Saccharomyces cerevisiae proteinase A excretion and wine making

Aspergillus oryzae as a Cell Factory: Research and Applications in Industrial Production

Aspergillus oryzae, a biosafe strain widely utilized in bioproduction and fermentation technology, exhibits a robust hydrolytic enzyme secretion system. Therefore, it is frequently employed as a cell factory for industrial enzyme production. Moreover, A. oryzae has the ability to synthesize various secondary metabolites, such as kojic acid and L-malic acid. Nevertheless, the complex secretion system and protein expression regulation mechanism of A. oryzae pose challenges for expressing numerous heterologous products. By leveraging synthetic biology and novel genetic engineering techniques, A. oryzae has emerged as an ideal candidate for constructing cell factories. In this review, we provide an overview of the latest advancements in the application of A. oryzae-based cell factories in industrial production. These studies suggest that metabolic engineering and optimization of protein expression regulation are key elements in realizing the widespread industrial application of A. oryzae cell factories. It is anticipated that this review will pave the way for more effective approaches and research avenues in the future implementation of A. oryzae cell factories in industrial production.

Analysis on driving factors of microbial community succession in Jiuyao of Shaoxing Huangjiu (Chinese yellow rice wine)

The microbial ecosystem of fermented food is greatly disturbed by human activities.Jiuyao is important saccharification starter for brewing huangjiu. The interaction between environmental factors and microorganisms significantly affected the microbial community structure at different stages of Jiuyao manufacturing. This study combined environmental factor analysis and high-throughput sequencing technology to comprehensively analyze the specific changes of microbial community and environmental factors in each fermentation stage of Jiuyao production and their correlation. The results showed that the activities of liquefaction enzyme, glycosylation enzyme and acid protease reached the highest value on the 8 th day (192 h) after the beginning of fermentation, and the cellulase activity reached the highest value at the end of fermentation. Pediococcus（37.5 %-58.2 %）, Weissella（9.2 %-27.0 %） and Pelomonas（0.1 %-12.1 %） were the main microbial genera in the genus bacteria, and Saccharomycopsis（37.1 %-52.0 %）, Rhizopus（12.5 %-31.0 %） and Saccharomyces（4.0 %-20.5 %） were the main microbial genera in the genus fungi. The results of correlation analysis showed that the microbial communities in Jiuyao were closely related to environmental factors. Most microbial communities were positively correlated with temperature, but negatively correlated with ambient humidity, CO2 concentration, acidity and water content of Jiuyao. In addition, the transcription levels of enzymes related to microbial glucose metabolism in Jiuyao were higher in the late stage of Jiuyao fermentation. Interestingly, these enzymes had high transcription levels in fungi such as Saccharomycopsis, Rhizopus and Saccharomyces, as well as in bacteria such as Pediococcus and Lactobacillus. This study provides a reference for revealing the succession rule of microbial community structure caused by environmental factors during the preparation of Jiuyao in Shaoxing Huangjiu.

Disruption of protease A and B orthologous genes in the basidiomycetous yeast Pseudozyma antarctica GB-4(0) yields a stable extracellular biodegradable plastic-degrading enzyme

The yeast Pseudozyma antarctica (currently designated Moesziomyces antarcticus) secretes a xylose-induced biodegradable plastic-degrading enzyme (PaE). To suppress degradation of PaE during production and storage, we targeted the inhibition of proteolytic enzyme activity in P. antarctica. Proteases A and B act as upper regulators in the proteolytic network of the model yeast, Saccharomyces cerevisiae. We searched for orthologous genes encoding proteases A and B in the genome of P. antarctica GB-4(0) based on the predicted amino acid sequences. We found two gene candidates, PaPRO1 and PaPRO2, with conserved catalytically important domains and signal peptides indicative of vacuolar protease function. We then prepared gene-deletion mutants of strain GB-4(0), ΔPaPRO1 and ΔPaPRO2, and evaluated PaE stability in culture by immunoblotting analysis. Both mutants exhibited sufficient production of PaE without degradation fragments, while the parent strain exhibited the degradation fragments. Therefore, we concluded that the protease A and B orthologous genes are related to the degradation of PaE. To produce a large quantity of PaE, we made a PaPRO2 deletion mutant of a PaE-overexpression strain named XG8 by introducing a PaE high-production cassette into the strain GB-4(0). The ΔPaPRO2 mutant of XG8 was able to produce PaE without the degradation fragments during large-scale cultivation in a 3-L jar fermenter for 3 days at 30°C. After terminating the agitation, the PaE activity in the XG8 ΔPaPRO2 mutant culture was maintained for the subsequent 48 h incubation at 25°C regardless of remaining cells, while activity in the XG8 control was reduced to 55.1%. The gene-deleted mutants will be useful for the development of industrial processes of PaE production and storage.

