Heterologous Expression of the Leuconostoc Bacteriocin Leucocin C in Probiotic Yeast Saccharomyces boulardii

Enabling technologies for in situ biomanufacturing using probiotic yeast

Saccharomyces boulardii (Sb) is a Generally Regarded As Safe (GRAS) probiotic yeast currently used to alleviate symptoms from various gastrointestinal diseases. Sb is a promising platform for probiotic and biotherapeutic engineering as it is the only probiotic eukaryote and carries with it a unique set of advantages compared to bacterial strains, including resistance to phage, high protein secretion abilities, and intrinsic resistance to antibiotics. While engineered Sb has not been studied as extensively as its close relative Saccharomyces cerevisiae (Sc), many genetic engineering tools developed for Sc have also shown promise in Sb. In this review, we address recent research to develop tools for genetic engineering, colonization modulation, biomarker sensing, and drug production in Sb. Ongoing efforts, especially those that overcome gut-specific challenges to engineered performance, are highlighted as they advance this chassis as a scalable platform for treating gastrointestinal diseases.

A yeast-based oral therapeutic delivers immune checkpoint inhibitors to reduce intestinal tumor burden

Engineered probiotics are an emerging platform for in situ delivery of therapeutics to the gut. Herein, we developed an orally administered, yeast-based therapeutic delivery system to deliver next-generation immune checkpoint inhibitor (ICI) proteins directly to gastrointestinal tumors. We engineered Saccharomyces cerevisiae var. boulardii (Sb), a probiotic yeast with high genetic tractability and innate anticancer activity, to secrete "miniature" antibody variants that target programmed death ligand 1 (Sb_haPD-1). When tested in an ICI-refractory colorectal cancer (CRC) mouse model, Sb_haPD-1 significantly reduced intestinal tumor burden and resulted in significant shifts to the immune cell profile and microbiome composition. This oral therapeutic platform is modular and highly customizable, opening new avenues of targeted drug delivery that can be applied to treat a myriad of gastrointestinal malignancies.

Engineering Saccharomyces cerevisiae for medical applications

BACKGROUND

During the last decades, the advancements in synthetic biology opened the doors for a profusion of cost-effective, fast, and ecologically friendly medical applications priorly unimaginable. Following the trend, the genetic engineering of the baker's yeast, Saccharomyces cerevisiae, propelled its status from an instrumental ally in the food industry to a therapy and prophylaxis aid.

MAIN TEXT

In this review, we scrutinize the main applications of engineered S. cerevisiae in the medical field focusing on its use as a cell factory for pharmaceuticals and vaccines, a biosensor for diagnostic and biomimetic assays, and as a live biotherapeutic product for the smart in situ treatment of intestinal ailments. An extensive view of these fields' academic and commercial developments as well as main hindrances is presented.

CONCLUSION

Although the field still faces challenges, the development of yeast-based medical applications is often considered a success story. The rapid advances in synthetic biology strongly support the case for a future where engineered yeasts play an important role in medicine.

Heterologous Expression of the Antiviral Lectin Griffithsin in Probiotic Saccharomyces boulardii and In Vitro Characterization of Its Properties

In this study, the probiotic yeast Saccharomyces boulardii was engineered to secrete the antiviral lectin griffithsin. Twelve genetic tools with the griffithsin gene were cloned into the vector pSF-TEF1-URA3 and introduced into S. boulardii. In the recombinant strains, a 16.9 kDa band was detected using SDS-PAGE and further recognized by griffithsin antibody with Western blotting. S. boulardii strains FM, FT, HC, and HE with a high yield of griffithsin were acquired for property characterization in vitro. The four recombinant strains displayed a similar growth pattern to that of the control strains, while their morphological characteristics had changed according to scanning electron microscopy. In simulated gastrointestinal digestive fluids, the survival rates of S. boulardii FM, FT, and HC were significantly decreased (86.32 ± 1.49% to 95.36 ± 1.94%) compared with those of the control strains, with survival rates between 95.88 ± 0.00% and 98.74 ± 1.97%. The hydrophobicity of S. boulardii FM, the strain with the highest griffithsin production, was significantly increased to 21.89 ± 1.07%, and it exhibited a reduced auto-aggregation rate (57.64 ± 2.61%). Finally, Vero cells infected with porcine epidemic diarrhea virus (PEDV) were used to evaluate the strains' antiviral activity, and the rate at which S. boulardii FM inhibited PEDV reached 131.36 ± 1.06%, which was significantly higher than that of the control group.

