The transcription factor FvHmg1 negatively regulates fruiting body development in Winter Mushroom Flammulina velutipes.

Fruiting body formation in Agaricomycetes represents the most complex and unclear process in the fungi. Mating type pathways (matA and matB) and transcription factors are important regulators in the process. Here, we report a new High-mobility-group (HMG) box domain protein FvHmg1 that acts as a negative transcription regulator in fruiting body development in Winter Mushroom Flammulina velutipes. However, the expression of Fvhmg1 in dikaryon and primordial stages was significantly lower than that of monokaryon. The Fvhmg1-RNAi mutants had a better ability of fruiting than wild type strain. Overall expression of Fvhmg1 was controlled under compatible matA and matB genes where compatible matA genes could increase its expression level, while compatible matB genes had the opposite effect. It means when two monokaryons with compatible matA and matB genes were crossed, the negatively transcription factor FvHmg1 was inhibited, and normal fully fruiting body could formation and develop. The relationship between FvHmg1 and mating type pathway would advance to understand of sexual reproduction and fruiting body development in edible mushrooms.

Selenium accumulation, speciation, and its effect on nutritive value of Flammulina velutipes (Golden needle mushroom).

Flammulina velutipes is one of the most popular edible mushrooms worldwide. A selenium-biofortification method for its fruiting body was developed using selenite. This study investigated the selenium content, distribution, speciation and the effect of selenium on mushroom growth, nutritive value, and mineral accumulation. Results showed that F. velutipes accumulated nearly 108 µg/g of organic selenium under treatment with 20 µg/g selenite, which accounts for over 97% of total selenium. Most (60-74%) of selenium combined with the protein fraction, whereas 15-21% combined with the polysaccharide fraction. Selenomethionine (56.8%), selenocysteine (22.8%), and methylselenocysteine (17.3%) were the main organic selenium compounds in the fruiting body. Selenium biofortification increased the biomass yield of fruiting body and elevated the content of polysaccharides, proteins, total amino acids, essential amino acids, and several minerals, including iron, calcium, and copper. F. velutipes might become a suitable selenium supplement.

Characterization and expression pattern analysis of pheromone receptor-like genes in Winter Mushroom Flammulina filiformis.

Pheromone receptor-like genes (PRLGs) belong to the G protein-coupled receptors (GPCRs) family that interacts with biotic and abiotic stimulants and transmits signals to intracellular downstream pathways in eukaryotic cells. In this study, we investigated the structure and expressions patterns of PRLGs in Winter Mushroom Flammulina filiformis. Based on the alignment analysis, the structure of PRLGs was found conserved in F. filiformis strains expect few single-nucleotide polymorphism (SNP) sites. Six PRLGs were found at five different unlinked loci, scattered in the genomes of F. filiformis strains. These genes contain 2-5 introns; however, the introns were not found in the same relative positions regarding the encoded protein sequences in tested strains of F. filiformis. Three conserved motifs were identified in peptides structures of PRLGs, however, FfSte3.s6 contained only two types, suggests its difference in evolution and function. We have further analyzed the expression patterns of each PRLGs in different developmental stages of the fruiting body in F. filiformis by quantitative real-time polymerase chain reaction (qRT-PCR). The results exhibited expression variation of PRLGs at different developmental stages of the F. filiformis. Especially, FfSte3.s1 and FfSte3.s2 exhibited maximum expression level in mycelia stage. Other PRLGs exhibited high expression level in fruiting body stages. This study suggests that PRLGs could be vital genes involving in fruiting body development in F. filiformis. However, further studies could be performed to reveal their specific functional pathways in the fruiting body development.

A putative transcription factor LFC1 negatively regulates development and yield of winter mushroom.

