Viability and Stability of Yeast Cells and Filamentous Fungus Spores During Freeze-Drying: Effects of Protectants and Cooling Rates

Biotechnological development of Trichoderma-based formulations for biological control

Trichoderma spp. are a genus of well-known fungi that promote healthy growth and modulate different functions in plants, as well as protect against various plant pathogens. The application of Trichoderma and its propagules as a biological control method can therefore help to reduce the use of chemical pesticides and fertilizers in agriculture. This review critically discusses and analyzes groundbreaking innovations over the past few decades of biotechnological approaches to prepare active formulations containing Trichoderma. The use of various carrier substances is covered, emphasizing their effects on enhancing the shelf life, viability, and efficacy of the final product formulation. Furthermore, the use of processing techniques such as freeze drying, fluidized bed drying, and spray drying are highlighted, enabling the development of stable, light-weight formulations. Finally, promising microencapsulation techniques for maximizing the performance of Trichoderma spp. during application processes are discussed, leading to the next-generation of multi-functional biological control formulations. KEY POINTS: • The development of carrier substances to encapsulate Trichoderma propagules is highlighted. • Advances in biotechnological processes to prepare Trichoderma-containing formulations are critically discussed. • Current challenges and future outlook of Trichoderma-based formulations in the context of biological control are presented.

Effect of two preservation methods on the viability and enzyme production of a recombinant Komagataella phaffii (Pichia pastoris) strain

The methylotrophic yeast Komagataella phaffii, previously known as Pichia pastoris, has been reported as a host for producing human recombinant lysosomal enzymes intended for enzyme replacement therapy. K. phaffii has advantages such as easy genetic handling, rapid growth, cost-effective mediums, and the ability to develop mammalian-like post-translational modifications. To maintain cell viability and enzyme activity over time, it is important to consider the bioprocess optimization and the proper selection and preservation of clones. In this study, we evaluated the effect of glycerol and skim milk in cryopreservation at -80 °C, as well as the use of skim milk or its combination with NaCl, disaccharides or sorbitol in freeze-drying on the cell viability and activity of a recombinant lysosomal enzyme (i.e., human β-hexosaminidase-A) produced in K. phaffii GS115 strain. The results showed that cryopreservation with glycerol and skim milk, as well as freeze-drying using disaccharides and sorbitol with skim milk, maintained the viability above 80%. Although variations in enzyme activity among treatments were found, the use of disaccharides had a positive effect on the enzymatic activity levels. This is the first report of the evaluation of two suitable methods to preserve a recombinant K. phaffii strain, preventing the loss of viability and maintaining the activity of the recombinant protein.

Combinatorial Effects of Protective Agents on Survival Rate of the Yeast Starter, Saccharomyces cerevisiae 88-4, after Freeze-Drying

A yeast starter is formulated for commercial practices, including storage and distribution. The cell viability of the yeast starter is one of the most important factors for manufacturing alcoholic beverages to ensure their properties during the fermentation and formulation processes. In this study, 64 potential protective agents were evaluated to enhance the survival rate of the brewing yeast Saccharomyces cerevisiae 88-4 after freeze-drying. In addition, the optimized combination of protective agents was assessed for long-term storage. Finally, response surface methodology was applied to investigate the optimal concentration of each protectant. Twenty of the 64 additives led to an increase in the survival rate of freeze-dried S. cerevisiae 88-4. Among the various combinations of protectants, four had a survival rate >95%. The combination of skim milk, maltose, and maltitol exhibited the best survival rate of 61% after 42 weeks in refrigerated storage, and the composition of protectants optimized by response surface methodology was 6.5–10% skim milk, 1.8–4.5% maltose, and 16.5–18.2% maltitol. These results demonstrated that the combination of multiple protectants could alleviate damage to yeasts during freeze-drying and could be applied to the manufacturing starters for fermented foods.

Seed coating as a delivery system for the endophyte Trichoderma koningiopsis Th003 in rice (Oryza sativa)

