An environment-friendly approach to isolate and purify glucan from spent cells of recombinant Pichia pastoris and the bioactivity characterization of the purified glucan

Solid-State 13C Nuclear Magnetic Resonance Study of Soluble and Insoluble β-Glucans Extracted from Candida lusitaniae

β-glucans are widely known for their biological activities. However, the choice of extraction method can significantly influence their structural characteristics, thereby potentially impacting their biological functions. In this paper, three fractions of β-glucans were obtained from Candida lusitaniae yeast via alkali and hot-water extraction methods and were analyzed using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Solid-state NMR spectroscopy was used as a nondestructive technique that preserves the structure of the analyzed molecules. The results suggest that differences in the β-glucan structure are affected by the choice of extraction method. The main difference occurred in the 82-92 ppm region with signal presence suggesting that β-glucans have a linear structure when hot-water-extracted, which is absent in alkali-extracted fractions resulting in the acquisition of β-glucans with an ordered, possibly helical structure. A hot-water extracted water-insoluble (HWN) fraction consists of linear β-1,3-glucans with other signals indicating the presence of β-1,6-linked side chains, chitin and small amounts of α-glucan impurities. For those that are alkali-extracted, alkali-insoluble (AN) and water-soluble (AWS) fractions are structurally similar and consist of an ordered β-1,3-glucan structure with β-1,6-linked side chains and a significant amount of α-glucan and chitin in both fractions.

Emerging relevance of cell wall components from non-conventional yeasts as functional ingredients for the food and feed industry

Non-conventional yeast species, or non-Saccharomyces yeasts, are increasingly recognized for their involvement in fermented foods. Many of them exhibit probiotic characteristics that are mainly due to direct contacts with other cell types through various molecular components of their cell wall. The biochemical composition and/or the molecular structure of the cell wall components are currently considered the primary determinant of their probiotic properties. Here we first present the techniques that are used to extract and analyze the cell wall components of food industry-related non-Saccharomyces yeasts. We then review the current understanding of the cell wall composition and structure of each polysaccharide from these yeasts. Finally, the data exploring the potential beneficial role of their cell wall components, which could be a source of innovative functional ingredients, are discussed. Such research would allow the development of high value-added products and provide the food industry with novel inputs beyond the well-established S. cerevisiae.

Production and applications of pullulan from lignocellulosic biomass: Challenges and perspectives

Pullulan is an exopolysaccharide produced by Aureobasidium pullulans, with interesting characteristics which lead to its application in industries such as pharmaceuticals, cosmetics, food, and others. To reduce production costs for industrial applications, cheaper raw materials such as lignocellulosic biomass can be utilized as a carbon and nutrient source for the microbial process. In this study, a comprehensive and critical review was conducted, encompassing the pullulan production process and the key influential variables. The main properties of the biopolymer were presented, and different applications were discussed. Subsequently, the utilization of lignocellulosics for pullulan production within the framework of a biorefinery concept was explored, considering the main published works that deal with materials such as sugarcane bagasse, rice husk, corn straw, and corn cob. Next, the main challenges and future prospects in this research area were highlighted, indicating the key strategies to favor the industrial production of pullulan from lignocellulosic biomasses.

Quantification methods of determining brewer's and pharmaceutical yeast cell viability: accuracy and impact of nanoparticles

For industrial processes, a fast, precise, and reliable method of determining the physiological state of yeast cells, especially viability, is essential. However, an increasing number of processes use magnetic nanoparticles (MNPs) for yeast cell manipulation, but their impact on yeast cell viability and the assay itself is unclear. This study tested the viability of Saccharomyces pastorianus ssp. carlsbergensis and Pichia pastoris by comparing traditional colourimetric, high-throughput, and growth assays with membrane fluidity. Results showed that methylene blue staining is only reliable for S. pastorianus cells with good viability, being erroneous in low viability (R2 = 0.945; [Formula: see text] = 5.78%). In comparison, the fluorescence microscopy-based assay of S. pastorianus demonstrated a coefficient of determination of R2 = 0.991 at [Formula: see text] ([Formula: see text] = 2.50%) and flow cytometric viability determination using carboxyfluorescein diacetate (CFDA), enabling high-throughput analysis of representative cell numbers; R2 = 0.972 ([Formula: see text]; [Formula: see text] = 3.89%). Membrane fluidity resulted in a non-linear relationship with the viability of the yeast cells ([Formula: see text]). We also determined similar results using P. pastoris yeast. In addition, we demonstrated that MNPs affected methylene blue staining by overestimating viability. The random forest model has been shown to be a precise method for classifying nanoparticles and yeast cells and viability differentiation in flow cytometry by using CFDA. Moreover, CFDA and membrane fluidity revealed precise results for both yeasts, also in the presence of nanoparticles, enabling fast and reliable determination of viability in many experiments using MNPs for yeast cell manipulation or separation.

