Simultaneous production of biosurfactant and extracellular unspecific peroxygenases by Moesziomyces aphidis XM01 enables an efficient strategy for crude oil degradation

Crude oil is a hazardous pollutant that poses significant and lasting harm to human health and ecosystems. In this study, Moesziomyces aphidis XM01, a biosurfactant mannosylerythritol lipids (MELs)-producing yeast, was utilized for crude oil degradation. Unlike most microorganisms relying on cytochrome P450, XM01 employed two extracellular unspecific peroxygenases, MaUPO.1 and MaUPO.2, with preference for polycyclic aromatic hydrocarbons (PAHs) and n-alkanes respectively, thus facilitating efficient crude oil degradation. The MELs produced by XM01 exhibited a significant emulsification activity of 65.9% for crude oil and were consequently supplemented in an "exogenous MELs addition" strategy to boost crude oil degradation, resulting in an optimal degradation ratio of 72.3%. Furthermore, a new and simple "pre-MELs production" strategy was implemented, achieving a maximum degradation ratio of 95.9%. During this process, the synergistic up-regulation of MaUPO.1, MaUPO.1 and the key MELs synthesis genes contributed to the efficient degradation of crude oil. Additionally, the phylogenetic and geographic distribution analysis of MaUPO.1 and MaUPO.1 revealed their wide occurrence among fungi in Basidiomycota and Ascomycota, with high transcription levels across global ocean, highlighting their important role in biodegradation of crude oil. In conclusion, M. aphidis XM01 emerges as a novel yeast for efficient and eco-friendly crude oil degradation.

NsdD, a GATA-type transcription factor is involved in regulation and biosynthesis of macromolecules melanin, pullulan, and polymalate in Aureobasidium melanogenum

In this study, an NSDD gene, which encoded a GATA-type transcription factor involved in the regulation and biosynthesis of melanin, pullulan, and polymalate (PMA) in Aureobasidium melanogenum, was characterized. After the NSDD gene was completely removed, melanin production by the Δnsd mutants was enhanced, while pullulan and polymalate production was significantly reduced. Transcription levels of the genes involved in melanin biosynthesis were up-regulated while expression levels of the genes responsible for pullulan and PMA biosynthesis were down-regulated in the Δnsdd mutants. In contrast, the complementation of the NSDD gene in the Δnsdd mutants made the overexpressing mutants restore melanin production and transcription levels of the genes responsible for melanin biosynthesis. Inversely, the complementation strains, compared to the wild type strains, showed enhanced pullulan and PMA yields. These results demonstrated that the NsdD was not only a negative regulator for melanin biosynthesis, but also a key positive regulator for pullulan and PMA biosynthesis in A. melanogenum. It was proposed how the same transcriptional factor could play a negative role in melanin biosynthesis and a positive role in pullulan and PMA biosynthesis. This study provided novel insights into the regulatory mechanisms of multiple A. melanogenum metabolites and the possibility for improving its yields of some industrial products through genetic approaches.

Liamocins overproduction via the two-pH stage fermentation and anti-Aspergillus flavus activity of Massoia lactone

Aureobasidium melanogenum was found to be grown the best at the constant pH 7.0 and to produce the highest amount of liamocins at the constant pH 3.0. Therefore, the wild type strain A. melanogenum 9-1 and the engineered strain V33 constructed in the laboratory were grown at the constant pH 7.0 for 48 h, then, they were continued to be cultivated at the constant pH 3.0. Under such conditions, A. melanogenum 9-1 produced 36.51 ± 0.55 g L-1 of liamocin and its cell mass was 27.43 ± 0.63 and 6.00 ± 0.11 g L-1 of glucose was left in the finished medium within 168 h while the engineered strain V33 secreted 70.86 ± 2.04 g L-1 of liamocin, its cell mass was 31.63 ± 0.74 g L-1 , 0.16 ± 0.01 g L-1 of glucose was maintained in the finished medium. Then, Massoia lactone was released from the produced liamocins. The released Massoia lactone loaded in the nanoemulsions could be used to actively damage cell wall and cell membrane of both spores and mycelia of Aspergillus flavus, leading to its cell necrosis. Massoia lactone loaded in the nanoemulsions also actively inhibited cell growth of A. flavus, its conidia production and aflatoxin biosynthesis on peanuts, indicating that Massoia lactone loaded in the nanoemulsions had highly potential application in controlling cell growth of A. flavus and aflatoxin biosynthesis in foods and feedstuffs.

Liamocin biosynthesis is induced by an autogenous host acid activation in Aureobasidium melanogenum

It has been known that maximal liamocin production must be carried out at low environmental pH (around 3.0). In this study, it was found that the low pH was mainly caused by the secreted citric acid which is one precursor of acetyl-CoA for liamocin biosynthesis. Determination of citric acid in the culture, deletion, complementation and overexpression of the CEXA gene encoding specific citrate exporter demonstrated that the low pH was indeed caused by the secreted citric acid. Deletion, complementation and overexpression of the ACL gene encoding ATP-citric acid lyase and effects of different initial pHs and added citric acid showed that the low pH in the presence of citric acid was suitable for lysis of intracellular citric acid, liamocin production and expression of the PACC gene encoding the pH signaling transcription factor PacC. This meant that the PACC gene was an acid-expression gene. Deletion, complementation and overexpression of the PACC gene indicated that expression of the key gene cluster GAL1-EST1-PKS1 for liamocin biosynthesis was driven by the pH signaling transcription factor PacC and there was weak nitrogen catabolite repression on liamocin biosynthesis at the low pH. That was why liamocin biosynthesis was induced at a low pH in the presence of citric acid. The mechanisms of the enhanced liamocin biosynthesis by the autogenous host acid activation, together with the pH signaling pathway, were proposed.