Basidioma is the fruiting body of mushroom species. The deep understanding on the mechanism of basidioma development is valuable for mushroom breeding and cultivation. From winter mushroom (Flammulina velutipes), one of the top five industrially cultivated mushrooms, a novel putative Zn(II)2Cys6 transcription factor LFC1 with negative regulatory function in basidioma development was identified. The transcript level of lfc1 was dramatically decreased during basidioma development. Neither overexpression nor knockdown of lfc1 affected hyphal vegetative growth. However, knockdown of lfc1 could promote basidioma development and shorten cultivation time by 2 days, while overexpression of lfc1 delayed the optimal harvest time by 3 days. In the lfc1 knockdown strain, in which the lfc1 expression was reduced by 72%, mushroom yield and biological efficiency could be increased at least by 24%. Knockdown of lfc1 did not affect the shape of caps but significantly increased basidioma length and number, while its overexpression did not affect basidioma length but dramatically reduced basidioma number. In addition, rather than producing basidiomata with round caps as in wild type, the caps of basidiomata in the lfc1 overexpression mutants were significantly larger and the cap edge was wrinkled. RNA-seq analysis revealed that 455 genes had opposite transcriptional responses to lfc1 overexpression and knockdown. Some of them were previously reported as genes involved in basidioma development, including 3 hydrophobin encoding genes, 2 lectin encoding genes, FVFD16, an Eln2 ortholog encoding gene, and 3 genes encoding membrane components. As LFC1 homologs are widely present in mushroom species, lfc1 can be useful in mushroom breeding.Key Points• A novel transcription factor LFC1 negatively regulates fruiting in winter mushroom• LFC1 regulated transcription of more than 400 genes.• Reduction of LFC1 expression could shorten cultivation time and increase yield.• lfc1 could be a potentially useful reference gene for mushroom breeding.

Combining transcriptomics and metabolomics to reveal the underlying molecular mechanism of ergosterol biosynthesis during the fruiting process of Flammulina velutipes.

BACKGROUND: Flammulina velutipes has been recognized as a useful basidiomycete with nutritional and medicinal values. Ergosterol, one of the main sterols of F. velutipes is an important precursor of novel anticancer and anti-HIV drugs. Therefore, many studies have focused on the biosynthesis of ergosterol and have attempted to upregulate its content in multiple organisms. Great progress has been made in understanding the regulation of ergosterol biosynthesis in Saccharomyces cerevisiae. However, this molecular mechanism in F. velutipes remains largely uncharacterized. RESULTS: In this study, nine cDNA libraries, prepared from mycelia, young fruiting bodies and mature fruiting bodies of F. velutipes (three replicate sets for each stage), were sequenced using the Illumina HiSeq™ 4000 platform, resulting in at least 6.63 Gb of clean reads from each library. We studied the changes in genes and metabolites in the ergosterol biosynthesis pathway of F. velutipes during the development of fruiting bodies. A total of 13 genes (6 upregulated and 7 downregulated) were differentially expressed during the development from mycelia to young fruiting bodies (T1), while only 1 gene (1 downregulated) was differentially expressed during the development from young fruiting bodies to mature fruiting bodies (T2). A total of 7 metabolites (3 increased and 4 reduced) were found to have changed in content during T1, and 4 metabolites (4 increased) were found to be different during T2. A conjoint analysis of the genome-wide connection network revealed that the metabolites that were more likely to be regulated were primarily in the post-squalene pathway. CONCLUSIONS: This study provides useful information for understanding the regulation of ergosterol biosynthesis and the regulatory relationship between metabolites and genes in the ergosterol biosynthesis pathway during the development of fruiting bodies in F. velutipes.

Comparative Transcriptomics of Flammulina filiformis Suggests a High CO2 Concentration Inhibits Early Pileus Expansion by Decreasing Cell Division Control Pathways.

