Community-level signatures of ecological succession in natural bacterial communities

Addressing challenges and advancing solutions: Enhancing semi-coking wastewater treatment for a sustainable prospect

During the semi-coke process, the semi-coking wastewater (SCWW) produced contains high concentrations of organic pollutants. This wastewater has the characteristics of abundant coal tar, high ammonia nitrogen content, high phenol concentration, high chemical oxygen demand (COD), and a low B/C ratio. These features make its treatment extremely difficult and bring significant environmental risks. Given that such wastewater is difficult to meet discharge standards, researchers have been actively exploring and applying various physical, chemical and biological treatment technologies, thus forming multiple wastewater treatment processes. This paper systematically and comprehensively studies the current research status and practical application scenarios of SCWW treatment technologies, and summarizes their application effects in practice. In response to the problems and challenges in wastewater treatment, this paper deeply analyzes and proposes feasible improvement paths and future development directions. At the same time, it also comprehensively reviews the current status of resource recovery. Research on the physical-chemical pretreatment stage, biochemical treatment, advanced treatment, and the sustainability characteristics of various treatment technologies for SCWW is conducted. The aim is to provide valuable reference insights for researchers and practitioners in related fields, thereby promoting technological innovation and sustainable development in this field.

In-situ remediation of water and sediment in aquaculture system using novel ecological floating bed coupled with microbial electrochemical system

It is essential to remediate the polluted aquaculture water and sediment, which destroys aquatic ecosystem. In this study, a novel ecological floating bed coupled with close-circuit microbial electrochemical system was designed for aquaculture system in-situ remediation. The average concentration of COD (13.4 mg/L), TN (3.8 mg/L) and TP (0.4 mg/L) in effluent met the Class II (SC/T 9101-2007). The TP and SS were migrated into sediment driven by the self-generated electric field. According to the analysis of microbial community, electroactive bacteria such as norank_f__Anaerolineaceae, Pseudomonas, and Paraclostridium at the anode oxidized organics. Nitrogen converting bacteria enrich at the biocathode and floating bed, including Defluviimonas, Nitrospira and Bacillus, promoted the removal of nitrogen. Simultaneous nitrification and autotrophic denitrification were realized at the biocathode. The electrons generated from the anode were compensated to the cathode, forming the electron sharing network. The study presents a rewarding ecotechnology for in-situ remediation of aquaculture system.

Increased temperature enhances microbial-mediated lignin decomposition in river sediment

BACKGROUND

Lignin, as the most abundant recalcitrant organic carbon in terrestrial ecosystems, plays a crucial role in the Earth's carbon cycle. After lignin entering aquatic environments, portion of it tends to accumulate in sediments, forming a stable carbon relatively reservoir. However, the increasing temperature caused by human activities may impact microbial-mediated lignin decomposition, thereby affecting sedimentary carbon reservoirs. Therefore, revealing how temperature affects microbial-mediated lignin decomposition in river sediment, a topic that remains elusive, is essential for comprehending the feedbacks between river carbon reservoirs and climate. To address this, we conducted stable isotope probing of river surface sediment using 13C-lignin and 13C-vanillin, and utilized a series of techniques, including CO2 production analysis, 16S rRNA gene amplicon sequencing, metagenomics, and metatranscriptomics, to identify the lignin-decomposing microbes and the effects of temperature on microbial-mediated lignin decomposition.

RESULTS

We found that elevated temperatures not only increased the total sediment respiration (total CO2) and the CO2 emissions from lignin/vanillin decomposition, but also enhanced priming effects. The 13C-labled taxa, including Burkholderiales, Sphingomonadales, and Pseudomonadales, were identified as the main potential lignin/vanillin decomposers, and their abundances and activity significantly increased as temperature increased. Furthermore, we observed that increasing temperature significantly increased the activity of lignin decomposing pathways, including β-aryl ether fragments and 4,5-PDOG pathway. Additionally, as temperature increases, the transcriptional abundances of other carbon cycling related genes, such as pulA (starch decomposition) and xyla (hemicellulose decomposition), also exhibited increasing trends. Overall, our study elucidated the potential lignin-decomposing microbes and pathways in river sediment and their responses to temperature increasing.