Gut Distribution, Impact Factor, and Action Mechanism of Bacteriocin-Producing Beneficial Microbes as Promising Antimicrobial Agents in Gastrointestinal Infection

Gastrointestinal (GI) infection by intestinal pathogens poses great threats to human health, and the therapeutic use of antibiotics has reached a bottleneck due to drug resistance. The developments of antimicrobial peptides produced by beneficial bacteria have drawn attention by virtue of effective, safe, and not prone to developing resistance. Though bacteriocin as antimicrobial agent in gut infection has been intensively investigated and reviewed, reviews on that of bacteriocin-producing beneficial microbes are very rare. It is important to explicitly state the prospect of bacteriocin-producing microbes in prevention of gastrointestinal infection towards their application in host. This review discusses the potential of gut as an appropriate resource for mining targeted bacteriocin-producing microbes. Then, host-related factors affecting the bacteriocin production and activity of bacteriocin-producing microbes in the gut are summarized. Accordingly, the multiple mechanisms (direct inhibition and indirect inhibition) behind the preventive effects of bacteriocin-producing microbes on gut infection are discussed. Finally, we propose several targeted strategies for the manipulation of bacteriocin-producing beneficial microbes to improve their performance in antimicrobial outcomes. We anticipate an upcoming emergence of developments and applications of bacteriocin-producing beneficial microbes as antimicrobial agent in gut infection induced by pathogenic bacteria.

A Saccharomyces boulardii-derived antioxidant protein, thioredoxin, ameliorates intestinal inflammation through transactivating epidermal growth factor receptor

Saccharomyces boulardii (Sb) is a probiotic yeast for the treatment of gastrointestinal disorders, including inflammatory bowel disease (IBD). Little is known about the modulatory capacity of the Sb in IBD. Here, we found that oral gavage of Sb supernatant (SbS) alleviated gut inflammation, protected the intestinal barrier, and reversed DSS-induced down-regulated activation of epidermal growth factor receptor (EGFR) in colitis. Mass spectrum analysis showed that thioredoxin (Trx) is one of the critical secreted soluble proteins participating in EGFR activation detected in SbS. Trx exerted an array of significant effects on anti-inflammatory activity, including alleviating inflammation, protecting gut barrier, suppressing apoptosis, as well as reducing oxidative stress. Mechanistically, Trx promoted EGFR ligand gene expression and transactivated EGFR in a concentration-dependent manner. EGFR kinase inhibitor could block Trx-mediated preventive effects of intestinal epithelial injury. Our data suggested that Sb-derived soluble protein Trx could serve as a potential prophylactic, as a novel postbiotic against colitis, which provides a new strategy for the precision prevention and treatment of IBD.

The Progress of the Biotechnological Production of Class IIa Bacteriocins in Various Cell Factories and Its Future Challenges

Class IIa bacteriocins produced in lactic acid bacteria are short cationic peptides with antimicrobial activity. In the search for new biopreservation agents, class IIa bacteriocins are considered to be the best potential candidates, not only due to their large abundance but also because of their high biological activity and excellent thermal stability. However, regulated by the biosynthetic regulatory system, the natural class IIa bacteriocin yield is low, and the extraction process is complicated. The biotechnological production of class IIa bacteriocins in various cell factories has been attempted to improve this situation. In this review, we focus on the application of biotechnological routes for class IIa bacteriocin production. The drawbacks and improvements in the production of class IIa bacteriocins in various cell factories are discussed. Furthermore, we present the main challenge of class IIa bacteriocins, focusing on increasing their production by constructing suitable cell factories. Recombinant bacteriocins have made considerable progress from inclusion body formation, dissolved form and low antibacterial activity to yield recovery. The development of prospective cell factories for the biotechnological production of bacteriocins is still required, which may facilitate the application of bacteriocins in the food industry.