Seed coating is a technique to cover seeds with external agents to upgrade their performance, handling, and plant establishment. Plant beneficial microbes (PBMs), such as plant growth-promoting bacteria, mycorrhizal fungi, and other fungi (e.g., Trichoderma spp.), decrease agrochemical inputs, enhance tolerance to biotic-abiotic stresses, and increase essential plant nutrition. The demand for pre-treated seeds as delivery systems for biological agents is advancing. Here, a seed coating formulation containing Trichoderma koningiopsis is presented. The physicochemical and biological characterization of the seed coating prototypes included drying protector screening, the effect of the inoculum concentration on survival, the assessment of microbial release profiles in soil extract, and plant tissue colonization capability under semi-controlled conditions. Gelatine and pectin, two of the tested drying protectors, maintained fungus germination after 60 days at 18 °C with significantly higher values of up to 38% compared with the control. The initial concentration of 10⁶ colony-forming units (CFU) per seed undergoes a positive effect on survival over time. Regarding plant tissue colonization, the fungus establishes endophytically in rice. In conclusion, seed coating is a promising alternative for the formulation of beneficial microbial agents such as Trichoderma sp., maintaining cell survival and further promoting the establishment in rice systems.Key points• Enhancing drying survival of T. koningiopsis formulates• Seed coating formulation approach for T. koningiopsis in rice• Colonization capacity of formulated T. koningiopsis in rice tissue.

Polysaccharides can improve the survival of Lactiplantibacillus plantarum subjected to freeze-drying

Freeze-drying is one of the most commonly used methods of bacteria preservation. During this process, cryoprotectants can greatly reduce cellular damage. Micromolecular cryoprotectants have been widely adopted but have limited selectivity and protective effects. Therefore, explorations of other types of cryoprotectants are needed. This study aimed to explore the possibility of the macromolecular cryoprotectants and combinations of cryoprotectants to maintain bacterial activity. We found that the survival rate of Lactiplantibacillus plantarum AR113 after freeze-drying was 19% higher in the presence of soy polysaccharides than with trehalose, the best-performing micromolecular cryoprotectant. Moreover, a 90.52% survival rate of L. plantarum WCFS1 was achieved using the composite cryoprotectant containing soy polysaccharide and trehalose, which increased by 31.48 and 36.47% compared with adding solely trehalose or soy polysaccharide, respectively. These results demonstrate that macromolecular and micromolecular cryoprotectants have similar effects, and that combinations of macromolecular and micromolecular cryoprotectants have better protective effects. We further observed that the composite cryoprotectant can increase Lactobacilli survival by improving cell membrane integrity and lactate dehydrogenase activity. Our finding provides a new type of cryoprotectant that is safer and more effective, which can be extensively applied in the relevant food industry.

Along the Process Chain to Probiotic Tablets: Evaluation of Mechanical Impacts on Microbial Viability

Today, probiotics are predominantly used in liquid or semi-solid functionalized foods, showing a rapid loss of cell viability. Due to the increasing spread of antibiotic resistance, probiotics are promising in pharmaceutical development because of their antimicrobial effects. This increases the formulation requirements, e.g., the need for an enhanced shelf life that is achieved by drying, mainly by lyophilization. For oral administration, the process chain for production of tablets containing microorganisms is of high interest and, thus, was investigated in this study. Lyophilization as an initial process step showed low cell survival of only 12.8%. However, the addition of cryoprotectants enabled survival rates up to 42.9%. Subsequently, the dried cells were gently milled. This powder was tableted directly or after mixing with excipients microcrystalline cellulose, dicalcium phosphate or lactose. Survival rates during tableting varied between 1.4% and 24.1%, depending on the formulation and the applied compaction stress. More detailed analysis of the tablet properties showed advantages of excipients in respect of cell survival and tablet mechanical strength. Maximum overall survival rate along the complete manufacturing process was >5%, enabling doses of 6 × 108 colony forming units per gram (CFU gtotal−1), including cryoprotectants and excipients.

Optimization of Production Parameters for Probiotic Lactobacillus Strains as Feed Additive

In animal nutrition, probiotics are considered as desirable alternatives to antibiotic growth promoters. The beneficial effects of probiotics primarily depend on their viability in feed, which demands technical optimization of biomass production, since processing and storage capacities are often strain-specific. In this study, we optimized the production parameters for two broiler-derived probiotic lactobacilli (L. salivarius and L. agilis). Carbohydrate utilization of both strains was determined and preferred substrates that boosted biomass production in lab-scale fermentations were selected. The strains showed good aerobic tolerance, which resulted in easier scale-up production. For the freeze-drying process, the response surface methodology was applied to optimize the composition of cryoprotective media. A quadratic polynomial model was built to study three protective factors (skim milk, sucrose, and trehalose) and to predict the optimal working conditions for maximum viability. The optimal combination of protectants was 0.14g/mL skim milk/ 0.08 g/mL sucrose/ 0.09 g/mL trehalose (L. salivarius) and 0.15g/mL skim milk/ 0.08 g/mL sucrose/ 0.07 g/mL (L. agilis), respectively. Furthermore, the in-feed stabilities of the probiotic strains were evaluated under different conditions. Our results indicate that the chosen protectants exerted an extensive protection on strains during the storage. Although only storage of the strains at 4 °C retained the maximum stability of both Lactobacillus strains, the employed protectant matrix showed promising results at room temperature.