Carbon dioxide is commonly used as one of the significant environmental factors to control pileus expansion during mushroom cultivation. However, the pileus expansion mechanism related to CO2 is still unknown. In this study, the young fruiting bodies of a popular commercial mushroom Flammulina filiformis were cultivated under different CO2 concentrations. In comparison to the low CO2 concentration (0.05%), the pileus expansion rates were significantly lower under a high CO2 concentration (5%). Transcriptome data showed that the up-regulated genes enriched in high CO2 concentration treatments mainly associated with metabolism processes indicated that the cell metabolism processes were active under high CO2 conditions. However, the gene ontology (GO) categories and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with cell division processes contained down-regulated genes at both 12 h and 36 h under a high concentration of CO2. Transcriptome and qRT-PCR analyses demonstrated that a high CO2 concentration had an adverse effect on gene expression of the ubiquitin-proteasome system and cell cycle-yeast pathway, which may decrease the cell division ability and exhibit an inhibitory effect on early pileus expansion. Our research reveals the molecular mechanism of inhibition effects on early pileus expansion by elevated CO2, which could provide a theoretical basis for a CO2 management strategy in mushroom cultivation.

A Single Transcription Factor (PDD1) Determines Development and Yield of Winter Mushroom (Flammulina velutipes).

Most of the edible mushrooms cannot be cultivated or have low yield under industrial conditions, partially due to the lack of knowledge on how basidioma (fruiting body) development is regulated. From winter mushroom (Flammulina velutipes), one of the most popular industrially cultivated mushrooms, a transcription factor, PDD1, with a high-mobility group (HMG)-box domain was identified based on its increased transcription during basidioma development. pdd1 knockdown by RNA interference affected vegetative growth and dramatically impaired basidioma development. A strain with an 89.9% reduction in the level of pdd1 transcription failed to produce primordia, while overexpression of pdd1 promoted basidioma development. When the transcriptional level of pdd1 was increased to 5 times the base level, the mushroom cultivation time was shortened by 9.8% and the yield was increased by at least 33%. RNA sequencing (RNA-seq) analysis revealed that pdd1 knockdown downregulated 331 genes and upregulated 463 genes. PDD1 positively regulated several genes related to fruiting, including 6 pheromone receptor-encoding genes, 3 jacalin-related lectin-encoding genes, FVFD16, and 2 FVFD16 homolog-encoding genes. PDD1 is a novel transcription factor with regulatory function in basidioma development found in industrially cultivated mushrooms. Since its orthologs are widely present in fungal species of the Basidiomycota phylum, PDD1 might have important application prospects in mushroom breeding.IMPORTANCE Mushrooms are sources of food and medicine and provide abundant nutrients and bioactive compounds. However, most of the edible mushrooms cannot be cultivated commercially due to the limited understanding of basidioma development. From winter mushroom (Flammulina velutipes; also known as Enokitake), one of the most commonly cultivated mushrooms, we identified a novel transcription factor, PDD1, positively regulating basidioma development. PDD1 increases expression during basidioma development. Artificially increasing its expression promoted basidioma formation and dramatically increased mushroom yield, while reducing its expression dramatically impaired its development. In its PDD1 overexpression mutants, mushroom number, height, yield, and biological efficiency were significantly increased. PDD1 regulates the expression of some genes that are important in or related to basidioma development. PDD1 is the first identified transcription factor with defined functions in mushroom development among commercially cultivated mushroom species, and it might be useful in mushroom breeding.

Overexpression of the saccharopine dehydrogenase gene improves lysine biosynthesis in Flammulina velutipes.