New biomarkers underlying acetic acid tolerance in the probiotic yeast Saccharomyces cerevisiae var. boulardii

Evolutionary engineering experiments, in combination with omics technologies, revealed genetic markers underpinning the molecular mechanisms behind acetic acid stress tolerance in the probiotic yeast Saccharomyces cerevisiae var. boulardii. Here, compared to the ancestral Ent strain, evolved yeast strains could quickly adapt to high acetic acid levels (7 g/L) and displayed a shorter lag phase of growth. Bioinformatic-aided whole-genome sequencing identified genetic changes associated with enhanced strain robustness to acetic acid: a duplicated sequence in the essential endocytotic PAN1 gene, mutations in a cell wall mannoprotein (dan4Thr192del), a lipid and fatty acid transcription factor (oaf1Ser57Pro) and a thiamine biosynthetic enzyme (thi13Thr332Ala). Induction of PAN1 and its associated endocytic complex SLA1 and END3 genes was observed following acetic acid treatment in the evolved-resistant strain when compared to the ancestral strain. Genome-wide transcriptomic analysis of the evolved Ent acid-resistant strain (Ent ev16) also revealed a dramatic rewiring of gene expression among genes associated with cellular transport, metabolism, oxidative stress response, biosynthesis/organization of the cell wall, and cell membrane. Some evolved strains also displayed better growth at high acetic acid concentrations and exhibited adaptive metabolic profiles with altered levels of secreted ethanol (4.0-6.4% decrease), glycerol (31.4-78.5% increase), and acetic acid (53.0-60.3% increase) when compared to the ancestral strain. Overall, duplication/mutations and transcriptional alterations are key mechanisms driving improved acetic acid tolerance in probiotic strains. We successfully used adaptive evolutionary engineering to rapidly and effectively elucidate the molecular mechanisms behind important industrial traits to obtain robust probiotic yeast strains for myriad biotechnological applications. KEY POINTS: •Acetic acid adaptation of evolutionary engineered robust probiotic yeast S. boulardii •Enterol ev16 with altered genetic and transcriptomic profiles survives in up to 7 g/L acetic acid •Improved acetic acid tolerance of S. boulardii ev16 with mutated PAN1, DAN4, OAF1, and THI13 genes.

Evaluation of the impact of polypeptide-p on diabetic rats upon its cloning, expression, and secretion in Saccharomyces boulardii

This study was designed to evaluate the effectiveness of recombinant polypeptide-p derived from Momordica charantia on diabetic rats. In this research, the optimized sequence of polypeptide-p gene fused to a secretion signal tag was cloned into the expression vector and transformed into probiotic Saccharomyces boulardii. The production of recombinant secretion protein was verified by western blotting, HPLC, and mass spectrometry. To assay recombinant yeast bioactivity in the gut, diabetic rats were orally fed wild-type and recombinant S. boulardii, in short SB and rSB, respectively, at two low and high doses as well as glibenclamide as a reference drug. In untreated diabetic and treated diabetic + SB rats (low and high doses), the blood glucose increased from 461, 481, and 455 (mg/dl), respectively, to higher than 600 mg/dl on the 21st day. Whereas glibenclamide and rSB treatments showed a significant reduction in the blood glucose level. The result of this study promised a safe plant-source supplement for diabetes through probiotic orchestration.

Improving therapeutic protein secretion in the probiotic yeast Saccharomyces boulardii using a multifactorial engineering approach

The probiotic yeast Saccharomyces boulardii (Sb) is a promising chassis to deliver therapeutic proteins to the gut due to Sb's innate therapeutic properties, resistance to phage and antibiotics, and high protein secretion capacity. To maintain therapeutic efficacy in the context of challenges such as washout, low rates of diffusion, weak target binding, and/or high rates of proteolysis, it is desirable to engineer Sb strains with enhanced levels of protein secretion. In this work, we explored genetic modifications in both cis- (i.e. to the expression cassette of the secreted protein) and trans- (i.e. to the Sb genome) that enhance Sb's ability to secrete proteins, taking a Clostridioides difficile Toxin A neutralizing peptide (NPA) as our model therapeutic. First, by modulating the copy number of the NPA expression cassette, we found NPA concentrations in the supernatant could be varied by sixfold (76-458 mg/L) in microbioreactor fermentations. In the context of high NPA copy number, we found a previously-developed collection of native and synthetic secretion signals could further tune NPA secretion between 121 and 463 mg/L. Then, guided by prior knowledge of S. cerevisiae's secretion mechanisms, we generated a library of homozygous single gene deletion strains, the most productive of which achieved 2297 mg/L secretory production of NPA. We then expanded on this library by performing combinatorial gene deletions, supplemented by proteomics experiments. We ultimately constructed a quadruple protease-deficient Sb strain that produces 5045 mg/L secretory NPA, an improvement of > tenfold over wild-type Sb. Overall, this work systematically explores a broad collection of engineering strategies to improve protein secretion in Sb and highlights the ability of proteomics to highlight under-explored mediators of this process. In doing so, we created a set of probiotic strains that are capable of delivering a wide range of protein titers and therefore furthers the ability of Sb to deliver therapeutics to the gut and other settings to which it is adapted.

