Genome Sequence of the Probiotic Yeast Kluyveromyces marxianus fragilis B0399

The probiotic lactic yeast Kluyveromyces marxianus fragilis B0399 (TURVAL B0399) is a strain belonging to a species naturally occurring in kefir and cheese, which is isolated from whey and curds of cow milk.

It is the first yeast not belonging to the genus Saccharomyces with probiotic activity that has appeared in the market, and it was approved as a probiotic for both animal feeding (1) and human consumption (2). This strain was shown to remain viable after consumption, surpassing the gastric barrier and colonizing the gut adhering to the enterocytes of the intestinal epithelium (3). Moreover, it regulates intestinal activity during antibiotic therapy, thanks to the yeast intrinsic resistance to bacterium-targeting antibiotics (4). Furthermore, its β-galactosidase activity, absent in strains of the genus Saccharomyces, permits the degradation of lactose, generating glucose and galactose; therefore, it is useful in lowering the effects of lactose intolerance in susceptible individuals (5). Several in vitro (3) and in vivo (4, 6) experimental evidences demonstrated that K. marxianus B0399 is able to modulate the immune response, reducing the proinflammatory cytokine levels, thus being useful for mitigation of the effect of several diseases, such as irritable bowel syndrome (6, 7).

Sequencing of its genome was performed to gain more detailed information on its characteristics as a probiotic and to broaden knowledge on the genomic biodiversity in the species K. marxianus, since other strains whose genome sequences are available are used for bioethanol production or other applications (8,–10).