Aureobasidium melanogenum is a saprophytic, dematiaceous, yeast-like fungus rarely implicated in human infections. Here, we report the first case of A. melanogenum fungemia in a 30-week-old preterm, ...very low birth weight neonate born to a primigravida with history of gestational diabetes, pregnancy induced hypertension and oligohydramnios. The baby developed respiratory distress, hypotension, bradycardia, coagulopathy and septic shock shortly after birth, and eventually succumbed to multiple organ dysfunction syndrome on day 9 of life. Paired blood culture showed growth of a dematiaceous yeast-like fungus which was identified as A. melanogenum by rDNA internal transcribed spacer (ITS) sequencing. Antifungal susceptibility testing of the isolate showed high minimum inhibitory concentration of fluconazole (32 µg/mL), indicating resistance. Diagnosis of A. melanogenum fungemia is difficult as it is easily confused with Candida species in Gram stained smears and similar colony morphology during the initial stages of growth. Also, the conventional diagnostic methods, such as VITEK 2 and MALDI-TOF MS are unreliable for identification of this pathogen. Accurate identification using molecular techniques is crucial for making treatment decisions as A. melanogenum shows substantial antifungal resistance. Clinicians should be aware that yeast-like cells in blood culture are not only indicative of Candida species, but also rare pathogens like A. melanogenum and should exercise caution while starting fluconazole therapy. At present, there are no established susceptibility breakpoints for Aureobasidium spp. Further studies are needed to determine the optimal treatment for such infections.
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.
The three demension structure of the estertase obtained in this study.
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•A. melanogenum HN6.2 can produce an esterase of 208.1±2.7 units per 100ml.•The molecular weight of the purified ...esterase was 60.2kDa.•The produced esterase was different from that produced by any other fungal strains.•The cloned esterase gene was indeed closely related to the esterase activity.
Aureobasidium melanogenum HN6.2 was found to able to produce an esterase of 208.1±2.7 units per ml within 72h. A molecular weight of the purified esterase was 60.2kDa and its PI was 4.86. The optimal pH and temperature of the purified esterase were 8.0 and 40°C, respectively. The purified esterase was stable at the temperature less than 40°C and in the pH range of 7.5–8.0. The esterase activity was greatly inhibited in the presence of Zn2+, Hg2+, Fe2+, Ni2+ and SDS. Km and Vmax values of the enzyme for ρ-nitrophenyl butyrate were 68.6μM and 251.4μM per min, respectively. Mass analysis showed that it belonged to a carboxylesterase. After an esterase gene (Car-Est) cloned from the genomic DNA of the marine yeast strain HN6.2 was disrupted, the disruptant Y44 obtained exhibited a significant decrease in esterase activity. Meanwhile, a transcriptional level of the Car-Est gene of the disruptant Y44 was only 5.18% that of the Car-Est gene of its wild type strain HN6.2, confirming that the cloned esterase gene was indeed closely related to the esterase activity of the yeast HN6.2 strain.
Being a key industrial enzyme, tannase is extensively applied in various fields. Despite the characterizations of a large number of tannases, there are hardly a few tannases with exceptional ...thermostability. In this detailed study, a tannase-encoding gene named
was identified from
T9 and heterologously expressed in
host of food grade. The purified tannase TanA with a molecular weight of above 63.0 kDa displayed a specific activity of 941.4 U/mg. Moreover, TanA showed optimum activity at 60°C and pH 6.0. Interestingly, TanA exhibited up to 61.3% activity after incubation for 12 h at 55°C, signifying its thermophilic property and distinguished thermostability. Additionally, TanA was a multifunctional tannase with high specific activities to catalyze the degradation of various gallic acid esters. Therefore, this study presents a novel tannase, TanA, with remarkable properties, posing as a potential candidate for food and agricultural processing.
