Investigation of associations of Yarrowia lipolytica, Staphylococcus xylosus, and Lactococcus lactis in culture as a first step in microbial interaction analysis

Abstract

The interactions that may occur between microorganisms in different ecosystems have not been adequately studied yet. We investigated yeast-bacterium interactions in a synthetic medium using different culture associations involving the yeast Yarrowia lipolytica 1E07 and two bacteria, Staphylococcus xylosus C2a and Lactococcus lactis LD61. The growth and biochemical characteristics of each microorganism in the different culture associations were studied. The expression of genes related to glucose, lactate, and amino acid catabolism was analyzed by reverse transcription followed by quantitative PCR. Our results show that the growth of Y. lipolytica 1E07 is dramatically reduced by the presence of S. xylosus C2a. As a result of a low amino acid concentration in the medium, the expression of Y. lipolytica genes involved in amino acid catabolism was downregulated in the presence of S. xylosus C2a, even when L. lactis was present in the culture. Furthermore, the production of lactate by both bacteria had an impact on the lactate dehydrogenase gene expression of the yeast, which increased up to 30-fold in the three-species culture compared to the Y. lipolytica 1E07 pure culture. S. xylosus C2a growth dramatically decreased in the presence of Y. lipolytica 1E07. The growth of lactic acid bacteria was not affected by the presence of S. xylosus C2a or Y. lipolytica 1E07, although the study of gene expression showed significant variations.

FIG. 1.

Growth of Y. lipolytica 1E07 (A), S. xylosus C2a (B), and L. lactis LD61 (C) in SM.

FIG. 2.

pH variation for microorganisms in pure cultures (A) and in mixed cultures (B).

FIG. 3.

Glucose and lactate concentrations in the supernatants of microorganism cultures after 14 h of incubation in SM. B, blank.

FIG. 4.

Levels of expression of the GDH2, GDH3, BAT1, HXT2, CHA1, KAD, PDA1, PDB1, and CYB2-2 genes, measured by real-time RT-PCR. The levels of expression of genes in a Y culture were compared to those in cocultures after 14 h of incubation in SM.

FIG. 5.

Levels of expression of the poxL, noxE, ldh, and pgiA genes, measured by real-time RT-PCR. The levels of expression of genes in an L culture were compared to those in cocultures after 14 h of incubation in SM.

FIG. 6.

Levels of expression of the ldh, pdhA, pgiA, and aat genes, measured by real-time RT-PCR. The levels of expression of genes in an S culture were compared to those in cocultures after 14 h of incubation in SM.