Deleting the VTC3 gene from Saccharomyces cerevisiae produced a yeast strain whose culture supernatant inhibited multiple pathogenic bacteria, including multidrug-resistant isolates, while live yeast reduced bacterial burdens and protected mice from Salmonella Typhimurium-induced enteritis. Experiments involving 11 bacterial strains, Galleria mellonella larvae and a mouse infection model found that the engineered yeast altered bacterial growth, adhesion and biofilm formation without substantially impairing its own proliferation. Untargeted metabolomics indicated that its antibacterial activity was associated with increased production of organic acids and other small molecules, although the investigators did not isolate or validate individual active compounds or establish that they work together or alone.
The study focused on VTC3, which encodes a component of a vacuolar membrane transport complex involved in polyphosphate synthesis and transport. Polyphosphate participates in phosphate homeostasis, cellular stress responses and virulence regulation, but the gene is not directly involved in organic-acid synthesis. The researchers therefore proposed that its deletion may indirectly reshape carbon metabolism, increasing the secretion of acidic compounds with activity against bacteria. Growth curves for VTC3-knockout yeast and its parental BY4743 strain were nearly identical over 24 hours, indicating that the modification did not cause a detectable growth defect under standard laboratory conditions.
In liquid culture, cell-free supernatant from the knockout yeast delayed the transition from lag to log phase, reduced maximum bacterial growth rates and lowered final counts of Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. Controls containing sterile water and complete YPD medium produced similar growth parameters, indicating that nutrient depletion did not explain the effect. A broader screen found that the knockout supernatant was more inhibitory than supernatants from parental BY4743 and the probiotic yeast Saccharomyces boulardii. Residual bacterial growth of 21.04% ± 0.39% was recorded for Escherichia coli mcr-1 and 1.74% ± 0.03% for Acinetobacter baumannii 21-1, compared with 53.94% ± 0.60% and 21.46% ± 6.08%, respectively, in the parental-strain control. Activity was not uniform across all isolates: the knockout supernatant had little or no significant advantage over BY4743 for two Klebsiella pneumoniae strains and one Pseudomonas aeruginosa strain.
The culture supernatant also interfered with several processes associated with biofilm development. Crystal violet assays showed dose-dependent inhibition of biofilm formation in E. coli ATCC 25922, E. coli mcr-1, S. aureus ATCC 29213, methicillin-resistant S. aureus and K. pneumoniae ATCC 700603. At a supernatant concentration of 90% by volume, reported inhibition rates ranged from 83.05% to 87.44% across these five bacteria. At 50% supernatant, adhesion by E. coli and S. aureus fell by 29.45% and 37.89%, respectively. Cell-surface hydrophobicity decreased by 13.05% and 16.28%, while extracellular polysaccharide production fell by 22.61% and 16.57%. These measurements concern planktonic bacteria transitioning toward biofilm formation; the study did not test whether the supernatant could remove established, mature biofilms. Nor did the biofilm and surface-characterization experiments include a parallel BY4743 supernatant control, preventing a direct assessment of which effects were specifically enhanced by the knockout.
Live coculture experiments supported an effect beyond inhibition by a cell-free product. Viable VTC3-knockout yeast reduced viable counts of E. coli, S. aureus and K. pneumoniae after 16 and 24 hours compared with bacterial monocultures in YPD or water. Inhibition after 16 hours was 48.44% for E. coli, 89.88% for S. aureus and 45.77% for K. pneumoniae; the corresponding values after 24 hours were 49.21%, 89.81% and 45.07%. The knockout yeast also showed 16.48% greater autoaggregation than BY4743 and increased coaggregation with E. coli and S. aureus by 26.31% and 15.4%, respectively. In simulated gastric fluid at pH 3.0, 82.13% of the knockout yeast survived after one hour and more than 75% after three hours. Following four hours in simulated intestinal fluid containing 0.3% bile salts, 65.17% remained viable. These static assays suggest gastrointestinal tolerance and a capacity for close contact with pathogens, but they do not establish long-term intestinal colonization, persistence in a moving gut environment or competition within a complex microbiota.
In G. mellonella, neither live yeast, heat-inactivated yeast nor culture supernatant noticeably changed the survival of uninfected larvae over five days, indicating no substantial toxicity in this screening model. After infection with E. coli or S. aureus, however, live VTC3-knockout yeast and its supernatant significantly extended host survival and reduced bacterial burdens, whereas heat-inactivated yeast provided no protective effect. This contrast indicates that protection depended on active metabolic or secretory activity rather than simply on the physical presence of yeast-cell structures. The result also links the activity in larvae to the same secretory mechanism observed in liquid culture, while remaining an early whole-organism test rather than evidence of therapeutic efficacy in people.
