The safety of a Kluyveromyces lactis strain lineage for enzyme production

Biochemical Properties of a Promising Milk-Clotting Enzyme, Moose (Alces alces) Recombinant Chymosin

Moose (Alces alces) recombinant chymosin with a milk-clotting activity of 86 AU/mL was synthesized in the Kluyveromyces lactis expression system. After precipitation with ammonium sulfate and chromatographic purification, a sample of genetically engineered moose chymosin with a specific milk-clotting activity of 15,768 AU/mg was obtained, which was used for extensive biochemical characterization of the enzyme. The threshold of the thermal stability of moose chymosin was 55 °C; its complete inactivation occurred after heating at 60 °C. The total proteolytic activity of moose chymosin was 0.332 A280 units. The ratio of milk-clotting and total proteolytic activities of the enzyme was 0.8. The Km, kcat and kcat/Km values of moose chymosin were 4.7 μM, 98.7 s-1, and 21.1 μM-1 s-1, respectively. The pattern of change in the coagulation activity as a function of pH and Ca2+ concentration was consistent with the requirements for milk coagulants for cheese making. The optimum temperature of the enzyme was 50-55 °C. The introduction of Mg2+, Zn2+, Co2+, Ba2+, Fe2+, Mn2+, Ca2+, and Cu2+ into milk activated the coagulation ability of moose chymosin, while Ni ions on the contrary inhibited its activity. Using previously published data, we compared the biochemical properties of recombinant moose chymosin produced in bacterial (Escherichia coli) and yeast (K. lactis) producers.

Mutation, food-grade expression, and characterization of a lactonase for zearalenone degradation

Zearalenone (ZEN) is a mycotoxin that causes serious threats to human health. People are exposed to ZEN contamination externally and internally through many ways, while environmental-friendly strategies for efficient elimination of ZEN are urgently needed worldwide. Previous studies revealed that the lactonase Zhd101 from Clonostachys rosea can hydrolyze ZEN to low toxicity compounds. In this work, the enzyme Zhd101 was conducted with combinational mutations to enhance its application properties. The optimal mutant (V153H-V158F), named Zhd101.1, was selected and introduced into the food-grade recombinant yeast strain Kluyveromyces lactis GG799(pKLAC1-Zhd101.1), followed by induced expression and secretion into the supernatant. The enzymatic properties of this mutant were extensively examined, revealing a 1.1-fold increase in specific activity, as well as improved thermostability and pH stability, compared to the wild-type enzyme. The ZEN degradation tests and the reaction parameters optimization were carried out in both solutions and the ZEN-contaminated corns, using the fermentation supernatants of the food-grade yeast strain. Results showed that the degradation rates for ZEN by fermentation supernatants reached 96.9% under optimal reaction conditions and 74.6% in corn samples, respectively. These new results are a useful reference to zearalenone biodegradation technologies and indicated that the mutant enzyme Zhd101.1 has potential to be used in food and feed industries. KEY POINTS: • Mutated lactonase showed 1.1-fold activity, better pH stability than the wild type. • The strain K. lactis GG799(pKLAC1-Zhd101.1) and the mutant Zhd101.1 are food-grade. • ZEN degradation rates by supernatants reached 96.9% in solution and 74.6% in corns.

Kluyveromyces as promising yeast cell factories for industrial bioproduction: From bio-functional design to applications

As the two most widely used Kluyveromyces yeast, Kluyveromyces marxianus and K. lactis have gained increasing attention as microbial chassis in biocatalysts, biomanufacturing and the utilization of low-cost raw materials owing to their high suitability to these applications. However, due to slow progress in the development of molecular genetic manipulation tools and synthetic biology strategies, Kluyveromyces yeast cell factories as biological manufacturing platforms have not been fully developed. In this review, we provide a comprehensive overview of the attractive characteristics and applications of Kluyveromyces cell factories, with special emphasis on the development of molecular genetic manipulation tools and systems engineering strategies for synthetic biology. In addition, future avenues in the development of Kluyveromyces cell factories for the utilization of simple carbon compounds as substrates, the dynamic regulation of metabolic pathways, and for rapid directed evolution of robust strains are proposed. We expect that more synthetic systems, synthetic biology tools and metabolic engineering strategies will adapt to and optimize for Kluyveromyces cell factories to achieve green biofabrication of multiple products with higher efficiency.

