Global diversity and distribution of mushroom-inhabiting bacteria

Spores of arbuscular mycorrhizal fungi host surprisingly diverse communities of endobacteria

Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts, which can house two endobacteria: Ca. Moeniiplasma glomeromycotorum (CaMg) and Ca. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria. We isolated AMF from two environments and conducted detailed analyses of endobacterial communities associated with surface-sterilised AMF spores. Consistent with the previous reports, we found that CaMg were extremely abundant (80%) and CaGg were extremely rare (2%) in both environments. Unexpectedly, we discovered an additional and previously unknown level of bacterial diversity within AMF spores, which extended beyond the known endosymbionts, with bacteria belonging to 10 other phyla detected across our spore data set. Detailed analysis revealed that: CaGg were not limited in distribution to the Gigasporaceae family of AMF, as previously thought; CaMg population structure was driven by AMF host genotype; and a significant inverse correlation existed between the diversity of CaMg and diversity of all other endobacteria. Based on these data, we generate novel testable hypotheses regarding the function of CaMg in AMF biology by proposing that they might act as conditional mutualists of AMF.

Suillus: an emerging model for the study of ectomycorrhizal ecology and evolution

Research on mycorrhizal symbiosis has been slowed by a lack of established study systems. To address this challenge, we have been developing Suillus, a widespread ecologically and economically relevant fungal genus primarily associated with the plant family Pinaceae, into a model system for studying ectomycorrhizal (ECM) associations. Over the last decade, we have compiled extensive genomic resources, culture libraries, a phenotype database, and protocols for manipulating Suillus fungi with and without their tree partners. Our efforts have already resulted in a large number of publicly available genomes, transcriptomes, and respective annotations, as well as advances in our understanding of mycorrhizal partner specificity and host communication, fungal and plant nutrition, environmental adaptation, soil nutrient cycling, interspecific competition, and biological invasions. Here, we highlight the most significant recent findings enabled by Suillus, present a suite of protocols for working with the genus, and discuss how Suillus is emerging as an important model to elucidate the ecology and evolution of ECM interactions.

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.

Prokaryote communities associated with different types of tissue formed and substrates inhabited by Serpula lacrymans

The basidiomycete Serpula lacrymans is responsible for major timber devastation in houses. Basidiomycetes are known to harbour a diverse but poorly understood microbial community of bacteria, archaea, yeasts and filamentous fungi. In this study, we used amplicon-sequencing to analyse the abundance and composition of prokaryotic communities associated with fruiting bodies of S. lacrymans and compared them to communities of surrounding material to access the 'background' community structure. Our findings indicate that bacterial genera cluster depended on sample type and that the main driver for microbial diversity is specimen, followed by sample origin. The most abundant bacterial phylum identified in the fruiting bodies was Pseudomonadota, followed by Actinomycetota and Bacteroidota. The prokaryote community of the mycelium was dominated by Actinomycetota, Halobacterota and Pseudomonadota. Actinomycetota was the most abundant phylum in both environment samples (infested timber and underground scree), followed by Bacillota in wood and Pseudomonadota in underground samples. Nocardioides, Pseudomonas, Pseudonochardia, Streptomyces and Rubrobacter spp. were among others found to comprise the core microbiome of S. lacrymans basidiocarps. This research contributes to the understanding of the holobiont S. lacrymans and gives hints to potential bacterial phyla important for its development and lifestyle.

Positive interactions between mycorrhizal fungi and bacteria are widespread and benefit plant growth

Bacteria, ectomycorrhizal (EcM) fungi, and land plants have been coevolving for nearly 200 million years, and their interactions presumably contribute to the function of terrestrial ecosystems. The direction, stability, and strength of bacteria-EcM fungi interactions across landscapes and across a single plant host, however, remains unclear. Moreover, the genetic mechanisms that govern them have not been addressed. To these ends, we collected soil samples from Bishop pine forests across a climate-latitude gradient spanning coastal California, fractionated the soil samples based on their proximity to EcM-colonized roots, characterized the microbial communities using amplicon sequencing, and generated linear regression models showing the impact that select bacterial taxa have on EcM fungal abundance. In addition, we paired greenhouse experiments with transcriptomic analyses to determine the directionality of these relationships and identify which genes EcM-synergist bacteria express during tripartite symbioses. Our data reveal that ectomycorrhizas (i.e., EcM-colonized roots) enrich conserved bacterial taxa across climatically heterogeneous regions. We also show that phylogenetically diverse EcM synergists are positively associated with plant and fungal growth and have unique gene expression profiles compared with EcM-antagonist bacteria. In sum, we identify common mechanisms that facilitate widespread and diverse multipartite symbioses, which inform our understanding of how plants develop in complex environments.

Fungal Hyphosphere Microbiomes Are Distinct from Surrounding Substrates and Show Consistent Association Patterns