The mammalian experiment used specific-pathogen-free male C57BL/6J mice and a prophylactic regimen of daily intragastric administration for seven days before Salmonella Typhimurium challenge. Thirty-six animals were divided among knockout-yeast, parental-yeast and saline groups, with 12 mice per group, and each group was then divided into six-mouse sub-cohorts for a five-day infection study or a 10-day survival study. Knockout-yeast treatment reduced infection-associated body-weight loss and increased survival relative to the controls. Five days after infection, mice receiving the knockout yeast had lower S. Typhimurium loads in the ileum, colon and caecum. Their spleens and colons also appeared closer to normal, while histology showed better-preserved intestinal villi, less oedema and less inflammatory-cell infiltration than in the saline and parental-yeast groups.
Molecular measurements in the ileum accompanied those pathological findings. Knockout-yeast treatment reduced transcription of the pro-inflammatory cytokines IL-6 and TNF-α and increased IL-10 transcription. It also increased expression of the tight-junction proteins occludin, claudin-1 and ZO-1 relative to the saline control. Together, these observations associate the treatment with lower inflammation and better epithelial-barrier integrity in the mouse model. Because yeast was administered before infection, the experiment evaluates protection against pathogen establishment rather than treatment of an already established infection. The relatively simple microbiota of specific-pathogen-free mice, absence of colonization and persistence measurements, and incomplete assessment of tissue translocation also limit translation to human gastrointestinal disease.
Untargeted liquid chromatography-tandem mass spectrometry identified 369 differentially abundant metabolites in the knockout and parental strain supernatants, including 135 with higher levels in the knockout. Organic acids and their derivatives represented 64.71% of one reported differential-metabolite classification, and increased compounds included orotic acid, dihydroorotic acid, ureidosuccinic acid, phenylpyruvic acid and D-3-phenyllactic acid. Pathway analysis found enrichment involving amino-acid metabolism, pyrimidine metabolism, aminoacyl-tRNA biosynthesis, nicotinate metabolism and ABC transporters. Physicochemical experiments showed that antibacterial activity was strongest at pH 2–4 and diminished or disappeared at pH 6–8. Proteases did not materially reduce activity, and it remained after one hour at temperatures as high as 100°C. These properties support a heat-stable, non-proteinaceous mechanism consistent with organic acids or other small molecules, but they do not prove that the differentially detected metabolites caused the antibacterial effect. The investigators also note that some metabolites had previously been associated with antibacterial, antioxidant or immunomodulatory activities, which does not establish their activity at the concentrations present here.
Several limitations constrain the conclusions and the path toward clinical use. Untargeted metabolomics did not resolve which individual compounds were active, whether one acid dominated the effect or whether several acted synergistically, and the regulatory pathway connecting VTC3 deletion, polyphosphate metabolism and organic-acid secretion remains unresolved. The researchers also did not assess whether repeated exposure could select for bacterial resistance, evaluate activity under controlled physiological pH, or establish the effective dose range. The absence of an incubated, no-culture YPD control in every comparison prevents complete subtraction of possible medium-degradation products. Long-term toxicity, immunogenicity, genetic stability, horizontal gene transfer and efficacy in complex human-like microbiota remain untested. The study therefore supports VTC3-knockout S. cerevisiae as a promising experimental probiotic and metabolic-engineering target, not as an established anti-infection therapy, and further work must identify the active metabolites, test resistance and chronic safety, and evaluate dosing and colonization in more physiologically representative systems.
Subject of Research: Laboratory evaluation of VTC3-knockout yeast against multidrug-resistant bacterial pathogens
Article Title: Antibacterial efficacy and mechanism of action of VTC3-knockout Saccharomyces cerevisiae against multidrug- resistant pathogenic bacteria
Article References: Yang, W., Li, M., Zhang, Y., Hu, K., Lu, B., Yuan, A., Zhu, Z., & Li, Y. (2026). Antibacterial efficacy and mechanism of action of VTC3-knockout Saccharomyces cerevisiae against multidrug- resistant pathogenic bacteria. Frontiers in Microbiology, 17, Article 1937861. https://doi.org/10.3389/fmicb.2026.1937861
Image Credits: AI Generated
DOI: 10.3389/fmicb.2026.1937861
Keywords: VTC3 knockout, Saccharomyces cerevisiae, multidrug resistance, antimicrobial metabolites, organic acids, biofilm inhibition, mouse enteritis, Salmonella Typhimurium, probiotic yeast, Antibacterial, efficacy, mechanism
