Probiotic Properties and Safety Evaluation in the Invertebrate Model Host Galleria mellonella of the Pichia kudriavzevii YGM091 Strain Isolated from Fermented Goat Milk

Issatchenkia orientalis as a platform organism for cost-effective production of organic acids

Driven by the urgent need to reduce the reliance on fossil fuels and mitigate environmental impacts, microbial cell factories capable of producing value-added products from renewable resources have gained significant attention over the past few decades. Notably, non-model yeasts with unique physiological characteristics have emerged as promising candidates for industrial applications, particularly for the production of organic acids. Among them, Issatchenkia orientalis stands out for its exceptional natural tolerance to low pH and high osmotic pressure, traits that are critical for overcoming the limitations of conventional microbial organisms. The acid tolerance of I. orientalis enables organic acid production under low pH conditions, bypassing the need for expensive neutral pH control typically required in conventional processes. Organic acids produced by I. orientalis, such as lactic acid, succinic acid, and itaconic acid, are widely used as building blocks for bioplastics, food additives, and pharmaceuticals. This review summarizes the key findings from systems biology studies on I. orientalis over the past two decades, providing insights into its unique metabolic and physiological traits. Advances in genetic tool development for this non-model yeast are also discussed, enabling targeted metabolic engineering to enhance its production capabilities. Additionally, case studies are highlighted to illustrate the potential of I. orientalis as a platform organism. Finally, the remaining challenges and future directions are addressed to further develop I. orientalis into a robust and versatile microbial cell factory for sustainable biomanufacturing.

Safety Assessment of Two Human Fecal Bacteroides Strain Isolates in Immunodeficient Mice

Bacteroides are potential candidates  for next-generation probiotics (NGPs), which require preclinical safety and efficacy evaluations to ensure their rational use. This study aimed to verify the safety of two Bacteroides strains isolated from human fecal samples, Bacteroides dorei CK16 (B. dorei CK16) and Bacteroides vulgatus CK29 (B. vulgatus CK29), using genomic analysis and in vivo experiments. Whole-genome sequencing analysis of B. dorei CK16 revealed a predicted 4,898 protein-coding sequences (CDS), about 5.5 Mb of total genome length with a G + C content of 42.08%, and B. vulgatus CK29 revealed a predicted 4,610 CDS, about 5.3 Mb of total genome length with a G + C content of 42.56%. Moreover, the genome demonstrated the absence of virulence factors, and insertion sequences related to clinically relevant strains in either strain. A 42-day in vivo experiment was conducted on BALB/c and BALB/c nude mice, with each mouse receiving a daily dose of 1 × 108 colony forming units (CFU) /mL of B. dorei CK16 or B. vulgatus CK29. No significant in vivo pathogenic characteristics were observed based on body weight, organ index, hematological, serum biochemical, or histological analyses, particularly in nude mice. Therefore, the initial safety assessment of the two novel Bacteroides strains exhibited no notable adverse effects in both immunocompetent and immunodeficient mice models.

The Biotherapeutic Potential of a Novel Probiotic Kluyveromyces marxianus Isolated from a Sourdough Starter Against Vaginal Candida albicans Strains

There is an increasing interest in yeasts isolated from natural sources to be used as probiotics. Saccharomyces-based probiotics have been proposed as a valid alternative to the conventional drug therapy for the prevention and treatment of vulvovaginal candidiasis, also considering the resistance of some Candida strains to many antifungals. Here, we isolated from an artisanal sourdough a new yeast strain which was identified as Kluyveromyces marxianus and assessed its probiotic and safety properties, which resulted in comparable properties to all those exhibited by the commercial probiotic Saccharomyces boulardii. Then, we checked the antagonistic activity of the new isolate against some clinical fluconazole resistant C. albicans strains, showing its ability to inhibit filamentation, biofilm formation, and the adhesion of C. albicans to vaginal epithelial A-431 cells. Also, K. marxianus reduced the cell damage provoked by C. albicans and the expression of SAP2 and SAP6 genes. On the whole, our results enlarge the spectrum of the beneficial properties of the food-grade yeast K. marxianus showing for the first time its biotherapeutic potential against C. albicans.

Beneficial and Safety Properties of a Bacteriocinogenic and Putative Probiotic Latilactobacillus sakei subsp. sakei 2a Strain

This work aimed to evaluate some of the probiotic features and safety of the bacteriocin-producing Latilactobacillus sakei subsp. sakei 2a. The effect of selected commercial drugs from different generic groups and antibiotics on the growth of Ltb. sakei subsp. sakei 2a was also determined. The presence of virulence factors was determined based on PCR with total DNA from Ltb. sakei subsp. sakei 2a. Good growth of Ltb. sakei subsp. sakei 2a was recorded in MRS broth supplemented with 0.2% or 0.4% oxbile or in MRS broth adjusted to a pH from 5.0-9.0. Auto-aggregation of Ltb. sakei subsp. sakei 2a was 62.59%. Different levels of co-aggregation were recorded between Ltb. sakei subsp. sakei 2a and Enterococcus faecalis ATCC19443, Ltb. sakei ATCC15521 and Listeria monocytogenes ScottA. Growth of Ltb. sakei subsp. sakei 2a was not inhibited by commercial drugs from different generic groups. The inhibitory effect on the growth of Ltb. sakei subsp. sakei 2a was recorded only in the presence of Arotin [selective serotonin reuptake inhibitor antidepressant] Minimal Inhibition Concentration (MIC) 1.0 mg/mL, Atlansil [Antiarrhythmic] MIC 0.625 mg/mL, Diclofenac potassium [non-steroidal anti-inflammatory drug (NSAID)] MIC 2.5 mg/mL and Spidufen [NSAID] MIC 15.0 mg/mL. Only two antibiotics tested in this study, Amoxil and Urotrobel, inhibited the growth of Ltb. sakei subsp. sakei 2a with a MIC of <0.5 mg/mL and 5.0 mg/mL, respectively. However, Ltb. sakei subsp. sakei 2a generated positive PCR results on the DNA level for vanA (vancomycin resistance), hyl (hyaluronidase), esp (enterococcal surface protein), ace (adhesion of collagen) and cilA (cytolisin) and a high virulence profile when examined for the presence of virulence factors. It is important to underline that cytolysis has been described as a virulence and antibacterial factor.

