Pectin utilization by the methylotrophic yeast Pichia methanolica

Substances of health concern in home-distilled and commercial alcohols from Texas

Objective

Poor distillation practices in the production of spirits have historically resulted in many instances of adverse health outcomes including death. Concern has focused on lead and copper contamination as well as unhealthy levels of methanol and glyphosate. This study assesses home-distilled and commercially distilled alcohols from Texas for these substances of concern, highlighting their potential risks to public health.

Methods

Atomic absorption spectroscopy, gas chromatography, and enzyme-linked immunosorbent assay were employed to determine lead and copper, methanol, and glyphosate levels in 12 commercial and 36 home-distilled alcohol samples.

Results

Our findings showed that 11 % of the home-distilled alcohols exceeded the U.S. Alcohol and Tobacco Tax and Trade Bureau's copper safety limits of 0.5 mg/L for wine. Additionally, 36 % of these samples surpassed the European Commission (EC)'s lead legal threshold of 0.15 mg/L set for wine products. Results from commercial alcohols indicated that no samples exceeded the same safety limits for copper, and 33 % exceeded the same legal threshold for lead. Both commercial and home-distilled alcohols exhibited methanol concentrations remarkably below the 0.35 % limit for brandy set by the U.S. Food and Drug Administration. Only two home-distilled samples contained detectable glyphosate concentrations well below 100 μg/L, the maximum residue level in beer and wine established by the EC.

Conclusions

Our findings suggested that consumption of alcohol in Texas may pose potential health risks associated with the elevated content of lead and copper. There is a need for increased focus on alcohol as a potential source of exposure to heavy metals.

Methanol Mitigation during Manufacturing of Fruit Spirits with Special Consideration of Novel Coffee Cherry Spirits

Methanol is a natural ingredient with major occurrence in fruit spirits, such as apple, pear, plum or cherry spirits, but also in spirits made from coffee pulp. The compound is formed during fermentation and the following mash storage by enzymatic hydrolysis of naturally present pectins. Methanol is toxic above certain threshold levels and legal limits have been set in most jurisdictions. Therefore, the methanol content needs to be mitigated and its level must be controlled. This article will review the several factors that influence the methanol content including the pH value of the mash, the addition of various yeast and enzyme preparations, fermentation temperature, mash storage, and most importantly the raw material quality and hygiene. From all these mitigation possibilities, lowering the pH value and the use of cultured yeasts when mashing fruit substances is already common as best practice today. Also a controlled yeast fermentation at acidic pH facilitates not only reduced methanol formation, but ultimately also leads to quality benefits of the distillate. Special care has to be observed in the case of spirits made from coffee by-products which are prone to spoilage with very high methanol contents reported in past studies.

Diversity and occurrence of methylotrophic yeasts used in genetic engineering

Methylotrophic yeasts have been used as the platform for expression of heterologous proteins since the 1980’s. They are highly productive and allow producing eukaryotic proteins with an acceptable glycosylation level. The first Pichia pastoris-based system for expression of recombinant protein was developed on the basis of the treeexudate- derived strain obtained in the US southwest. Being distributed free of charge for scientific purposes, this system has become popular around the world. As methylotrophic yeasts were classified in accordance with biomolecular markers, strains used for production of recombinant protein were reclassified as Komagataella phaffii. Although patent legislation suggests free access to these yeasts, they have been distributed on a contract basis. Whereas their status for commercial use is undetermined, the search for alternative stains for expression of recombinant protein continues. Strains of other species of methylotrophic yeasts have been adapted, among which the genus Ogataea representatives prevail. Despite the phylogenetic gap between the genus Ogataea and the genus Komagataella representatives, it turned out possible to use classic vectors and promoters for expression of recombinant protein in all cases. There exist expression systems based on other strains of the genus Komagataella as well as the genus Candida. The potential of these microorganisms for genetic engineering is far from exhausted. Both improvement of existing expression systems and development of new ones on the basis of strains obtained from nature are advantageous. Historically, strains obtained on the southwest of the USA were used as expression systems up to 2009. Currently, expression systems based on strains obtained in Thailand are gaining popularity. Since this group of microorganisms is widely represented around the world both in nature and in urban environments, it may reasonably be expected that new expression systems for recombinant proteins based on strains obtained in other regions of the globe will appear.

