Pseudomonas sp. UW4 acdS gene promotes primordium initiation and fruiting body development of Agaricus bisporus

Identification of Growth-Promoting Bacterial Resources by Investigating the Microbial Community Composition of Polyporus umbellatus Sclerotia

The sclerotium of the edible mushroom Polyporus umbellatus (Zhuling) exhibits various medicinal properties. However, given its long growth cycle and overexploitation, wild resources are facing depletion. Macrofungal growth depends on diverse microbial communities; however, the impact of soil bacteria on P. umbellatus development is unknown. Here, we combined high-throughput sequencing and pure culturing to characterize the diversity and potential function of bacteria and fungi inhabiting the P. umbellatus sclerotium and tested the bioactivities of their isolates. Fungal operational taxonomic units (OTUs) were clustered and classified, revealing 1275 genera. Bacterial OTUs yielded 891 genera. Additionally, 81 bacterial and 15 fungal strains were isolated from P. umbellatus sclerotia. Antagonism assays revealed three bacterial strains (FN2, FL19, and CL15) promoting mycelial growth by producing indole-3-acetic acid, solubilizing phosphate, and producing siderophores, suggesting their role in regulating growth, development, and production of active compounds in P. umbellatus. FN2-CL15 combined with bacterial liquid promoted growth and increased the polysaccharide content of P. umbellatus mycelia. This study reports new bioactive microbial resources for fertilizers or pesticides to enhance the growth and polysaccharide accumulation of P. umbellatus mycelia and offers guidance for exploring the correlation between medicinal macrofungi and associated microbial communities.

Current Advances in the Functional Genes of Edible and Medicinal Fungi: Research Techniques, Functional Analysis, and Prospects

Functional genes encode various biological functions required for the life activities of organisms. By analyzing the functional genes of edible and medicinal fungi, varieties of edible and medicinal fungi can be improved to enhance their agronomic traits, growth rates, and ability to withstand adversity, thereby increasing yield and quality and promoting industrial development. With the rapid development of functional gene research technology and the publication of many whole-genome sequences of edible and medicinal fungi, genes related to important biological traits have been mined, located, and functionally analyzed. This paper summarizes the advantages and disadvantages of different functional gene research techniques and application examples for edible and medicinal fungi; systematically reviews the research progress of functional genes of edible and medicinal fungi in biological processes such as mating type, mycelium and fruit growth and development, substrate utilization and nutrient transport, environmental response, and the synthesis and regulation of important active substances; and proposes future research directions for functional gene research for edible and medicinal fungi. The overall aim of this study was to provide a valuable reference for further promoting the molecular breeding of edible and medicinal fungi with high yield and quality and to promote the wide application of edible and medicinal fungi products in food, medicine, and industry.

Structure and ecological function of the soil microbiome associated with 'Sanghuang' mushrooms suffering from fungal diseases

BACKGROUND

The most serious challenges in medicinal 'Sanghuang' mushroom production are the fungal diseases caused by various molds. Application of biological agents has been regarded as a potential crop disease management strategy. Here, the soil microbiome associated with 'Sanghuang' mushroom affected by fungal diseases grown under field cultivation (FC) and hanging cultivation (HC) was characterized using culture-dependent and culture-independent methods.

RESULTS

A total of 12,525 operational taxonomic units (OTUs) and 168 pure cultures were obtained using high-throughput sequencing and a culture-dependent method, respectively. From high-throughput sequencing, we found that HC samples had more OTUs, higher α-diversity, and greater microbial community complexity than FC samples. Analysis of β-diversity divided the soil microbes into two groups according to cultivation mode. Basidiomycota (48.6%) and Ascomycota (46.5%) were the two dominant fungal phyla in FC samples, with the representative genera Trichoderma (56.3%), Coprinellus (29.4%) and Discosia (4.8%), while only the phylum Ascomycota (84.5%) was predominant in HC samples, with the representative genera Discosia (34.0%), Trichoderma (30.2%), Penicillium (14.9%), and Aspergillus (7.8%). Notably, Trichoderma was predominant in both the culture-independent and culture-dependent analyses, with Trichoderma sp. FZ0005 showing high host pathogenicity. Among the 87 culturable bacteria, 15 exhibited varying extents of antifungal activity against Trichoderma sp. FZ0005, with three strains of Bacillus spp. (HX0037, HX0016, and HX0039) showing outstanding antifungal capacity.