Recombinant Probiotic Preparations: Current State, Development and Application Prospects

The article is devoted to the latest achievements in the field of research, development, and implementation of various types of medicinal products based on recombinant probiotics. The benefits of probiotics, their modern use in medicine along with the most frequently used genera and species of probiotic microorganisms were highlighted. The medicinal and therapeutic activities of the studied probiotics were indicated. The review suggests various methods of creating recombinant probiotic microorganisms, including standard genetic engineering methods, as well as systems biology approaches and new methods of using the CRISPR-Cas system. The range of potential therapeutic applications of drugs based on recombinant probiotics was proposed. Special attention was paid to modern research on the creation of new, more effective recombinant probiotics that can be used for various therapeutic purposes. Considering the vast diversity of therapeutic applications of recombinant probiotics and ambiguous functions, their use for the potential treatment of various common human diseases (non-infectious and infectious diseases of the gastrointestinal tract, metabolic disorders, and allergic conditions) was investigated. The prospects for creating different types of vaccines based on recombinant probiotics together with the prospects for their implementation into medicine were considered. The possibilities of using recombinant probiotics in veterinary medicine, particularly for the prevention of domestic animal diseases, were reviewed. The prospects for the implementation of recombinant probiotics as vaccines and diagnostic tools for testing certain diseases as well as modeling the work of the human digestive system were highlighted. The risks of creation, application, including the issues related to the regulatory sphere regarding the use of new recombinant microorganisms, which can potentially enter the environment and cause unforeseen circumstances, were outlined.

High-Titer Production of the Fungal Anhydrotetracycline, TAN-1612, in Engineered Yeasts

Antibiotic resistance is a growing global health threat, demanding urgent responses. Tetracyclines, a widely used antibiotic class, are increasingly succumbing to antibiotic resistance; generating novel analogues is therefore a top priority for public health. Fungal tetracyclines provide structural and enzymatic diversity for novel tetracycline analogue production in tractable heterologous hosts, like yeasts, to combat antibiotic-resistant pathogens. Here, we successfully engineered Saccharomyces cerevisiae (baker's yeast) and Saccharomyces boulardii (probiotic yeast) to produce the nonantibiotic fungal anhydrotetracycline, TAN-1612, in synthetic defined media─necessary for clean purifications─through heterologously expressing TAN-1612 genes mined from the fungus, Aspergillus niger ATCC 1015. This was accomplished via (i) a promoter library-based combinatorial pathway optimization of the biosynthetic TAN-1612 genes coexpressed with a putative TAN-1612 efflux pump, reducing TAN-1612 toxicity in yeasts while simultaneously increasing supernatant titers and (ii) the development of a medium-throughput UV-visible spectrophotometric assay that facilitates TAN-1612 combinatorial library screening. Through this multipronged approach, we optimized TAN-1612 production, yielding an over 450-fold increase compared to previously reported S. cerevisiae yields. TAN-1612 is an important tetracycline analogue precursor, and we thus present the first step toward generating novel tetracycline analogue therapeutics to combat current and emerging antibiotic resistance. We also report the first heterologous production of a fungal polyketide, like TAN-1612, in the probiotic S. boulardii. This highlights that engineered S. boulardii can biosynthesize complex natural products like tetracyclines, setting the stage to equip probiotic yeasts with synthetic therapeutic functionalities to generate living therapeutics or biocontrol agents for clinical and agricultural applications.