CONCLUSIONS

Our study demonstrated that the temperature increasing can increase the rate of lignin/vanillin decomposition via affecting the activity of lignin-decomposing microbes. This finding indicates that the ongoing intensification of global warming may enhance the decomposition of recalcitrant organic carbon in river sediment, thereby impacting global carbon cycling. Video Abstract.

Replicating community dynamics reveals how initial composition shapes the functional outcomes of bacterial communities

Bacterial communities play key roles in global biogeochemical cycles, industry, agriculture, human health, and animal husbandry. There is therefore great interest in understanding bacterial community dynamics so that they can be controlled and engineered to optimise ecosystem services. We assess the reproducibility and predictability of bacterial community dynamics by creating a frozen archive of hundreds of naturally-occurring bacterial communities that we repeatedly revive and track in a standardised, complex resource environment. Replicate communities follow reproducible trajectories and the community dynamics closely map to ecosystem functioning. However, even under standardised conditions, the communities exhibit tipping-points, where small differences in initial community composition create divergent compositional and functional outcomes. The predictability of community trajectories therefore requires detailed knowledge of rugged compositional landscapes where ecosystem properties are not the inevitable result of prevailing environmental conditions but can be tilted toward different outcomes depending on the initial community composition. Our results shed light on the relationship between composition and function, opening new avenues to understand the feasibility and limitations of function prediction in complex microbial communities.

The core microbiomes and associated metabolic potential of water kefir as revealed by pan multi-omics

Water kefir (WK) is an artisanal fermented beverage made from sugary water, optional fruits and WK grains. WK grains can be reused to start new fermentations. Here we investigate the microbial composition and function of 69 WK grains and their ferments by shotgun metagenomics. A subset of samples was subjected to metabolomic, including volatilomic, analysis. The impact of different fermentation practices on microbial composition and fermentation characteristics was analysed and it was noted that, for example, the common practice of drying water kefir grains significantly reduces microbial diversity and negatively impacts subsequent grain growth. Metagenomic analysis allowed the detection of 96 species within WK, the definition of core genera and the detection of different community states after 48 h of fermentation. A total of 485 bacterial metagenome assembled genomes were obtained and 18 putatively novel species were predicted. Metabolite and volatile analysis show associations between key species with flavour compounds. We show the complex microbial composition of WK and links between fermentation practices, microbes and the fermented product. The results can be used as a foundation for the selection of species for large scale WK production with desired flavour profiles and to guide the regulatory framework for commercial WK production.

A Microbial Phenomics Approach to Determine Metabolic Signatures to Enhance Seabream Sparus aurata Traceability, Differentiating between Wild-Caught and Farmed

BACKGROUND

The need for efficient and simplified techniques for seafood traceability is growing. This study proposes the Biolog EcoPlate assay as an innovative method for assessing wild and farmed Sparus aurata traceability, offering advantages over other molecular techniques in terms of technical simplicity.

METHODS

The Biolog EcoPlate assay, known for its high-throughput capabilities in microbial ecology, was utilized to evaluate the functional diversity of microbial communities from various organs of S. aurata (seabream) from the Mediterranean area. Samples were taken from the anterior and posterior gut, cloaca swabs and gills to distinguish between farmed and wild-caught individuals. The analysis focused on color development in OmniLog Units for specific carbon sources at 48 h.

RESULTS

Gills provided the most accurate clusterization of sample origin. The assay monitored the development of color for carbon sources such as α-cyclodextrin, D-cellobiose, glycogen, α-D-lactose, L-threonine and L-phenylalanine. A mock experiment using principal component analysis (PCA) successfully identified the origin of a blind sample. Shannon and Simpson indexes were used to statistically assess the diversity, reflecting the clusterization of different organ samples; Conclusions: The Biolog EcoPlate assay proves to be a quick, cost-effective method for discriminate S. aurata traceability (wild vs. farmed), demonstrating reliable reproducibility and effective differentiation between farmed and wild-caught seabream.

