The diversity among the species Tetragenococcus halophilus including new isolates from a lupine seed fermentation

BACKGROUND

Tetragenococcus (T.) halophilus can be isolated from a variety of fermented foods, such as soy sauce, different soy pastes, salted fish sauce and from cheese brine or degraded sugar beet thick juice. This species contributes by the formation of short chain acids to the flavor of the product. Recently, T. halophilus has been identified as a dominant species in a seasoning sauce fermentation based on koji made with lupine seeds.

RESULTS

In this study we characterized six strains of T. halophilus isolated from lupine moromi fermentations in terms of their adaptation towards this fermentation environment, salt tolerance and production of biogenic amines. Phylogenic and genomic analysis revealed three distinctive lineages within the species T. halophilus with no relation to their isolation source, besides the lineage of T. halophilus subsp. flandriensis. All isolated strains from lupine moromi belong to one lineage in that any of the type strains are absent. The strains form lupine moromi could not convincingly be assigned to one of the current subspecies. Taken together with strain specific differences in the carbohydrate metabolism (arabinose, mannitol, melibiose, gluconate, galactonate) and amino acid degradation pathways such as arginine deiminase pathway (ADI) and the agmatine deiminase pathway (AgDI) the biodiversity in the species of T. halophilus is greater than expected. Among the new strains, some strains have a favorable combination of traits wanted in a starter culture.

CONCLUSIONS

Our study characterized T. halophilus strains that were isolated from lupine fermentation. The lupine moromi environment appears to select strains with specific traits as all of the strains are phylogenetically closely related, which potentially can be used as a starter culture for lupine moromi. We also found that the strains can be clearly distinguished phylogenetically and phenotypically from the type strains of both subspecies T. halophilus subsp. halophilus and T. halophilus subsp. flandriensis.

Monitoring the growth dynamics of Tetragenococcus halophilus strains in lupine moromi fermentation using a multiplex-PCR system

OBJECTIVE

The microbiota of a seasoning sauce fermentation process is usually complex and includes multiple species and even various strains of one species. Moreover, composition and cell numbers of individual strains vary over the course of the entire fermentation. This study demonstrates the applicability of a multiplex PCR system to monitor growth dynamics of Tetragenococcus (T.) halophilus strains in order to evaluate their performance and help to select the most competitive starter strain.

RESULTS

In a previous study we isolated T. halophilus strains from multiple lupine moromi fermentation processes and characterized them. In this study we wanted to monitor the growth dynamics of these strains in a competitive lupine moromi model fermentation process using a multiplex PCR system. Therefore, pasteurized lupine koji was inoculated with eight different T. halophilus strains, six from lupine moromi, one from an experimental buckwheat moromi fermentation process and the type strain DSM 20,339^T, to create the inoculated lupine moromi pilot scale fermentation process. With the multiplex PCR system, we could detect that all strains could grow in lupine moromi but, that TMW 2.2254 and TMW 2.2264 outperformed all other strains. Both strains dominated the fermentation after three weeks with cell counts between 4 × 10⁶ to 4 × 10⁷ CFU/mL for TMW 2.2254 and 1 × 10⁷ to 5 × 10⁷ CFU/mL for TMW 2.2264. The pH dropped to value below 5 within the first 7 days, the selection of these strains might be related to their acid tolerance.