Effects of ingredient size on microbial communities and metabolites of radish kimchi.

In this study, changes in physicochemical characteristics, microbial communities, and metabolites were investigated to identify the fermentation characteristics of radish kimchi according to the size of radish cubes used. The small-sized radish kimchi group showed the highest hardness value and glucose content in the early stages of fermentation. The relative abundance of major lactic acid bacteria, including Leuconostoc, Weissella, and Lactobacillus, was the highest in the small-sized radish kimchi group on day 5 of fermentation, which resulted in rapid production of lactic acid, thereby causing a decrease in pH and an increase in titratable acidity. The size of the radish in kimchi plays a pivotal role in determining various factors, most notably during the first 5 days of fermentation, leading to marked metabolic changes. A total of 17 metabolites, including glucose, sucrose, lactic acid, malic acid, citric acid, and GABA, exhibited significant differences in the small-size radish kimchi group. Interestingly, the sucrose content was higher in the large-sized radish group at the beginning of fermentation. This study revealed that ingredient size can selectively affect the growth of specific microorganisms in an environment where several microorganisms coexist, which could change the quality of radish kimchi.

Arthrobacter echini sp. nov., isolated from the gut of a purple sea urchin, Heliocidaris crassispina.

A novel strain, designated AM23T, was isolated from the gut of a purple sea urchin Heliocidaris crassispina collected from the coastal waters of the Korean island Dokdo. 16S rRNA gene sequence analysis showed that strain AM23T belonged to the genus Arthrobacter in the family Micrococcaceae and shared highest sequence similarity with Arthrobacter agilis DSM 20550T (98.77%). Strain AM23T was catalase-positive, oxidase-negative and grew optimally at 20 °C, in the presence of 1% (w/v) NaCl and at pH 7. The isolate was a Gram-stain-positive, non-motile, strictly aerobic and coccus-shaped bacterium. The major cellular fatty acids were anteiso-C15:0 and iso-C15:0. The polar lipids of strain AM23T were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, one unidentified glycolipid and four unidentified lipids. The components of the cell-wall peptidoglycan were lysine, glutamic acid and alanine and the predominant cell-wall sugars were galactose, mannose, rhamnose and ribose. The major respiratory quinone was identified as menaquinone MK-9(H2). The genomic DNA G+C content was 67.3 mol% and the DNA-DNA hybridization values showed the strain shared less than 29% genomic relatedness with A. agilis DSM 20550T. The results of the phylogenetic, phenotypic and genotypic analysis indicate that strain AM23T represents a novel species in the genus Arthrobacter, for which the name Arthrobacter echini sp. nov. is proposed. The type strain is AM23T (=KACC 18260T=DSM 29493T).