Growing edible mushrooms: a conversation between bacteria and fungi

Comparison of Bacterial Communities in Five Ectomycorrhizal Fungi Mycosphere Soil

Ectomycorrhizal fungi have huge potential value, both nutritionally and economically, but most of them cannot be cultivated artificially. To better understand the influence of abiotic and biotic factors upon the growth of ectomycorrhizal fungi, mycosphere soil and bulk soil of five ectomycorrhizal fungi (Calvatia candida, Russula brevipes, Leucopaxillus laterarius, Leucopaxillus giganteus, and Lepista panaeola) were used as research objects for this study. Illumina MiSeq sequencing technology was used to analyze the community structure of the mycosphere and bulk soil bacteria of the five ectomycorrhizal fungi, and a comprehensive analysis was conducted based on soil physicochemical properties. Our results show that the mycosphere soil bacteria of the five ectomycorrhizal fungi are slightly different. Escherichia, Usitatibacter, and Bradyrhizobium are potential mycorrhizal-helper bacteria of distinct ectomycorrhizal fungi. Soil water content, soil pH, and available potassium are the main factors shaping the soil bacterial community of the studied ectomycorrhizal fungi. Moreover, from the KEGG functional prediction and LEfSe analysis, there are significant functional differences not only between the mycosphere soil and bulk soil. 'Biosynthesis of terpenoidsand steroids', 'alpha-Linolenic acid metabolism', 'Longevity regulating pathway-multiple species', 'D-Arginine and D-ornithine metabolism', 'Nitrotoluene degradation' and other functions were significantly different in mycosphere soil. These findings have pivotal implications for the sustainable utilization of ectomycorrhizal fungi, the expansion of edible fungus cultivation in forest environments, and the enhancement of derived economic benefits.

Improved XLNet modeling for Chinese named entity recognition of edible fungus

Introduction

The diversity of edible fungus species and the extent of mycological knowledge pose significant challenges to the research, cultivation, and popularization of edible fungus. To tackle this challenge, there is an urgent need for a rapid and accurate method of acquiring relevant information. The emergence of question and answer (Q&A) systems has the potential to solve this problem. Named entity recognition (NER) provides the basis for building an intelligent Q&A system for edible fungus. In the field of edible fungus, there is a lack of a publicly available Chinese corpus suitable for use in NER, and conventional methods struggle to capture long-distance dependencies in the NER process.

Methods

This paper describes the establishment of a Chinese corpus in the field of edible fungus and introduces an NER method for edible fungus information based on XLNet and conditional random fields (CRFs). Our approach combines an iterated dilated convolutional neural network (IDCNN) with a CRF. First, leveraging the XLNet model as the foundation, an IDCNN layer is introduced. This layer addresses the limited capacity to capture features across utterances by extending the receptive field of the convolutional kernel. The output of the IDCNN layer is input to the CRF layer, which mitigates any labeling logic errors, resulting in the globally optimal labels for the NER task relating to edible fungus.

Results

Experimental results show that the precision achieved by the proposed model reaches 0.971, with a recall of 0.986 and an F1-score of 0.979.

Discussion

The proposed model outperforms existing approaches in terms of these evaluation metrics, effectively recognizing entities related to edible fungus information and offering methodological support for the construction of knowledge graphs.

Biocontrol potential of endophytic Bacillus subtilis A9 against rot disease of Morchella esculenta

Introduction

Morchella esculenta is a popular edible fungus with high economic and nutritional value. However, the rot disease caused by Lecanicillium aphanocladii, pose a serious threat to the quality and yield of M. esculenta. Biological control is one of the effective ways to control fungal diseases.

Methods and results

In this study, an effective endophytic B. subtilis A9 for the control of M. esculenta rot disease was screened, and its biocontrol mechanism was studied by transcriptome analysis. In total, 122 strains of endophytic bacteria from M. esculenta, of which the antagonistic effect of Bacillus subtilis A9 on L. aphanocladii G1 reached 72.2% in vitro tests. Biological characteristics and genomic features of B. subtilis A9 were analyzed, and key antibiotic gene clusters were detected. Scanning electron microscope (SEM) observation showed that B. subtilis A9 affected the mycelium and spores of L. aphanocladii G1. In field experiments, the biological control effect of B. subtilis A9 reached to 62.5%. Furthermore, the transcritome profiling provides evidence of B. subtilis A9 bicontrol at the molecular level. A total of 1,246 differentially expressed genes (DEGs) were identified between the treatment and control group. Gene Ontology (GO) enrichment analysis showed that a large number of DEGs were related to antioxidant activity related. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the main pathways were Nitrogen metabolism, Pentose Phosphate Pathway (PPP) and Mitogen-Activated Protein Kinases (MAPK) signal pathway. Among them, some important genes such as carbonic anhydrase CA (H6S33_007248), catalase CAT (H6S33_001409), tRNA dihydrouridine synthase DusB (H6S33_001297) and NAD(P)-binding protein NAD(P) BP (H6S33_000823) were found. Furthermore, B. subtilis A9 considerably enhanced the M. esculenta activity of Polyphenol oxidase (POD), Superoxide dismutase (SOD), Phenylal anineammonia lyase (PAL) and Catalase (CAT).

Conclusion

This study presents the innovative utilization of B. subtilis A9, for effectively controlling M. esculenta rot disease. This will lay a foundation for biological control in Morchella, which may lead to the improvement of new biocontrol agents for production.

Effects of initial corncob particle size on the short-term composting for preparation of cultivation substrates for Pleurotus ostreatus

The short-term composting based on corncob for preparing Pleurotus ostreatus cultivation medium originated from agricultural production practices and so lacked systematic investigation. In this study, the influences of a Dafen (15 mm, DFT) and Xiaofen (5 mm, XFT) initial particle size (IPS) of corncob on the microbial succession and compost quality were examined. Results demonstrated that XFT compost was better suited for mushroom cultivation due to its high biological efficiency of 70 % and the absence of contamination. The composting microbes differed significantly between the DFT and XFT composts. During composting, the genera of Bacillus, Acinetobacter, Lactobacillus, Streptomyces, and Paenibacillus were majorly found in the DFT compost, while Acinetobacter, Lactobacillus, Puccinia, Bacteroides, and Bacillus genera dominated the XFT compost. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that throughout the thermophilic phase, XFT compost had much greater relative abundances of sequences relevant to energy, carbohydrate, and amino acid metabolism than DFT compost. Analysis of network correlations and Mantel tests indicated that IPS reduction could increase microbial interactions. Overall, adjusting the IPS of corncob to 5 mm increased microbial interactions, improved compost quality, and thereby boosted the P. ostreatus yield. These findings will be pertinent in optimizing the composting process of cultivation medium for P. ostreatus.

Association of Bacterial Communities with Psychedelic Mushroom and Soil as Revealed in 16S rRNA Gene Sequencing

Microbial communities' resident in the mushroom fruiting body and the soil around it play critical roles in the growth and propagation of the mushroom. Among the microbial communities associated with psychedelic mushrooms and the rhizosphere soil, bacterial communities are considered vital since their presence greatly influences the health of the mushrooms. The present study aimed at finding the microbiota present in the psychedelic mushroom Psilocybe cubensis and the soil the mushroom inhabits. The study was conducted at two different locations in Kodaikanal, Tamil Nadu, India. The composition and structure of microbial communities in the mushroom fruiting body and the soil were deciphered. The genomes of the microbial communities were directly assessed. High-throughput amplicon sequencing revealed distinct microbial diversity in the mushroom and the related soil. The interaction of environmental and anthropogenic factors appeared to have a significant impact on the mushroom and soil microbiome. The most abundant bacterial genera were Ochrobactrum, Stenotrophomonas, Achromobacter, and Brevundimonas. Thus, the study advances the knowledge of the composition of the microbiome and microbial ecology of a psychedelic mushroom, and paves the way for in-depth investigation of the influence of microbiota on the mushroom, with special emphasis on the impact of bacterial communities on mushroom growth. Further studies are required for a deeper understanding of the microbial communities that influence the growth of P. cubensis mushroom.