Cross-biome microbial networks reveal functional redundancy and suggest genome reduction through functional complementarity

The structure of microbial communities arises from a multitude of factors, including the interactions of microorganisms with each other and with the environment. In this work, we sought to disentangle those drivers by performing a cross-study, cross-biome meta-analysis of microbial occurrence data in more than 5000 samples, applying a novel network clustering algorithm aimed to capture conditional taxa co-occurrences. We then examined the phylogenetic and functional composition of the resulting clusters, and searched for global patterns of assembly both at the community level and in the presence/absence of individual metabolic pathways.Our analysis highlighted the prevalence of functional redundancy in microbial communities, particularly between taxa that co-occur in more than one environment, pointing to a relationship between functional redundancy and environmental adaptation. In spite of this, certain pathways were observed in fewer taxa than expected by chance, suggesting the presence of auxotrophy, and presumably cooperation among community members. This hypothetical cooperation may play a role in genome reduction, since we observed a negative relationship between the size of bacterial genomes and the size of the community they belong to.Overall, our results suggest the microbial community assembly is driven by universal principles that operate consistently across different biomes and taxonomic groups.

Low-level resource partitioning supports coexistence among functionally redundant bacteria during successional dynamics

Members of microbial communities can substantially overlap in substrate use. However, what enables functionally redundant microorganisms to coassemble or even stably coexist remains poorly understood. Here, we show that during unstable successional dynamics on complex, natural organic matter, functionally redundant bacteria can coexist by partitioning low-concentration substrates even though they compete for one simple, dominant substrate. We allowed ocean microbial communities to self-assemble on leachates of the brown seaweed Fucus vesiculosus and then analyzed the competition among 10 taxonomically diverse isolates representing two distinct stages of the succession. All, but two isolates, exhibited an average of 90% ± 6% pairwise overlap in resource use, and functional redundancy of isolates from the same assembly stage was higher than that from between assembly stages, leading us to construct a simpler four-isolate community with two isolates from each of the early and late stages. We found that, although the short-term dynamics of the four-isolate communities in F. vesiculosus leachate was dependent on initial isolate ratios, in the long term, the four isolates stably coexist in F. vesiculosus leachate, albeit with some strains at low abundance. We therefore explored the potential for nonredundant substrate use by genomic content analysis and RNA expression patterns. This analysis revealed that the four isolates mainly differed in peripheral metabolic pathways, such as the ability to degrade pyrimidine, leucine, and tyrosine, as well as aromatic substrates. These results highlight the importance of fine-scale differences in metabolic strategies for supporting the frequently observed coexistence of large numbers of rare organisms in natural microbiomes.

r/K selection of GC content in prokaryotes

The guanine/cytosine (GC) content of prokaryotic genomes is species-specific, taking values from 16% to 77%. This diversity of selection for GC content remains contentious. We analyse the correlations between GC content and a range of phenotypic and genotypic data in thousands of prokaryotes. GC content integrates well with these traits into r/K selection theory when phenotypic plasticity is considered. High GC-content prokaryotes are r-strategists with cheaper descendants thanks to a lower average amino acid metabolic cost, colonize unstable environments thanks to flagella and a bacillus form and are generalists in terms of resource opportunism and their defence mechanisms. Low GC content prokaryotes are K-strategists specialized for stable environments that maintain homeostasis via a high-cost outer cell membrane and endospore formation as a response to nutrient deprivation, and attain a higher nutrient-to-biomass yield. The lower proteome cost of high GC content prokaryotes is driven by the association between GC-rich codons and cheaper amino acids in the genetic code, while the correlation between GC content and genome size may be partly due to functional diversity driven by r/K selection. In all, molecular diversity in the GC content of prokaryotes may be a consequence of ecological r/K selection.

Characterization of Microbial Diversity of Two Tomato Cultivars through Targeted Next-Generation Sequencing 16S rRNA and ITS Techniques

Even though the nutritional and economic values of Solanum lycopersicum (tomato) are substantially impacted by microbial spoilage, the available data on its microbial community, particularly during spoilage, are limited and have primarily been characterized using conventional culture-dependent methods. This study employed a targeted high-throughput next-generation sequencing method to longitudinally characterize the microbial diversity of two South African tomato cultivars (jam and round) at varied storage intervals (1, 6, and 12 days). Throughout the storage period, the bacterial communities of the two cultivars were more diverse than the fungal communities. The microbial diversity of both bacteria and fungi was greater and comparable between the cultivars on day 1, but becomes distinct as the storage period increases, with round tomatoes being more diverse than jam tomato, though, on day 12, jam tomato develops greater diversity than round tomato. Overall, the most abundant phyla (though Proteobacteria was most dominant) were Proteobacteria, Firmicutes, and Bacteriodota in the bacterial communities, while Ascomycota and Basidiomycota formed most fungal communities with Ascomycota being dominant. At the genus level, Pantoea and Klebsiella (bacteria), Hanseniaspora, Stemphylium, and Alternaria (fungi) were prevalent. Taken together, this study casts light on a broad microbial diversity profile thus, confirms the cultivars' diversity and abundance differences.

