Summary auto-generated
Researchers isolated a novel bacterium designated strain IH25T from kimchi, a traditional Korean fermented vegetable product made from Chinese cabbage. Using a polyphasic taxonomic approach combining morphological, biochemical, molecular, and genetic analyses, they demonstrated that this isolate represents a previously unknown species within the genus Leuconostoc, a group of lactic acid bacteria important in food fermentation. The bacterium is Gram-positive, facultatively anaerobic, and catalase-negative with a DNA G+C content of 37 mol%, characteristics typical of Leuconostoc species. Phylogenetic analysis based on 16S rDNA sequences showed the strain clustered within the Leuconostoc genus with highest sequence similarity to L. gelidum (98.9%) and L. citreum (98.3%). Critically, DNA-DNA hybridization experiments revealed less than 70% homology with all known Leuconostoc species, establishing this as a distinct genomic species. The isolate could be differentiated from related species by its unique sugar fermentation pattern, particularly its production of acid from galactose and lactose while failing to ferment arabinose, melibiose, raffinose, and xylose. The authors propose classifying this organism as Leuconostoc kimchii sp. nov., with strain IH25T as the type strain, expanding our understanding of microbial diversity in kimchi fermentation.
Key findings
- A novel Leuconostoc species, designated L. kimchii, was isolated from kimchi and characterized using polyphasic taxonomy including 16S rDNA sequencing, DNA-DNA hybridization, and biochemical profiling.
- DNA-DNA hybridization values below 70% with all known Leuconostoc species confirmed that strain IH25T represents a genetically distinct genomic species despite 97-98.9% 16S rDNA sequence similarity to related species.
- L. kimchii has a distinctive fatty acid profile and sugar fermentation pattern that clearly differentiates it from closely related species such as L. gelidum and L. citreum.
- The discovery of L. kimchii indicates that microbial diversity in kimchi fermentation has been underestimated, highlighting the importance of molecular methods for accurate bacterial identification in traditional fermented foods.
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Abstract
A Gram-positive, catalase-negative, facultatively anaerobic, coccus-shaped bacterium, designated IH25(T), was isolated from kimchi, a traditional Korean vegetable product. Phylogenetic analysis based on almost complete 16S rDNA sequences placed the isolate in a monophyletic clade corresponding to the genus Leuconostoc. All validly described species in the genus Leuconostoc, with the exception of Leuconostoc fallax, showed high sequence identity of over 97%. The 16S rDNA sequence of strain IH25(T) showed the highest homology to those of Leuconostoc gelidum DSM 5578(T) (98.9%) and Leuconostoc citreum KCTC 3526(T) (98.3%). However, DNA--DNA hybridization experiments indicated that the organism represents a novel genomic species in the genus, since the previously known leuconostocs share DNA homology with strain IH25(T) of less than 70%. In this work, it is proposed that isolate IH25(T) be classified in the genus Leuconostoc as Leuconostoc kimchii sp. nov. The type strain of Leuconostoc kimchii is IH25(T) (=KCTC 2386(T)=IMSNU 11154(T)).