Methanol contamination in traditionally fermented alcoholic beverages: the microbial dimension

Incidence of methanol contamination of traditionally fermented beverages is increasing globally resulting in the death of several persons. The source of methanol contamination has not been clearly established in most countries. While there were speculations that unscrupulous vendors might have deliberately spiked the beverages with methanol, it is more likely that the methanol might have been produced by contaminating microbes during traditional ethanol fermentation, which is often inoculated spontaneously by mixed microbes, with a potential to produce mixed alcohols. Methanol production in traditionally fermented beverages can be linked to the activities of pectinase producing yeast, fungi and bacteria. This study assessed some traditional fermented beverages and found that some beverages are prone to methanol contamination including cachaca, cholai, agave, arak, plum and grape wines. Possible microbial role in the production of methanol and other volatile congeners in these fermented beverages were discussed. The study concluded by suggesting that contaminated alcoholic beverages be converted for fuel use rather than out rightly banning the age—long traditional alcohol fermentation.

Maltase protein of Ogataea (Hansenula) polymorpha is a counterpart to the resurrected ancestor protein ancMALS of yeast maltases and isomaltases

Saccharomyces cerevisiae maltases use maltose, maltulose, turanose and maltotriose as substrates, isomaltases use isomaltose, α‐methylglucoside and palatinose and both use sucrose. These enzymes are hypothesized to have evolved from a promiscuous α‐glucosidase ancMALS through duplication and mutation of the genes. We studied substrate specificity of the maltase protein MAL1 from an earlier diverged yeast, Ogataea polymorpha (Op), in the light of this hypothesis. MAL1 has extended substrate specificity and its properties are strikingly similar to those of resurrected ancMALS. Moreover, amino acids considered to determine selective substrate binding are highly conserved between Op MAL1 and ancMALS. Op MAL1 represents an α‐glucosidase in which both maltase and isomaltase activities are well optimized in a single enzyme. Substitution of Thr200 (corresponds to Val216 in S. cerevisiae isomaltase IMA1) with Val in MAL1 drastically reduced the hydrolysis of maltose‐like substrates (α‐1,4‐glucosides), confirming the requirement of Thr at the respective position for this function. Differential scanning fluorimetry (DSF) of the catalytically inactive mutant Asp199Ala of MAL1 in the presence of its substrates and selected monosaccharides suggested that the substrate‐binding pocket of MAL1 has three subsites (–1, +1 and +2) and that binding is strongest at the –1 subsite. The DSF assay results were in good accordance with affinity (K_m) and inhibition (K_i) data of the enzyme for tested substrates, indicating the power of the method to predict substrate binding. Deletion of either the maltase (MAL1) or α‐glucoside permease (MAL2) gene in Op abolished the growth of yeast on MAL1 substrates, confirming the requirement of both proteins for usage of these sugars. © 2016 The Authors. Yeast published by John Wiley & Sons, Ltd.

A potential role for an extracellular methanol oxidase secreted by Moniliophthora perniciosa in Witches' broom disease in cacao

The hemibiotrophic basidiomycete fungus Moniliophthora perniciosa, the causal agent of Witches' broom disease (WBD) in cacao, is able to grow on methanol as the sole carbon source. In plants, one of the main sources of methanol is the pectin present in the structure of cell walls. Pectin is composed of highly methylesterified chains of galacturonic acid. The hydrolysis between the methyl radicals and galacturonic acid in esterified pectin, mediated by a pectin methylesterase (PME), releases methanol, which may be decomposed by a methanol oxidase (MOX). The analysis of the M. pernciosa genome revealed putative mox and pme genes. Real-time quantitative RT-PCR performed with RNA from mycelia grown in the presence of methanol or pectin as the sole carbon source and with RNA from infected cacao seedlings in different stages of the progression of WBD indicate that the two genes are coregulated, suggesting that the fungus may be metabolizing the methanol released from pectin. Moreover, immunolocalization of homogalacturonan, the main pectic domain that constitutes the primary cell wall matrix, shows a reduction in the level of pectin methyl esterification in infected cacao seedlings. Although MOX has been classically classified as a peroxisomal enzyme, M. perniciosa presents an extracellular methanol oxidase. Its activity was detected in the fungus culture supernatants, and mass spectrometry analysis indicated the presence of this enzyme in the fungus secretome. Because M. pernciosa possesses all genes classically related to methanol metabolism, we propose a peroxisome-independent model for the utilization of methanol by this fungus, which begins with the extracellular oxidation of methanol derived from the demethylation of pectin and finishes in the cytosol.