Synthetic phylogenetically diverse communities promote denitrification and stability

Denitrification is an important process of the global nitrogen cycle as some of its intermediates are environmentally important or related to global warming. However, how the phylogenetic diversity of denitrifying communities affects their denitrification rates and temporal stability remains unclear. Here we selected denitrifiers based on their phylogenetic distance to construct two groups of synthetic denitrifying communities: one closely related (CR) group with all strains from the genus Shewanella and the other distantly related (DR) group with all constituents from different genera. All synthetic denitrifying communities (SDCs) were experimentally evolved for 200 generations. The results showed that high phylogenetic diversity followed by experimental evolution promoted the function and stability of synthetic denitrifying communities. Specifically, the productivity and denitrification rates were significantly (P < 0.05) higher with Paracocus denitrificans as the dominant species (since the 50th generation) in the DR community than those in the CR community. The DR community also showed significantly (t = 7.119, df = 10, P < 0.001) higher stability through overyielding and asynchrony of species fluctuations, and showed more complementarity than the CR group during the experimental evolution. This study has important implications for applying synthetic communities to remediate environmental problems and mitigate greenhouse gas emissions.

Localized coevolution between microbial predator and prey alters community-wide gene expression and ecosystem function

Closely interacting microbial species pairs (e.g., predator and prey) can become coadapted via reciprocal natural selection. A fundamental challenge in evolutionary ecology is to untangle how coevolution in small species groups affects and is affected by biotic interactions in diverse communities. We conducted an experiment with a synthetic 30-species bacterial community where we experimentally manipulated the coevolutionary history of a ciliate predator and one bacterial prey species from the community. Altering the coevolutionary history of the focal prey species had little effect on community structure or carrying capacity in the presence or absence of the coevolved predator. However, community metabolic potential (represented by per-cell ATP concentration) was significantly higher in the presence of both the coevolved focal predator and prey. This ecosystem-level response was mirrored by community-wide transcriptional shifts that resulted in the differential regulation of nutrient acquisition and surface colonization pathways across multiple bacterial species. Our findings show that the disruption of localized coevolution between species pairs can reverberate through community-wide transcriptional networks even while community composition remains largely unchanged. We propose that these altered expression patterns may signal forthcoming evolutionary and ecological change.

Latent functional diversity may accelerate microbial community responses to temperature fluctuations

How complex microbial communities respond to climatic fluctuations remains an open question. Due to their relatively short generation times and high functional diversity, microbial populations harbor great potential to respond as a community through a combination of strain-level phenotypic plasticity, adaptation, and species sorting. However, the relative importance of these mechanisms remains unclear. We conducted a laboratory experiment to investigate the degree to which bacterial communities can respond to changes in environmental temperature through a combination of phenotypic plasticity and species sorting alone. We grew replicate soil communities from a single location at six temperatures between 4°C and 50°C. We found that phylogenetically and functionally distinct communities emerge at each of these temperatures, with K-strategist taxa favored under cooler conditions and r-strategist taxa under warmer conditions. We show that this dynamic emergence of distinct communities across a wide range of temperatures (in essence, community-level adaptation) is driven by the resuscitation of latent functional diversity: the parent community harbors multiple strains pre-adapted to different temperatures that are able to 'switch on' at their preferred temperature without immigration or adaptation. Our findings suggest that microbial community function in nature is likely to respond rapidly to climatic temperature fluctuations through shifts in species composition by resuscitation of latent functional diversity.