Saccharopine dehydrogenase (EC 1.5.1.7) regulates the last step of fungal lysine biosynthesis. The gene (Fvsdh) encoding saccharopine dehydrogenase was identified and cloned from the whole genome of Flammulina velutipes. The genomic DNA of Fvsdh is 1257 bp, comprising three introns and four exons. The full-length complementary DNA of Fvsdh comprises 1107 bp with a deduced amino acid sequence of 368 residues. A 1,000-bp promoter sequence containing the TATA box, CAAT box, and several putative cis-acting elements was also identified. The results of tissue expression analysis showed that the expression level of the Fvsdh gene was higher in the pileus than in the stipe whether in the elongation or maturation stage. Further research showed that the lysine contents were 3.03 and 2.95 mg/g in maturation-pileus and elongation-pileus, respectively. In contrast, the lysine contents were 2.49 and 2.07 mg/g in elongation-stipe and maturation-stipe, respectively. To study the function of Fvsdh, we overexpressed Fvsdh in F. velutipes and found that Fvsdh gene expression was increased from 1.1- to 3-fold in randomly selected transgenic strains. The lysine contents were also increased from 1.12- to 1.3-fold in these five transformants, except for strain T3, in which the lysine contents were the same as the control. These results indicate that the expression of the Fvsdh gene can affect the lysine content of F. velutipes.

Agronomic and environmental factors affecting cultivation of the winter mushroom or Enokitake: achievements and prospects.

The global interest in production of the winter mushroom or Enokitake (Flammulina filiformis previously known as Flammulina velutipes) is increasing owing to its nutritional and medicinally important bioactive compounds along with a marketable texture and flavor. This review presents the state of knowledge on achievements in solid-state cultivation and submerged cultures of Enokitake and how they are influenced by environmental factors and agronomic characteristics. A wide range of basic lignocellulosic substrates and supplementations have been reviewed in order to formulate an efficient and locally available substrate. Domestication of wild types of Enokitake and its economic and research implications are also discussed. Besides, the influence of environmental and agronomic factors on production and efficacy of the most important biologically active metabolites of Enokitake in both solid-state cultivation and submerged cultures has been discussed. Some of shortcomings of studies reporting cultivation of Enokitake are described and their contribution to future prospects is also discussed in this review.

Application of winter mushroom powder as an alternative to phosphates in emulsion-type sausages.

This research evaluated the utilization of winter mushrooms as a replacement for phosphate in emulsion-type sausages. Winter mushroom powder (WMP) was added to the sausages at 0, 0.5, 1.0, 1.5, and 2.0% (w/w), and phosphate was added at 0.3% as a positive control. The WMP additions above 1.0% increased the pH of meat batter and efficiently inhibited the exudation of fat from the sausages (p < 0.05). Lipid oxidation of sausages was inhibited by the addition of WMP (p < 0.05). On the other hand, the addition of phosphate and WMP provided different instrumental texture properties. However, no adverse effects were observed with respect to the color and sensory properties of the sausages containing WMP, except for that containing 2.0% WMP. Therefore, this research indicates that WMP can effectively replace phosphate in meat products, and that the most effective addition level may be 1.0% WMP.

Comparative Proteome Reveals Metabolic Changes during the Fruiting Process in Flammulina velutipes.

Understanding the molecular mechanisms regulating the fruiting process in macro-fungi, especially industrially cultivated mushrooms, has long been a goal in mycological research. To gain insights into the events accompanying the transformation of mycelia into fruit-bodies in Flammulina velutipes, proteins expressed characteristically and abundantly at primordium and fruit-body stages were investigated by using the iTRAQ labeling technique. Among the 171 differentially expressed proteins, a total of 68 displayed up-regulated expression levels that were associated with 84 specific KEGG pathways. Some up-regulated proteins, such as pyruvate carboxylase, aldehyde dehydrogenase, fatty acid synthase, aspartate aminotransferase, 2-cysteine peroxiredoxin, FDS protein, translation elongation factor 1-alpha, mitogen-activated protein kinases (MAPKs), and heat-shock protein 70 that are involved in carbohydrate metabolism, carotenoid formation, the TCA cycle, MAPK signaling pathway, and the biosynthesis of fatty acids and branched-chain amino acids, could serve as potential stage-specific biomarkers to study the fruiting process in F. velutipes. Knowledge of the proteins might provide valuable evidence to better understand the molecular mechanisms of fruit-body initiation and development in basidiomycete fungi. Furthermore, this study also offers valuable evidence for yield improvement and quality control of super golden-needle mushroom in practice.