The Pathogenic Yeast Metschnikowia bicuspidata var. bicuspidata in the Aquacultured Ecosystem and Its Biocontrol

M. bicuspidata var. bicuspidata is a pathogenic yeast which can affect aquacultured and marine-cultured animals such as brine shrimp, ridgetail white prawn, chinook salmon, giant freshwater prawn, the Chinese mitten crab, marine crab, the mud crab, the mangrove land crab, the Chinese grass shrimp, sea urchins, sea urchins, Daphnia dentifera and even snails, causing a milky disease, and it has caused big economic losses in aquacultural and marine-cultural industries in the past. However, the detailed mechanisms and the reasons for the milky disease in the diseased aquatic animals are still completely unknown. So far, only some antimycotics, killer toxins and Massoia lactone haven been found to be able to actively control and kill its growth. The ecofriendly, green and renewable killer toxins and Massoia lactone have high potential for application in controlling the milky disease.

Novel chromosomes and genomes provide new insights into evolution and adaptation of the whole genome duplicated yeast-like fungus TN3-1 isolated from natural honey

Aureobasidium melanogenum TN3-1 strain and A. melanogenum P16 strain were isolated from the natural honey and the mangrove ecosystem, respectively. The former can produce much higher pullulan from high concentration of glucose than the latter. In order to know what happened to their genomes, the PacBio sequencing and Hi-C technologies were used to create the first high-quality chromosome-level reference genome assembly of A. melanogenum TN3-1 (51.61 Mb) and A. melanogenum P16 (25.82 Mb) with the contig N50 of 2.19 Mb and 2.26 Mb, respectively. Based on the Hi-C results, a total of 93.33% contigs in the TN3-1 strain and 92.31% contigs in the P16 strain were anchored onto 24 and 12 haploid chromosomes, respectively. The genomes of the TN3-1 strain had two subgenomes A and B. Synteny analysis showed that the genomic contents of the two subgenomes were asymmetric with many structural variations. Intriguingly, the TN3-1 strain was revealed as a recent hybrid/fusion between the ancestor of A. melanogenum CBS105.22/CBS110374 and the ancestor of another unidentified strain of A. melanogenum similar to P16 strain. We estimated that the two ancient progenitors diverged around 18.38 Mya and merged around 10.66-9.98 Mya. It was found that in the TN3-1 strain, telomeres of each chromosome contained high level of long interspersed nuclear elements (LINEs), but had low level of the telomerase encoding gene. Meanwhile, there were high level of transposable elements (TEs) inserted in the chromosomes of the TN3-1 strain. In addition, the positively selected genes of the TN3-1 strain were mainly enriched in the metabolic processes related to harsh environmental adaptability. Most of the stress-related genes were found to be related to the adjacent LTRs, and the glucose derepression was caused by the mutation of the Glc7-2 in the Snf-Mig1 system. All of these could contribute to its genetic instability, genome evolution, high stress resistance, and high pullulan production from glucose.

Genome-Wide Editing Provides Insights into Role of Unsaturated fatty Acids in Low Temperature Growth of the Psychrotrophic Yeast Metschnikowia bicuspidata var. australis W7-5

In order to know the function of C_18:2 and C_18:3 fatty acids in the cold growth of the psychrotrophic yeast M. bicuspidata var. australis W7-5, the mutant 1 without C_18:2 fatty acid and the mutant 2 without C_18:3 fatty acids were obtained. Only the trace amount of C_18:2 fatty acid in the mutant 1 occurred while no C_18:3 fatty acid in the mutant 2 was detected. The growth rate of only the mutant 1 cultured at 5 ℃ and 25 ℃ was significantly reduced compared with that of the wild-type strain W7-5. But there was no difference between the growth of the mutant 2 and that of the W7-5 strain. These meant that only C_18:2 synthesized by the psychrotrophic yeast played an important role in cell growth at low temperature (5 °C) and high temperature (25 °C). Meanwhile, cell wall in the mutant 1 without C_18:2 fatty acid gown at 5 and 25 °C was also negatively affected, leading to the reduced cell growth rate of the mutant 1 grown at 5 and 25 °C.

Bioconversion of non-food corn biomass to polyol esters of fatty acid and single-cell oils

BACKGROUND

Lignocellulose is a valuable carbon source for the production of biofuels and biochemicals, thus having the potential to substitute fossil resources. Consolidated bio-saccharification (CBS) is a whole-cell-based catalytic technology previously developed to produce fermentable sugars from lignocellulosic agricultural wastes. The deep-sea yeast strain Rhodotorula paludigena P4R5 can produce extracellular polyol esters of fatty acids (PEFA) and intracellular single-cell oils (SCO) simultaneously. Therefore, the integration of CBS and P4R5 fermentation processes would achieve high-value-added conversion of lignocellulosic biomass.

