Foodborne Yeasts: New Heroes of Gut Health?

In the realm of food production, strains of microorganisms, including fungi, have always been pivotal in various processes, from fermenting to flavor production. However, while their biotechnological value has been extensively studied, their interactions with the human host remain a relatively uncharted territory. In a time when the gut microbiota plays a central role in understanding numerous health-related pathologies, the potential effects of foodborne yeasts on gut health come into focus.

In this comprehensive study, we shed light on five yeast strains extensively used in food production, particularly in cheese and meat processing: Cyberlindnera jadinii, Debaryomyces hansenii, Kazachstania unispora, Kluyveromyces lactis, and Pichia membranifaciens. These strains, renowned for their contribution to cheese aroma development and pH modification, have been selected for their potential to exhibit anti-inflammatory properties and their ability to persist within the gut.

Fungal Diversity in Food Production

For centuries, fungi have played an integral role in the production of fermented foods such as wine, bread, and cheese across different cultures. Notably, Saccharomyces cerevisiae, a well-known yeast strain, has been instrumental in the production of wine, beer, and bread. Beyond Saccharomyces cerevisiae, a plethora of other yeast genera have found their place in food biotechnology. Candida, Debaryomyces, Kluyveromyces, Pachysolen, Phaffia, Pichia, Saccharomyces, and Yarrowia, to name a few, contribute to diverse food processes, each with distinct physiological properties. These strains function not only as biochemical factories for bioproduct production but are also ingested alive in food products, such as cheese, consequently accumulating in the digestive tract.

Although these yeast strains are generally considered harmless, having been used in food production for decades, little is known about their potential direct or indirect positive effects on the host. Traditionally, research has been concentrated on their role in aroma production and fermentation capabilities. This study takes a pioneering step in characterizing their potential as probiotics, focusing on their anti-inflammatory properties and their ability to thrive in the gut.

Methods and Materials

Cell Culture:

Human enterocyte-like Caco-2 cells were cultured in a medium containing Dulbecco’s modified Eagle’s medium (DMEM) supplemented with various essential components. Similarly, HT29-MTX cells, derived from the human colon, were cultured under specified conditions.

Preparation of Fungi:

The yeast strains used in the study were cultured and processed according to a rigorous protocol. For some experiments, culture supernatants were filtered to remove microorganisms, while for heat-killed experiments, yeasts were subjected to specific conditions to ensure their inactivation.

Fungal Adhesion on Caco2 and HT29-MTX Cells:

The adhesion of yeast strains to cultured enterocytes was assessed quantitatively using the CFU method. This involved a series of steps, including washing, lysing, and CFU determination.

DNA Extraction:

Samples were disrupted and processed to obtain DNA, which was then assessed for quality and concentration. Real-time quantitative PCR (RT-qPCR) was conducted to determine adhesion percentages for each strain.

IL-8 Production by HT29 Cells after Coculture with Fungi:

In stimulation protocols, HT29 cells were stressed, and yeast strains were coincubated with the cells. TNF-α was added as part of the stimulation process.

Findings and Implications

The results of this pioneering study are groundbreaking. The research unveils the largely unexplored potential of foodborne yeasts in positively impacting gut health. Notably, two yeast strains, Cyberlindnera jadinii and Kluyveromyces lactis, demonstrated their potential as probiotics to combat gut inflammation. Cyberlindnera jadinii, in particular, exhibited the ability to survive the gastrointestinal transit, while Kluyveromyces lactis did not. Transcriptomic analysis suggests a role of IL-8, Mif, and Fkbp5 in the effect of C. jadinii on the immune system.

Moreover, the study also revealed a modification in the microbiota composition after treatment with C. jadinii, characterized by an increase in beneficial microorganisms and a decrease in pathobionts. These findings collectively suggest that both C. jadinii and K. lactis strains hold the potential to serve as probiotic yeast strains in the fight against gut inflammation.

While this research provides a promising foundation, further studies are imperative to unravel the intricate mechanisms underlying the beneficial effects of these yeast strains on gut health. The knowledge garnered from this study has the potential to revolutionize our understanding of the symbiotic relationship between foodborne yeasts and the human digestive system.

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