Compositional Differences of the Winter Culinary-Medicinal Mushroom, Flammulina velutipes (Agaricomycetes), under Three Types of Light Conditions.

The focus of this study was to investigate the effect of light on the cultivation and the amounts of bio-active components in Flammulina velutipes. The mushrooms were cultivated under fluorescent tube (T8) grow lights, lightemitting diodes (LEDs), and cold-cathode fluorescent lamps. The biological efficiency of the T8 lights was the highest, at 92%. The crude fat content, crude fiber content, polysaccharide content, and ergosterol content were highest under the LEDs, at 2.9 g/100 g, 7.9 g/100 g, 3.9 g/100 g, and 1.4 mg/g, respectively. Moreover, vitamin D2 (1.9 µg/g) was generated only under light from LEDs. Principal component analysis showed that F. velutipes cultivated under the 3 different lighting conditions showed different profiles for proximate composition, nutritional compounds, and principal fatty acids.

iTRAQ-based quantitative proteome revealed metabolic changes of Flammulina velutipes mycelia in response to cold stress.

Temperature is one of the pivotal factors influencing mycelium growth and fruit-body formation of Flammulina velutipes. To gain insights into hyphae growth and fruit-body formation events and facilitate the identification of potential stage-specific biomarker candidates, we investigated the proteome response of F. velutipes mycelia to cold stresses using iTRAQ-coupled two-dimensional liquid chromatography tandem mass spectrometry (2D LC-MS/MS) technique. Among 1198 proteins identified with high confidence, a total of 63 displayed altered expression level after cold stress treatments. In-depth data analysis reveals that differentially expressed proteins were involved in a variety of cellular processes, particularly metabolic processes. Among the 31 up-regulated proteins, 24 (77.42%) were associated with 22 specific KEGG pathways. These up-regulated proteins could possibly serve as potential biomarkers to study the molecular mechanisms of F. velutipes mycelia response to cold stresses. These data of the proteins might provide valuable evidences to better understand the molecular mechanisms of mycelium resistance to cold stress and fruit-body formation in fungi. BIOLOGICAL SIGNIFICANCE: Low-temperature is one of the pivotal factors in some Flammulina velutipes industrial processes influencing mycelium growth, inducing primordia and controlling fruit-body development. Preliminary study has indicated that effectively regulating cultivation could augment the yield by controlling optimal cold stress level on mycelia. However, we are still far from understanding the molecular and physiological mechanisms of adaptation of these fungi at cold stress. In the present study, the experiments reported above were undertaken to investigate chronological changes of protein expression during F. velutipes mycelia in response to cold stress by using iTRAQ-coupled 2D LC-MS/MS technique. This result would provide new insights to the underlying mycelium growth and fruit-body formation mechanisms of basidiomycetes under cold stress.

iTRAQ-Based Comparative Proteomics Analysis of the Fruiting Dikaryon and the Non-fruiting Monokaryon of Flammulina velutipes.

Flammulina velutipes is a potentially excellent fungus to study basic mechanisms of basidiomycete mycelium biology. To provide a better understanding of the mechanism of hyphae growth and fruit-body formation, the biological functions of the differentially abundant proteins between the fruiting dikaryon and the non-fruiting monokaryon of F. velutipes were investigated at the proteomic level using iTRAQ-coupled two-dimensional liquid chromatography tandem mass spectrometry technique. Among the 1198 proteins identified with high confidence, a total of 472 proteins were detected differentially abundant at least one of the mycelium development stages. In-depth data analysis revealed that differentially expressed proteins were influenced a variety of cellular processes, particularly metabolic processes. Functional pathway analysis indicated that 63 up-regulated proteins at only the fruiting dikaryon (Fv13) stage were mainly distributed in 51 specific Kyoto Encyclopedia of Genes and Genome pathways, such as amino acids biosynthesis and metabolism, signaling pathway, and central carbon metabolism. These up-regulated proteins could possibly serve as potential biomarkers to study the mycelium development pathways as well as provide new insights on the mycelium heterogenic compatibility and fruit-body formation mechanisms of basidiomycetes.