Structural characterization and high-efficiency prebiotic activity of the polysaccharide from Tremella aurantialba endophytic bacteria

Herein, the low-molecular-weight heteropolysaccharide (designated as TABP), with a weight-average Mw of 5408 Da, was produced by the endophytic bacterium Bacillus sp. TAB, which was initially isolated from the fruiting bodies of the wild Tremella aurantialba. A relatively high TABP accumulation was obtained and enhanced to 6.94 g/L in 5 L fed-batch fermentation by high-density cultivation. Monosaccharide composition analysis showed that the TABP comprised arabinose, glucosamine, galactose, glucose, and mannose with a molar ratio of 0.073: 0.145: 0.406: 0.182: 0.195, respectively. Methylation and NMR analyses indicated that TABP contained 1,4-linked β-d-Galp and 1,4-linked β-d-Manp pyranosyl backbone, extensively substituted at the side chains to form a complex structure. Prebiotic potential analysis exhibited significant growth-promoting effects for various lactic acid bacteria by more than 90 %. Overall, this study initially provides valuable insights into the endophytic exopolysaccharides from T. aurantialba and their biological activity, which provides prospective sources of prebiotics for functional foods and aids in understanding the endophytes symbiosis mechanism in edible mushrooms.

Dynamics of the soil microbial community associated with Morchella cultivation: diversity, assembly mechanism and yield prediction

Introduction

The artificial cultivation of morels has been a global research focus owing to production variability. Understanding the microbial ecology in cultivated soil is essential to increase morel yield and alleviate pathogen harm.

Methods

A total of nine Morchella cultivation experiments in four soil field types, forest, paddy, greenhouse, and orchard in Shanghai city were performed to determine the potential ecological relationship between Morchella growth and soil microbial ecology.

Results

Generally, significant variation was observed in the soil microbial diversity and composition between the different experimental field types. The niche width analysis indicated that the bacterial habitat niche breadth was significantly greater than the fungal community width, which was further confirmed by a null model that revealed that homogeneous selection could explain 46.26 and 53.64% of the variance in the bacterial and fungal assemblies, respectively. Moreover, the neutral community model revealed that stochastic processes dominate the bacterial community in forests and paddies and both the bacterial and fungal communities in orchard crops, whereas deterministic processes mostly govern the fungal community in forests and paddies and both the bacterial and the fungal communities in greenhouses. Furthermore, co-occurrence patterns were constructed, and the results demonstrated that the dynamics of the soil microbial community are related to fluctuations in soil physicochemical characteristics, especially soil potassium. Importantly, structural equation modeling further demonstrated that the experimental soil type significantly affects the potassium content of the soil, which can directly or indirectly promote Morchella yield by inhibiting soil fungal richness.

Discussion

This was the first study to predict morel yield through soil potassium fertilizer and soil fungal community richness, which provides new insights into deciphering the importance of microbial ecology in morel agroecosystems.

The effect of casing and gypsum on the yield and psychoactive tryptamine content of Psilocybe cubensis (Earle) Singer

Psychedelic fungi have experienced a surge in interest in recent years. Most notably, the fungal secondary metabolite psilocybin has shown tremendous promise in the treatment of various psychiatric disorders. The mushroom species that produce this molecule are poorly understood. Here we sought to examine for the first time, the response of a psilocybin-producing species Psilocybe cubensis to casing (peat moss and vermiculite) and supplementation with gypsum (calcium sulfate dihydrate), two common practices in commercial mushroom cultivation. Mycelial samples of genetically authenticated P. cubensis were used to inoculate popcorn grain bags. The fully colonized bags of popcorn grain (0.15 kg) were transferred to bins of 0.85 kg pasteurized horse manure, with or without 1 cm thick layer of casing and/or 5 % gypsum. Our results indicate that the use of a casing layer significantly increases the biological efficiency (161.5 %), by approximately four fold, in comparison to control (40.5 %), albeit with a slight delay (∼2 days) for obtaining fruiting bodies and a somewhat reduced total tryptamine content (0.85 %) as gauged by High Performance Liquid Chromatography measurements. Supplementation with both casing and gypsum, however, appears to promote maximal yields (896.6 g/kg of dried substrate), with a biological efficiency of 89.6 %, while also maintaining high total tryptamine expressions (0.95 %). These findings, revealing methods for maximizing yield of harvest and expressions of psychoactive tryptamines, may prove useful for both home growers and commercial cultivators of this species, and ultimately support the growth of a robust industry with high quality natural products.

Nitrogen balance and supply in Australasian mushroom composts

Mushrooms are an important source of protein in the human diet. They are increasingly viewed as a sustainable meat replacement in an era of growing populations, with button mushrooms (Agaricus bisporus) the most popular and economically important mushroom in Europe, Australia and North America. Button mushrooms are cultivated on a defined, straw-derived compost, and the nitrogen (N) required to grow these high-protein foods is provided mainly by the addition of poultry manure and horse manure. Using the correct balance of carbon (C) and N sources to produce mushroom compost is critically important in achieving maximum mushroom yields. Changes in the amount and form of N added, the rate and timing of N addition and the other compost components used can dramatically change the proportion of added N recovered in the mushroom caps, the yield and quality of the mushrooms and the loss of N as ammonia and nitrogen oxide gases during composting. This review examines how N supply for mushroom production can be optimised by the use of a broad range of inorganic and organic N sources for mushroom composting, together with the use of recycled compost leachate, gypsum and protein-rich supplements. Integrating this knowledge into our current molecular understanding of mushroom compost biology will provide a pathway for the development of sustainable solutions in mushroom production that will contribute strongly to the circular economy. KEY POINTS: • Nitrogen for production of mushroom compost can be provided as a much wider range of organic feedstocks or inorganic compounds than currently used • Most of the nitrogen used in production of mushroom compost is not recovered as protein in the mushroom crop • The sustainability of mushroom cropping would be increased through alternative nitrogen management during composting and cropping.

Valorizing spent mushroom substrate into syngas by the thermo-chemical process

This study investigated the conversion of agricultural biomass waste (specifically, spent mushroom substrate) into syngas via pyrolysis. Carbon dioxide was used to provide a green/sustainable feature in the pyrolysis process. All the experimental data highlight the mechanistic role of carbon dioxide (CO2) in the process, demonstrated by the enhanced carbon monoxide (CO) yield from pyrolysis under CO2. Carbon dioxide was indeed reactive at ≥ 500 ˚C. Carbon dioxide was reduced and subsequently oxidized volatiles stemming from the thermolysis of spent mushroom substrate via the gas-phase reaction, thereby resulting in the enhanced formation of CO. Carbon dioxide radically diverted the carbon distribution patterns of the pyrogenic products, as more carbon in the oil was allocated to syngas by the gas-phase reaction of volatiles and CO2. To enhance the mechanistic role of CO2, a Ni-based catalyst was added to the pyrolysis process, which greatly accelerated the gas-phase reaction of volatiles and CO2.

Manipulating Agaricus bisporus developmental patterns by passaging microbial communities in complex substrates

IMPORTANCE

Agaricus bisporus is an economically important edible mushroom and manipulating its developmental patterns is crucial for maximizing yield and quality. One of the potential strategies for achieving such a goal is passaging microbial communities in compost or casing. The current study demonstrated that passaging substrates develop enriched microbial communities, and after a few passages, certain levels of changes in mushroom developmental patterns (the timing of fruiting bodies formation) were observed as well as shifts in the bacterial communities. Overall, a better understanding of the complex interactions between microorganisms present in the cultivation system may help farmers and researchers to develop more efficient and sustainable cultivation practices that can both benefit the environment and human health.

Effects of Two Different Proportions of Microbial Formulations on Microbial Communities in Kitchen Waste Composting

The objective of this research was to investigate the effect of bulking agents on the maturity and gaseous emissions of composting kitchen waste. The composing experiments were carried out by selected core bacterial agents and universal bacterial agents for 20 days. The results demonstrated that the addition of core microbial agents effectively controlled the emission of typical odor-producing compounds. The addition of core and universal bacterial agents drastically reduced NH3 emissions by 94% and 74%, and decreased H2S emissions by 78% and 27%. The application of core microbial agents during composting elevated the peak temperature to 65 °C and in terms of efficient temperature evolution (>55 °C for 8 consecutive days). The organic matter degradation decreased by 65% from the initial values for core microbial agents were added, while for the other treatments the reduction was slight. Adding core microbial agents to kitchen waste produced mature compost with a higher germination index (GI) 112%, while other treatments did not fully mature and had a GI of <70%. Microbial analysis demonstrated that the core microbial agents in composting increased the relative abundances of Weissella, Ignatzschineria, and Bacteroides. Network and redundancy analysis (RDA) revealed that the core microbial agents enhanced the relationship between bacteria and the eight indicators (p < 0.01), thereby improving the bio transformation of compounds during composting. Overall, these results suggest that the careful selection of appropriate inoculation microorganisms is crucial for improved biological transformation and nutrient content composting efficacy of kitchen waste.