Aaprb1, a subtilsin-like protease, required for autophagy and virulence of the tangerine pathotype of Alternaria alternata

Subtilisin-like serine protease secreted by pathogenic fungi can facilitate the infection and acquisition of nutrients. Functions of subtilisin-like serine proteases in the phytopathogenic fungus Alternaria alternata remains unknown. In the current study, 15 subtilisin-like serine proteases were individually deleted in the citrus fungal pathogen A. alternata. Only one, designated AaPrb1, was found to be required for A. alternata pathogenesis. The AaPrb1 deficiency strain (ΔAaprb1) reduced growth, conidiation, the formation of aerial hyphae, protease production, and virulence on citrus leaves. However, biochemical analyses and bioassays revealed that ΔAaprb1 plays no role in the production of ACT toxin. Through Y2H assays, Aaprb1 was found to interact with Aapep4, a vacuole-localized proteinase A in A. alternata. Furthermore, silencing AaPep4 in A. alternata resulted in phenotypes similar with those of ΔAaprb1. Expression of AaPrb1 was found to be regulated by AaPep4. TEM showed that AaPrb1and AaPep4 were involved in the suppression of the degradation of autophagosomes. Deletion of the autophagy gene AaAtg8 in A. alternata decreased conidiation, the formation of aerial hyphae and pathogenicity similar to ΔAaprb1, implying that some phenotypes of ΔAaprb1 were due to the impairment of autophagy. Overall, this study expands our understanding of how A. alternata utilizes the subtilisin-like serine protease to achieve successful infection in the plant host.

Vps10-mediated targeting of Pep4 determines the activity of the vacuole in a substrate-dependent manner

The vacuole is the hydrolytic compartment of yeast cells and has a similar function as the lysosome of higher eukaryotes in detoxification and recycling of macromolecules. We analysed the contribution of single vacuolar enzymes to pexophagy and identified the phospholipase Atg15, the V-ATPase factor Vma2 and the serine-protease Prb1 along with the already known aspartyl-protease Pep4 (Proteinase A) to be required for this pathway. We also analysed the trafficking receptor Vps10, which is required for an efficient vacuolar targeting of the precursor form of Pep4. Here we demonstrate a novel context-dependent role of Vps10 in autophagy. We show that reduced maturation of Pep4 in a VPS10-deletion strain affects the proteolytic activity of the vacuole depending on the type and amount of substrate. The VPS10-deletion has no effect on the degradation of the cytosolic protein Pgk1 via bulk autophagy or on the degradation of ribosomes via ribophagy. In contrast, the degradation of an excess of peroxisomes via pexophagy as well as mitochondria via mitophagy was significantly hampered in a VPS10-deletion strain and correlated with a decreased maturation level of Pep4. The results show that Vps10-mediated targeting of Pep4 limits the proteolytic capacity of the vacuole in a substrate-dependent manner.

Regulating the Golgi apparatus sorting of proteinase A to decrease its excretion in Saccharomyces cerevisiae

Beer foam stability, a key factor in evaluating overall beer quality, is influenced by proteinase A (PrA). Actin-severing protein cofilin and Golgi apparatus-localized Ca²⁺ ATPase Pmr1 are involved in protein sorting at the trans-Golgi network (TGN) in yeast Curwin et al. (Mol Biol Cell 23:2327-2338, 2012). To reduce PrA excretion into the beer fermentation broth, we regulated the Golgi apparatus sorting of PrA, thereby facilitating the delivery of more PrA to the vacuoles in the yeast cells. In the present study, the cofilin-coding gene COF1 and the Pmr1-coding gene PMR1 were overexpressed in the parental strain W303-1A and designated as W + COF1 and W + PMR1, respectively. The relative expression levels of COF1 in W + COF1 and PMR1 in W + PMR1 were 5.26- and 19.76-fold higher than those in the parental strain. After increases in the expression levels of cofilin and Pmr1 were confirmed, the PrA activities in the wort broth fermented with W + COF1, W + PMR1, and W303-1A were measured. Results showed that the extracellular PrA activities of W + COF1 and W + PMR1 were decreased by 9.24% and 13.83%, respectively, at the end of the main fermentation compared with that of W303-1A. Meanwhile, no apparent differences were found on the fermentation performance of recombinant and parental strains. The research uncovers an effective strategy for decreasing PrA excretion in Saccharomyces cerevisiae.

Extracellular maltotriose hydrolysis by Saccharomyces cerevisiae cells lacking the AGT1 permease

In brewing, maltotriose is the least preferred sugar for uptake by Saccharomyces cerevisiae cells. Although the AGT1 permease is required for efficient maltotriose fermentation, we have described a new phenotype in some agt1Δ strains of which the cells do not grow on maltotriose during the first 3-4 days of incubation, but after that, they start to grow on the sugar aerobically. Aiming to characterize this new phenotype, we performed microarray gene expression analysis which indicated upregulation of high-affinity glucose transporters (HXT4, HXT6 and HXT7) and α-glucosidases (MAL12 and IMA5) during this delayed cellular growth. Since these results suggested that this phenotype might be due to extracellular hydrolysis of maltotriose, we attempted to detect glucose in the media during growth. When an hxt-null agt1Δ strain was grown on maltotriose, it also showed the delayed growth on this carbon source, and glucose accumulated in the medium during maltotriose consumption. Considering that the poorly characterized α-glucosidase encoded by IMA5 was among the overexpressed genes, we deleted this gene from an agt1Δ strain that showed delayed growth on maltotriose. The ima5Δ agt1Δ strain showed no maltotriose utilization even after 200 h of incubation, suggesting that IMA5 is likely responsible for the extracellular maltotriose hydrolysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Maltotriose is the second most abundant sugar present in brewing. However, many yeast strains have difficulties to consume maltotriose, mainly because of its low uptake rate by the yeast cells when compared to glucose and maltose uptake. The AGT1 permease is required for efficient maltotriose fermentation, but some strains deleted in this gene are still able to grow on maltotriose after an extensive lag phase. This manuscript shows that such delayed growth on maltotriose is a consequence of extracellular hydrolysis of the sugar. Our results also indicate that the IMA5-encoded α-glucosidase is likely the enzyme responsible for this phenotype.