Metabolic interactions of Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614 in co-culture: implications for multi-strain probiotics

AIMS

Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614 are potential probiotic bacteria. The mechanisms of enhanced benefits by muti-strain probiotics are yet fully understood. We elucidated the influence of co-culturing on the metabolite profiles of Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614 to decipher the impacts of co-culturing on metabolic interactions between the strains.

METHODS AND RESULTS

Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614 were grown in single and co-cultures in defined media. Bacterial cell metabolites were extracted at the mid-stationary growth phase and analysed using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS). Mass-spectral data were preprocessed and analysed using unsupervised and supervised methods based on the group allocations. A total of 1387 metabolites were identified, with 18.31% significant metabolites (P < 0.05) and 10.17% differential metabolites (P < 0.05, variable importance on projection > 1). The differential metabolites identified include arabinofuranose, methyl-galactoside, N-acetylglutamic acid, phosphoric acid, and decanoic acid. The metabolites impacted carbohydrate and amino-sugar metabolism.

CONCLUSION

Co-culturing of Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614 influenced the metabolite profiles of the strains and impacted metabolic/biosynthetic pathways, indicating cell-to-cell interactions between the strains.

Formulation of Chemically Defined Media and Growth Evaluation of Ligilactobacillus salivarius ZJ614 and Limosilactobacillus reuteri ZJ625

Lactic acid bacteria are increasingly becoming important dietary supplements due to their health benefits when consumed in adequate quantity. The increasing attention on these important microbes has necessitated an in-depth understanding of their physiological processes, such as nutritional requirements and growth patterns, to better harness their probiotic potentials. This study was carried out to determine the nutritional requirements for the growth of L. salivarius ZJ614 and L. reuteri ZJ625 from a chemically defined medium and evaluate growth kinetics by fitting different sigmoidal growth models. The complete CDM contains 49 nutritional ingredients such as glucose, Tween 80^®, mineral salts, buffers, amino acids, vitamins, and nucleotides at defined concentrations. In addition, the minimal nutritional requirements of the isolates were determined in a series of single-omission experiments (SOEs) to compose the MDM. Growth curve data were generated by culturing in an automated 96-well micro-plate reader at 37°C for 36 h, and photometric readings (optical density: OD₆₀₀) were taken. The data were summarized in tables and charts using Microsoft Excel, while growth evaluation was carried out using open-source software (Curveball) on Python. The results revealed that omission of the amino acids, vitamins, and nucleotides groups resulted in 2.0, 20.17, and 60.24% (for L. salivarius ZJ614) and 0.95, 42.7, and 70.5% (for L. reuteri ZJ625) relative growths, respectively. Elimination of the individual CDM components also indicates varying levels of growth by the strains. The growth curve data revealed LogisticLag2 and Baranyi–Roberts models as the best fits for L. reuteri ZJ625 and L. salivarius ZJ614, respectively. All the strains showed appreciable growth on the CDM and MDM as observed in de Man–Rogosa–Sharpe (MRS) broth. We also described the growth kinetics of L. reuteri ZJ625 and L. salivarius ZJ614 in the CDM, and the best models revealed the estimated growth parameters.

A protein-free chemically defined medium for the cultivation of various micro-organisms with food safety significance

AIMS

To develop a broadly applicable medium free of proteins with well-defined and reproducible chemical composition for the cultivation of various micro-organisms with food safety significance.

METHODS AND RESULTS

The defined medium was designed as a buffered minimal salt medium supplemented with amino acids, vitamins, trace metals and other nutrients. Various strains commonly used for food safety research were selected to test the new defined medium. We investigated single growth factors needed by different strains and the growth performance of each strain cultivated in the defined medium. Results showed that the tested strains initially grew slower in the defined medium compared to tryptic soy broth, but after an overnight incubation cultures from the defined medium reached adequately high cell densities.

CONCLUSIONS

The newly designed defined medium can be widely applied in food safety studies that require media with well-defined chemical constituents.

SIGNIFICANCE AND IMPACT OF THE STUDY

Defined media are important in studies of microbial metabolites and physiological properties. A defined medium capable of cultivating different strains simultaneously is needed in the food safety area. The new defined medium has broader applications in comparing different strains directly and provides more reproducible results.