Genomic insight into the salt tolerance and proteolytic activity of Bacillus subtilis.

We assessed the salt tolerance and proteolytic activity of 40 genome-published Bacillus subtilis strains isolated from fermented Korean foods to illuminate the genomic background behind the functionality of B. subtilis in high-salt fermentation. On the basis of the salt tolerance and phenotypic proteolytic activity of the 40 strains, we selected five strains exhibiting different phenotypic characteristics. Comparative genomic analyses of these five strains provided genomic insight into the salt tolerance and proteolytic activity of B. subtilis. Two-component system (TCS) genes annotated as ybdGJK and laterally acquired authentic ATP-binding cassette (ABC) transporter system genes of tandem repeat structure might contribute to increase salt tolerance. The additional possession of gene homologs for CAAX protease family proteins and components of Clp (caseinolytic protease) complex, ATP-dependent Clp proteolytic subunit ClpP and AAA+ (ATPases associated with diverse cellular Activities) family ATPases, might determine the proteolytic activity of B. subtilis. This study established the scientific foundation for the viability and functionality of B. subtilis in high-salt fermentation.

Antibiotic susceptibility of Bacillus velezensis.

We evaluated the antibiotic minimum inhibitory concentrations (MICs) of 123 Bacillus velezensis strains predominantly isolated from fermented soybean foods from Korea. When the 2018 European Food Safety Authority breakpoint values for Bacillus spp. were applied, all the strains were sensitive to chloramphenicol, clindamycin, erythromycin, gentamicin, kanamycin, tetracycline and vancomycin, and eight strains (6.5%) were resistant to streptomycin. The population distribution in MIC tests with streptomycin was continuous and the profile was clearly different from that expected for acquired antibiotic resistance. As of 25 October 2021, there were 181 complete published genomes of B. velezensis strains; 175 (96.7%) and 136 (75.2%) of these strains, respectively, possess potential tetracycline and streptomycin resistance genes tetL and ant(6) in the chromosome. In Bacillus licheniformis, SpeG confers resistance to clindamycin and there is an 'speG' gene annotated in the genomes of 180 B. velezensis strains; however, the gene products exhibit ≤26.6% amino acid identity with that from B. licheniformis DSM 13T. All the potential antibiotic resistance genes in the 181 B. velezensis strains were intrinsic, and traits of lateral gene transfer were not found. In this context, B. velezensis may not present a high risk in terms of antibiotic resistance in food fermentation or human use.

Safety and Technological Characterization of Staphylococcus xylosus and Staphylococcus pseudoxylosus Isolates from Fermented Soybean Foods of Korea.

We evaluated the antibiotic susceptibilities, hemolytic activities, and technological properties of 36 Staphylococcus xylosus strains and 49 S. pseudoxylosus strains predominantly isolated from fermented soybean foods from Korea. Most of the strains were sensitive to chloramphenicol, erythromycin, gentamycin, kanamycin, lincomycin, oxacillin, tetracycline, and trimethoprim. However, 23 strains exhibited potential phenotypic acquired resistance to erythromycin, lincomycin, and tetracycline. Based on breakpoint values for staphylococci from the Clinical and Laboratory Standards Institute, >30% of the isolates were resistant to ampicillin and penicillin G, but the population distributions in minimum inhibitory concentration tests were clearly different from those expected for acquired resistance. None of the strains exhibited clear α- or ß-hemolytic activity. S. xylosus and S. pseudoxylosus exhibited salt tolerance on agar medium containing 20% and 22% (w/v) NaCl, respectively. S. xylosus and S. pseudoxylosus strains possessed protease and lipase activities, which were affected by the NaCl concentration. Protease activity of S. pseudoxylosus was strain-specific, but lipase activity might be a characteristic of both species. This study confirms the potential of both species for use in high-salt soybean fermentation, but the safety and technological properties of strains must be determined to select suitable starter candidates.

Pachymic acid promotes induction of autophagy related to IGF-1 signaling pathway in WI-38 cells.

BACKGROUND: The insulin-like growth factor 1 (IGF-1) signaling pathway has spotlighted as a mechanism to elucidate aging associated with autophagy in recent years. Therefore, we have tried to screen an effective compound capable of inducing autophagy to delay aging process. PURPOSE: The aim of this study is to investigate whether pachymic acid, a main compound in Poria cocos, induces autophagy in the aged cells. METHODS: The aging of young cells was induced by treatment with IGF-1 at 50 ng/ml three times every two days. The effect of pachymic acid on cell viability was evaluated in human lung fibroblasts, WI-38 cells, using MTT assay. The induction of autophagy was detected using autophagy detection kit. The expression of proteins related to autophagy and IGF-1 signaling pathway was examined by western blot analysis and immunofluorescence assay. RESULTS: In this study, pachymic acid showed cytotoxic effect in a dose dependent manner and remarkably induced autophagy at the same time. Moreover, pachymic acid increased the expression of proteins related to autophagy such as LC3-II and Beclin1 and decreased the levels of mTor phosphorylation and p70S6K in the aged cells. In particular, pachymic acid increased the expression of p-PI3K, p-FoxO and Catalase. In addition, pachymic acid remarkably increased the expression of IGFBP-3. CONCLUSION: Above results suggest that pachymic acid could induce autophagy related to IGF-1 signaling pathway in the aged cells.