RESULTS

The strain P4R5 could co-utilize glucose and xylose, the main monosaccharides from lignocellulose, and also use fructose and arabinose for PEFA and SCO production at high levels. By regulating the sugar metabolism pathways for different monosaccharides, the strain could produce PEFA with a single type of polyol head. The potential use of PEFA as functional micelles was also determined. Most importantly, when sugar-rich CBS hydrolysates derived from corn stover or corncob residues were used to replace grain-derived pure sugars for P4R5 fermentation, similar PEFA and SCO productions were obtained, indicating the robust conversion of non-food corn plant wastes to high-value-added glycolipids and lipids. Since the produced PEFA could be easily collected from the culture via short-time standing, we further developed a semi-continuous process for PEFA production from corncob residue-derived CBS hydrolysate, and the PEFA titer and productivity were enhanced up to 41.1 g/L and 8.22 g/L/day, respectively.

CONCLUSIONS

Here, we integrated the CBS process and the P4R5 fermentation for the robust production of high-value-added PEFA and SCO from non-food corn plant wastes. Therefore, this study suggests a feasible way for lignocellulosic agro-waste utilization and the potential application of P4R5 in industrial PEFA production.

Massoia Lactone Displays Strong Antifungal Property Against Many Crop Pathogens and Its Potential Application

Massoia lactone could be released from liamocins produced by Aureobasidium melanogenum M39. The obtained Massoia lactone was very stable and highly active against many fungal crop pathogens which cause many plant diseases and food unsafety. Massoia lactone treatment not only could effectively inhibit their hyphal growth and spore germination, but also caused pore formation in cell membrane, reduction of ergosterol content, rise in intracellular ROS levels, and leakage of intracellular components, consequently leading to cellular necrosis and cell death. The direct contact of Massoia lactone with Fusarium graminearum spores could stop the development of Fusarium head blight symptom in the diseased wheats. Therefore, Massoia lactone could be a promising candidate for development as an effective and green bio-fungicide because of its high anti-fungal activity and the multiplicity of mode of its action.

A high molecular weight polymalate is synthesized by the whole genome duplicated strain Aureobasidium melanogenum OUC

Polymalate (PMA) produced by the whole genome duplicated strain Aureobasidium melanogenum OUC had a high molecular weight (Mw) of 3.9 × 10⁵ Da while the Mw of PMA produced by A. melanogenum ATCC62921 was 3.8 × 10⁴ Da. Therefore, the purified PMA produced by A. melanogenum OUC could form hydrogel and film and the precipitated Ca²⁺-PMA looked like noodle whereas the purified PMA produced by A. melanogenum ATCC62921 could not form such a hydrogel and a film and the precipitated PMA was powder-like. The high Mw PMA biosynthesis in A. melanogenum OUC was also controlled by the PMA synthetase. However, it was still unclear why the PMA synthetase in A. melanogenum OUC could catalyze the high Mw PMA biosynthesis. Both removal of two copies of the PKS genes and overexpression of the PYC1 gene, the VGB gene and the CRZ2 gene rendered the new transformant Crz46 to produce 34.6 ± 0.3 g/L of extracellular Ca²⁺-PMA with Mw of 4.9 × 10⁵ Da while its native A. melanogenum OUC only produced 17.2 ± 0.3 g/L of Ca²⁺-PMA. During the 10-Liter fermentation, 35.6 ± 1.2 g/L of Ca²⁺-PMA and 13.9 g/Lof cell mass were produced within 168 h, leading to the yield of 0.36 g/g of glucose and the productivity of 0.21 g/L/h. This was the first time to report that the whole genome duplicated strain A. melanogenum OUC and its engineered mutants could produce the high Mw PMA.

The GATA type transcriptional factors regulate pullulan biosynthesis in Aureobasidium melanogenum P16

Aureobasidium melanogenum P16, the high pullulan producer, had only one GATA type transcriptional activator AreA and one GATA type transcriptional repressor AreB. It was found that 2.4 g/L of (NH₄)₂SO₄ had obvious nitrogen repression on pullulan biosynthesis by A. melanogenum P16. Removal of the AreB gene could make the disruptant DA6 produce 34.8 g/L pullulan while the P16 strain only produced 28.8 g/L pullulan at the efficient nitrogen condition. Further both removal of the native AreA gene and overexpression of the mutated AreA_S628-S678 gene with non-phosphorylatable residues could render the transformant DEA12 to produce 39.8 g/L pullulan. The transcriptional levels of most of the genes related to pullulan biosynthesis in the transformant DEA12 were greatly enhanced. The mutated AreA_S628-S678 was localized in the nuclei of the transformant DEA12 while the native AreA was distributed in the cytoplasm in A. melanogenum P16. This meant that nitrogen repression on pullulan biosynthesis in the transformant DEA12 was indeed significantly relieved. This was the first time to report that the GATA type transcriptional factors of nitrogen catabolite repression system could regulate pullulan biosynthesis in Aureobasidium spp.

