Mycobiota of Eucommia ulmoides bark: Diversity, rare biosphere and core taxa

Fungal communities are more sensitive to mildew than bacterial communities during tobacco storage processes

Mildew poses a significant threat to tobacco production; however, there is limited information on the structure of the abundant and rare microbial subcommunities in moldy tobacco leaves. In this study, we employed high-throughput sequencing technology to discern the disparities in the composition, diversity, and co-occurrence patterns of abundant and rare fungal and bacterial subcommunities between moldy and normal tobacco leaves collected from Guizhou, Shanghai, and Jilin provinces, China. Furthermore, we explored the correlation between microorganisms and metabolites by integrating the metabolic profiles of moldy and normal tobacco leaves. The results showed that the fungi are more sensitive to mildew than bacteria, and that the fungal abundant taxa exhibit greater resistance and environmental adaptability than the rare taxa. The loss of rare taxa results in irreversible changes in the diversity, richness, and composition of the fungal community. Moreover, rare fungal taxa and abundant bacterial taxa played crucial roles in maintaining the stability and functionality of the tobacco microecosystem. In moldy tobacco, however, the disappearance of rare taxa as key nodes resulted in reduced connectivity and stability within the fungal network. In addition, metabolomic analysis showed that the contents of indoles, pyridines, polyketones, phenols, and peptides were significantly enriched in the moldy tobacco leaves, while the contents of amino acids, carbohydrates, lipids, and other compounds were significantly reduced in these leaves. Most metabolites showed negative correlations with Dothideomycetes, Alphaproteobacteria, and Gammaproteobacteria, but showed positive correlations with Eurotiales and Bacilli. This study has demonstrated that abundant fungal taxa are the predominant biological agents responsible for tobacco mildew, while bacteria may indirectly contribute to this process through the production and degradation of metabolites. KEY POINTS: • Fungi exhibited greater sensitivity to mildew of tobacco leaf compared to bacteria • Rare fungal taxa underwent significant damage during the mildew process • Mildew may damage the defense system of the tobacco leaf microecosystem.

Dynamic changes of endophytic bacteria in the bark and leaves of medicinal plant Eucommia ulmoides in different seasons

The bark and leaves of the Eucommia ulmoides Oliv. (E. ulmoides) have good medicinal value. Studies show endophytes play important roles in host medicinal plant secondary metabolite synthesis, with season being a key influencing factor. Therefore, we used 16 S rRNA to detect endophytic bacteria (EB) in E. ulmoides bark and leaves collected in winter, spring, summer, and autumn, and analyzed the contents of major active components respectively. The results showed that the species diversity and richness of EB of the E. ulmoides bark were higher than those of leaves in all seasons except fall. Among them, the higher species diversity and richness were found in the E. ulmoides bark in winter and spring. EB community structure differed significantly between medicinal tissues and seasons. Concurrently, the bark and leaves of E. ulmoides showed abundant characteristic EB across seasons. For active components, geniposidic acid showed a significant positive correlation with EB diversity and richness, while the opposite was true for aucubin. Additionally, some dominant EB exhibited close correlations with the accumulation of active components. Delftia, enriched in autumn, correlated significantly positively with aucubin. Notably, the impact of the same EB genera on active components differed across medicinal tissues. For example, Sphingomonas, enriched in summer, correlated significantly positively with pinoresinol diglucoside (PDG) in the bark, but with aucubin in the leaves. In summary, EB of E. ulmoides was demonstrated high seasonal dynamics and tissue specificity, with seasonal characteristic EB like Delftia and Sphingomonas correlating with the accumulation of active components in medicinal tissues.

Interactions of rhizosphere microbiota-environmental factors-pharmacological active ingredients of Eucommia ulmoides

MAIN CONCLUSION

The composition, diversity and co-occurrence patterns of the rhizosphere microbiota of E. ulmoides were significantly influenced by environmental factors, and which were potentially associated with the contents of pharmacological active ingredients. Eucommia ulmoides is an important perennial medicinal plant. However, little is known about the interactions among microbiota, environmental factors (EFs), and pharmacological active ingredients (PAIs) of E. ulmoides. Herein, we analyzed the interactions among rhizosphere microbiota-EFs-PAIs of E. ulmoides by amplicon sequencing and multi-analytical approach. Our results revealed variations in the dominant genera, diversity, and co-occurrence networks of the rhizosphere microbiota of E. ulmoides across different geographical locations. Notably, available nitrogen exerted the strongest influence on fungal dominant genera, while pH significantly impacted bacterial dominant genera. Rainfall and relative humidity exhibited pronounced effects on the α-diversity of fungal groups, whereas available phosphorus influenced the number of nodes in fungal co-occurrence networks. Altitude and total phosphorus had substantial effects on the average degree and nodes in bacterial co-occurrence networks. Furthermore, the dominant genera, diversity and co-occurrence network of rhizosphere microbiota of E. ulmoides were significantly correlated with the content of PAIs. Specifically, the abundance of rhizosphere dominant genera Filobasidium, Hannaella and Nitrospira were significantly correlated with the content of pinoresinol diglucoside (PD). Similarly, the abundance of Vishniacozyma and Bradyrhizobium correlated significantly with the content of geniposidic acid (GC), while the abundance of Gemmatimonas was significantly correlated with the content of aucubin. Moreover, the bacterial co-occurrence network parameters including average degree, density, and edge, were significantly correlated with the content of GC and aucubin. The α-diversity index Chao1 also displayed a significant correlation with the content of PD. These findings contribute to a more comprehensive understanding of the interactions between medicinal plants and microbes.