Screening and identification of a strain of Aureobasidium pullulans and its application in potato starch industrial waste

Pullulan and melanin have become important secondary metabolites that are now widely studied. In this study, a strain of Aureobasidium pullulans HIT-LCY3^T was used to ferment potato starch industrial waste to produce pullulan and melanin. After optimization, the culture conditions for the fermentation medium were obtained: inoculum age of 48 h, initial pH of 6.0, inoculation quantity of 1.5%, temperature of 26 °C, fermentation time of 5 d and speed of 160 rpm. Under these conditions, the yield of pullulan was 23.47 g/L with a molecular weight (MW) of 1.21 × 10⁶ Da and the yield of melanin was 18.98 g/L. In addition, the adaptive evolution could significantly increase the yield of pullulan and melanin and the air-floating fermenters was more conductive to product accumulation. Through the 5 L small-scale test and 1000 L pilot test, the yield of pullulan reached 16.52 g/L with molecular weight of 0.92 × 10⁶ Da and the yield of melanin was 12.08 g/L at the trial production of 30,000 L. This work could provide strong support for industrial production and new guidance for waste utilization and environmental protection.

FT-IR Method Limitations for β-Glucan Analysis

β-glucans are known as biological response modifiers. However, different sources can result in structural differences and as a result differences in their biological activity. The hot water extraction method allows to obtain, high molecular weight β-glucans without altering their structure by using strong chemicals, such as alkalis or acids. Analysis of β-glucans by FT-IR and NMR spectroscopy in solid state is superior to analysis in solution as it allows researchers to study the preserved structure of the extracted polysaccharides. FT-IR spectroscopy was used in this study to make side-by-side comparison analysis of hot water extracted β-glucans from different yeast sources. NMR spectroscopy was used to confirm findings made by FT-IR spectroscopy. Extracted β-glucans exhibit characteristic structure of β-1,3/1,6-linked glucans with noticeable levels of proteins, possibly in a form of oligopeptides, chitin and other impurities. β-glucans obtained from C. guilliermondii, P. pastoris and S. pastorianus exhibited higher protein content. Differences in mannan, chitin and α-glucan content were also observed; however, the species-specific structure of obtained β-glucans could not be confirmed without additional studies. Structural analysis of high molecular weight β-glucans in solid state by FT-IR spectroscopy is difficult or limited due to band intensity changes and overlapping originating from different molecules.

The Transcriptomic Mechanism of a Novel Autolysis Induced by a Recombinant Antibacterial Peptide from Chicken Expressed in Pichia pastoris

Autolysis is a common physiological process in eukaryotic cells that is often prevented or applied, especially in yeast expression systems. In this study, an antimicrobial peptide from chicken (AMP) was recombinantly expressed in the Pichia pastoris expression system, which induced a series of cellular autolysis phenotypes after methanol treatment, such as the aggregated, lysed, irregular, and enlarged cell morphology, while the cells expressing a recombinant aflatoxin-detoxifizyme (ADTZ) were not autolyzed. A comparative transcriptomic analysis showed that the transcriptomic profiles of cells derived from the autolysis and non-autolysis groups were well discriminated, suggesting that the mechanisms of autolysis were at the transcriptional level. A further differential expression gene (DEG) analysis showed that the DEGs from the two groups were involved mainly in autophagy, the MAPK signaling pathway, transcriptional factors, the central carbon metabolism, anti-stress functions, and so on. In the autolysis group, the cell activity was significantly reduced with the MAPK signaling pathway, the central carbon metabolism was down-regulated, and components of the cytoplasm-to-vacuole targeting (CVT) and mitophagy pathways were up-regulated, suggesting that the autophagy involved in the trafficking of intracellular molecules in the vacuole and mitochondrion contributed to autolysis, which was regulated by transcriptional factors and signal pathways at the transcriptional level. This study provides a theoretical basis for genetic modifications to prevent or utilize cell autolysis in the recombinant protein expression system.

Antifungal and Aflatoxin-Reducing Activity of β-Glucan Isolated from Pichia norvegensis Grown on Tofu Wastewater

Yeast can be isolated from tofu wastewater and the cell wall in the form of β-glucan can act as a natural decontaminant agent. This study aimed to isolate and characterize native yeast from tofu wastewater, which can be extracted to obtain β-glucan and then identify the yeast and its β-glucan activity regarding antifungal ability against Aspergillus flavus and aflatoxin-reducing activity towards aflatoxin B1 (AFB1) and B2 (AFB2). Tofu wastewater native yeast was molecularly identified, and the growth observed based on optical density for 96 h and the pH also measured. β-glucan was extracted from native yeast cell walls with the acid-base method and then the inhibition activity towards A. flavus was tested using the well diffusion method and microscopic observation. AFB1 and AFB2 reduction were identified using HPLC LC-MS/MS. The results showed that the native yeast isolated was Pichia norvegensis with a β-glucan yield of 6.59%. Pichia norvegensis and its β-glucan showed an inhibition zone against Aspergillus flavus of 11.33 ± 4.93 and 7.33 ± 3.51 mm, respectively. Total aflatoxin-reducing activity was also shown by Pichia norvegensis of 26.85 ± 2.87%, and β-glucan of 27.30 ± 1.49%, while AFB1- and AFB2-reducing activity by Pichia norvegensis was 36.97 ± 3.07% and 27.13 ± 1.69%, and β-glucan was 27.13 ± 1.69% and 32.59 ± 4.20%, respectively.