Differential gene expression between the biotrophic-like and saprotrophic mycelia of the witches' broom pathogen Moniliophthora perniciosa

Moniliophthora perniciosa is a hemibiotrophic fungus that causes witches' broom disease (WBD) in cacao. Marked dimorphism characterizes this fungus, showing a monokaryotic or biotrophic phase that causes disease symptoms and a later dikaryotic or saprotrophic phase. A combined strategy of DNA microarray, expressed sequence tag, and real-time reverse-transcriptase polymerase chain reaction analyses was employed to analyze differences between these two fungal stages in vitro. In all, 1,131 putative genes were hybridized with cDNA from different phases, resulting in 189 differentially expressed genes, and 4,595 reads were clusterized, producing 1,534 unigenes. The analysis of these genes, which represent approximately 21% of the total genes, indicates that the biotrophic-like phase undergoes carbon and nitrogen catabolite repression that correlates to the expression of phytopathogenicity genes. Moreover, downregulation of mitochondrial oxidative phosphorylation and the presence of a putative ngr1 of Saccharomyces cerevisiae could help explain its lower growth rate. In contrast, the saprotrophic mycelium expresses genes related to the metabolism of hexoses, ammonia, and oxidative phosphorylation, which could explain its faster growth. Antifungal toxins were upregulated and could prevent the colonization by competing fungi. This work significantly contributes to our understanding of the molecular mechanisms of WBD and, to our knowledge, is the first to analyze differential gene expression of the different phases of a hemibiotrophic fungus.

Molecular characterization of thePEX5 gene encoding peroxisomal targeting signal 1 receptor from the methylotrophic yeastPichia methanolica

In this study, we describe the molecular characterization of the PEX5 gene encoding the peroxisomal targeting signal 1 (PTS1) receptor from the methylotrophic yeast Pichia methanolica. The P. methanolica PEX5 (PmPEX5) gene contains a open reading frame corresponding to a gene product of 646 amino acid residues, and its deduced amino acid sequence shows a high similarity to those of Pex5ps from other methylotrophic yeasts. Like other Pex5ps, the PmPex5p possesses seven repeats of the TPR motif in the C-terminal region and three WXXXF/Y motifs. A strain with the disrupted PEX5 gene (pex5Delta) lost its ability to grow on peroxisome-inducible carbon sources, methanol and oleate, but grew normally on glucose and glycerol. Disruption of PmPEX5 caused a drastic decrease in peroxisomal enzyme activities and mislocalization of GFP-PTS1 and some peroxisomal methanol-metabolizing enzymes in the cytosol. Expression of the PmPEX5 gene was regulated by carbon sources, and it was strongly expressed by peroxisome-inducible carbon sources, especially methanol. Taken together, these findings show that PmPex5p has an essential physiological role in peroxisomal metabolism of P. methanolica, including methanol metabolism, and in peroxisomal localization and activation of methanol-metabolizing enzymes, e.g. AOD isozymes, DHAS and CTA.

Regulation of two distinct alcohol oxidase promoters in the methylotrophic yeastPichia methanolica

In this study, two Pichia methanolica alcohol oxidase (AOD) promoters, P(MOD1) and P(MOD2), were evaluated in a promoter assay system utilizing the acid phosphatase (AP) gene from Saccharomyces cerevisiae (ScPHO5) as a reporter. Heterologous gene expression driven by the P(MOD1) and P(MOD2) promoters was found to be strong and tightly regulated by carbon source at the transcriptional level. P(MOD1) was induced not only by methanol but also by glycerol. P(MOD2) was induced only by methanol, although it was not repressed on the addition of glycerol to a methanol medium, suggesting that P(MOD2) is regulated in a manner distinct from that of other AOD-gene promoters. On the other hand, methanol and oxygen level-influenced gene expression mediated by P(MOD1) and P(MOD2). P(MOD1) expression was optimal at low methanol concentrations, whereas P(MOD2) was predominantly expressed at high methanol and high oxygen concentrations. Based on these results, both P(MOD2) and P(MOD1) should be useful tools for controlling heterologous gene expression in P. methanolica. In particular, it should be possible to differentially control the production phases of two heterologous proteins, using P(MOD1) and P(MOD2) in the same host cell and in the same flask.