Bioengineered Probiotics: Synthetic Biology Can Provide Live Cell Therapeutics for the Treatment of Foodborne Diseases

The rising prevalence of antibiotic resistant microbial pathogens presents an ominous health and economic challenge to modern society. The discovery and large-scale development of antibiotic drugs in previous decades was transformational, providing cheap, effective treatment for what would previously have been a lethal infection. As microbial strains resistant to many or even all antibiotic drug treatments have evolved, there is an urgent need for new drugs or antimicrobial treatments to control these pathogens. The ability to sequence and mine the genomes of an increasing number of microbial strains from previously unexplored environments has the potential to identify new natural product antibiotic biosynthesis pathways. This coupled with the power of synthetic biology to generate new production chassis, biosensors and “weaponized” live cell therapeutics may provide new means to combat the rapidly evolving threat of drug resistant microbial pathogens. This review focuses on the application of synthetic biology to construct probiotic strains that have been endowed with functionalities allowing them to identify, compete with and in some cases kill microbial pathogens as well as stimulate host immunity. Weaponized probiotics may have the greatest potential for use against pathogens that infect the gastrointestinal tract: Vibrio cholerae, Staphylococcus aureus, Clostridium perfringens and Clostridioides difficile. The potential benefits of engineered probiotics are highlighted along with the challenges that must still be met before these intriguing and exciting new therapeutic tools can be widely deployed.

Bioactive peptides produced by engineered probiotics and other food-grade bacteria: A review

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Synthetic biology improves probiotics therapeutic approaches.

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Engineering technologies contribute to design probiotics mechanisms of action.

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Edition of proteolytic systems induce the generation of specific bioactive peptides.

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Engineered probiotics should be evaluated as therapeutic agents in clinical trials.

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Therapeutical and technological uses of engineered probiotics are still controversial.

Synthetic biology is employed for the study and design of engineered microbes with new and improved therapeutic functions. The main advantage of synthetic biology is the selective genetic manipulation of living organisms with desirable beneficial effects such as probiotics. Engineering technologies have contributed to the edition of metabolic processes involved in the mechanisms of action of probiotics, such as the generation of bioactive peptides. Hence, current information related to bioactive peptides, produced by different engineering probiotics, with antimicrobial, antiviral, antidiabetic, and antihypertensive activities, as well as their potential use as functional ingredients, is discussed here. Besides, the effectiveness and safety aspects of these bioactive peptides were also described.

The development of live biotherapeutics against Clostridioides difficile infection towards reconstituting gut microbiota

Clostridioides difficile is the most prevalent pathogen of nosocomial diarrhea. In the United States, over 450,000 cases of C. difficile infection (CDI), responsible for more than 29,000 deaths, are reported annually in recent years. Because of the emergence of hypervirulent strains and strains less susceptible to vancomycin and fidaxomicin, new therapeutics other than antibiotics are urgently needed. The gut microbiome serves as one of the first-line defenses against C. difficile colonization. The use of antibiotics causes gut microbiota dysbiosis and shifts the status from colonization resistance to infection. Hence, novel CDI biotherapeutics capable of reconstituting normal gut microbiota have become a focus of drug development in this field.

Production of neoagarooligosaccharides by probiotic yeast Saccharomyces cerevisiae var. boulardii engineered as a microbial cell factory

Background

Saccharomyces cerevisiae var. boulardii is a representative probiotic yeast that has been widely used in the food and pharmaceutical industries. However, S. boulardii has not been studied as a microbial cell factory for producing useful substances. Agarose, a major component of red macroalgae, can be depolymerized into neoagarooligosaccharides (NAOSs) by an endo-type β-agarase. NAOSs, including neoagarotetraose (NeoDP4), are known to be health-benefiting substances owing to their prebiotic effect. Thus, NAOS production in the gut is required. In this study, the probiotic yeast S. boulardii was engineered to produce NAOSs by expressing an endo-type β-agarase, BpGH16A, derived from a human gut bacterium Bacteroides plebeius.

Results

In total, four different signal peptides were compared in S. boulardii for protein (BpGH16A) secretion for the first time. The SED1 signal peptide derived from Saccharomyces cerevisiae was selected as optimal for extracellular production of NeoDP4 from agarose. Expression of BpGH16A was performed in two ways using the plasmid vector system and the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system. The production of NeoDP4 by engineered S. boulardii was verified and quantified. NeoDP4 was produced by S. boulardii engineered using the plasmid vector system and CRISPR-Cas9 at 1.86 and 0.80 g/L in a 72-h fermentation, respectively.

Conclusions

This is the first report on NAOS production using the probiotic yeast S. boulardii. Our results suggest that S. boulardii can be considered a microbial cell factory to produce health-beneficial substances in the human gut.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01644-w.