Laccase Production Among Medicinal Mushrooms from the Genus Flammulina (Agaricomycetes) Under Different Treatments in Submerged Fermentation.

The laccase activities of 13 strains of medicinal and edible mushrooms from the Flammulina genus (F. velutipes, F. rossica, and F. fennae) were studied. The effects of both fungal isolates and culture media were investigated. The laccase activities indicated significant differences among Flammulina strains (P < 0.001), and the cultural media significantly affected the laccase activities in Flammulina spp. (P < 0.001). The morphological characteristics of the 3 Flammulina species were similar, but differences in phylogenetic analysis and laccase activity existed among different species. Although isolates of each Flammulina species differed, the laccase variables among different Flammulina species were greater than those within the same species. The presence of simple carbon and nitrogen sources increased the maximum laccase enzyme activity, but the occurrence of both laccase activity and maximum laccase enzyme activity was delayed compared with lignocellulosic material. The laccase activities of most Flammulina isolates were increased when exposed to copper ions. Our findings offer insights into laccase productivity in response to different Flammulina species or strains and different submerged fermentation treatments.

A Jacalin-Related Lectin Regulated the Formation of Aerial Mycelium and Fruiting Body in Flammulina velutipes.

Flammulina velutipes, one of the most popular mushroom species in the world, has been recognized as a useful model system to study the biochemical and physiological aspects of the formation and elongation of fruit body. However, few reports have been published on the regulation of fruiting body formation in F. velutipes at the molecular level. In this study, a jacalin-related lectin gene from F. velutipes was characterized. The phylogenetic tree revealed that Fv-JRL1 clustered with other basidiomycete jacalin-like lectins. Moreover, the transcriptional pattern of the Fv-JRL1 gene in different developmental stages of F. velutipes implied that Fv-JRL1 could be important for formation of fruit body. Additionally, RNA interference (RNAi) and overexpression analyses provided powerful evidence that the lectin gene Fv-JRL1 from F. velutipes plays important roles in fruiting body formation.

Changes in trehalose content, enzyme activity and gene expression related to trehalose metabolism in Flammulina velutipes under heat shock.

Trehalose plays important roles in the protection of organisms against adverse environmental conditions. The growth and development of Flammulina velutipes is regulated and controlled under complex external conditions. This study investigated the effect of heat stress on trehalose metabolism in mycelia and fruiting bodies. The activities of enzymes involved in trehalose metabolism, the transcriptional levels of the corresponding genes and the trehalose content in the mycelia of Flammulina velutipes strain Dan3 under relatively high temperatures were investigated. The mycelia and fruiting bodies of a strain cultivated in a factory were collected at different stages to examine the trehalose content and expression levels of various genes. The results showed that intracellular trehalose significantly accumulated in the mycelia in response to 37 °C heat shock. Heat shock significantly stimulated the activities of trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase, thereby promoting the accumulation of trehalose for the first 2-6 h. The activity of neutral trehalase also decreased during this period. In addition, changes in the activities of trehalose-6-phosphate synthase, trehalose-6-phosphate phosphatase and neutral trehalase paralleled changes in the expression levels of the regulatory genes. As for the trehalose phosphorylase, the degradation of trehalose was stronger than its synthesis under heat stress. Heat shock can induce a stress response in the mycelia through the regulation of genes related to trehalose metabolism and the subsequent promotion and control of the transcription and translation of enzymes. The analysis of the trehalose and gene expression levels in the cultivated strain suggests that a substantial amount of trehalose had accumulated in the mycelia prior to induction of the primordia, and the fruiting bodies could possibly utilize degraded trehalose that translocated from the mycelia to maintain their growth.