Study of growth-improving and sporophore-inducing endobacteria isolated from Pleurotus pulmonarius

Several Pleurotus species (oyster mushrooms) are commercially cultivated in India owing to the favorable tropical agro-climatic conditions. However, there are only a few studies on the microbiome of mushrooms, especially oyster mushrooms. The aim of this study was to assess the effect of endobacteria on mycelial growth, spawning, sporophore development, and proximate composition of P. pulmonarius. We isolated several bacterial strains from the sporophores of P. pulmonarius and assessed the in vitro production of indole acetic acid, ammonia, and siderophores. The selected bacteria were individually supplemented with spawn, substrate, or both for sporophore production. Three of 130 isolates were selected as mycelial growth-promoting bacteria in both solid and submerged fermentation. These bacterial isolates were identified through Gram staining, biochemical characterization, and 16S rRNA sequencing. Isolate PP showed 99.24% similarity with Priestia paraflexa, whereas isolates PJ1 and PJ2 showed 99.78% and 99.65% similarities, respectively, with Rossellomorea marisflavi. The bacterial supplementation with spawn, substrate, or both, increased the biological efficiency (BE) and nutrient content of the mushrooms. The bacterial supplementation with substrate augmented BE by 64.84%, 13.73%, and 27.13% using PJ2, PP, and PJ1, respectively; under similar conditions of spawn supplementation, BE was increased by 15.24%, 47.30%, 48.10%, respectively. Overall, the supplementation of endobacteria to improve oyster mushroom cultivation may open a new avenue for sustainable agricultural practices in the mushroom industry.

Dazomet changes microbial communities and improves morel mushroom yield under continuous cropping

Morels (Morchella spp.) are highly prized and popular edible mushrooms. The outdoor cultivation of morels in China first developed at the beginning of the 21st century. Several species, such as Morchella sextelata, M. eximia, and M. importuna, have been commercially cultivated in greenhouses. However, the detriments and obstacles associated with continuous cropping have become increasingly serious, reducing yields and even leading to a complete lack of fructification. It has been reported that the obstacles encountered with continuous morel cropping may be related to changes in the soil microbial community. To study the effect of dazomet treatment on the cultivation of morel under continuous cropping, soil was fumigated with dazomet before morel sowing. Alpha diversity and beta diversity analysis results showed that dazomet treatment altered the microbial communities in continuous cropping soil, which decreased the relative abundance of soil-borne fungal pathogens, including Paecilomyces, Trichoderma, Fusarium, Penicillium, and Acremonium, increased the relative abundance of beneficial soil bacteria, including Bacillius and Pseudomonas. In addition, the dazomet treatment significantly increased the relative abundance of morel mycelia in the soil and significantly improved morel yield under continuous cropping. These results verified the relationship between the obstacles associated with continuous cropping in morels and the soil microbial community and elucidated the mechanism by which the obstacle is alleviated when using dazomet treatment.

Multinational Outbreak of Listeria monocytogenes Infections Linked to Enoki Mushrooms Imported from the Republic of Korea 2016-2020

Keeping the global food supply safe necessitates international collaborations between countries. Health and regulatory agencies routinely communicate during foodborne illness outbreaks, allowing partners to share investigational evidence. A 2016-2020 outbreak of Listeria monocytogenes infections linked to imported enoki mushrooms required a multinational collaborative investigation among the United States, Canada, Australia, and France. Ultimately, this outbreak included 48 ill people, 36 in the United States and 12 in Canada, and was linked to enoki mushrooms sourced from one manufacturer located in the Republic of Korea. Epidemiologic, laboratory, and traceback evidence led to multiple regulatory actions, including extensive voluntary recalls by three firms in the United States and one firm in Canada. In the United States and Canada, the Korean manufacturer was placed on import alert while other international partners provided information about their respective investigations and advised the public not to eat the recalled enoki mushrooms. The breadth of the geographic distribution of this outbreak emphasizes the global reach of the food industry. This investigation provides a powerful example of the impact of national and international coordination of efforts to respond to foodborne illness outbreaks and protect consumers. It also demonstrates the importance of fast international data sharing and collaboration in identifying and stopping foodborne outbreaks in the global community. Additionally, it is a meaningful example of the importance of food sampling, testing, and integration of sequencing results into surveillance databases.

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.

A narrative action on the battle against hunger using mushroom, peanut, and soybean-based wastes

Numerous generations have been affected by hunger, which still affects hundreds of millions of people worldwide. The hunger crisis is worsening although many efforts have been made to minimize it. Besides that, food waste is one of the critical problems faced by most countries worldwide. It has disrupted the food chain system due to inefficient waste management, while negatively impacting the environment. The majority of the waste is from the food production process, resulting in a net zero production for food manufacturers while also harnessing its potential. Most food production wastes are high in nutritional and functional values, yet most of them end up as low-cost animal feed and plant fertilizers. This review identified key emerging wastes from the production line of mushroom, peanut, and soybean (MPS). These wastes (MPS) provide a new source for food conversion due to their high nutritional content, which contributes to a circular economy in the post-pandemic era and ensures food security. In order to achieve carbon neutrality and effective waste management for the production of alternative foods, biotechnological processes such as digestive, fermentative, and enzymatic conversions are essential. The article provides a narrative action on the critical potential application and challenges of MPS as future foods in the battle against hunger.

Nitrate determines the bacterial habitat specialization and impacts microbial functions in a subsurface karst cave

Karst caves are usually considered as natural laboratories to study pristine microbiomes in subsurface biosphere. However, effects of the increasingly detected nitrate in underground karst ecosystem due to the acid rain impact on microbiota and their functions in subsurface karst caves have remained largely unknown. In this study, samples of weathered rocks and sediments were collected from the Chang Cave, Hubei province and subjected to high-throughput sequencing of 16S rRNA genes. The results showed that nitrate significantly impacted bacterial compositions, interactions, and functions in different habitats. Bacterial communities clustered according to their habitats with distinguished indicator groups identified for each individual habitat. Nitrate shaped the overall bacterial communities across two habitats with a contribution of 27.2%, whereas the pH and TOC, respectively, structured bacterial communities in weathered rocks and sediments. Alpha and beta diversities of bacterial communities increased with nitrate concentration in both habitats, with nitrate directly affecting alpha diversity in sediments, but indirectly on weathered rocks by lowering pH. Nitrate impacted more on bacterial communities in weathered rocks at the genus level than in sediments because more genera significantly correlated with nitrate concentration in weathered rocks. Diverse keystone taxa involved in nitrogen cycling were identified in the co-occurrence networks such as nitrate reducers, ammonium-oxidizers, and N₂-fixers. Tax4Fun2 analysis further confirmed the dominance of genes involved in nitrogen cycling. Genes of methane metabolism and carbon fixation were also dominant. The dominance of dissimilatory and assimilatory nitrate reduction in nitrogen cycling substantiated nitrate impact on bacterial functions. Our results for the first time revealed the impact of nitrate on subsurface karst ecosystem in terms of bacterial compositions, interactions, and functions, providing an important reference for further deciphering the disturbance of human activities on the subsurface biosphere.

Investigating Endobacteria that Thrive Within Mucoromycota

Metagenomics approaches have revealed the importance of Mucoromycota in the evolution and functioning of plant microbiomes. Comprised of three subphyla (Glomeromycotina, Mortierellomycotina, and Mucoromycotina), this early diverging lineage of fungi encompasses species of mycorrhizal fungi, root endophytes, plant pathogens, and many decomposers of plant debris. Interestingly, several taxa of Mucoromycota share a common feature, that is, the presence of endobacteria within their mycelia and spores. The study of these endosymbiotic bacteria is still a challenging task. However, given recent improvements in the sensitivity of culture-free approaches, a deeper understanding of such microbial interactions is now possible and fuels an emerging research field. In this chapter, we report how Mucoromycota, in particular Mortierellomycotina, and their endobacteria can be investigated using a combination of diverse cellular biology, microscopy, and molecular techniques.