Biodiversity and probiotic potential of yeasts isolated from sumbawa horse milk

BACKGROUND

The microbial composition of Sumbawa Horse Milk is influenced by various factors, including environmental elements that encompass geographical location, climate, and conditions specific to Sumbawa. This study aimed to determine the biodiversity and genetic diversity of the microbiome of Sumbawa Horse Milk, with an emphasis on yeast.

METHODS

The diversity and group of yeast isolates were evaluated by the sequence-related amplified polymorphism (SRAP) method using ME2F-EM15R (1) and ME2F-EM12R (2) primers. Molecular identification using 18 S rRNA primers was then carried out on nine selected isolates (K_21, K_31, K_42, K_45, K_1, K_6, K_8, K_17, and K_19) to determine the type of yeast. Probiotic candidate tests were carried out on three isolates, namely K_1, K_6 and K_8.

RESULTS

Analysis with NTSYS software on the SRAP results using Primer 1 revealed the presence of two major groups, where Group I was exclusively comprised of K_45 isolate, whereas the other isolates belonged to Group II. On the other hand, analysis with NTSYS software on the SRAP analysis with Primer 2 also showed two major groups with different compositions. Group I consisted of isolates K_39, 38, 37, 36, 35, 34, 33, 31, 29, 28, 27, 26, 25, 24, 23, 22, and 21, while the remaining isolates belonged to Group II. Results of 18 S rRNA analysis demonstrated that K_17 and K_19 had 99.8 and 100% similarity, respectively, and identified as Candida humilis. K_21, K_31, and K_45 were identified as having a 100% similarity to Clavispora lusitaniae, while K_42 had a 99.8% similarity to Candida parapsilosis. Three isolates were identified as belonging to the genus Ogataea, namely Ogataea polymorpha (K_6 and K_8) and Ogataea siamensis (K_1) with similarity of 100% and 99.8%, respectively.

CONCLUSIONS

These findings suggest that the three yeast have potential as probiotics.

Probiotic Yeasts: A Developing Reality?

Yeasts are gaining increasing attention for their potential health benefits as probiotics in recent years. Researchers are actively searching for new yeast strains with probiotic properties (i.e, Debaryomyces hansenii; Kluyveromyces marxianus; Yarrowia lipolytica; Pichia hudriavzevii; and Torulaspora delbrueckii) from various sources, including traditional fermented foods, the human gut, and the environment. This exploration is expanding the pool of potential probiotic yeasts beyond the well-studied Saccharomyces boulardii. Research suggests that specific yeast strains possess properties that could be beneficial for managing conditions like inflammatory bowel disease, irritable bowel syndrome, skin disorders, and allergies. Additionally, probiotic yeasts may compete with pathogenic bacteria for adhesion sites and nutrients, thereby inhibiting their growth and colonization. They might also produce antimicrobial compounds that directly eliminate harmful bacteria. To achieve these goals, the approach that uses probiotics for human health is changing. Next-generation yeast probiotics are emerging as a powerful new approach in the field of live biotherapeutics. By using genetic engineering, scientists are able to equip these tools with specialized capabilities. However, most research on these probiotic yeasts is still in its early stages, and more clinical trials are needed to confirm their efficacy and safety for various health conditions. This review could provide a brief overview of the situation in this field.

Evaluation of Potential Probiotic Properties and In Vivo Safety of Lactic Acid Bacteria and Yeast Strains Isolated from Traditional Home-Made Kefir

Probiotics are known for their health-promoting resources and are considered as beneficial microorganisms. The current study focuses on the isolation, and on a complete in vitro and in vivo characterization, of yeast and lactic acid bacteria acquired from traditional homemade kefir in order to assess their potentiality as probiotic candidates. In particular, the isolates Pichia kudriavzevii Y1, Lactococcus lactis subsp. hordniae LAB1 and Lactococcus lactis subsp. lactis LAB2 were subjected to in vitro characterization to evaluate their suitability as probiotics. Resistance to acid and bile salts, auto-aggregation, co-aggregation, hydrophobicity, and biofilm production capability were examined, as well as their antioxidant activity. A safety assessment was also conducted to confirm the non-pathogenic nature of the isolates, with hemolysis assay and antibiotic resistance assessment. Moreover, mortality in the invertebrate model Galleria mellonella was evaluated. Current findings showed that P. kudriavzevii exhibited estimable probiotic properties, placing them as promising candidates for functional foods. Both lactic acid bacteria isolated in this work could be classified as potential probiotics with advantageous traits, including antimicrobial activity against enteric pathogens and good adhesion ability on intestinal cells. This study revealed that homemade kefir could be a beneficial origin of different probiotic microorganisms that may enhance health and wellness.