Chungnam National University traces seasonal lettuce microbiota to human gut in 143-sample study

Biologists at Chungnam National University and Jeju National University investigated the temporal dynamics of epiphytic microorganisms on fresh vegetables and evaluated their presence in the human digestive tract, according to nature.com nature.comnature.comnature.comOpen source ↗. The team analyzed 143 retail samples of green and red lettuce collected monthly over a 12-month period in Daejeon, South Korea. High-throughput amplicon sequencing of the 16S rRNA gene for bacteria and the ITS2 region for fungi revealed 5,610 bacterial and 5,016 fungal amplicon sequence variants.

Microbial load measurements showed approximately 5.0 log CFU of culturable bacteria and 3.4 log CFU of culturable fungi per gram of plant tissue. Lettuce-specific profiles differed from published datasets representing 14 other produce types, showing enrichment in fungal genera Cladosporium and Bulleromyces, alongside bacterial taxa Massilia and Sphingomonas.

Seasonal succession and network structure

The phyllosphere microbiota exhibited temporal variation governed primarily by sampling month and local meteorological conditions, rather than lettuce cultivar. The communities segregated into two distinct seasonal cycles: early-season (S1, December to June) and late-season (S2, July to November) nature.comnature.comnature.comOpen source ↗. This seasonal progression was confirmed by classification models, with 87.3% of green lettuce and 75.6% of red lettuce samples clustering according to their collection period.

The transition from S1 to S2 led to increased species richness in season-specific taxa, alongside compositional shifts in persistent populations. These dynamics yielded denser, more stable ecological networks during the late season, which coincided with a lower enrichment frequency of fungal genera associated with potential pathogenicity.

Detection in gut microbiome cohorts

To trace potential transfer through the food-gut axis, the investigators compared lettuce operational taxonomic units clustered at 97% sequence similarity against fecal sequencing datasets from 3,254 individuals for bacteria and 2,831 individuals for fungi nature.comnature.comnature.comOpen source ↗. Lettuce-associated microbial taxa were widely identified in human gut profiles, with bacterial lineages appearing at higher frequencies than fungal counterparts.

Season-specific vegetable taxa were identified more frequently in gut cohorts than persistent taxa. Within the digestive tract, lettuce-associated bacteria co-occurred predominantly with commensal bacteria capable of degrading non-plant glycans. The abundance of these co-occurring clusters showed a positive correlation with overall gut microbiota richness and structural composition. The authors noted that microbial community assembly in the gut reflects both deterministic and neutral ecological processes.