Bacterial communities associated with mushrooms in the Qinghai-Tibet Plateau are shaped by soil parameters

Fungi capable of producing fruit bodies are essential food and medicine resources. Despite recent advances in the study of microbial communities in mycorrhizospheres, little is known about the bacterial communities contained in fruit bodies. Using high-throughput sequencing, we investigated the bacterial communities in four species of mushrooms located on the alpine meadow and saline-alkali soil of the Qinghai-Tibet Plateau (QTP). Proteobacteria (51.7% on average) and Actinobacteria (28.2% on average) were the dominant phyla in all of the sampled fairy ring fruit bodies, and Acidobacteria (27.5% on average) and Proteobacteria (25.7% on average) dominated their adjacent soils. For the Agria. Bitorquis, Actinobacteria was the dominant phylum in its fruit body (67.5% on average) and adjacent soils (65.9% on average). The alpha diversity (i.e., Chao1, Shannon, Richness, and Simpson indexes) of the bacterial communities in the fruit bodies were significantly lower than those in the soil samples. All of the fungi shared more than half of their bacterial phyla and 16.2% of their total operational taxonomic units (OTUs) with their adjacent soil. Moreover, NH₄⁺ and pH were the key factors associated with bacterial communities in the fruit bodies and soils, respectively. These results indicate that the fungi tend to create a unique niche that selects for specific members of the bacterial community. Using culture-dependent methods, we also isolated 27 bacterial species belonging to three phyla and five classes from fruit bodies and soils. The strains isolated will be useful for future research on interactions between mushroom-forming fungi and their bacterial endosymbionts.

Dynamics of microbial community and enzyme activities during preparation of Agaricus bisporus compost substrate

Button mushrooms (Agaricus bisporus) are grown commercially on a specialized substrate that is usually prepared from wheat straw and poultry manure in a microbially-mediated composting process. The quality and yield of the mushroom crop depends critically on the quality of this composted substrate, but details of the microbial community responsible for compost production have only emerged recently. Here we report a detailed study of microbial succession during mushroom compost production (wetting, thermophilic, pasteurization/conditioning, spawn run). The wetting and thermophilic phases were characterized by a rapid succession of bacterial and fungal communities, with maximum diversity at the high heat stage. Pasteurization/conditioning selected for a more stable community dominated by the thermophilic actinomycete Mycothermus thermophilus and a range of bacterial taxa including Pseudoxanthomonas taiwanensis and other Proteobacteria. These taxa decreased during spawn run and may be acting as a direct source of nutrition for the proliferating Agaricus mycelium, which has previously been shown to use microbial biomass in the compost for growth. Comparison of bacterial communities at five geographically separated composting yards in south-eastern Australia revealed similarities in microbial succession during composting, although the dominant bacterial taxa varied among sites. This suggests that specific microbial taxa or combinations of taxa may provide useful biomarkers of compost quality and may be applied as predictive markers of mushroom crop yield and quality.

Arsenic Metabolism, Toxicity and Accumulation in the White Button Mushroom Agaricus bisporus

Mushrooms have unique properties in arsenic metabolism. In many commercial and wild-grown mushrooms, arsenobetaine (AsB), a non-toxic arsenical, was found as the dominant arsenic species. The AsB biosynthesis remains unknown, so we designed experiments to study conditions for AsB formation in the white button mushroom, Agaricus bisporus. The mushrooms were treated with various arsenic species including arsenite (As(III)), arsenate (As(V)), methylarsenate (MAs(V)), dimethylarsenate (DMAs(V)) and trimethylarsine oxide (TMAsO), and their accumulation and metabolism were determined using inductively coupled mass spectrometer (ICP-MS) and high-pressure liquid chromatography coupled with ICP-MS (HPLC-ICP-MS), respectively. Our results showed that mycelia have a higher accumulation for inorganic arsenicals while fruiting bodies showed higher accumulation for methylated arsenic species. Two major arsenic metabolites were produced in fruiting bodies: DMAs(V) and AsB. Among tested arsenicals, only MAs(V) was methylated to DMAs(V). Surprisingly, AsB was only detected as the major arsenic product when TMAsO was supplied. Additionally, AsB was only detected in the fruiting body, but not mycelium, suggesting that methylated products were transported to the fruiting body for arsenobetaine formation. Overall, our results support that methylation and AsB formation are two connected pathways where trimethylated arsenic is the optimal precursor for AsB formation.

Metaprofiling of the Bacterial Community in Colonized Compost Extracts by Agaricus subrufescens

It is well-known that bacteria and fungi play important roles in the relationships between mycelium growth and the formation of fruiting bodies. The sun mushroom, Agaricus subrufescens, was discovered in Brazil ca. 1960 and it has become known worldwide due to its medicinal and nutritional properties. This work evaluated the bacterial community present in mushroom-colonized compost extract (MCCE) prepared from cultivation of A. subrufescens, its dynamics with two different soaking times and the influence of the application of those extracts on the casing layer of a new compost block for A. subrufescens cultivation. MCCEs were prepared through initial submersion of the colonized compost for 1 h or 24 h in water followed by application on casing under semi-controlled conditions. Full-length 16S rRNA genes of 1 h and 24 h soaked MCCE were amplified and sequenced using nanopore technology. Proteobacteria, followed by Firmicutes and Planctomycetes, were found to be the most abundant phyla in both the 1 h and 24 h soaked MCCE. A total of 275 different bacterial species were classified from 1 h soaked MCCE samples and 166 species from 24 h soaked MCCE, indicating a decrease in the bacterial diversity with longer soaking time during the preparation of MCCE. The application of 24 h soaked MCCE provided increases of 25% in biological efficiency, 16% in precociousness, 53% in the number of mushrooms and 40% in mushroom weight compared to control. Further investigation is required to determine strategies to enhance the yield and quality of the agronomic traits in commercial mushroom cultivation.

Dynamic succession of microbial compost communities and functions during Pleurotus ostreatus mushroom cropping on a short composting substrate

Cultivating oyster mushrooms (Pleurotus ostreatus), a typical primary decomposer of lignocellulose, on a short composting substrate is a novel procedure which possesses energy conserves, reduced the chance of infection by competitive species, shorter production duration and achieved high production efficiency. However, the microbiome and microbial metabolic functions in the composting substrate during the mushroom cropping is unknown. In the present study, the contents of hemicellulose, cellulose and lignin and the activities of protease, laccase and cellulase were evaluated in the corncob short composting substrate from before oyster mushroom spawning to first flush fructification; meanwhile the changes in the microbiome and microbial metabolic functions were surveyed by using metagenomic sequencing. Results showed that the hemicellulose, cellulose and lignin in the short composting substrate were decomposed of 42.76, 34.01, and 30.18%, respectively, during the oyster mushroom cropping process. In addition, the contents of hemicellulose, cellulose and lignin in the composting substrate were reduced rapidly and negatively correlated with the abundance of the Actinobacteria phylum. The activities of protease, laccase and cellulase fastly increased in the period of before oyster mushroom spawning to full colonization and were positively correlated to the abundance of Actinobacteria phylum. The total abundance of bacteria domain gradually decreased by only approximately 15%, while the abundance of Actinobacteria phylum increased by 68% and was positively correlated with that of oyster mushroom. The abundance of oyster mushroom increased by 50 times from spawning to first flush fructification. The dominant genera, all in the order of Actinomycetales, were Cellulosimicrobium, Mycobacterium, Streptomyces and Saccharomonospora. The total abundance of genes with functions annotated in the Clusters of Orthologous Groups of proteins (COG) for Bacteria and Archaea and Kyoto Encyclopedia of Genes and Genomes (KEGG) database for all three life domains was positively correlated.

The three metabolic pathways for carbohydrates, amino acids and energy were the primary enrichment pathways in KEGG pathway, accounting for more than 30% of all pathways, during the mushroom cropping in which the glycine metabolic pathway, carbon fixation pathways in prokaryotes and methane metabolism were all dominated by bacteria. The genes of cellulolytic enzymes, hemicellulolytic enzymes, laccase, chitinolytic enzymes, peptidoglycanlytic enzymes and ammonia assimilation enzymes with abundances from 0.28 to 0.24%, 0.05 to 0.02%, 0.02 to 0.01%, 0.14 to 0.08%, 0.39 to 0.16%, and 0.13 to 0.12% during the mushroom cropping identified in the Evolutionary Genealogy of Genes: Non-supervised Orthologous Groups (eggNOG) database for all three life domains were all aligned to COG database. These results indicated that bacteria, especially Actinomycetales, were the main metabolism participants in the short composting substrate during the oyster mushroom cropping. The relationship between oyster mushrooms and bacteria was cooperative, Actinomycetales were oyster mushroom growth promoting bacteria (OMGPB).

