Growth promotion of milk-associated Candida zeylanoides by a cyclic lipopeptide produced by Pseudomonas.

Milk has a rich microbiota that engages in complex interactions. These interactions can be mutualistic or antagonistic, shaping the microbial composition of dairy products and affecting fermentation, preservation, and product quality. In this study, we investigate the interaction between Pseudomonas bacteria and the yeast Candida zeylanoides in the context of traditional dairy fermentation. We identified a collection of cyclic lipopeptides (CLPs) from Pseudomonas sp. SM4, isolated from the traditional Mongolian dairy product öröm and elucidated the structure of six CLPs belonging to the amphisin family using a combination of bioinformatic predictions, mass spectrometry, Marfey's analysis, nuclear magnetic resonance (NMR) spectroscopy, and X-ray crystallography. Milk-based bioassays and 16S rRNA gene amplicon sequencing analyses revealed changes in the microbial composition of milk due to the addition of the CLP tensin A and allowed us to identify its function in promoting the growth of C. zeylanoides, a yeast commonly found in dairy environments. Through transcriptomic analysis, we obtained preliminary insights into the potential metabolic pathways that may contribute to the growth-promoting effect, which indicates a role for the glyoxylate metabolism. This represents the first report of a CLP directly stimulating yeast growth. Understanding how Pseudomonas-derived lipopeptides modulate microbial communities, particularly by supporting yeasts relevant to dairy fermentations, could inform strategies for optimizing dairy fermentation processes like kefir production and improving the stability and quality of fermented dairy products.