Liamocins biosynthesis, its regulation in Aureobasidium spp., and their bioactivities

Liamocins synthesized by Aureobasidium spp. are glycolipids composed of a single mannitol or arabitol headgroup linked to either three, four or even six 3,5-dihydroxydecanoic ester tail-groups. The highest titer of liamocin achieved was over 40.0 g/L. The substrates for liamocins synthesis include glucose, sucrose, xylose, mannitol, and others. The Pks1 is responsible for the biosynthesis of the tail-group 3,5-dihydroxydecanoic acid, both mannitol dehydrogenase (MDH) and mannitol 1-phosphate 5-dehydrogenase (MPDH) catalyze the mannitol biosynthesis and the arabitol biosynthesis is controlled by arabitol dehydrogenase (ArDH). The ester bond formation between 3,5-dihydroxydecanoic acid and mannitol or arabitol is catalyzed by the esterase (Est1). Liamocin biosynthesis is regulated by the specific transcriptional activator (Gal1), global transcriptional activator (Msn2), various signaling pathways, acetyl-CoA flux while Pks1 activity is controlled by PPTase activity. The synthesized liamocins have high bioactivity against the pathogenic bacteria Streptococcus spp. and some kinds of cancer cells while Massoia lactone released liamocins which exhibited obvious antifungal and anticancer activities. Therefore, liamocins and Massoia lactone have many applications in various sectors of biotechnology.

Molecular evolution and regulation of DHN melanin-related gene clusters are closely related to adaptation of different melanin-producing fungi

Many genes responsible for melanin biosynthesis in fungi were physically linked together. The PKS gene clusters in most of the melanin-producing fungi were regulated by the Cmr1. It was found that a close rearrangement of the PKS gene clusters had evolved in most of the melanin-producing fungi and various functions of melanin in them were beneficial to their adaptation to the changing environments. The melanin-producing fungi had undergone at least five large-scale differentiations, making their PKS gene clusters be quickly evolved and the fungi be adapted to different harsh environments. The recent gene losses and expansion were remarkably frequent in the PKS gene clusters, leading to their rapid evolution and adaptation of their hosts to different environments. The PKS gene and the CMR1 gene in them were subject to a strong co-evolution, but the horizontal gene transfer events might have occurred in the genome-duplicated species, Aspergillus and Penicillium.

Polymalate (PMA) biosynthesis and its molecular regulation in Aureobasidium spp

It has been well documented that different strains of Aureobasidium spp. can synthesize and secrete over 30.0 g/L of polymalate (PMA) and the produced PMA has many potential applications in biomaterial, medical and food industries. The substrates for PMA biosynthesis include glucose, xylose, fructose, sucrose and glucose or fructose or xylose or sucrose-containing natural materials from industrial and agricultural wastes. Malate, the only monomer for PMA biosynthesis mainly comes from TCA cycle, cytosolic reduction TCA pathway and the glyoxylate cycle. The PMA synthetase (a NRPS) containing A like domain, T domain and C like domain is responsible for polymerization of malate into PMA molecules by formation of ester bonds between malates. PMA biosynthesis is regulated by the transcriptional activator Crz1 from Ca²⁺ signaling pathway, the GATA-type transcription factor Gat1 from nitrogen catabolite repression and the GATA-type transcription factor NsdD.

The Genome-Wide Mutation Shows the Importance of Cell Wall Integrity in Growth of the Psychrophilic Yeast Metschnikowia australis W7-5 at Different Temperatures

In this study, it was found that a Cre/loxP system could be successfully used as a tool for editing the genome of the psychrophilic yeast Metschnikowia australis W7-5 isolated from Antarctica. The deletion and over-expression of the TPS1 gene for trehalose biosynthesis, the GSY gene for glycogen biosynthesis, and the GPD1 and GPP genes for glycerol biosynthesis had no influence on cell growth of the mutants and transformants compared to cell growth of their wild-type strain M. australis W7-5, indicating that trehalose, glycogen, and glycerol had no function in growth of the psychrophilic yeast at different temperatures. However, removal of the SLT2 gene encoding the mitogen-activated protein kinase in the cell wall integrity (CWI) signaling pathway and the SWI4 and SWI6 genes encoding the transcriptional activators Swi4/6 had the crucial influence on cell growth of the psychrophilic yeast at the low temperature, especially at 25 °C and expression of the genes related to cell wall and lipid biosynthesis. Therefore, the cell wall could play an important role in growth of the psychrophilic yeast at different temperatures and biosynthesis of cell wall was actively regulated by the CWI signaling pathway. This was the first time to show that the genome of the psychrophilic yeast was successfully edited and the molecular evidences were obtained to elucidate mechanisms of low temperature growth of the psychrophilic yeast from Antarctica.

Glycerol, trehalose and vacuoles had relations to pullulan synthesis and osmotic tolerance by the whole genome duplicated strain Aureobasidium melanogenum TN3-1 isolated from natural honey