Antitumor and Antioxidant Properties of Water-Soluble Polysaccharides from Submerged Mycelium of Flammulina velutipes.

The aim of the study was to evaluate antitumor and antioxidant properties of water-soluble polysaccharides from submerged myceliumn of Flammulina velutipes grown under optimized conditions. The optimization of the nutrient medium composition allowed to increase the biomass yield by more than 2 times (up to 35 g/l) and to reduce the time of the cultivation process. The submerged mycelium of F.velutipes strain Fv-1 contained 14.8% of a water-soluble polysaccharides, 31.6% of proteins, 2.5% of total lipids, vitamins B (B1, B5, B6). The polysaccharides contained glucose, galactose, fucose, mannose, xylose, rhamnose. The proteins contained all the essential amino acids except for tryptophan. Dry powder of the submerged mycelium, water extract of the mycelium and total fraction of the water-soluble polysaccharides demonstrated the antitumor activity against murine lymphocytic leukemia P 388 in vivo. The antitumor activity of the substances was mainly due to the polysaccharides, since their purification increased the tumor growth inhibition. The maximum tumor growth inhibition by the water-soluble polysaccharides amounted to 94%. The total fraction of the water-soluble polysaccharides from F.velutipes strain Fv-1 demonstrated antioxidant activity. The antioxidant capacity (AOC) of the water-soluble fraction from F.velutipes was higher than that of the water-soluble polysaccharides from the sub- merged mycelium of Grifolafrondosa, but inferior to the AOC of the water-soluble polysaccharides from the submerged mycelium of Ganoderma luciduma.

Mushroom tumor: a new disease on Flammulina velutipes caused by Ochrobactrum pseudogrignonense.

Mushroom tumor on Flammulina velutipes has become the main disease during the off-season cultivation of F. velutipes while the causal organism has remained unknown. The present study was aimed at identifying the pathogen confirming its pathogenisity following Koch's Postulates, characterizing it using morphological, physiological, biochemical and molecular features, and studying its current distribution. We determined that mushroom tumor is a new bacterial infection disease caused by Ochrobactrum pseudogrignonense. It produces tumor-like structures on the surface of the substrate, and inhibits the formation of primordia and fruiting of F. velutipes. The molecular studies showed that this new pathogen is closely related to Ochrobactrum based on 16S rRNA sequences. This is the first time that Ochrobactrum has been shown to be a pathogen of a mushroom.

Synthesis and characterization of biomatrixed-gold nanoparticles by the mushroom Flammulina velutipes and its heterogeneous catalytic potential.

Sustainable and greener synthesis of intracellular gold nanoparticles using mushroom Flammulina velutipes is reported. Incubation of a mushroom in chloroaurate solution resulted in the synthesis and immobilization of stable gold nanoparticles inside the mushroom mycelia. Transmission electron microscopic (TEM) analysis revealed the presence of gold nanoparticles (⩽20nm) inside the mycelia, primarily on the inner surface of the cell membrane. Inductively coupled plasma-optical emission spectrometry (ICP-OES) revealed that the accumulated gold concentration ranged from 64.4 to 330.5mgkg(-1) dry weight (DW) in the mushroom mycelia. The reduction of Au(3+) ions to Au(0) and stabilization of gold nanoparticles occurred within 1h, and the formation of fcc crystalline gold nanoparticles was confirmed by X-ray diffraction (XRD) analysis. This facile intracellular synthesis of gold nanoparticles by a mushroom without using any toxic chemicals or technologically expensive processes is used as a heterogeneous catalyst in the reduction of organic pollutants methylene blue (MB) and 4-nitrophenol (4NP). The reduction reaction follows pseudo-first order kinetics with a reaction rate constant of 0.0529min(-1) and 0.1236min(-1) for MB and 4NP, respectively. This biological process of biomatrixing of metal nanoparticles for heterogeneous catalytic reactions is simple, nontoxic, environmentally benign, and economically viable compared to the chemical synthetic routes.