Rhodococcus and Yarrowia-Based Lipid Production Using Lignin-Containing Industrial Residues

Improvement in biorefining technologies coupled with development of novel fermentation strategies and analysis will be paramount in establishing supplementary and sustainable biofuel pathways. Oleaginous microorganisms that are capable of accumulating triacylglycerides (TAGs) and fatty acid methyl esters (FAMEs), such as Rhodococcus and Yarrowia species, can be used to produce second-generation biofuels from non-food competing carbon sources. These "microbiorefineries" provide a pathway to upgrade agricultural and industrial waste streams to fungible fuels or precursors to chemicals and materials. Here we provide a general overview on cultivating Rhodococcus and Yarrowia on agro-waste/industrial biomass pretreatment waste streams to produce single-cell oils/lipids and preparing samples for FAME detection.

Immobilisation of yeasts on oak chips or cellulose powder for use in bottle-fermented sparkling wine

Sparkling wine production comprises two successive fermentations performed by Sacharomyces cerevisiae strains. This research aimed to: develop yeast immobilisation processes on two wine-compatible supports; study the effects of yeast type (IOC 18-2007 and 55A) and the immobilisation support type (oak chips and cellulose powder) on the fermentation kinetics, the deposition rate of lees and the volatile composition of the finished sparkling wine; compare the fermentation parameters of the wines inoculated with immobilised or non-immobilised cells. Proper immobilisation of yeast on oak chips and cellulose powder was demonstrated by electron microscopy. Total sugar consumption occurred in under 60 days in all bottles, regardless of the strain used and the way they were inoculated in wine. Deposition of lees was 3-fold faster in the bottles containing immobilised cells than in those with free cells; no addition of adjuvants was necessary. The analysis of the volatile compounds of the finished sparkling wines showed significant differences in the formation of esters, acids, alcohols, aldehydes and lactones according to the yeast and the immobilisation support used. Oak chips were the more appropriate support for yeast immobilisation. No significant differences in the sensorial analysis of the sparkling wines produced by the different strategies were found.

Improved stability of live attenuated vaccine gdhA derivative Pasteurella multocida B:2 by freeze drying method for use as animal vaccine

The efficacy of attenuated strain of gdhA derivative Pasteurella multocida B:2 mutant as a live vaccine to control haemorrhagic septicaemia (HS) disease in cattle and buffaloes has been demonstrated. In order to use P. multocida B:2 mutant as a commercial product, it is essential to optimise its formulation for high viability and stability of the live cells. The effectiveness of freeze-drying process using different protective agent formulations for improving cells viability was explored. Sugar and nitrogen compounds were used as protective agents in freeze-drying and the capability of these compounds in maintaining the viability of mutant P. multocida B:2 during subsequent storage was investigated. A complete loss in viability of freeze-dried mutant P. multocida B:2 was monthly observed until 6-12 months of storage at -30 °C, 4 °C and 27 °C when nitrogen compound or no protective agent was added. Trehalose and sucrose showed significantly high survival rate of 93-95% immediately after freeze-drying and the viability was retained during the subsequent storage at -30 °C and 4 °C. A smooth cell surface without any cell-wall damage was observed for the cells formulated with trehalose under scanning electron micrograph. This study presented a freeze-drying process generating a dried live attenuated vaccine formulation with high stability for commercial applications.

Optimization of a protective medium for freeze-dried Pichia membranifaciens and application of this biocontrol agent on citrus fruit

AIMS

To optimize a protective medium for freeze-dried Pichia membranifaciens and to evaluate biocontrol efficacies of agents against blue and green mould and anthracnose in citrus fruit.

METHODS AND RESULTS

Based on the screening assays of saccharides and antioxidants, response surface methodology was used to optimize sucrose, sodium glutamate and skim milk to improve viability of freeze-dried Pi. membranifaciens. Biocontrol assays were conducted between fresh and freeze-dried Pi. membranifaciens against Penicillium italicum, Penicillium digitatum and Colletotrichum gloeosporioides in citrus fruit. Solving the regression equation indicated that the optimal protective medium was 6·06% (w/v) sucrose combined with 3·40% (w/v) sodium glutamate and 5·43% (w/v) skim milk. Pi. membranifaciens freeze-dried in the optimal protective medium showed 76·80% viability, and retained biocontrol efficacy against Pe. italicum, Pe. digitatum and Co. gloeosporioides in citrus fruit.