Mat-forming fungi are common in forest and grassland soils across the world, where their activity contributes to important soil ecological processes. These fungi maintain dominance through aggressive and abundant hyphae that modify their internal physical and chemical environments and through these modifications select for what appears to be a suite of mycophilic bacteria. Here, the bacteria associated with the fungal mats of Leucopaxillus gentianeus and Leucopaxillus albissimus from western North America are compared to adjacent nonmat substrates. Within the mats, the bacterial richness and diversity were significantly reduced, and the community composition was significantly different. The bacterial community structure between the two fungal hosts was marginally significant and indicated a shared set of bacterial associates. The genera Burkholderia, Streptomyces, Bacillus, Paenibacillus, and Mycobacterium were significantly abundant within the fungal mats and represent core members of these hypha-rich environments. Comparison with the literature from fungal mat studies worldwide showed that these genera are common and often significantly found within fungal mats, further reinforcing the concept of a mycophilic bacterial guild. These genera are incorporated into a synthesis discussion in the context of our current understanding of the nature of fungal-bacterial interactions and the potential outcomes of these interactions in soil nutrient cycling, plant productivity, and human health. IMPORTANCE Fungi and bacteria are the most abundant and diverse organisms in soils (perhaps more so than any other habitat on earth), and together these microorganisms contribute to broad soil ecosystem processes. There is a suite of bacteria that appears consistently within the physical space called the hyphosphere, the area of influence surrounding fungal hyphae. How these bacteria are selected for, how they are maintained, and what broader ecological functions they perform are subjects of interest in this relatively new field-the cross-kingdom interactions between fungi and bacteria. Understanding their cooccurrence and their interactions can open new realms of understanding in soil ecological processes with global consequences.

Dynamics of soil microbiome throughout the cultivation life cycle of morel (Morchella sextelata)

Although Morchella sextelata (morel) is a well-known, edible, and medicinal fungus widely cultivated in China, the dynamics and roles of its soil microbiome during cultivation are unclear. Using rhizosphere soil samples collected throughout the M. sextelata cultivation life cycle, we conducted a high-throughput metagenomic sequencing analysis, with an emphasis on variations in soil microbial composition, characteristic biomarkers, and ecological functions. We found that microbial relative abundance, alpha diversity, and structure varied significantly among fungal growth stages. A total of 47 stage-associated biomarkers were identified through a linear discriminant analysis of effect size. In addition, horizontal comparison of soil microbiomes exhibiting successful and failed primordium formation further confirmed primordium-associated microbes with possible key roles in primordium formation. A microbial function analysis revealed that nutrient metabolism-related pathways were enriched during mycelium and fruiting body stages, whereas the signal transduction pathway was enriched during the primordium stage. This result indicates that diverse microbes are required at different growth stages of M. sextelata. Our research has revealed the dynamic scenario of the soil microbiome throughout the cultivation life cycle of M. sextelata. The high-resolution microbial profiles uncovered in the present study provide novel insights that should contribute to the improvement of morel cultivation using microbial inoculants.

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.

Community composition and trophic mode diversity of fungi associated with fruiting body of medicinal Sanghuangporus vaninii

Background:

The microbial symbionts of macrofungal fruiting body have been shown to play momentous roles in host growth, development, and secondary metabolism. Nevertheless, there is no report on the fungal diversity of Sanghuangporus, a medicinal and edible homologous macrofungus as “forest gold”, which has good effects on antioxidation, boosting immunity and curing stomachache. Here, the diversity and functional group of fungi associated with the fruiting body of the most widely applied S. vaninii were characterized by high-throughput sequencing and FUNGuild tool for the first time.

Results:

Total 11 phyla, 34 classes, 84 orders, 186 families, and 328 genera were identified in the fruiting body, and our results revealed that the fungal community was dominated by the host fungal taxonomy with absolute superiority (more than 70%), namely, Basidiomycota, Agaricomycetes, Hymenochaetales, Hymenochaetaceae, and genus of Phellinus corrected to Sanghuangporus. Simultaneously, the reads allocated into non-host fungal operational taxonomic units were largely dominated by Ascomycota, Sordariomycetes, Sordariales, Mortierellaceae, and Mortierella. Furthermore, the endophytic fungi were assigned into three trophic modes of “saprotroph” (53.2%), “symbiotroph” (32.2%), and “pathotroph” (14.1%), in which the category of “plant pathogen” was highest enriched with relative abundance of 91.8%, indicating that the endophytic fungi may have the potential to adjust the growth and metabolism of host S. vaninii.

Conclusion:

Altogether, this report firstly provided new findings that can be inspiring for further in-depth studies to exploit bioactive microbial resources for increased production of Sanghuangporus via coculture, as well as to explore the relationship between macrofungi and their associated endophytes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02663-2.

Identification and profiling of the community structure and potential function of bacteria from the fruiting bodies of Sanghuangporus vaninii

Sanghuangporus sp., a medicinal and edible homologous macrofungus known as 'forest gold', which has good effects on antitumor, hypolipidemia and the treatment of gynecological diseases. However, the natural resources of fruiting body are on the verge of depletion due to its long growth cycle and over exploitation. The growth and metabolism of macrofungi are known to depend on the diverse bacterial community. Here, we characterized the diversity and potential function of bacteria inhabiting in the fruiting body of the most widely applied S. vaninii using a combination method of high-throughput sequencing with pure culturing for the first time, and tested the biological activities of bacterial isolates, of which Illumina NovaSeq provided a more comprehensive results on the bacterial community structure. Total 33 phyla, 82 classes, 195 orders, 355 families, 601 genera and 679 species were identified in the fruiting body, and our results revealed that the community was predominated by the common Proteobacteria, Gammaproteobacteria, Burkholderiales, Methylophilaceae (partly consistent with pure-culturing findings), and was dominated by the genera of distinctive Methylotenera and Methylomonas (yet-uncultured taxa). Simultaneously, the functional analysis showed that companion bacteria were involved in the pathways of carbohydrate transport and metabolism, metabolism of terpenoids and polyketides, cell wall/membrane/envelope biogenesis, etc. Hence, it was inferred that bacteria associated with fruiting body may have the potential to adjust the growth, development and active metabolite production of host S. vaninii combined with the tested results of indole-3-acetic acid and total antioxidant capacity. Altogether, this report first provided new findings which can be inspiring for further in-depth studies to exploit bioactive microbial resources for increased production of Sanghuangporus, as well as to explore the relationship between medicinal macrofungi and their associated endophytes.