In this study, it was found that reducing consumption of acetyl-CoA in mitochondria, peroxisome and lipid biosynthesis could not obviously enhance liamocin biosynthesis by engineered strains of ...Aureobasidium melanogenm 9–1, but decreased cell growth of the mutants. On the contrary, expression of heterologous PTA gene for phosphotransacetylase in PK pathway and native ALD gene for acetaldehyde dehydrogenase and ACS gene encoding acetyl-CoA synthetase in the PDH bypass pathway reduced liamocin biosynthesis. However, expression the PK gene for phosphoketolase, the PDC gene encoding pyruvate decarboxylase and VHb gene coding for Vitreoscilla hemoglobin (VHb) in the glucose derepression mutants could greatly enhance liamocin production. The resulting strain V33 could produce 55.38 g/L of liamocin and 25.10 g/L of cell dry weight from 117.27 g/L of glucose within 168 h of 10-liter fermentation, leading to the yield of 0.47 g/g of glucose, the productivity of 0.33 g/L/h and rate of glucose utilization of 0.70 ± 0.01 g/L/h. This was a new and efficient strategy for overproduction of liamocin by A. melanogenm.
•Reducing consumption of acetyl-CoA could not obviously enhance liamocin biosynthesis.•Expression of PTA gene, ALD gene and ACS gene reduced liamocin biosynthesis.•Only glucose derepressed V33 strain overexpressing the PK gene, PDC gene and VHb gene could produce 55.38 g/L of liamocin.
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.
•Many melanin-synthesizing genes are linked together as the PKS gene clusters.•Most of the PKS gene clusters are regulated by Cmr1.•Evolution of different genes in the clusters is closely related to adaptation of the melanin-producing fungi.
A novel disease of mango (Mangifera indica L.) was observed in the main mango growing regions (Minab, Bandar Abbas and Roudan) of Hormozgan province, southern Iran. Disease symptoms included leaf and ...fruit blights as well as twigs and branches dieback. The disease incidence in the field conditions ranged from 15.3% to 27.3%. A black yeast-like fungus was consistently isolated from symptomatic tissues and identified as Aureobasidium melanogenum using cultural and morphological features as well as partial nucleotide sequence data derived from two gene loci, including internal transcribed spacer region (ITS1–5.8S-ITS2) and D1/D2 domains of the large subunit (26S) (LSU-rRNA) of the ribosomal DNA gene. BLASTn searches of the ITS and LSU sequences in the NCBI GenBank revealed 99–100% nucleotide similarity to several A. melanogenum strains. A phylogeny inferred using sequence data from ITS and LSU sequences placed our isolates together with the other A. melanogenum in the GenBank. Koch's postulates were fulfilled by inoculating stems, leaves and fruits with A. melanogenum isolates. To our knowledge, this is the first report worldwide of A. melanogenum on mango.
Selenium (Se) plays a critical role in diverse biological processes and is widely used across manufacturing industries. However, the contamination of Se oxyanions also poses a major public health ...concern. Microbial transformation is a promising approach to detoxify Se oxyanions and produce elemental selenium nanoparticles (SeNPs) with versatile industrial potential. Yeast-like fungi are an important group of environmental microorganisms, but their mechanisms for Se oxyanions reduction remain unknown. In this study, we found that Aureobasidium melanogenum I15 can reduce 1.0 mM selenite by over 90% within 48 h and efficiently form intracellular or extracellular spherical SeNPs. Metabolomic and proteomic analyses disclosed that A. melanogenum I15 evolves a complicated selenite reduction mechanism involving multiple metabolic pathways, including the glutathione/glutathione reductase pathway, the thioredoxin/thioredoxin reductase pathway, the siderophore-mediated pathway, and multiple oxidoreductase-mediated pathways. This study provides the first report on the mechanism of selenite reduction and SeNPs biogenesis in yeast-like fungi and paves an alternative avenue for the bioremediation of selenite contamination and the production of functional organic selenium compounds.
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•melanogenum I15 can reduce over 90% of 1 mM selenite within 48 h.•Selenite reduction occurs both intracellularly and extracellularly in I15.•Selenite reduction occurs through multiple oxidoreductase-mediated pathways in I15.•Selenite stress alters the cell morphology and the cell membrane structure of I15.•Glutathione and siderophores were actively involved in the selenite reduction of I15.
L-piperazic acid (L-Piz) is one of components in many bioactive compounds synthesized by Streptomyces spp. Therefore, it is very important to develop a sustainable and eco-friendly bioprocess to ...produce L-Piz from renewable glucose. In this study, it was found that the engineered Aureobasidium melanogenum DFAK-ArgB6 strain overexpressing the ArgB gene encoding N-acetylglutamate kinase could produce 3.0 g/L L-Piz from glucose during the fed-batch fermentation. The yield was 55.6 mg L-Piz/g of glucose and the productivity was 24.8 mg/L/h. This was the highest amount of L-Piz produced by microorganisms so far. Finally, the partially purified L-Piz had purity of 86.4%.
