Genomic analysis of Leuconostoc citreum TR116 with metabolic reconstruction and the effects of fructose on gene expression for mannitol production.

The species Leuconostoc citreum is often isolated from grain and vegetable fermentations such as sourdough, sauerkraut and kimchi. Lc. citreum has seen an increase in its use as a starter culture for various fermentations and food applications. The strain Lc. citreum TR116 has been applied previously in this laboratory aimed at sugar depletion through metabolism resulting in the reduction of fructose to mannitol, a polyol considered as a sweet carbohydrate. Besides reducing sugar, TR116 showed flavour modulating characteristics and contributes to the extension of microbial shelf life. In order to obtain a better understanding of this strain and to fully use its set of abilities, the genome of Lc. citreum TR116 was sequenced using the Illumina MiSeq, assembly with SPAdes and annotated by the Prokaryotic Genome Annotation Pipeline. Metabolic reconstruction was employed to elucidate carbohydrate, organic acid and amino acid metabolism in the strain. Of particular interest was the gene expression analysis ascertained the influence of fructose on the genes mdh and manX involved in the uptake of fructose and its conversion to mannitol. This investigation, the first in Lc. citreum, illustrates the metabolic processes involved in fermentation used by this strain and demonstrates that in the presence of fructose, expression of the genes mdh and manX is increased. The resulting transparency of the skill set of TR116 contributes highly to future functionalisation of food systems and food ingredients.