Secretory expression of a phospholipase A2 from Lactobacillus casei DSM20011 in Kluyveromyces lactis

Biopurification using non-growing microorganisms to improve plant protein ingredients

Securing a sustainable global food supply for a growing population requires a shift toward a more plant-based diet. The application of plant-based proteins is therefore increasing, but unpleasant off-flavors complicate their use. Here, we screened 97 microorganisms for their potential to remove off-flavors in a process with limiting amounts of fermentable sugar. This allowed the production of a more neutral-tasting, purified food ingredient while limiting microbial growth and the production of typical fermentation end products. We demonstrate that various lactic acid bacteria (LAB) and yeasts remove "green" aldehydes and ketones. This conversion can be carried out in less than one hour in almond, pea, potato, and oat proteins. Heterofermentative LAB was best at aldehyde and ketone neutralization with minimum de novo formation of microbial volatiles such as ethylacetate (sweet, fruity) or alpha-diketones (butter- and cheese-like). While sensory properties were improved, changes in protein solubility, emulsification, foaming, and in vitro digestibility were limited.

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.

Whole-Genome Sequencing of a Potential Ester-Synthesizing Bacterium Isolated from Fermented Golden Pomfret and Identification of Its Lipase Encoding Genes

Microbial ester synthases are regarded as valuable catalysts in the food industry. Here, one strain of Acinetobacter venetianus with ester synthase-production capacity, SCSMX-3, was isolated from traditional fermented golden pomfret. It exhibited good growth in mesophilic, low salt, and slightly alkaline environments. The ester synthase produced by SCSMX-3 displayed maximum activity at pH 8.0 and 35 °C. Genome sequencing revealed that the strain contains one circular chromosome of 336313 bp and two circular plasmids (plasmid A-14424 bp and plasmid B-11249 bp). Six CRISPR structures enhance the genomic stability of SCSMX-3 and provide the opportunity to create new functional strains. Gene function analysis indicated that SCSMX-3 produces the necessary enzymes for survival under different conditions and for flavor substance synthesis. Furthermore, 49 genes encoding enzymes associated with lipid metabolism, including three triacylglycerol lipases and two esterases, were identified through the NCBI Non-Redundant Protein Database. The lipase encoded by gene0302 belongs to the GX group and the abH15.02 (Burkholderia cepacia lipase) homolog of the abH15 superfamily. Our results shed light on the genomic diversity of and lipid metabolism in A. venetianus isolated from fermented golden pomfret, laying a foundation for the exploration of new ester synthases to improve the flavor of fermented fish products.

Immobilization of Phospholipase A1 Using a Protein-Inorganic Hybrid System

In this study, four kinds of phospholipase A1-metal (Al/Co/Cu/Mn) hybrid nanostructures were prepared for enhancing the stability of the free PLA1. The formed hybrid complexes were characterized by scanning electron microscope (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The stability and substrate specificity of immobilized enzymes were subsequently determined. After immobilization, the temperature tolerance of PLA1–metal hybrid nanostructures was enhanced. The relative activity of PLA1–Al/Co/Cu hybrid nanostructures remained above 60% at 50 °C, while that of free enzyme was below 5%. The thermal transition temperature measured by differential scanning calorimetry (DSC) was found to increase from 65.59 °C (free enzyme) to 173.14 °C, 123.67 °C, 96.31 °C, and 114.79 °C, referring to PLA1–Cu/Co/Al/Mn hybrid nanostructures, respectively. Additionally, after a storage for fourteen days at 4 °C, the immobilized enzymes could exhibit approximately 60% of the initial activity, while the free PLA1 was inactivated after four days of storage. In brief, using Co²⁺, Cu²⁺, Al³⁺, and Mn²⁺ as the hybridization materials for immobilization could improve the catalytic properties and stability of the free PLA1, suggesting a promising method for a wider application of PLA1 in many fields such as food, cosmetics, and the pharmaceutical industry.

Disrupting a phospholipase A2 gene increasing lipid accumulation in the oleaginous yeast Yarrowia lipolytica

AIMS

Phospholipase A₂ (PLA₂ ) is a diverse superfamily that hydrolyzes fatty acyl ester bonds at the sn-2 position of phospholipids. The correlation between phospholipid metabolism and the anabolism of neutral lipids remains unclear in yeasts. This study aims to explore the effects of PLA₂ on lipid accumulation in the oleaginous yeast Yarrowia lipolytica.

METHODS AND RESULTS

This study identified an actively expressed phospholipase A₂ gene (PLA2-3, YAIL0_E16060g) in Y. lipolytica by quantitative PCR analysis. The gene PLA2-3 was disrupted in the strain po1gΔKu70 by homologous recombination and in the strain po1g-G3 by a CRISPR-Cas9 system, which caused an increase in stress sensitivity while the cell growth was not altered under fermentative conditions. Lipid production was performed in both flasks and bioreactors. The results showed that the lipid titre and lipid content were improved over 25% and 8-30%, respectively, in PLA2-3 disrupted strains compared to the controls.

CONCLUSIONS

Disruption of the phospholipase PLA2-3 gene could effectively improve lipid production in Y. lipolytica.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study presented a strategy on improving the lipid production of oleaginous yeasts and a similar strategy might be used in other oleaginous microbes.

Comparison of Yeasts as Hosts for Recombinant Protein Production

Recombinant protein production emerged in the early 1980s with the development of genetic engineering tools, which represented a compelling alternative to protein extraction from natural sources. Over the years, a high level of heterologous protein was made possible in a variety of hosts ranging from the bacteria Escherichia coli to mammalian cells. Recombinant protein importance is represented by its market size, which reached $1654 million in 2016 and is expected to reach $2850.5 million by 2022. Among the available hosts, yeasts have been used for producing a great variety of proteins applied to chemicals, fuels, food, and pharmaceuticals, being one of the most used hosts for recombinant production nowadays. Historically, Saccharomyces cerevisiae was the dominant yeast host for heterologous protein production. Lately, other yeasts such as Komagataella sp., Kluyveromyces lactis, and Yarrowia lipolytica have emerged as advantageous hosts. In this review, a comparative analysis is done listing the advantages and disadvantages of using each host regarding the availability of genetic tools, strategies for cultivation in bioreactors, and the main techniques utilized for protein purification. Finally, examples of each host will be discussed regarding the total amount of protein recovered and its bioactivity due to correct folding and glycosylation patterns.