In our previous study, it was found that Aureobasidium melanogenum TN3-1 was a high pullulan producing and osmotic tolerant yeast-like fungal strain. In this study, the HOG1 signaling pathway controlling glycerol synthesis, glycerol, trehalose and vacuoles were found to be closely related to its pullulan biosynthesis and high osmotic tolerance. Therefore, deletion of the key genes for the HOG1 signaling pathway, glycerol and trehalose biosynthesis and vacuole formation made all the mutants reduce pullulan biosynthesis and increase sensitivity of the growth of the mutants to high glucose concentration. Especially, abolishment of both the VSP11 and VSP12 genes which controlled the fission/fusion balance of vacuoles could cause big reduction in pullulan production (less than 7.4 ± 0.4 g/L) by the double mutant ΔDV-5 and increased sensitivity to high concentration glucose, while expression of the VSP11 gene in the double mutant ΔDV-5 made the transformants EV-2 restore pullulan production and tolerance to high concentration glucose. But cell growth of them were the similar. The double mutant ΔDV-5 had much bigger vacuoles and less numbers of vacuoles than the transformant EV-2 and its wild type strain TN3-1 while it grew weakly on the plate with 40% (w/v) glucose while the transformant EV-2 and its wild type strain TN3-1 could grow normally on the plate even with 60% (w/v) glucose. The double mutant ΔDV-5 also had high level of pigment and its cells were swollen. This was the first time to give the evidence that glycerol, trehalose and vacuoles were closely related to pullulan biosynthesis and high osmotic tolerance by A. melanogenum.

cAMP-PKA and HOG1 signaling pathways regulate liamocin production by different ways via the transcriptional activator Msn2 in Aureobasidium melanogenum

Liamocins, as the secondary metabolites synthesized and secreted by Aureobasidium spp., consist of a single mannitol or a single arabitol head group partially O-acylated with three 3,5-dihydroxydecanoic ester groups or directly esterified with three or four 3,5-dihydroxydecanoic ester tails. Very recently, the whole synthetic pathway of liamocins in A. melanogenum 6-1-2 has been elucidated. It was found that the promoter sequences of all the genes related to liamocin synthesis in A. melanogenum 6-1-2 had stress regulatory elements with core sequences of AGGGG or CCCCT. Therefore, expression of all the genes would be regulated by the Msn2. In this study, it was found that removal of the single one MSN2 gene in A. melanogenum 6-1-2 made the mutant decrease yield of extracellular liamocin by 92.28 %, while complementation of the MSN2 gene in the mutant rendered liamocin synthesis to be restored. When A. melanogenum 6-1-2 was cultured in the liamocin fermentation medium with high glucose and low nitrogen, the Msn2 was localized in the nucleus and positively regulated the expression of the genes related to liamocin biosynthesis. Furthermore, when the key BCY1 gene encoding regulatory subunit of the cAMP-PKA signaling pathway in A. melanogenum 6-1-2 was knocked out, the amount of extracellular liamocins synthesized by the mutant was decreased by 96.73 % and the Msn2 was localized in the cytoplasm. Similarly, when the key HOG1 gene in the HOG1 signaling pathway was deleted, liamocin biosynthesis in the knockout strain was decreased by 98.09 %. However, it was found that the Hog1 may be one part of the general transcription complex to regulate the transcription of the MSN2 gene, leading to the reduced Msn2 and liamocin synthesis in the mutant. In addition, the key TOR1 gene and SNF1 gene in the TOR1 signaling pathway and the SNF1 signaling pathway were not involved in the regulation of the Msn2 activity and liamocin synthesis. It was concluded that the transcriptional activator Msn2, the HOG1 signaling pathway and the cAMP-PKA signaling pathway were involved in the regulation of liamocin biosynthesis and production.

Fungi in mangrove ecosystems and their potential applications

Mangrove fungi, their ecological role in mangrove ecosystems, their bioproducts, and potential applications are reviewed in this article. Mangrove ecosystems can play an important role in beach protection, accretion promotion, and sheltering coastlines and creeks as barriers against devastating tropical storms and waves, seawater, and air pollution. The ecosystems are characterized by high average and constant temperatures, high salinity, strong winds, and anaerobic muddy soil. The mangrove ecosystems also provide the unique habitats for the colonization of fungi which can produce different kinds of enzymes for industrial uses, recycling of plants and animals in the ecosystems, and the degradation of pollutants. Many mangrove ecosystem-associated fungi also can produce exopolysaccharides, Ca²⁺-gluconic acid, polymalate, liamocin, polyunsaturated fatty acids, biofuels, xylitol, enzymes, and bioactive substances, which have many potential applications in the bioenergy, food, agricultural, and pharmaceutical industries. Therefore, mangrove ecosystems are rich bioresources for bioindustries and ecology. It is necessary to identify more mangrove fungi and genetically edit them to produce a distinct array of novel chemical entities, enzymes, and bioactive substances.

Pullulan biosynthesis in yeast-like fungal cells is regulated by the transcriptional activator Msn2 and cAMP-PKA signaling pathway

Pullulan is an important polysaccharide. Although its synthetic pathway in Aureobasidium melanogenum has been elucidated, the mechanism underlying its biosynthesis as regulated by signaling pathway and transcriptional regulator is still unknown. In this study, it was found that the expression of the UGP1 gene encoding UDPG-pyrophosphorylase (Ugp1) and other genes which were involved in pullulan biosynthesis was controlled by the transcriptional activator Msn2 in the nuclei of yeast-like fungal cells. The Ugp1 was a rate-limiting enzyme for pullulan biosynthesis. In addition, the activity and subcellular localization of the Msn2 were regulated only by the cAMP-PKA signaling pathway. When the cAMP-PKA activity was low, the Msn2 was localized in the nuclei, the UGP1 gene was highly expressed, and pullulan was actively synthesized. By contrast, when the cAMP-PKA activity was high, the Msn2 was localized in the cytoplasm and the UGP1 gene expression was disabled so that pullulan was stopped, but lipid biosynthesis was actively enhanced. This study was the first to report that pullulan and lipid biosynthesis in yeast-like fungal cells were regulated by the Msn2 and cAMP-PKA signaling pathway. Elucidating the regulation mechanisms was important to understand their functions and enhance pullulan and lipid biosynthesis.