Isolation, genomic characterization, and mushroom growth-promoting effect of the first fungus-derived Rhizobium

Polyporus umbellatus is a well-known edible and medicinal mushroom, and some bacteria isolated from mushroom sclerotia may have beneficial effects on their host. These mushroom growth-promoting bacteria (MGPBs) are of great significance in the mushroom production. In this work, we aimed to isolate and identify MGPBs from P. umbellatus sclerotia. Using the agar plate dilution method, strain CACMS001 was isolated from P. umbellatus sclerotia. The genome of CACMS001 was sequenced using PacBio platform, and the phylogenomic analysis indicated that CACMS001 could not be assigned to known Rhizobium species. In co-culture experiments, CACMS001 increased the mycelial growth of P. umbellatus and Armillaria gallica and increased xylanase activity in A. gallica. Comparative genomic analysis showed that CACMS001 lost almost all nitrogen fixation genes but specially acquired one redox cofactor cluster with pqqE, pqqD, pqqC, and pqqB involved in the synthesis of pyrroloquinoline quinone, a peptide-derived redox participating in phosphate solubilization activity. Strain CACMS001 has the capacity to solubilize phosphate using Pikovskaya medium, and phnA and phoU involved in this process in CACMS001 were revealed by quantitative real-time PCR. CACMS001 is a new potential Rhizobium species and is the first identified MGPB belonging to Rhizobium. This novel bacterium would play a vital part in P. umbellatus, A. gallica, and other mushroom cultivation.

Bacterial Community Patterns in the Agaricus bisporus Cultivation System, from Compost Raw Materials to Mushroom Caps

Different from other fungal species that can be largely cultivated in 'axenic conditions' using plant material (e.g., species of Lentinula and Pleurotus in 'sterile' straw-based substrate), the commercial Agaricus bisporus cultivation system relies heavily on ecological relationships with a broad range of microorganisms present in the system (compost and casing). Since the A. bisporus cultivation system consists of a microbial manipulation process, it is important to know the microbial community dynamics during the entire cultivation cycle to design further studies and/or crop management strategies to optimize this system. To capture the bacterial community 'flow' from compost raw materials to the casing to the formation and maturation of mushroom caps, community snapshots were generated by direct DNA recovery (amplicon sequencing). The 'bacterial community flow' revealed that compost, casing and mushrooms represent different niches for bacteria present in the cultivation system, but at the same time, a bacterial exchange between microenvironments can occur for a portion of the community. Within each microenvironment, compost showed intense bacterial populational dynamics, probably due to the environmental changes imposed by composting conditions. In casing, the colonization of A. bisporus appeared, to reshape the native bacterial community which later, with some other members present in compost, becomes the core community in mushroom caps. The current bacterial survey along with previous results provides more cues of specific bacteria groups that can be in association with A. bisporus development and health.

Application of the mushroom volatile 1-octen-3-ol to suppress a morel disease caused by Paecilomyces penicillatus

Morels (Morchella spp.) are of great economic and scientific value. Paecilomyces penicillatus can cause white mold disease (WMD) widely emerging on morel ascocarps and is also a potential factor causing morel fructification failure. 1-octen-3-ol is a mushroom volatile compound with broad-spectrum antimicrobial activities. This study aimed to control the morel disease caused by P. penicillatus through suppressing P. penicillatus in the soil cultivated with Morchella sextelata using 1-octen-3-ol. Safe concentration of 1-octen-3-ol was estimated by comparing its inhibitory effect against P. penicillatus and M. sextelata, respectively, with mycelium-growth experiments on agar plates. The results showed that M. sextelata possesses a higher tolerance to 1-octen-3-ol than P. penicillatus with a 1-octen-3-ol concentration between 0 and 200 µL/L. Based on that, a sandy soil was supplemented with low (50 µL/L) or high concentration (200 µL/L) of 1-octen-3-ol. The effects of 1-octen-3-ol on soil microbial communities, WMD incidence, and morel yield were investigated. Compared to the non-supplemented control group, the incidence of WMD and the proportion of Paecilomyces in the soils of low- and high-concentration treatment groups were significantly decreased, corresponding to a significant increase in morel ascocarp yield. It suggests that 1-octen-3-ol effectively suppressed P. penicillatus in the soil, thereby reducing the severity of WMD and improving the morel yield. The diversity of soil bacterial communities was also altered by 1-octen-3-ol supplement. The proportion of Rhodococcus spp. in the soil was positively correlated with the 1-octen-3-ol concentration and ascocarp yield, suggesting its potential role in improving morel yield. KEY POINTS: • A novel method for morel disease suppression was proposed. • Paecilomyces in soil affects white mold disease and fructification yield of morel. • 1-Octen-3-ol suppresses Paecilomyces and alters bacterial community in soil.

Bacterial-fungal interactions under agricultural settings: from physical to chemical interactions

Bacteria and fungi are dominant members of environmental microbiomes. Various bacterial-fungal interactions (BFIs) and their mutual regulation are important factors for ecosystem functioning and health. Such interactions can be highly dynamic, and often require spatiotemporally resolved assessments to understand the interplay which ranges from antagonism to mutualism. Many of these interactions are still poorly understood, especially in terms of the underlying chemical and molecular interplay, which is crucial for inter-kingdom communication and interference. BFIs are highly relevant under agricultural settings; they can be determinative for crop health. Advancing our knowledge related to mechanisms underpinning the interactions between bacteria and fungi will provide an extended basis for biological control of pests and pathogens in agriculture. Moreover, it will facilitate a better understanding of complex microbial community networks that commonly occur in nature. This will allow us to determine factors that are crucial for community assembly under different environmental conditions and pave the way for constructing synthetic communities for various biotechnological applications. Here, we summarize the current advances in the field of BFIs with an emphasis on agriculture.

Analysis of the Composition of Substrate for Industrial Fermentation of Agaricus bisporus Based on Secondary and Tertiary Fermentation Mode Composition Analysis of Industrial Fermentation Substrates of A. bisporus

In this study, changes in metabolites during the fermentation of Agaricus bisporus compost under the Shanghai Lianzhong secondary fermentation method and Jiangsu Yuguan tertiary fermentation method were analysed by applying gas chromatography–mass spectrometry (GC–MS) to understand the differences in metabolites under different fermentation methods and find metabolic markers at different fermentation stages in different fermentation methods. The results showed that 1002 compounds were identified. Based on the differential metabolites from pathways of significant enrichment, it was found that L-aspartic acid and 5-aminobenzolevulinic acid could be used as potential metabolic markers to evaluate the phase 2 fermentation method of Shanghai Lianzhong and the phase 3 fermentation method of Jiangsu Yuguan, respectively. This study provides a reference for the preparation of quality-stable fermentation materials and further understanding of the cultivation of A. bisporus with fermentation materials.

Impact of Cultivation Substrate and Microbial Community on Improving Mushroom Productivity: A Review

Simple Summary

Lignocellulosic material and substrate formulations affect mushroom productivity. The microbial community in cultivation substrates affects the quality of the substrates and the efficiency of mushroom production. The elucidation of the key microbes and their biochemical function can serve as a useful guide in the development of a more effective system for mushroom cultivation.

Abstract

Lignocellulosic materials commonly serve as base substrates for mushroom production. Cellulose, hemicellulose, and lignin are the major components of lignocellulose materials. The composition of these components depends upon the plant species. Currently, composted and non-composted lignocellulosic materials are used as substrates in mushroom cultivation depending on the mushroom species. Different substrate compositions can directly affect the quality and quantity of mushroom production yields. Consequently, the microbial dynamics and communities of the composting substrates can significantly affect mushroom production. Therefore, changes in both substrate composition and microbial diversity during the cultivation process can impact the production of high-quality substrates and result in a high degree of biological efficiency. A brief review of the current findings on substrate composition and microbial diversity for mushroom cultivation is provided in this paper. We also summarize the advantages and disadvantages of various methods of mushroom cultivation by analyzing the microbial diversity of the composting substrates during mushroom cultivation. The resulting information will serve as a useful guide for future researchers in their attempts to increase mushroom productivity through the selection of suitable substrate compositions and their relation to the microbial community.