has been used as an animal feed additive for improving thehealth of pets, however, it has not yet been applied in honey bees. Here, a fungal strain CK-CsC isolated from bee bread pollen, was ...identified as
. Following characterizing CK-CsC fermentation broth, the 4-days fermentation broth (SYM medium or bee pollen) of the CK-CsC was used to feed newly emerged adult honey bees in cages under laboratory-controlled conditions for analysis of survival, gene expression of nutrient and antibacterial peptide, and gut microbiota of honey bees. It was found that the CK-CsC fermentation broth (SYM medium or bee pollen) is nontoxic to honey bees, and can regularly increase nutrient gene expression of honey bees. However, significant mortality of bees was observed after bees were fed on the supernatant liquid of the fermentation broth. Notably, this mortality can be lowered by the simultaneous consumption of bee pollen. The honey bees that were fed bee pollen exhibited more γ-Proteobacteria, Bacteriodetes, and Actinobacteria in their gut flora than did the honey bees fed only crude supernatant liquid extract. These findings indicate that
CK-CsC has high potential as a bee probiotic when it was fermented with bee pollen.
Aureobasidium melanogenum
HN6.2 is a unique yeast strain who can produce the siderophore of fusigen under iron starvation to guarantee its survival. However, a comprehensive understanding of ...mechanisms involved in iron acquisition and homeostasis for it is still vacant. In this study, genome sequencing and mining revealed that
A. melanogenum
HN6.2 strain was the first yeast species that exclusively possessed all the four known mechanisms for the iron acquisition: (i) the siderophore-mediated iron uptake; (ii) reductive iron assimilation; (iii) low-affinity ferrous uptake; and (iv) heme utilization, which suggested its stronger adaptability than
Aspergillus fumigatus
and
Saccharomyces cerevisiae
. This HN6.2 strain also employed the vacuolar iron storage for immobilizing the excessive iron to avoid its cellular toxicity. Specially, genome mining indicated that
A. melanogenum
HN6.2 strain could also synthesize ferricrocin siderophore. Further HPLC and Q-Tof-MS analysis confirmed that the siderophores synthesized by this strain consisted of cyclic fusigen, linear fusigen, ferricrocin, and hydroxyferricrocin and they played parallel roles as both intracellular and extracellular siderophores. Also, the heme utilization for this strain was experimentally verified by the knock-out of heme oxygenase gene. For iron homeostasis, the transcriptome analysis revealed that this strain mainly employed two central regulators of SreA/HapX to tune iron uptake and storage at the transcriptional level. It was also noted that mitogen-activated protein kinase C gene (
MpkC
) exhibited a transcriptional up-regulation under iron sufficiency, suggesting that it may serve as another factor involved in the repression of siderophore biosynthesis. This is the first genetic blueprint of iron acquisition and homeostasis for
A. melanogenum
.
Poly(β-L-malic acid) (PMA) is a promising polyester formed from L-malate in microbial cells. Malate biosynthesis is crucial for PMA production. Previous studies have shown that the non-oxidative ...pathway or oxidative pathway (TCA cycle) is the main biosynthetic pathway of malate in most of PMA-producing strains, while the glyoxylate cycle is only a supplementary pathway. In this study, we investigated the effect of exogenous metabolic intermediates and inhibitors of the malate biosynthetic pathway on PMA production by
Aureobasidium melanogenum
GXZ-6. The results showed that PMA production was stimulated by maleic acid (a fumarase inhibitor) and sodium malonate (a succinate dehydrogenase inhibitor) but inhibited by succinic acid and fumaric acid. This indicated that the TCA cycle might not be the only biosynthetic pathway of malate. In addition, the PMA titer increased by 18.1% upon the addition of glyoxylic acid after 72 h of fermentation, but the PMA titer decreased by 7.5% when itaconic acid (an isocitrate lyase inhibitor) was added, which indicated that malate for PMA production was synthesized significantly via the glyoxylate cycle rather than the TCA cycle. Furthermore,
in vitro
enzyme activities of the TCA and glyoxylate cycles suggested that the glyoxylate cycle significantly contributed to the PMA production, which is contradictory to what has been reported previously in other PMA-producing
A. pullulans
.