Genome sequencing of a yeast-like fungal strain P6, a novel species of Aureobasidium spp.: insights into its taxonomy, evolution, and biotechnological potentials

Purpose

This study aimed to look insights into taxonomy, evolution, and biotechnological potentials of a yeast-like fungal strain P6 isolated from a mangrove ecosystem.

Methods

The genome sequencing for the yeast-like fungal strain P6 was conducted on a Hiseq sequencing platform, and the genomic characteristics and annotations were analyzed. The central metabolism and gluconate biosynthesis pathway were studied through the genome sequence data by using the GO, KOG, and KEGG databases. The secondary metabolite potentials were also evaluated.

Results

The whole genome size of the P6 strain was 25.41Mb and the G + C content of its genome was 50.69%. Totally, 6098 protein-coding genes and 264 non-coding RNA genes were predicted. The annotation results showed that the yeast-like fungal strain P6 had complete metabolic pathways of TCA cycle, EMP pathway, pentose phosphate pathway, glyoxylic acid cycle, and other central metabolic pathways. Furthermore, the inulinase activity associated with β-fructofuranosidase and high glucose oxidase activity in this strain have been demonstrated. It was found that this yeast-like fungal strain was located at root of most species of Aureobasidium spp. and at a separate cluster of all the phylogenetic trees. The P6 strain was predicted to contain three NRPS gene clusters, five type-I PKS gene clusters, and one type-I NRPS/PKS gene cluster via analysis at the antiSMASH Website. It may synthesize epichloenin A, fusaric acid, elsinochromes, and fusaridione A.

Conclusions

Based on its unique DNA sequence, taxonomic position in the phylogenetic tree and evolutional position, the yeast-like fungal strain P6 was identified as a novel species Aureobasidium hainanensis sp. nov. P6 isolate and had highly potential applications.

Biosynthesis of some organic acids and lipids in industrially important microorganisms is promoted by pyruvate carboxylases

Pyruvate carboxylase (Pyc) catalyzes formation of oxaloacetic acid from pyruvic acid by fixing one mole of CO2. Many evidences have confirmed that biosynthesis of some different kinds of organic acids and intracellular and extracellular lipids is driven by Pyc and over-expression of the PYC gene in the industrial microorganisms can promote production of the different kinds of organic acids and intracellular and extracellular lipids. Therefore, the Pyc from different sources is regarded as a key enzyme in microbial biotechnology and is an important target for metabolic engineering of the industrial microbial strains. However, very little is known about the native Pycs and their functions and regulation in the industrial microorganisms.

Production, Gene Cloning, and Overexpression of a Laccase in the Marine-Derived Yeast Aureobasidium melanogenum Strain 11-1 and Characterization of the Recombinant Laccase

Aureobasidium melanogenum strain 11-1 with a high laccase activity was isolated from a mangrove ecosystem. Under the optimal conditions, the 11-1 strain yielded the highest laccase activity up to 3120.0 ± 170 mU/ml (1.2 U/mg protein) within 5 days. A laccase gene (LAC1) of the yeast strain 11-1 contained two introns and encoded a protein with 570 amino acids and four conserved copper-binding domains typical of the fungal laccase. Expression of the LAC1 gene in the yeast strain 11-1 made a recombinant yeast strain produce the laccase activity of 6005 ± 140 mU/ml. The molecular weight of the recombinant laccase after removing the sugar was about 62.5 kDa. The optimal temperature and pH of the recombinant laccase were 40 °C and 3.2, respectively, and it was stable at a temperature less than 25 °C. The laccase was inhibited in the presence of sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic acid (EDTA), phenylmethanesulfonyl fluoride (PMSF), and DL-dithiothreitol (DTT). The K_m and V_max values of the laccase for 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) was 6.3 × 10^-2 mM and 177.4 M/min, respectively. Many synthetic dyes were greatly decolored by the laccase.

Overexpression of an Inulinase Gene in an Oleaginous Yeast, P10, for Efficient Lipid Production from Inulin

In this study, in order to directly and efficiently convert inulin into a single-cell oil (SCO), an <i>INU1</i> gene encoding inulinase from<b><i></i></b> <i>Kluyveromyces marxianus</i> was integrated into the genomic DNA and actively expressed in an SCO producer <i>Aureobasidium</i> <i>melanogenum</i> P10. The transformant API41 obtained produced 28.5 U/mL of inulinase and its wild-type strain P10 yielded only 8.62 U/mL. Most (97.5%) of the inulinase produced by the transformant API41 was secreted into the culture. During a 10-L fermentation, 66.2% (w/w) lipid in the yeast cells of the transformant API41 and 14.38 g/L of cell dry weight were attained from inulin of 80.0 g/L within 120 h, high inulinase activity (23.7 U/mL) was also produced within 72 h, and the added inulin was actively hydrolyzed. This confirmed that the genetically engineered yeast of <i>A. melanogenum</i> P10 is suitable for direct production of lipids from inulin. The lipids produced could be used as feedstocks for biodiesel production.