Morel Production Associated with Soil Nitrogen-Fixing and Nitrifying Microorganisms

True morels (Morchella, Pezizales) cultivated in soil are subject to complex influences from soil microbial communities. To explore the characteristics of soil microbial communities on morel cultivation, and evaluate whether these microbes are related to morel production, we collected 23 soil samples from four counties in Sichuan and Yunnan Provinces, China. Based on ITS and 16S rDNA amplicon sequencing, the alpha diversity analysis indicated that the biodiversity of morel cultivation soil showed a downward trend compared with the bare soil. The results also showed that there were no significant differences in soil microbial communities between OC (bare soil) and OO (after one-year suspension of sowing). This means that, after about one year of stopping sowing, the component and structure of soil that once cultivated morel would be restored. In co-occurrence networks, some noteworthy bacterial microbes involved in nitrogen fixation and nitrification have been identified in soils with high morel yields, such as Arthrobacter, Bradyhizobium, Devosia, Pseudarthrobacter, Pseudolabrys, and Nitrospira. In contrast, in soils with low or no morel yield, some pathogenic fungi accounted for a high proportion, including Gibberella, Microidium, Penicillium, Sarocladium, Streptomyces, and Trichoderma. This study provided valuable information for the isolation and culturing of some beneficial microbes for morel cultivation in further study and, potentially, to harness the power of the microbiome to improve morel production and health.

Fungal and Bacterial Communities in Tuber melanosporum Plantations from Northern Spain

Tuber melanosporum (Ascomycota, Pezizales) is an ectomycorrhizal fungus that produces highly appreciated hypogeous fruiting bodies called black truffles. The aim of this paper was to research the composition of ectomycorrhiza-associated fungal and bacterial communities in T. melanosporum oak plantations. Results of this paper showed the competitive effect of T. melanosporum on other fungal species, especially other mycorrhizal and pathogenic species. T. melanosporum was shown to be associated mainly with bacteria, some of them important for their properties as mycorrhizal helper bacteria. A dendrogram analysis of co-occurrence showed that T. melanosporum tended to co-occur with the following bacteria species: Singulisphaera limicola, Nannocistis excedens and Sporosarcina globispora. In addition, it was linked to fungal species such as Mortierella elongata, M. minutissima, Cryptococcus uzbekistanensis, C. chernovii and C. aerius. This study provides an exhaustive analysis of the diversity, structure and composition of fungal and bacterial communities associated with T. melanosporum to enhance understanding of the biology, composition and role of these communities in truffle plantations.

Bacterial Community Composition in the Growth Process of Pleurotus eryngii and Growth-Promoting Abilities of Isolated Bacteria

The effects of biological factors on the vegetative growth process of mushrooms remain largely unexplored. We investigated the bacterial community in different growth stages of Pleurotus eryngii by high-throughput sequencing technology to explore the relationship between interacting bacteria and the growth and development of P. eryngii. We found significant variances in mushroom interacting association bacteria (MIAB) compositions among the samples from different growth stages, and 410 genera were identified. The bacteria in the full-bag and post-ripe stages were shifted to the biocontrol and growth-promotion ones. The mushroom growth-promoting bacteria (MGPB) were also isolated successfully and identified as B. cereus Bac1. The growth speed and density of mycelial pellets of P. eryngii, and activities of two exoenzymes (laccase and amylase), were analyzed by adding the different volumes of cell-free fermentation broth of B. cereus Bac1 to fungal culture media. The results showed that when a 5 mL cell-free fermentation broth was used, the growth speed of P. eryngii hyphae was enhanced by 1.15-fold over the control and reached 0.46 mm/h. The relative activity of laccase and amylase was increased by 26.9 and 43.83%. Our study revealed that the abundant interacting bacteria coexist with P. eryngii hyphae. Moreover, the abundance of some bacteria exhibiting a positive correlation with the growth periods of their host fungi can effectively promote the growth of the host, which will provide technical supports on the high-efficiency production of P. eryngii in factory cultivation.

Methods used for extraction of plant volatiles have potential to preserve truffle aroma: A review

Truffles are considered one of the world's most highly prized foods mainly due to their desirable organoleptic properties and rarity. However, truffles are seasonal (harvested mostly in winter from June to August in the Southern Hemisphere and from December to February in the Northern Hemisphere) and extremely perishable. Truffles deteriorate rapidly showing undesirable changes within 10 days from harvest in aroma and visual appearance after harvest. The very short postharvest shelf life (about 7-10 days) limits the potential for export and domestic consumption all year round. Several preservation methods have been studied to prolong their shelf life without the loss of aroma. However, all traditional preservation techniques have their own shortcomings and remain challenging. The extraction of natural truffle aroma volatiles for food applications could be a potential alternative to replace the existing synthetic flavoring used for processed truffle products. Four commonly used extraction methods for recovering volatile compounds from plants, namely, supercritical carbon dioxide extraction, Soxhlet extraction, distillation, and cold pressing, are critically analyzed. Up to date, existing research about the extraction of aroma volatiles from truffles is limited in the literature but based on the volatility of the key truffle volatile compounds, supercritical carbon dioxide extraction may offer the best possibility so that a natural truffle-based product that can be used in food applications throughout the year can be made available.

Morel Production Related to Soil Microbial Diversity and Evenness

Black morel is a widely prized ascomycetous mushroom with culinary value. It was once uncultivable but can now be cultivated routinely in ordinary farmland soils. Large-scale morel farming sometimes encounters nonfructification for unknown reasons. In spring 2020, many morel farms in the area of Chengdu-Plain, China, exhibited no fructification at all, causing disastrous economic loss to the farmers. To determine potential ecological factors associated with the different performance of morel production in these farms, 21 affected sites versus 11 sites with normal fructification performance were analyzed to compare soil microbiota and physiochemical characteristics during fructification. The results indicated that soil physiochemical characteristics were unlikely to be a major reason for the difference between successful fructification and nonfructification. The soils with successful fructification had significantly higher diversity in both the fungal and bacterial communities than those with nonfructification. Morel yield was positively correlated with the α-diversity of fungal communities. The higher diversity of the successfully fructified soils was contributed by community evenness rather than taxonomic richness. In contrast, most nonfructification soils were dominated by a high proportion of a certain fungal genus, typically Acremonium or Mortierella, in the fungal communities. Our findings demonstrate the importance of microbial ecology to the large-scale agroindustry of soil-cultivated mushrooms. IMPORTANCE Saprotrophic mushrooms cultivated in soils are subject to complex influences from soil microbial communities. Research on growing edible mushrooms has revealed connections between fungi and a few species of growth-promoting bacteria colonizing the mycosphere. The composition and diversity of the whole microbial community may also have an influence on the growth and production of soil-saprotrophic mushrooms. Morel mushrooms (Morchella spp.) are economically and culturally important and are widely prized throughout the world. This study used the large-scale farming of morels as an example of an agroecosystem for soil-saprotrophic mushroom cultivation. It demonstrated a typical pattern of how the microbial ecology in soil agroecosystems, especially the α-diversity level and community evenness among soil fungal taxa, could affect the production of high-value cash crops and the income of farmers.

Dynamics of fungal and bacterial microbiome associated with green-mould contaminated sawdust substrate of Pleurotus pulmonarius (grey oyster mushroom)

AIMS

Green-mould contamination is identified as one of the challenges faced by mushroom cultivation industry globally which believed to be caused by Trichoderma spp.

METHODS AND RESULTS

To explore the dynamics of microbial population in mushroom substrate during commercial mushroom cultivation and how microbiota might play a role in green-mould contamination, we applied both culturing and targeted metagenomics approaches to identify microbiota in noncomposted sawdust substrates at different cultivation stages. The microbiological analysis showed that the green-mould contaminated substrates harboured higher total mesophilic bacteria count. The green-moulds isolated from the contaminated mushroom substrates were identified as Trichoderma pleurotum (n = 15; 93.8%) and Graphium penicillioides (n = 1; 6.3%). To our surprise, the targeted metagenomic analysis revealed that Graphium comprised 56.3% while Trichoderma consisted of only 36.1% of the total fungi population, suggesting that green-mould contamination might not be caused by Trichoderma alone, but also Graphium that grows very slowly in the laboratory.