CONCLUSIONS

Overall, our results suggest that Trichoderma is the major causal agent of 'Sanghuang' fungal diseases and that Bacillus strains may be used as biocontrol agents in 'Sanghuang' cultivation.

Influence of the casing layer on the specific volatile compounds and microorganisms by Agaricus bisporus

One of the major variables affecting yield of the mushroom Agaricus bisporus is the casing layer, which directly affects the productivity and mass. Here, volatile organic compounds were extracted by headspace solid-phase microextraction and high-throughput sequencing was used to analyze the microbial community diversity. The relationship between mushroom yield at different cropping stages and the contents of volatile organic compounds and microorganisms in three different casing layers: peat, peat + soil and soil were systematically evaluated. The result shows that Benzaldehyde and (E)-2-octenal which stimulate yield, obviously increased as mushrooms grew, while 3-octanone, which inhibits yield, decreased over time in all three casing layers. However, there was not a strong correlation between the concentration of volatile compounds and yield. In addition, more than 3,000 bacterial operational taxonomic units (OTUs) by performing high throughput sequencing of the microbes were obtained in the three casing layers. Interestingly, the microbial community compositions were very similar between the three casing layers at a later cropping stage, but the community richness varied significantly in different casing layers and at different cropping stages. At the phylum level, the communities had similar structures but were quantitively very different, and this was even more obvious at the genus level. Principal component analysis revealed significant alterations in microbial community structure in different casing layers. Sphingomonas, Dongia and Achromobacter were the dominant genera at cropping stage 1, and the stage 3 were abundant in Saccharibacteria_norank, Pseudomonas, Flavobacterium and Brevundimonas, which was positively correlated with yield, while the abundance of Pseudomonas at stage 1 and Lactococcus and Bacillus at stage 3 was negatively correlated with yield. These results provide a guide for the development and agricultural application of microbial agents for yield improvement in the production of A. bisporus.

Biodegradation of monocrotophos by Brucella intermedia Msd2 isolated from cotton plant

Widespread and inadequate use of Monocrotophos has led to several environmental issues. Biodegradation is an ecofriendly method used for detoxification of toxic monocrotophos. In the present study, Msd2 bacterial strain was isolated from the cotton plant growing in contaminated sites of Sahiwal, Pakistan. Msd2 is capable of utilizing the monocrotophos (MCP) organophosphate pesticide as its sole carbon source for growth. Msd2 was identified as Brucella intermedia on the basis of morphology, biochemical characterization and 16S rRNA sequencing. B. intermedia showed tolerance of MCP up to 100 ppm. The presence of opd candidate gene for pesticide degradation, gives credence to B. intermedia as an effective bacterium to degrade MCP. Screening of the B. intermedia strain Msd2 for plant growth promoting activities revealed its ability to produce ammonia, exopolysaccharides, catalase, amylase and ACC-deaminase, and phosphorus, zinc and potassium solubilization. The optimization of the growth parameters (temperatures, shaking rpm, and pH level) of the MCP-degrading isolate was carried out in minimal salt broth supplemented with MCP. The optimal pH, temperature, and rpm for Msd2 growth were observed as pH 6, 35 °C, and 120 rpm, respectively. Based on optimization results, batch degradation experiment was performed. Biodegradation of MCP by B. intermedia was monitored using HPLC and recorded 78% degradation of MCP at 100 ppm concentration within 7 days of incubation. Degradation of MCP by Msd2 followed the first order reaction kinetics. Plant growth promoting and multi-stress tolerance ability of Msd2 was confirmed by molecular analysis. It is concluded that Brucella intermedia strain Msd2 could be beneficial as potential biological agent for an effective bioremediation for polluted environments.

Salicylic Acid Treatment Alleviates the Heat Stress Response by Reducing the Intracellular ROS Level and Increasing the Cytosolic Trehalose Content in Pleurotus ostreatus