The ability of Phaeobacter inhibens to produce tropodithietic acid influences the community dynamics of a microalgal microbiome

Microbial secondary metabolites facilitate microbial interactions and are crucial for understanding the complexity of microbial community dynamics. The purpose of the present study was to determine how a secondary metabolite producing marine bacteria or its metabolite deficient mutant affected the microbiome of the marine microalgae Tetraselmis suecica during a 70 day long co-evolution experiment. Using 16S rRNA gene amplicon sequencing, we found that neither the tropodithietic acid (TDA)-producing Phaeobacter inhibens wildtype nor the TDA-deficient mutant had major impacts on the community composition. However, a subset of strains, displayed temporally different relative abundance trajectories depending on the presence of P. inhibens. In particular, a Winogradskyella strain displayed temporal higher relative abundance when the TDA-producing wildtype was present. Numbers of the TDA-producing wildtype were reduced significantly more than those of the mutant over time indicating that TDA production was not an advantage. In communities without the P. inhibens wildtype strain, an indigenous population of Phaeobacter increased over time, indicating that indigenous Phaeobacter populations cannot co-exist with the TDA-producing wildtype. Despite that TDA was not detected chemically, we detected transcripts of the tdaC gene indicating that TDA could be produced in the microbial community associated with the algae. Our work highlights the importance of deciphering longitudinal strain dynamics when addressing the ecological effect of secondary metabolites in a relevant natural community.

Assembling microbial communities: a genomic analysis of a natural experiment in neotropical bamboo internodes

Microbes participate in ecological communities, much like multicellular organisms. However, microbial communities lack the centuries of observation and theory describing and predicting ecological processes available for multicellular organisms. Here, we examine early bacterial community assembly in the water-filled internodes of Amazonian bamboos from the genus Guadua. Bamboo stands form distinct habitat patches within the lowland Amazonian rainforest and provide habitat for a suite of vertebrate and invertebrate species. Guadua bamboos develop sealed, water-filled internodes as they grow. Internodes are presumed sterile or near sterile while closed, but most are eventually opened to the environment by animals, after which they are colonized by microbes. We find that microbial community diversity increases sharply over the first few days of environmental exposure, and taxonomic identity of the microbes changes through this time period as is predicted for early community assembly in macroscopic communities. Microbial community taxonomic turnover is consistent at the bacteria phylum level, but at the level of Operational Taxonomic Units (OTUs), internode communities become increasingly differentiated through time. We argue that these tropical bamboos form an ideal study system for microbial community ecology due to their near-sterile condition prior to opening, relatively consistent environment after opening, and functionally limitless possibilities for replicates. Given the possible importance of opened internode habitats as locations of transmission for both pathogenic and beneficial microbes among animals, understanding the microbial dynamics of the internode habitat is a key conservation concern for the insect and amphibian species that use this microhabitat.

Assembly and dynamics of the apple carposphere microbiome during fruit development and storage

Microbial communities associated with fruit can contribute to quality and pathogen resistance, but little is known about their assembly and dynamics during fruit development and storage. Three apple cultivars growing under the same environmental conditions were utilized to examine the apple carposphere microbiome composition and structure at different developmental stages and storage. There was a significant effect (Adonis, p ≤ 0.001) of fruit genotype and its developmental stages and storage times on the fruit surface microbial assemblage and a strong temporal microbial community succession was detected (Mantel test: R ≤ 0.5, p = 0.001) in both bacterial and fungal communities. A set of 15 bacterial and 35 fungal core successional taxa and members exhibiting differential abundances at different fruit stages were identified. For the first time, we show the existence of underlying universal dynamics in the assembly of fruit-associated microbiomes. We also provide evidence of strong microbial cross-domain associations and uncover potential microbe-microbe correlations in the apple carposphere. Together our findings shed light on how the fruit carposphere assemble and change over time, and provide new insights into fruit microbial ecology.

Turnover in Life-Strategies Recapitulates Marine Microbial Succession Colonizing Model Particles

Particulate organic matter (POM) in the ocean sustains diverse communities of bacteria that mediate the remineralization of organic complex matter. However, the variability of these particles and of the environmental conditions surrounding them present a challenge to the study of the ecological processes shaping particle-associated communities and their function. In this work, we utilize data from experiments in which coastal water communities are grown on synthetic particles to ask which are the most important ecological drivers of their assembly and associated traits. Combining 16S rRNA amplicon sequencing with shotgun metagenomics, together with an analysis of the full genomes of a subset of isolated strains, we were able to identify two-to-three distinct community classes, corresponding to early vs. late colonizers. We show that these classes are shaped by environmental selection (early colonizers) and facilitation (late colonizers) and find distinctive traits associated with each class. While early colonizers have a larger proportion of genes related to the uptake of nutrients, motility, and environmental sensing with few pathways enriched for metabolism, late colonizers devote a higher proportion of genes for metabolism, comprising a wide array of different pathways including the metabolism of carbohydrates, amino acids, and xenobiotics. Analysis of selected pathways suggests the existence of a trophic-chain topology connecting both classes for nitrogen metabolism, potential exchange of branched chain amino acids for late colonizers, and differences in bacterial doubling times throughout the succession. The interpretation of these traits suggests a distinction between early and late colonizers analogous to other classifications found in the literature, and we discuss connections with the classical distinction between r- and K-strategists.