Pullulan is an extracellular water-soluble polysaccharide with wide applications. In this study, we screened strains that could selectively produce high molecular weight pullulan for application in ...industrial pullulan production. A new fungus strain A4 was isolated from soil and identified as Aureobasidium melanogenum based on colony characteristics, morphology, and internally transcribed spacer analysis. Thin-layer chromatography, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance analysis suggested that the dominant exopolysaccharide produced by this strain, which presented a molecular weight of 1.384 × 10
6
Dalton in in-gel permeation chromatography, was pullulan. The culture conditions for A. melanogenum A4 were optimized at 30 °C and 180 rpm: carbon source, 50 g/L maltose; initial pH 7; and 8 g/L Tween 80. Subsequently, batch fermentation was performed under the optimized conditions in a 5-L stirred-tank fermentor with a working volume of 3 L. The fermentation broth contained 303 g/L maltose, which produced 122.34 g/L pullulan with an average productivity of 1.0195 g/L/h and 82.32 g/L dry biomass within 120 h. The conversion efficiency of maltose to pullulan (Y%) and specific production rate (g/h/g dry cells) (Qs) reached 40.3% and 0.0251 g/L/g dry cells, respectively. The results showed strain A4 could be a good candidate for industrial production.
β-poly(
l
-malic acid) (PMLA) is a water-soluble biopolymer used in medicine, food, and other industries. However, the low level of PMLA biosynthesis in microorganisms limits its further application ...in the biotechnological industry. In this study, corn steep liquor (CSL), which processes high nutritional value and low-cost characteristics, was selected as a growth factor to increase the PMLA production in strain,
Aureobasidium melanogenum
, and its metabolomics change under the CSL addition was investigated. The results indicated that, with 3 g/L CSL, PMLA production, cell growth, and yield (Y
p/x
) were increased by 32.76%, 41.82%, and 47.43%, respectively. The intracellular metabolites of
A. melanogenum
, such as amino acids, organic acids, and key intermediates in the TCA cycle, increased after the addition of CSL, and the enrichment analysis showed that tyrosine may play a major role in the PMLA biosynthesis. The results presented in this study demonstrated that the addition of CSL would be an efficient approach to improve PMLA production.
The maximum yield of xylanase from
Aureobasidium melanogenum
PBUAP46 was 5.19 ± 0.08 U ml
−1
when cultured in a production medium containing 3.89% (w/v) rice straw and 0.75% (w/v) NaNO
3
as carbon ...and nitrogen sources, respectively, for 72 h. This enzyme catalyzed well and was relatively stable at pH 7.0 and room temperature (28 ± 2 °C). The produced xylanase was used to hydrolyze xylans from four tropical weeds, whereupon it was found that the highest amounts of reducing sugars in the xylan hydrolysates of cogon grass (
Imperata cylindrical
), Napier grass (
Pennisetum purpureum
), and vetiver grass (
Vetiveria zizanioides
) were at 20.44 ± 0.84, 17.50 ± 0.29, and 19.44 ± 0.40 mg 100 mg xylan
−1
, respectively, but it was not detectable in water hyacinth (
Eichhornia crassipes
) hydrolysate. The highest combined amount of xylobiose and xylotriose was obtained from vetiver grass; thus, it was selected for further optimization. After optimization, xylanase digestion of vetiver grass xylan at 27.94 U g xylan
−1
for 92 h 19 min gave the highest amount of reducing sugars (23.65 ± 1.34 mg 100 mg xylan
−1
), which were principally xylobiose and xylotriose. The enriched XOs exhibited a prebiotic property, significantly stimulating the growth of
Lactobacillus brevis
and
L. casei
by a factor of up to 3.5- and 6.5-fold, respectively, compared to glucose.
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