Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

Abstract

Lactic acid bacteria have been isolated from living, harvested, and fermented plant materials; however, the adaptations these bacteria possess for growth on plant tissues are largely unknown. In this study, we investigated plant habitat-specific traits ofLactococcus lactisduring growth in anArabidopsis thalianaleaf tissue lysate (ATL).L. lactisKF147, a strain originally isolated from plants, exhibited a higher growth rate and reached 7.9-fold-greater cell densities during growth in ATL than the dairy-associated strainL. lactisIL1403. Transcriptome profiling (RNA-seq) of KF147 identified 853 induced and 264 repressed genes during growth in ATL compared to that in GM17 laboratory culture medium. Genes induced in ATL included those involved in the arginine deiminase pathway and a total of 140 carbohydrate transport and metabolism genes, many of which are involved in xylose, arabinose, cellobiose, and hemicellulose metabolism. The induction of those genes corresponded withL. lactisKF147 nutrient consumption and production of metabolic end products in ATL as measured by gas chromatography-time of flight mass spectrometry (GC-TOF/MS) untargeted metabolomic profiling. To assess the importance of specific plant-inducible genes forL. lactisgrowth in ATL, xylose metabolism was targeted for gene knockout mutagenesis. Wild-typeL. lactisstrain KF147 but not anxylAdeletion mutant was able to grow using xylose as the sole carbon source. However, both strains grew to similarly high levels in ATL, indicating redundancy inL. lactiscarbohydrate metabolism on plant tissues. These findings show that certain strains ofL. lactisare well adapted for growth on plants and possess specific traits relevant for plant-based food, fuel, and feed fermentations.