Assembly Processes and Biogeographical Characteristics of Soil Bacterial Sub-communities of Different Habitats in Urban Green Spaces

The process of urbanization is one of the most important human-driven activities that reshape the natural distribution of soil microorganisms. However, it is still unclear about the effects of urbanization on the different taxonomic soil bacterial community dynamics. In this study, we collected soil samples from highly urbanized the regions of Yangtze River Delta, Beijing-Tianjin-Hebei in China, to explore the bio-geographic patterns, assembly processes, and symbiotic patterns of abundant, moderate, and rare bacterial communities. We found that the number of moderate and rare taxa species were lower than that of abundant taxa, but their α-diversity index was higher than abundant taxa. Proteobacteria, Acidobacteria, Actinobacteria, Bacterioidetes, and Chloroflexi were the dominant phylum across all three sub-communities. And the β-diversity value of rare taxa was significantly higher than those of moderate and abundant taxa. Abundant, moderate, and rare sub-communities showed a weak distance-decay relationship, and the moderate taxa had the highest turnover rate of microbial geography in the context of urbanization. Diffusion limitation was the dominant process of soil bacterial community assembly. The co-occurrence networks of abundant, moderate, and rare taxa were dominated by positive correlations. The network of moderate taxa had the highest modularity, followed by abundant taxa. The main functions of the abundant, moderate, and rare taxa were related to Chemoheterotrophy and N transformations. Redundancy analysis showed that the dispersal limitation, climate, and soil properties were the main factors dominating bio-geographic differences in soil bacterial community diversity. We conclude that human-dominated urbanization processes have generated more uncertain survival pressures on soil bacteria, which resulted in a stronger linkage but weak bio-geographic variation for soil bacteria. In the future urban planning process, we suggest that such maintenance of native vegetation and soil types should be considered to maintain the long-term stability of local microbial ecosystem functions.

New perspective: Symbiotic pattern and assembly mechanism of Cantharellus cibarius-associated bacteria

Cantharellus cibarius, an ectomycorrhizal fungus belonging to the Basidiomycetes, has significant medicinal and edible value, economic importance, and ecological benefits. However, C. cibarius remains incapable of artificial cultivation, which is thought to be due to the presence of bacteria. Therefore, much research has focused on the relationship between C. cibarius and bacteria, but rare bacteria are frequently overlooked, and symbiotic pattern and assembly mechanism of the bacterial community associated with C. cibarius remain unknown. In this study, the assembly mechanism and driving factors of both abundant and rare bacterial communities of C. cibarius were revealed by the null model. The symbiotic pattern of the bacterial community was examined using a co-occurrence network. Metabolic functions and phenotypes of the abundant and rare bacteria were compared using METAGENassist2, and the impacts of abiotic variables on the diversity of abundant and rare bacteria were examined using partial least squares path modeling. In the fruiting body and mycosphere of C. cibarius, there was a higher proportion of specialist bacteria compared with generalist bacteria. Dispersal limitation dominated the assembly of abundant and rare bacterial communities in the fruiting body and mycosphere. However, pH, 1-octen-3-ol, and total phosphorus of the fruiting body were the main driving factors of bacterial community assembly in the fruiting body, while available nitrogen and total phosphorus of the soil affected the assembly process of the bacterial community in the mycosphere. Furthermore, bacterial co-occurrence patterns in the mycosphere may be more complex compared with those in the fruiting body. Unlike the specific potential functions of abundant bacteria, rare bacteria may provide supplementary or unique metabolic pathways (such as sulfite oxidizer and sulfur reducer) to enhance the ecological function of C. cibarius. Notably, while volatile organic compounds can reduce mycosphere bacterial diversity, they can increase fruiting body bacterial diversity. Findings from this study further, our understanding of C. cibarius-associated microbial ecology.

Assembly, Core Microbiota, and Function of the Rhizosphere Soil and Bark Microbiota in Eucommia ulmoides

Medicinal plants are inhabited by diverse microbes in every compartment, and which play an essential role in host growth and development, nutrient absorption, synthesis of secondary metabolites, and resistance to biological and abiotic stress. However, the ecological processes that manage microbiota assembly and the phenotypic and metabolic characteristics of the core microbiota of Eucommia ulmoides remain poorly explored. Here, we systematically evaluated the effects of genotypes, compartment niches, and environmental conditions (climate, soil nutrition, and secondary metabolites) on the assembly of rhizosphere soil and bark associated bacterial communities. In addition, phenotypic and metabolic characteristics of E. ulmoides core microbiota, and their relationship with dominant taxa, rare taxa, and pharmacologically active compounds were deciphered. Results suggested that microbiota assembly along the two compartments were predominantly shaped by the environment (especially pH, relative humidity, and geniposide acid) and not by host genotype or compartment niche. There were 690 shared genera in the rhizosphere soil and bark, and the bark microbiota was mainly derived from rhizosphere soil. Core microbiota of E. ulmoides was a highly interactive “hub” microbes connecting dominant and rare taxa, and its phenotypic characteristics had a selective effect on compartment niches. Metabolic functions of the core microbiota included ammonia oxidation, nitrogen fixation, and polyhydroxybutyrate storage, which are closely related to plant growth or metabolism. Moreover, some core taxa were also significantly correlated with three active compounds. These findings provide an important scientific basis for sustainable agricultural management based on the precise regulation of the rhizosphere soil and bark microbiota of E. ulmoides.