CONCLUSION

It is worthwhile to note that G. penicillioides was also isolated in the early stages of mushroom cultivation, but not T. pleurotum. The results indicated that the structure and composition of the bacterial population in the mushroom substrate varied and the bacterial population shifted along the cultivation process.

SIGNIFICANCE AND IMPACT OF STUDY

This study revealed a possibility of G. penicillioides as an overlooked fungi causing green-mould contamination.

Differential bacterial endophytome in Foc-resistant banana cultivar displays enhanced antagonistic activity against Fusarium oxysporum f.sp. cubense (Foc)

Diverse endophytes with multiple functions exist in different banana cultivars. However, the diversity of cultivable bacterial endophytome that contributes to antifungal activity against Fusarium oxysporum f.sp. cubense (Foc) in resistant and susceptible banana cultivars is mostly unknown. In the present study, we isolated bacterial endophytes from resistant Yengambi KM5 (AAA) and susceptible banana cultivar Ney Poovan (AB) to determine the diversity of cultivable bacterial endophytes. Our study revealed the presence of 56 cultivable bacterial endophytes and 6 nectar-associated bacteria in YKM5 and 31 cultivable bacterial endophytes in Ney Poovan. The identified cultivable bacterial genera in YKM5 included Alcaligenes, Arthrobacter, Azotobacter, Acinetobacter, Agrobacterium, Bacillus, Brucella, Brevundimonas, Brachybacterium, Beijerinckia, Klebsiella, Leclercia, Lysinibacillus, Myroides, Ochrobactrum, Pseudomonas, Rhizobium, Stenotrophomonas, Serratia, and Verticiella. In Ney Poovan, the cultivable endophytic bacterial genera present were Agrobacterium, Bacillus, Bradyrhizobium, Enterobacter, Klebsiella, Lysinibacillus, Micrococcus, Ochrobactrum, Pseudomonas, Rhizobium, and Sphingobium. Thus, the composition and diversity of cultivable endophytic bacterial genera were higher in Foc-resistant YKM5. The antifungal efficacy of bacterial endophytes Brachybacterium paraconglomeratum YEBPT2 (65.5%), Brucella melitensis YEBPS3 (63.3%), Bacillus velezensis YEBBR6 (63.3%), and nectar-associated Bacillus albus YEBN2 (61.1%) from YKM5 showed the highest antifungal activity against Foc, compared with the antifungal activity of endophytes from the susceptible cultivar.

Changes in soil bacteria functional ecology associated with Morchella rufobrunnea fruiting in a natural habitat

Morchella rufobrunnea is a saprobic edible mushroom, found in a range of ecological niches, indicating nutritional adjustment to different habitats and possible interaction with soil prokaryotic microbiome (SPM). Using the 16S rRNA gene, we examined the SPM of M. rufobrunnea that appeared in a natural habitat in Northern Israel. Three sample types were included: bare soil without mushroom, soil beneath young mushroom initials and soil beneath the mature fruiting body. Morchella rufobrunnea developmental stage was significantly associated with changes in bacterial populations (PERMANOVA, p < 0.0005). Indicator analysis with point-biserial correlation coefficient found 180 operational taxonomic units (OTU) uniquely associated with distinct stages of development. The Functional Annotation of Prokaryotic Taxonomy (FAPROTAX) database helped to infer ecological roles for indicator OTU. The functional ecological progression begins with establishment of a photoautotrophic N-fixing bacterial mat on bare soil. Pioneer heterotrophs including oligotrophs, acidifying nutrient mobilizers and nitrifiers are congruent with appearance of young M. rufobrunnea initials. Under the mature fruiting body, the population changed to saprobes, organic-N degraders, denitrifiers, insect endosymbionts and fungal antagonists. Based on this work, M. rufobrunnea may be able to influence SPM and change the soil nutritional profile.

De novo genome sequencing of mycoparasite Mycogone perniciosa strain MgR1 sheds new light on its biological complexity

Mycogone perniciosa is a mycoparasite causing Wet Bubble Diseases (WBD) of Agaricus bisporus. In the present study, the whole genome of M. perniciosa strain MgR1 was sequenced using Illumina NextSeq500 platform. This sequencing generated 8.03 Gb of high-quality data and a draft genome of 39 Mb was obtained through a de novo assembly of the high-quality reads. The draft genome resulted into prediction of 9276 genes from the 1597 scaffolds. NCBI-based homology analysis revealed the identification of 8660 genes. Notably, non-redundant protein database analysis of the M. perniciosa strain MgR1 revealed its close relation with the Trichoderma arundinaceum. Moreover, ITS-based phylogenetic analysis showed the highest similarity of M. perniciosa strain MgR1 with Hypomyces perniciosus strain CBS 322.22 and Mycogone perniciosa strain PPRI 5784. Annotation of the 3917 genes of M. perniciosa strain MgR1 grouped in three major categories viz. biological process (2583 genes), cellular component (2013 genes), and molecular function (2919 genes). UniGene analysis identified 2967 unique genes in M. perniciosa strain MgR1. In addition, prediction of the secretory and pathogenicity-related genes based on the fungal database indicates that 1512 genes (16% of predicted genes) encode for secretory proteins. Moreover, out of 9276 genes, 1296 genes were identified as pathogenesis-related proteins matching with 51 fungal and bacterial genera. Overall, the key pathogenic genes such as lysine M protein domain genes, G protein, hydrophobins, and cytochrome P450 were also observed. The draft genome of MgR1 provides an understanding of pathogenesis of WBD in A. bisporus and could be utilized to develop novel management strategies.

Fungal Based Biopolymer Composites for Construction Materials

Environmental contamination, extensive exploitation of fuel sources and accessibility of natural renewable resources represent the premises for the development of composite biomaterials. These materials have controlled properties, being obtained through processes operated in mild conditions with low costs, and contributing to the valorization of byproducts from agriculture and industry fields. A novel board composite including lignocelullosic substrate as wheat straws, fungal mycelium and polypropylene embedded with bacterial spores was developed and investigated in the present study. The bacterial spores embedded in polymer were found to be viable even after heat exposure, helping to increase the compatibility of polymer with hydrophilic microorganisms. Fungal based biopolymer composite was obtained after cultivation of Ganoderma lucidum macromycetes on a mixture including wheat straws and polypropylene embedded with spores from Bacillus amyloliquefaciens. Scanning electron microscopy (SEM) and light microscopy images showed the fungal mycelium covering the substrates with a dense network of filaments. The resulted biomaterial is safe, inert, renewable, natural, biodegradable and it can be molded in the desired shape. The fungal biocomposite presented similar compressive strength and improved thermal insulation capacity compared to polystyrene with high potential to be used as thermal insulation material for applications in construction sector.

Build Your Own Mushroom Soil: Microbiota Succession and Nutritional Accumulation in Semi-Synthetic Substratum Drive the Fructification of a Soil-Saprotrophic Morel

Black morel, a widely prized culinary delicacy, was once an uncultivable soil-saprotrophic ascomycete mushroom that can now be cultivated routinely in farmland soils. It acquires carbon nutrients from an aboveground nutritional supplementation, while it remains unknown how the morel mycelium together with associated microbiota in the substratum metabolizes and accumulates specific nutrients to support the fructification. In this study, a semi-synthetic substratum of quartz particles mixed with compost was used as a replacement and mimic of the soil. Two types of composts (C1 and C2) were used, respectively, plus a bare-quartz substratum (NC) as a blank reference. Microbiota succession, substrate transformation as well as the activity level of key enzymes were compared between the three types of substrata that produced quite divergent yields of morel fruiting bodies. The C1 substratum, with the highest yield, possessed higher abundances of Actinobacteria and Chloroflexi. In comparison with C2 and NC, the microbiota in C1 could limit over-expansion of microorganisms harboring N-fixing genes, such as Cyanobacteria, during the fructification period. Driven by the microbiota, the C1 substratum had advantages in accumulating lipids to supply morel fructification and maintaining appropriate forms of nitrogenous substances. Our findings contribute to an increasingly detailed portrait of microbial ecological mechanisms triggering morel fructification.