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•L-piperazic acid (L-Piz) is one of components in many bioactive compounds.•The DFAK-ArgB6 strain could produce the highest amount of L-Piz (3.0 g/L).•The partially purified L-Piz was obtained.
•The natural honey contained pullulan producing yeasts.•114.0 g/L of pullulan was produced from 140 g/L sucrose within 134 h.•The high pullulan production was related to high glucosyltransferase ...activity and high phosphofructo-2-kinase activity.•The high pullulan production was also associated with high content of its cellular glycerol and low glucose repressor.
A very high pullulan producing yeast-like fungus, Aureobasidium melanogenum TN1-2 isolated from a natural honey was found to be able to produce 97.0 g/L of pullulan from 140.0 g/L sucrose at a flask level while it could yield 114.0 g/L of pullulan within 134 h during a 10-liter fermentation, the yield was 0.81 g/g and the productivity was 0.86 g/L/h. The high ability to biosynthesize pullulan by this yeast-like fungal strain TN1-2 was related to high glucosyltransferase activity, high phosphofructo-2-kinase activity, high content of its cellular glycerol and low glucose repressor. The Mw of the produced pullulan was 1.42 × 105 g/mol. The low Mw may be due to the high α-amylase, glucoamylase and isopullulanase activities. The intracellular level of trehalose had no influence on high pullulan production by the yeast-like fungal strain TN1-2.
Overexpression of the optimized Vitreoscilla hemoglobin (VHb) gene and the native flavohemoglobin (FHb) gene in Aureobasidium melanogenum P16 rendered a V6 strain and a F44 strain to overproduce ...pullulan compared to that produced by their wild type strain P16. The capacity to bind CO and oxygen in the V6 strain and the F44 strain was also obviously enhanced. At the same time, the transcriptional levels of the relevant genes were also increased in the V6 strain and the F44 strain and the fused vgbop + the gene encoding GFP and FHb gene + the gene encoding GFP were also actively expressed. During a 10-liter fermentation, the P16 strain produced only 72.0 ± 1.0 g/L pullulan, the yield was 0.77 g/g of sucrose, the productivity was 0.5 ± 0.01 g/L/h and only 79.4% of the total sugar was used. In contrast, the strain V6 yielded 102.3 ± 1.8 g/L of pullulan, the yield was 0.89 g/g of sucrose, the productivity was 0.7 ± 0.01 g/L/h and 96.0% of total sugar was used while 101.4 ± 2.9 g/L of pullulan was accumulated in the culture of the strain F44, the yield was 0.88 g/g of sucrose, the productivity was 0.7 ± 0.02 g/L/h and 96.4% of total sugar was utilized. These data strongly demonstrated that the concentration of pullulan, yield, productivity and sugar utilization were greatly enhanced by overexpression of the VHb and FHb. But their cell growth was almost the similar.
•The optimized vgbop gene and the native FHb gene were overexpressed.•Pullulan and the capacity to bind CO and oxygen were greatly enhanced.•The pullulan concentrations, productivity and sugar utilization were also greatly enhanced.
Fructooligosaccharides (FOSs) are excellent food ingredients or feed additives by stimulating probiotics. In this paper, a
gene encoding a glucose repressor in the β-fructofuranosidase producer
33 ...with high-level FOS biosynthesis was disrupted, and glucose repression in disruptant D28 was relieved. The disruptant D28 produced up to 2100 U/mL of β-fructofuranosidase activity, whereas the enzyme activities produced by parent strain 33 and complemented strain C11 were below 600 U/mL. The whole cells of the disruptant D28 was used to convert cane molasses into FOSs, and 0.58 g of FOSs/g of molasses sugar was synthesized from 350 g/L cane molasses sugar within 4 h. Results demonstrated that the industrial waste cane molasses can be efficiently converted into FOSs by the glucose derepression mutant D28 with high β-fructofuranosidase activity. This low-cost and environmentally friendly bioprocess has great potential applications in bioengineering and biotechnology for FOS production.
β-Poly(L-malic acid) (PMLA) is a water-soluble biopolymer used in food, medicine and other industries. To date, the biosynthesis pathway of PMLA has not been fully elucidated. In this study, we ...sequenced the transcriptome of strain Aureobasidium melanogenum under 20 g/L CaCO3 addition. The resulting sequencing reads were assembled and annotated for the differentially expressed genes (DEGs) analysis and novel transcripts identification. The result indicated that with the CaCO3 addition, the tricarboxylic cycle (TCA) cycle and glyoxylate pathway were up-regulated, and it also found that a non-ribosomal peptide synthetase (NRPS) like protein was highly expressed. The DEGs analysis showed a high expression level of malate dehydrogenase (MDHC) and phosphoenolpyruvate carboxykinase (PCKA) in the CaCO3 group, which indicated a cytosolic malate activity. We speculated that the malate should be transported to or synthesized in the cytoplasm, which was then polymerized to PMLA by the NRPS-like protein, accompanied by the up-regulated TCA cycle providing ATP for the polymerization. Depending on the analysis, we assumed that an NRPS-like protein, the TCA cycle, and the cytosolic malate together are contributing to the PMLA biosynthesis.
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