding sequences, accounting for 86.12% of the genome, with no drug resistance genes and eight CRISPR sequences. In conclusion, the newly isolated canine-derived P. acidilactici GLP06 had good probiotic potential, was nontoxic to mice and promoted the development of immune organs, improved the biodiversity of the intestinal flora, and had no risk of drug-resistant gene transfer, indicating that P. acidilactici GLP06 can be used as a potential probiotic for the prevention and treatment of gastrointestinal diseases in companion animals.

Newcastle disease (ND) is an acute and highly contagious infectious disease found in poultry. Although commercial ND virus (NDV) vaccines are universally used, some case reports persistently documented vaccination failure. Therefore, novel strategies are still required to control the occurrence of the disease in chickens. Recently, nanobodies (Nbs), which have the advantages of small molecular weight and low production costs, have been shown to be promising therapeutics against viral infection. In the present study, a total of 16 Nbs against NDV nucleocapsid protein (NP) were screened from two libraries against NDV using phage display technology. Of the 16 screened Nbs, eight were prevented from binding to NDV NP protein through administering positive chicken sera for anti-NDV antibodies, indicating that the epitopes recognized by these eight Nbs were able to induce the immune response after the chickens were infected with NDV stock. Subsequently, transfection assay, construction of recombinant DF-1 cells capable of expressing different nanobodies and viral inhibition assay were used to screen the nanobodies inhibiting NDV replication. The results demonstrated that Nb18, Nb30, and Nb88 significantly inhibited the replication of Class I and different genotypes of Class II NDV strains in DF-1 cells when they were expressed in the cytoplasm. Collectively, these nanobodies provided new tools for researching the functions of NDV NP protein and may be used as a novel strategy for designing drugs against NDV infection in chickens.

Chitinolyticbacter meiyuanensis SYBC-H1, a bacterium capable of hydrolyzing chitin and shrimp shell to N-acetyl glucosamine (GlcNAc) as the only product, was isolated previously. Here, the hydrolysis mechanism of this novel strain toward chitin was investigated. Sequencing and analysis of the complete genome of SYBC-H1 showed that it encodes 32 putatively chitinolytic enzymes including 30 chitinases affiliated with the glycoside hydrolase (GH) families 18 (26) and 19 (4), one GH family 20 β-N-acetylglucosaminidase (NAGase), and one Auxiliary Activities (AA) family 10 lytic polysaccharide monooxygenase (LPMO). However, only eight GH18 chitinases, one AA10 LPMO, and one GH20 NAGase were detected in the culture broth of the strain, according to peptide mass fingerprinting (PMF). Of these, genes encoding chitinolytic enzymes including five GH18 chitinases (Cm711, Cm3636, Cm3638, Cm3639, and Cm3769) and one GH20 NAGase (Cm3245) were successfully expressed in active form in Escherichia coli. The hydrolysis of chitinous substrates showed that Cm711, Cm3636, Cm3638, and Cm3769 were endo-chitinases and Cm3639 was exo-chitinase. Moreover, Cm3639 and Cm3769 can convert the GlcNAc dimer and colloidal chitin (CC) into GlcNAc, which showed that they also possess NAGase activity. In addition, NAGase Cm3245 possesses a very high exo-acting activity of hydrolyzing GlcNAc dimer. These results suggest that chitinases and NAGase from SYBC-H1 both play important roles in conversion of N-acetyl chitooligosaccharides to GlcNAc, resulting in the accumulation of the final product GlcNAc. To our knowledge, this is the first report of the complete genome sequence and chitinolytic enzyme genes discovery of this strain.