Pleurotus ostreatus is usually cultivated in horticultural facilities that lack environmental control systems and often suffer heat stress (HS). Salicylic acid (SA) is recognized as a plant defense-related hormone. Here, SA treatment (200 μM) induced fungal resistance to HS of P. ostreatus, with decreased malondialdehyde (MDA) content and HSP expression. Further analysis showed that SA treatment in P. ostreatus increased the cytosolic trehalose content and reduced the intracellular reactive oxygen species (ROS) level. Moreover, H₂O₂ could restore the MDA content and HSP expression of P. ostreatus treated with SA under HS. In addition, trehalose (25 mM) or CaCl₂ (5 mM) treatment induced fungal resistance to HS, and CaCl₂ treatment increased the cytosolic trehalose content of P. ostreatus under HS. However, inhibiting Ca²⁺ levels using Ca²⁺ inhibitors or mutants reversed the trehalose content induced by SA in P. ostreatus under HS. In addition, inhibiting trehalose biosynthesis using Tps-silenced strains reversed the MDA content and HSP expression of P. ostreatus treated with SA under HS. Taken together, these results indicate that SA treatment alleviates the HS response of P. ostreatus by reducing the intracellular ROS level and increasing the cytosolic trehalose content. IMPORTANCE Heat stress (HS) is a crucial environmental challenge for edible fungi. Salicylic acid (SA), a plant defense-related hormone, plays key roles in plant responses to biotic and abiotic stresses. In this study, we found that SA treatment increased the cytosolic trehalose content and induced fungal resistance to HS in P. ostreatus. Further analysis showed that SA can alleviate the HS of P. ostreatus by reducing the intracellular ROS level and increasing the cytosolic trehalose content. Our results help to understand the mechanism underlying the responses of P. ostreatus to HS. In addition, this research provides new insights for the cultivation of P. ostreatus.

Functional Roles of LaeA-like Genes in Fungal Growth, Cellulase Activity, and Secondary Metabolism in Pleurotus ostreatus

The global regulator LaeA plays crucial roles in morphological development and secondary metabolite biosynthesis in filamentous fungi. However, the functions of LaeA in basidiomycetes are less reported. The basidiomycete Pleurotus ostreatus is a well-known fungus used both in medicine and as food that produces polysaccharides and cellulolytic enzymes. In this study, we characterized three LaeA homologs (PoLaeA1, PoLaeA2, and PoLaeA3) in P. ostreatus. PoLaeA1 showed different expression patterns than PoLaeA2 and PoLaeA3 during different developmental stages. Silencing PoLaeA1 decreased the intracellular polysaccharide (IPS) content by approximately 28–30% and reduced intracellular ROS levels compared with those of the WT strain. However, silencing PoLaeA2 and PoLaeA3 decreased cellulase activity by 31–34% and 35–40%, respectively, and reduced the cytosolic Ca2+ content, compared with those of the WT strain. Further analysis showed that PoLaeA1 regulated IPS biosynthesis through intracellular ROS levels, whereas PoLaeA2 and PoLaeA3 regulated cellulase activity through intracellular Ca2+ signaling. Our results provide new insights into the regulation of polysaccharide biosynthesis and cellulase production in filamentous fungi.

Towards an Optimal Methodology for Basidiomes Production of Naturally Occurring Species of the Genus Oudemansiella (Basidiomycetes)

Oudemansiella species are worldwide distributed and they are characterized for having attractive appearance, a soft fleshy context and mild taste and odor, what makes them interesting for mushroom intensive production. However, studies on their cultivation are scarce and there is no information regarding productive and morphological parameters of fruiting bodies obtained in culture. Here, we propose a methodology to determine the best production technique for the cultivation of not only Oudemansiella species but also of other xylophagous species assaying five different mushroom cultivation systems. Also, the optimal temperature of vegetative growth, the optimal lignocellulosic substrates and the nutritional properties of two naturally occurring Oudemansiella species were determined. As a result, bags with holes-system proved to be the most appropriate technique for the production of fruiting bodies, 25 °C was determined as the optimal temperature for mycelial growth and wheat straw as the best substrate. The evaluated species showed a higher content of fats and fiber and a lower content of proteins and carbohydrates compared to other mushrooms. Furthermore, this is the first report of the cultivation of O. cubensis on agricultural wastes in the world.

Critical Factors Involved in Primordia Building in Agaricus bisporus: A Review

The button mushroom Agaricus bisporus is an economically important crop worldwide. Many aspects of its cultivation are well known, except for the precise biological triggers for its fructification. By and large, for most basidiomycete species, nutrient availability, light and a drop in temperature are critical factors for fructification. A. bisporus deviates from this pattern in the sense that it does not require light for fructification. Furthermore its fructification seems to be inhibited by a self-generated factor which needs to be removed by microorganisms in order to initiate fruiting. This review explores what is known about the morphogenesis of fruiting initiation in A. bisporus, the microflora, the self-inhibitors for fruiting initiation and transcription factors involved. This information is subsequently contrasted with an overall model of the regulatory system involved in the initiation of the formation of primordia in basidiomycetes. The comparison reveals a number of the blank spots in our understanding of the fruiting process in A. bisporus.