High and efficient isomaltulose production using an engineered Yarrowia lipolytica strain

Isomaltulose is an ideal functional sweetener and has been approved as a safe sucrose substitute. It is produced mainly through sucrose isomerization catalyzed by sucrose isomerase. Here, to produce food-grade isomaltulose and improve its yield, the sucrose isomerase gene from Pantoea dispersa UQ68J was overexpressed in the non-pathogenic yeast Yarrowia lipolytica. When the engineered strain, S47, was fermented on 600 g/L sucrose in a 10-L bioreactor, a maximum isomaltulose concentration of 572.1 g/L was achieved. Sucrose isomerase activity was 7.43 U/mL, and yield reached 0.96 g/g. Moreover, monosaccharide byproducts were simultaneously transformed into intracellular lipids, thus reducing the production of undesirable compounds and resulting in high isomaltulose purity (97.8%) in the final broth. In summary, the bioprocess employed in this study provides an efficient alternative strategy for isomaltulose production.

Cell wall integrity is required for pullulan biosynthesis and glycogen accumulation in Aureobasidium melanogenum P16

BACKGROUND

Pullulan and glycogen have many applications and physiological functions. However, to date, it has been unknown where and how the pullulan is synthesized in the yeast cells and if cell wall structure of the producer can affect pullulan and glycogen biosynthesis.

METHODS

The genes related to cell wall integrity were cloned, characterized, deleted and complemented. The cell wall integrity, pullulan biosynthesis, glycogen accumulation and gene expression were examined.

RESULTS

In this study, the GT6 and GT7 genes encoding different α1,2 mannosyltransferases in Aureobasidium melanogenum P16 were cloned and characterized. The proteins deduced from both the GT6 and GT7 genes contained the conserved sequences YNMCHFWSNFEI and YSTCHFWSNFEI of a Ktr mannosyltransferase family. The removal of each gene and both the two genes caused the changes in colony and cell morphology and enhanced glycogen accumulation, leading to a reduced pullulan biosynthesis and the declined expression of many genes related to pullulan biosynthesis. The swollen cells of the disruptants were due to increased accumulation of glycogen, suggesting that uridine diphosphate glucose (UDP-glucose) was channeled to glycogen biosynthesis in the disruptants, rather than pullulan biosynthesis. Complementation of the GT6 and GT7 genes in the corresponding disruptants and growth of the disruptants in the presence of 0.6 M KCl made pullulan biosynthesis, glycogen accumulation, colony and cell morphology be restored.

GENERAL SIGNIFICANCE

This is the first report that the two α1,2 mannosyltransferases were required for colony and cell morphology, glycogen accumulation and pullulan biosynthesis in the pullulan producing yeast.

Genetics of trehalose biosynthesis in desert-derived Aureobasidium melanogenum and role of trehalose in the adaptation of the yeast to extreme environments

Melanin plays an important role in the stress adaptation of Aureobasidium melanogenum XJ5-1 isolated from the Taklimakan desert. A trehalose-6-phosphate synthase gene (TPS1 gene) was cloned from K5, characterized, and then deleted to determine the role of trehalose in the stress adaptation of the albino mutant K5. No stress response element and heat shock element were found in the promoter of the TPS1 gene. Deletion of the TPS1 gene in the albino mutant rendered a strain DT43 unable to synthesize any trehalose, but DT43 still could grow in glucose, suggesting that its hexokinase was insensitive to inhibition by trehalose-6-phosphate. Overexpression of the TPS1 gene enhanced trehalose biosynthesis in strain ET6. DT43 could not grow at 33 °C, whereas K5, ET6, and XJ5-1 could grow well at this temperature. Compared with K5 and ET6, DT43 was highly sensitive to heat shock treatment, high oxidation, and high desiccation, but all the three strains demonstrated the same sensitivity to UV light and high NaCl concentration. Therefore, trehalose played an important role in the adaptation of K5 to heat shock treatment, high oxidation, and high desiccation.

Molecular cloning and sequence analysis of a PVGOX gene encoding glucose oxidase in Penicillium viticola F1 strain and it's expression quantitation

The PVGOX gene (accession number: KT452630) was isolated from genomic DNA of the marine fungi Penicillium viticola F1 by Genome Walking and their expression analysis was done by Fluorescent RT-PCR. An open reading frame of 1806bp encoding a 601 amino acid protein (isoelectric point: 5.01) with a calculated molecular weight of 65,535.4 was characterized. The deduced protein showed 75%, 71%, 69% and 64% identity to those deduced from the glucose oxidase (GOX) genes from different fungal strains including; Talaromyces variabilis, Beauveria bassiana, Aspergillus terreus, and Aspergillus niger, respectively. The promoter of the gene (intronless) had two TATA boxes around the base pair number -88 and -94 and as well as a CAAT box at -100. However, the terminator of the PVGOX gene does not contain any polyadenylation site (AATAAA). The protein deduced from the PVGOX gene had a signal peptide containing 17 amino acids, three cysteine residues and six potential N-linked glycosylation sites, among them, -N-K-T-Y- at 41 amino acid, -N-R-S-L- at 113 amino acid, -N-G-T-I- at 192 amino acid, -N-T-T-A at 215 amino acid, -N-F-T-E at 373 amino acid and -N-V-T-A- at 408 amino acid were the most possible N-glycosylation sites. Furthermore, the relative transcription level of the PVGOX gene was also stimulated in the presence of 4% (w/v) of calcium carbonate and 0.5 % (v/v) of CSL in the production medium compared with that of the PVGOX gene when the fungal strain F1 was grown in the absence of calcium carbonate and CSL in the production medium, suggesting that under the optimal conditions, the expression of the PVGOX gene responsible for gluconic acid biosynthesis was enhanced, leading to increased gluconic acid production. Therefore, the highly glycosylated oxidase enzyme produced by P. viticola F1 strain might be a good producer in the fermentation process for the industrial level production of gluconic acid.

