Lactic acid bacteria produce diverse functional metabolites in fermented foods. However, little is known regarding the metabolites and the fermentation process in kimchi. In this study, the culture broth from Leuconostoc lactis, a lactic acid bacterium isolated from kimchi, was analysed by liquid chromatography-tandem mass spectrometry and identified by the MS-DIAL program. The MassBank database was used to analyse the metabolites produced during fermentation. A mass spectrum corresponding to 2-hydroxyisocaproic acid (HICA) was validated based on a collision-induced dissociation (CID) fragmentation pattern with an identified m/z value of 131.07. HICA production by lactic acid bacteria was monitored and showed a positive correlation with hydroxyisocaproate dehydrogenases (HicDs), which play a key role in the production of HICA from leucine and ketoisocaproic acid. Interestingly, the HICA contents of kimchi varied with Leuconostoc and Lactobacillus content during the early stage of fermentation, and the addition of lactic acid bacteria enhanced the HICA content of kimchi. Our results suggest that HICA production in kimchi is dependent on the lactic acid bacterial composition.

Kimchi fermentation depends on diverse lactic acid bacteria, which convert raw materials into numerous metabolites that contribute to the taste of food. Amino acids and saccharides are important primary metabolites. Arginine is nearly exhausted during kimchi fermentation, whereas the concentrations of other amino acids are reported not to increase or decrease dramatically. These phenomena could imply that arginine is an important nutritional component among the amino acids during kimchi fermentation. In this study, we investigated the arginine-catabolism pathway of seven lactic acid bacteria isolated from kimchi and evaluated the products of arginine catabolism (citrulline and ornithine) associated with the bacteria. The arginine content dramatically decreased in cultures of Lactobacillus brevis and Weissella confusa from 300 μg/mL of arginine to 0.14 ± 0.19 and 1.3 ± 0.01 μg/mL, respectively, after 6 h of cultivation. Citrulline and ornithine production by L. brevis and W. confusa showed a pattern that was consistent with arginine catabolism. Interestingly, Pediococcus pentosaceus, Lactobacillus plantarum, Leuconostoc mesenteroides, and Leuconostoc lactis did not show increased citrulline levels after arginine was added. The ornithine contents were higher in all bacteria except for L. lactis after adding arginine to the culture. These results were consistent with the absence of the arginine deiminase gene among the lactic acid bacteria. Arginine consumption and ornithine production were monitored and compared with lactic acid bacteria by metagenomics analysis, which showed that the increment of ornithine production correlated positively with lactic acid bacteria growth.

cCronobacter spp. are opportunistic pathogens that cause neonatal meningitis and sepsis with high mortality in neonates. Despite the peril associated with Cronobacter infection, the mechanisms of pathogenesis are still being unraveled. Hfq, which is known as an RNA chaperone, participates in the interaction with bacterial small RNAs (sRNAs) to regulate posttranscriptionally the expression of various genes. Recent studies have demonstrated that Hfq contributes to the pathogenesis of numerous species of bacteria, and its roles are varied between bacterial species. Here, we tried to elucidate the role of Hfq in C. sakazakii virulence. In the absence of hfq, C. sakazakii was highly attenuated in dissemination in vivo, showed defects in invasion (3-fold) into animal cells and survival (10 3 -fold) within host cells, and exhibited low resistance to hydrogen peroxide (10 2 -fold). Remarkably, the loss of hfq led to hypermotility on soft agar, which is contrary to what has been observed in other pathogenic bacteria. The hyperflagellated bacteria were likely to be attributable to the increased transcription of genes associated with flagellar biosynthesis in a strain lacking hfq. Together, these data strongly suggest that hfq plays important roles in the virulence of C. sakazakii by participating in the regulation of multiple genes.

BackgroundPanax ginseng is a physiologically active plant widely used in traditional medicine that is characterized by the presence of ginsenosides. Rb1, a major ginsenoside, is used as the starting material for producing ginsenoside derivatives with enhanced pharmaceutical potentials through chemical, enzymatic, or microbial transformation.MethodsTo investigate the bioconversion of ginsenoside Rb1, we prepared kimchi originated bacterial strains Leuconostoc mensenteroides WiKim19, Pediococcus pentosaceus WiKim20, Lactobacillus brevis WiKim47, Leuconostoc lactis WiKim48, and Lactobacillus sakei WiKim49 and analyzed bioconversion products using LC-MS/MS mass spectrometer.ResultsL. mesenteroides WiKim19 and Pediococcus pentosaceus WiKim20 converted ginsenoside Rb1 into the ginsenoside Rg3 approximately five times more than Lactobacillus brevis WiKim47, Leuconostoc lactis WiKim48, and Lactobacillus sakei WiKim49. L mesenteroides WIKim19 showed positive correlation with β-glucosidase activity and higher transformation ability of ginsenoside Rb1 into Rg3 than the other strains whereas, P. pentosaceus WiKim20 showed an elevated production of Rb3 even with lack of β-glucosidase activity but have the highest acidity among the five lactic acid bacteria (LAB).ConclusionGinsenoside Rg5 concentration of five LABs have ranged from ∼2.6 μg/mL to 6.5 μg/mL and increased in accordance with the incubation periods. Our results indicate that the enzymatic activity along with acidic condition contribute to the production of minor ginsenoside from lactic acid bacteria.

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