Occurrence, behavior, and human exposure and health risks of potentially toxic elements in edible mushrooms with focus on Africa

Understanding the occurrence, behavior, and fate of potentially toxic elements (PTEs) in the substrate-mushroom-human nexus is critical for assessing and mitigating their human health risks. In this review, we (1) summarized the nature, sources, and biogeochemical behavior of PTEs in the substrate-mushroom systems; (2) discussed the occurrence, exposure, and human health risks of PTEs in mushrooms with emphasis on African geological hotspots such as metalliferous and highly mineralized substrates; (3) developed a 10-step conceptual framework for identifying, assessing, and mitigating the human health risks of PTEs in mushrooms, and highlight future directions. High human exposure risks potentially exist in Africa due to the following: (1) widespread consumption of mushrooms from various metalliferrous and highly mineralized substrates such as serpentines and mine waste dumps, (2) inadequate and poorly enforced environmental health and food safety regulations and policies, (3) limited environmental and human health monitoring data, and (4) potential synergistic interactions among PTEs in mushrooms and human health stressors such as a high burden of human diseases and infections. Although the human health effects of individual PTEs are well known, scientific evidence linking human health risk to PTEs in mushrooms remains weak. A framework for risk assessment and mitigation, and future research directions are recommended.

Microbiological Safety and Sensory Quality of Cultivated Mushrooms (Pleurotus eryngii, Pleurotus ostreatus and Lentinula edodes) at Retail Level and Post-Retail Storage

In this study, the microbiological and sensory quality of cultivated mushrooms (Pleurotus ostreatus and eryngii and Lentinula edodes) available at the Austrian retail level were determined. Aerobic mesophilic bacteria (AMC), Enterobacteriaceae (EB), Pseudomonadaceae (PS), lactic acid bacteria (LAB), yeast, moulds and presumptive Bacillus cereus were enumerated at the day of purchase and after storage at 4 °C for 7 or 12 days. Additionally, the presence of Salmonella spp. and Listeria monocytogenes was investigated. Isolates of presumptive spoilage bacteria were confirmed by partial 16S rRNA sequencing. At the day of purchase, 71.2% of the samples were of high microbiological quality and grouped into the low contamination category (AMC < 5.0 log cfu/g), while the sensory quality of 67.1% was categorized as “very good or good”. After storage, the number of samples with high microbial quality was 46.6%, and only 37.0% of the samples scored as “very good or good”. The most abundant species across all mushroom samples were the Pseudomonas fluorescens species complex (58.4%) and the potential mushroom pathogen Ewingella americana (28.3%). All mushroom samples tested negative for Salmonella spp., L. monocytogenes and Bacillus cereus. The microbiological and sensory quality of the analysed mushrooms at the day of purchase and after storage was considered to be good overall. Longer transport distances were found to have a significant influence on the microbiological and sensory quality.

Control of Fungal Diseases in Mushroom Crops while Dealing with Fungicide Resistance: A Review

Mycoparasites cause heavy losses in commercial mushroom farms worldwide. The negative impact of fungal diseases such as dry bubble (Lecanicillium fungicola), cobweb (Cladobotryum spp.), wet bubble (Mycogone perniciosa), and green mold (Trichoderma spp.) constrains yield and harvest quality while reducing the cropping surface or damaging basidiomes. Currently, in order to fight fungal diseases, preventive measurements consist of applying intensive cleaning during cropping and by the end of the crop cycle, together with the application of selective active substances with proved fungicidal action. Notwithstanding the foregoing, the redundant application of the same fungicides has been conducted to the occurrence of resistant strains, hence, reviewing reported evidence of resistance occurrence and introducing unconventional treatments is worthy to pave the way towards the design of integrated disease management (IDM) programs. This work reviews aspects concerning chemical control, reduced sensitivity to fungicides, and additional control methods, including genomic resources for data mining, to cope with mycoparasites in the mushroom industry.

Chemical signals driving bacterial-fungal interactions

Microorganisms reside in diverse environmental communities where interactions become indispensable due to close physical associations. These interactions are driven by chemical communication among different microbial kingdoms, particularly between fungi and bacteria. Knowledge about these communication signals provides useful information about the nature of microbial interactions and allows predictions of community development in diverse environments. Here, we provide an update on the role of small signalling molecules in fungal-bacterial interactions with focus on agricultural and medicinal environments. This review highlights the range of - and response to - diverse biochemicals produced by both kingdoms with view to harnessing their properties towards drug discovery applications.

Toxicological risks and nutritional value of wild edible mushroom species -a half-century monitoring study

The content of major- and trace elements in wild-growing mushrooms has been subject to numerous studies, but the data on long-term trends in this regard are scarce. The aim of research was to determine the content of 34 elements in four edible mushroom species Boletus edulis, Imleria badia, Leccinum scabrum and Macrolepiota procera, and associated soil collected from Polish forests between 1974 and 2019. As initially hypothesized, the element concentration in the studied soil revealed an increasing trend and was positively correlated with their levels found in fruit bodies. Bioconcentrafion Factor values exceeding 1 were documented for all mushroom species for K, P, Ag, Cd, Cu, Hg, and Zn. When compared to the Adequate Intakes, all the mushroom species were found to be a good dietary source of K, P, and Zn (range of 6260-8690, 6260-8690 and 97-135 mg kg^-1 dry weight (dw), respectively), and B. edulis and I. badia a moderate source of Fe (mean 71.5 and 76.5 mg kg^-1 dw, respectively), B. edulis of Mn and Mo (mean 20.0 and 0.42 mg kg^-1 dw, respectively), while L. scabrum and M. procera a source of Cu. Consumption of the studied mushrooms would not lead to significant exposure to Al, As, Cr, or Ni. Considering that wild mushrooms will continue to be collected in Poland, one should bear in mind that they are a limited source of minerals in the human diet while their frequent, regular consumption, associated with exposure to selected toxic elements, should not be recommended.

Enhanced growth and yield of oyster mushroom by growth-promoting bacteria Glutamicibacter arilaitensis MRC119

Promotion of mushroom growth by means of biological agents replacing chemicals is an emerging and highly demanded issue in the sector of mushroom cropping. The present study was aimed to search for a novel bacterium potentially able to enhance mushroom growth and yield. A total of 2165 bacterial isolates purified from different samples were scrutinized through various growth-promoting attributes. As a consequence of rigorous screening, 26 isolates found exhibiting positive traits of mushroom growth promotion. Thereafter, in response to the cocultivation (fungus and bacteria), a potent bacterial strain was isolated capable to improve significantly the mycelial growth. In cocultivation the highest radial and linear growth rate was 7.6 and 8.1 mm/day on 10th and 11th days, respectively. The fruitbody yields and biological efficiency (BE) of the inoculated sets were 28% and 58% higher than the uninoculated control sets. The bacterium was molecularly identified based on 16S ribosomal RNA sequencing and confirmed as Glutamicibacter arilaitensis MRC119. Therefore, the bioinoculant of the current bacterium can be potentially useful as an ecofriendly substitute stimulating the production of mushroom fruit bodies with improved BE.

Holistic assessment of the microbiome dynamics in the substrates used for commercial champignon (Agaricus bisporus) cultivation

Microorganisms strongly influence and are required to generate the selective substrate that provides nutrients and support for fungal growth, and ultimately to induce mushroom fructification under controlled environmental conditions. In this work, the fungal and bacterial microbiota living in the different substrates employed in a commercial crop (compost phase I, II and III, flush 1 and 2, and casing material on day 1, 6 and 8 after compost casing and during flush 1 and 2) have been characterized along the different stages of cultivation by metataxonomic analysis (16S rRNA and ITS2), analysis of phospholipid fatty acid content (PLFAs) and RT-qPCR. Additionally, laccase activity and the content of lignin and complex carbohydrates in compost and casing have been quantified. The bacterial diversity in compost and casing increased throughout the crop cycle boosted by the connection of both substrates. As reflected by the PLFAs, the total living bacterial biomass appears to be negatively correlated with the mycelium of the crop. Agaricus bisporus was the dominant fungal species in colonized substrates, displacing the pre-eminent Ascomycota, accompanied by a sustained increase in laccase activity, which is considered to be a major product of protein synthesis during the mycelial growth of champignon. From phase II onwards, the metabolic machinery of the fungal crop degrades lignin and carbohydrates in compost, while these components are hardly degraded in casing, which reflects the minor role of the casing for nourishing the crop. The techniques employed in this study provide a holistic and detailed characterization of the changing microbial composition in commercial champignon substrates. The knowledge generated will contribute to improve compost formulations (selection of base materials) and accelerate compost production, for instance, through biotechnological interventions in the form of tailored biostimulants and to design environmentally sustainable bio-based casing materials.