Preparation of recombinant Kluyveromyces lactis agents for simultaneous degradation of two mycotoxins

Aflatoxin B₁ (AFB₁) and zearalenone (ZEN) are widely distributed in corns, peanuts, and other cereals, causing serious threat to food safety and human health. As shown by our previous studies, the recombinant yeast strain Kluyveromyces lactis GG799(pKLAC1-ZPF1) had the ability of degrading AFB₁ and ZEN simultaneously. In this work, the agent preparation process was optimized for K. lactis GG799(pKLAC1-ZPF1), and the storage conditions of the prepared yeast agents were investigated, for obtaining the products with high storage activities and potent mycotoxin degradation efficiency. The optimal preparation process was as follows: centrifugation at 6000 rpm for 15 min for collection of the yeast cells, spray drying with the ratio of protective compounds to yeast cells at 3:1 (w/w) and then stored at − 20 °C. Simultaneous degradation tests of AFB₁ and ZEN were performed using the supernatants of reactivated yeast agents after three months of storage, and the degradation ratios for AFB₁ and ZEN in reaction system 1 (70.0 mmol/L malonic buffer, pH 4.5, with 1.0 mmol/L MnSO₄, 0.1 mmol/L H₂O₂, 5.0 μg/mL AFB₁ and ZEN, respectively) were 48.2 ± 3.2% and 34.8 ± 2.8%, while that for ZEN in reaction system 2 (50.0 mmol/L Tris–HCl, pH 7.5, with 5.0 μg/mL AFB₁ and ZEN, respectively) was 30.1 ± 2.7%. Besides, the supernatants of reactivated yeast agents degraded more than 80% of AFB₁ and 55% of ZEN in contaminated peanuts after twice treatments. Results of this work suggested that the optimized process for K. lactis GG799(pKLAC1-ZPF1) was with high value for industrial applications.

The recombinant strain K. lactis GG799(pKLAC1-ZPF1) was food-grade and safe for food and feed industry.

The preparation processes of the K. lactis GG799(pKLAC1-ZPF1) agents were optimized, and the storage properties were investigated.

The culture supernatants of the reactivated yeast agents, rather than the purified enzymes, were used to degrade AFB₁ and ZEN in practical samples for reducing the production cost.

Food-Grade Expression of Manganese Peroxidases in Recombinant Kluyveromyces lactis and Degradation of Aflatoxin B1 Using Fermentation Supernatants

Aflatoxins are naturally occurring high-toxic secondary metabolites, which cause worldwide environmental contaminations and wastes of food and feed resources and severely threaten human health. Thus, the highly efficient methods and technologies for detoxification of aflatoxins are urgently needed in a long term. In this work, we report the construction of recombinant Kluyveromyces lactis strains GG799(pKLAC1-Phsmnp), GG799(pKLAC1-Plomnp), GG799(pKLAC1-Phcmnp), and then the food-grade expression of the three manganese peroxidases in these strains, followed by the degradation of aflatoxin B₁ (AFB₁) using the fermentation supernatants. The expression of the manganese peroxidases was achieved in a food-grade manner since Kluyveromyces lactis is food-safe and suitable for application in food or feed industries. The inducible expression process of the optimal recombinant strain GG799(pKLAC1-Phcmnp) and the aflatoxin B₁ degradation process were both optimized in detail. After optimization, the degradation ratio reached 75.71%, which was an increase of 49.86% compared to the unoptimized results. The degradation product was analyzed and determined to be AFB₁-8,9-dihydrodiol. The recombinant strain GG799(pKLAC1-Phcmnp) supernatants degraded more than 90% of AFB₁ in the peanut samples after twice treatments. The structural computational analysis for further mutagenesis of the enzyme PhcMnp was also conducted in this work. The food-grade recombinant yeast strain and the enzyme PhcMnp have potential to be applied in food or feed industries.