Janthinobacterium foliorum sp. nov., isolated from the decayed leaves of wild alpine rhododendron.

Janthinobacterium strains, which belong to the family Oxalobacteraceae, have attracted considerable attention due to their ability to synthesize violacein and degrade polyphenols. Wild alpine rhododendrons dominate the mountainous vegetation in southwestern China, and their leaf litter decomposition contributes to humification in alpine lakes. The Janthinobacterium strains may play a key role in the decomposition of these leaf litters. In 2025, metagenomic approaches combined with isolation and cultivation methods were applied to investigate microbial resources in stacked decayed leaves from these alpine lakes. The predominant phyla are Pseudomonadota and Actinomycetota with the relative abundances of 47.9% and 39.9%, respectively. The relative abundance of genus Janthinobacterium is only 0.1% in the community, but 11 Janthinobacterium strains were isolated. Based on the ANI and phylogenomic analyses, strains Du111 and Du118 should represent a novel species, for which the name Janthinobacterium foliorum sp. nov. is proposed. The ANI and AAI values between Janthinobacterium aestuarii and Janthinobacterium violaceum are 95.5% and 97.1%, respectively, implying that the recent proposed J. violaceum is the synonym of J. aestuarii. Comparative genomic analyses further reveal that not each of Janthinobacterium strains could produce violacein and prodigiosin, but most Janthinobacterium strains have the potential for participating in the decomposition of lignin and cellulose. This study clarifies the novel role of Janthinobacterium strains, showing that the isolated strains do not represent a novel taxonomic species but have adapted to the alpine microenvironment associated with Rhododendron leaf litter.