Production, Purification, and Gene Cloning of a β-Fructofuranosidase with a High Inulin-hydrolyzing Activity Produced by a Novel Yeast Aureobasidium sp. P6 Isolated from a Mangrove Ecosystem

After screening of over 300 yeast strains isolated from the mangrove ecosystems, it was found that Aureobasidium sp. P6 strain had the highest inulin-hydrolyzing activity. Under the optimal conditions, this yeast strain produced an inulin-hydrolyzing activity of 30.98 ± 0.8 U/ml after 108 h of a 10-l fermentation. After the purification, a molecular weight of the enzyme which had the inulin-hydrolyzing activity was estimated to be 47.6 kDa, and the purified enzyme could actively hydrolyze both sucrose and inulin and exhibit a transfructosylating activity at 30.0 % sucrose, converting sucrose into fructooligosaccharides (FOS), indicating that the purified enzyme was a β-D-fructofuranosidase. After the full length of a β-D-fructofuranosidase gene (accession number KU308553) was cloned from Aureobasidium sp. P6 strain, a protein deduced from the cloned gene contained the conserved sequences MNDPNGL, RDP, ECP, FS, and Q of a glycosidehydrolase GH32 family, respectively, but did not contain a conserved sequence SVEVF, and the amino acid sequence of the protein from Aureobasidium sp. P6 strain had a high similarity to that of the β-fructofuranosidase from any other fungal strains. After deletion of the β-D-fructofuranosidase gene, the disruptant still had low inulin hydrolyzing and invertase activities and a trace amount of the transfructosylating activity, indicating that the gene encoding an inulinase may exist in the Aureobasidium sp. P6 strain.

DNA Methyltransferase Inhibitor Induced Fungal Biosynthetic Products: Diethylene Glycol Phthalate Ester Oligomers from the Marine-Derived Fungus Cochliobolus lunatus

Chemical epigenetic manipulation was applied to the marine-derived fungus Cochliobolus lunatus (TA26-46) with a DNA methyltransferase inhibitor resulting in the significant changes of the secondary metabolites. Cultivation of C. lunatus (TA26-46) with 5-azacytidine led to the isolation of seven new diethylene glycol phthalate esters, cochphthesters A-G (1-6, 10), along with four known analogues (7-9, 11). Their structures were determined by extensive NMR spectroscopic spectra as well as MS data. Compounds 2-6 and 8-11, characterized by the cross-polymerization of phthalate across diethylene glycol via ester bonds, represent the first example of naturally occurring phthalate ester oligomers. Graphical Abstract Chemical epigenetic manipulation was applied to a marine-derived fungus resulting in significant changes of secondary metabolites.

Cloning and Characterization of a Pyruvate Carboxylase Gene from Penicillium rubens and Overexpression of the Genein the Yeast Yarrowia lipolytica for Enhanced Citric Acid Production

In this study, a pyruvate carboxylase gene (PYC1) from a marine fungus Penicillium rubens I607 was cloned and characterized. ORF of the gene (accession number: KM397349.1) had 3534 bp encoding 1177 amino acids with a molecular weight of 127.531 kDa and a PI of 6.20. The promoter of the gene was located at -1200 bp and contained a TATAA box, several CAAT boxes and a sequence 5'-SYGGRG-3'. The PYC1 deduced from the gene had no signal peptide, was a homotetramer (α4), and had the four functional domains. After expression of the PYC1 gene from the marine fungus in the marine-derived yeast Yarrowia lipolytica SWJ-1b, the transformant PR32 obtained had much higher specific pyruvate carboxylase activity (0.53 U/mg) than Y. lipolytica SWJ-1b (0.07 U/mg), and the PYC1 gene expression (133.8%) and citric acid production (70.2 g/l) by the transformant PR32 were also greatly enhanced compared to those (100 % and 27.3 g/l) by Y. lipolytica SWJ-1b. When glucose concentration in the medium was 60.0 g/l, citric acid (CA) concentration formed by the transformant PR32 was 36.1 g/l, leading to conversion of 62.1% of glucose into CA. During a 10-l fed-batch fermentation, the final concentration of CA was 111.1 ± 1.3 g/l, the yield was 0.93 g/g, the productivity was 0.46 g/l/h, and only 1.72 g/l reducing sugar was left in the fermented medium within 240 h. HPLC analysis showed that most of the fermentation products were CA. However, minor malic acid and other unknown products also existed in the culture.