CONCLUSIONS

The optimal protective medium showed more effective protective properties than each of the three protectants used alone. The viability of freeze-dried Pi. membranifaciens finally reached 76·80%. Meanwhile, the biocontrol efficacies showed no significant difference between fresh and freeze-dried yeast against Pe. italicum, Pe. digitatum and Co. gloeosporioides in citrus fruit.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results showed the potential value of Pi. membranifaciens CICC 32259 for commercialization.

Impact of matrix properties on the survival of freeze-dried bacteria

BACKGROUND

Disaccharides are, in general, the first choice as formulation compounds when freeze-drying microorganisms. Although polysaccharides and other biopolymers are considered too large to stabilise and interact with cell components in the same beneficial way as disaccharides, polymers have been reported to support cell survival. In the present study we compare the efficiency of sucrose and the polymers Ficoll, hydroxyethylcellulose, hydroxypropylmethylcellulose and polyvinylalcohol to support the survival of three bacterial strains during freeze drying. The initial osmotic conditions were adjusted to be similar for all formulations. Formulation characterisation was used to interpret the impact that different compound properties had on cell survival.

RESULTS

Despite differences in molecular size, both sucrose and the sucrose-based polymer Ficoll supported cell survival after freeze drying equally well. All formulations became amorphous upon dehydration. Scanning electron microscopy and X-ray diffraction data showed that the discerned differences in structure of the dry formulations had little impact on the survival rates. The capability of the polymers to support cell survival correlated with the surface activity of the polymers in a similar way for all investigated bacterial strains.

CONCLUSION

Polymer-based formulations can support cell survival as effectively as disaccharides if formulation properties of importance for maintaining cell viability are identified and controlled.

Application of the yeast-surface-display system for orally administered salmon calcitonin and safety assessment

High manufacturing costs and oral delivery are the constraints in clinical application of calcitonin. We selected surface-displayed Saccharomyces cerevisiae as a low-cost and safe carrier for oral delivery of salmon calcitonin (sCT). The sCT DNA fragment, optimized according to the codon preference of S. cerevisiae, was synthesized and cloned into the plasmid M-pYD1 to yield recombinant yAGA2-sCT, which was induced to express sCT by galactose for 0, 12, and 24 h. sCT expression was detected on the cell surface by indirect immunofluorescence and peaked at 12 h. About 65% recombinants expressed sCT on flow cytometry. The in vivo and in vitro activity of recombinant sCT was determined by detecting bioactivity of antiosteoclastic absorption on bone wafers and orally administering yAGA2-sCT to Wistar rats, respectively. For safety assessment of yAGA2-sCT, we observed abnormalities, morbidity, and mortality and determined body weight, serum chemistry parameters, hematological parameters, and organ weight. In vitro bioactivity of the recombinant sCT was similar to that of commercial sCT, Miacalcic; oral administration of 5 g/kg yAGA2-sCT induced a long-term hypocalcemic effect in Wistar rats and no adverse effects. This study demonstrates that yAGA2-sCT anchoring sCT protein on a S. cerevisiae surface has potential for low-cost and safe oral delivery of sCT.

Effects of trehalose on stress tolerance and biocontrol efficacy of Cryptococcus laurentii

AIMS

To investigate the effects of internal trehalose on viability and biocontrol efficacy of antagonistic yeast Cryptococcus laurentii under stresses of low temperature (LT), controlled atmosphere (CA) and freeze drying.

METHODS AND RESULTS

The content of trehalose in C. laurentii was increased by culturing the yeast in trehalose-containing medium. Compared with yeast cells with low trehalose level, the yeast cells with high level of internal trehalose not only obtained higher viability, but also showed higher population and better biocontrol efficacy against Penicillium expansum on apple fruit both at 1 degrees C and in CA condition (5% O(2), 5% CO(2), 1 degrees C). After freeze drying, survival of the yeast with high trehalose level was markedly increased when stored at 25 degrees C for 0, 15 and 30 days. Meanwhile, high integrity of plasma membrane was detected in the freeze-dried yeast with high trehalose level by propidium iodide staining.

CONCLUSIONS

Induced accumulation of internal trehalose could improve viability and biocontrol efficacy of C. laurentii under stresses of LT and CA. Moreover, survival of the yeast was also increased as internal trehalose accumulation after freeze drying, and one of the reasons might be that trehalose gave an effective protection to plasma membrane.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this experiment show a promising way to improve the biocontrol performance of antagonistic yeasts under the commercial conditions.