Recent Differentiation of Aquatic Bacterial Communities in a Hydrological System in the Cuatro Ciénegas Basin, After a Natural Perturbation

Pozas Rojas is a hydrological system comprising nine isolated shallow ponds and a deep lagoon, which were temporally merged in 2010 by increased rainfall due to a tropical cyclone. In this work, we assess which components, biotic interactions, or environment filtering effects, drive the assembly of microbial communities after a natural perturbation. Arsenic, pH, and temperature are among the most significant environmental variables between each pond, clustering the samples in two main groups, whereas microbial composition is diverse and unique to each site, with no core at the operational taxonomic unit level and only 150 core genera when studied at the genus level. Los Hundidos lagoon has the most differentiated community, which is highly similar to the epipelagic Mediterranean Sea communities. On the other hand, the shallow ponds at the Pozas Rojas system resemble more to epicontinental hydrological systems, such as some cold rivers of the world and the phreatic mantle from Iowa. Overall, despite being a sole of water body 2 years prior to the sampling, interspecific interactions, rather than environmental selection, seem to play a more important role in Pozas Rojas, bolstered by founder effects on each poza and subsequent isolation of each water body.

Climate-Driven Legacies in Simulated Microbial Communities Alter Litter Decomposition Rates

The mechanisms underlying diversity-functioning relationships have been a consistent area of inquiry in biogeochemistry since the 1950s. Though these mechanisms remain unresolved in soil microbiomes, many approaches at varying scales have pointed to the same notion—composition matters. Confronting the methodological challenge arising from the complexity of microbiomes, this study used the model DEMENTpy, a trait-based modeling framework, to explore trait-based drivers of microbiome-dependent litter decomposition. We parameterized DEMENTpy for five sites along a climate gradient in Southern California, United States, and conducted reciprocal transplant simulations analogous to a prior empirical study. The simulations demonstrated climate-dependent legacy effects of microbial communities on plant litter decomposition across the gradient. This result is consistent with the previous empirical study across the same gradient. An analysis of community-level traits further suggests that a 3-way tradeoff among resource acquisition, stress tolerance, and yield strategies influences community assembly. Simulated litter decomposition was predictable with two community traits (indicative of two of the three strategies) plus local environment, regardless of the system state (transient vs. equilibrium). Although more empirical confirmation is still needed, community traits plus local environmental factors (e.g., environment and litter chemistry) may robustly predict litter decomposition across spatial-temporal scales. In conclusion, this study offers a potential trait-based explanation for climate-dependent community effects on litter decomposition with implications for improved understanding of whole-ecosystem functioning across scales.

Relationships between community composition, productivity and invasion resistance in semi-natural bacterial microcosms

Common garden experiments that inoculate a standardised growth medium with synthetic microbial communities (i.e. constructed from individual isolates or using dilution cultures) suggest that the ability of the community to resist invasions by additional microbial taxa can be predicted by the overall community productivity (broadly defined as cumulative cell density and/or growth rate). However, to the best of our knowledge, no common garden study has yet investigated the relationship between microbial community composition and invasion resistance in microcosms whose compositional differences reflect natural, rather than laboratory-designed, variation. We conducted experimental invasions of two bacterial strains (Pseudomonas fluorescens and Pseudomonas putida) into laboratory microcosms inoculated with 680 different mixtures of bacteria derived from naturally occurring microbial communities collected in the field. Using 16S rRNA gene amplicon sequencing to characterise microcosm starting composition, and high-throughput assays of community phenotypes including productivity and invader survival, we determined that productivity is a key predictor of invasion resistance in natural microbial communities, substantially mediating the effect of composition on invasion resistance. The results suggest that similar general principles govern invasion in artificial and natural communities, and that factors affecting resident community productivity should be a focal point for future microbial invasion experiments.

Role of Bacillus inoculation in rice straw composting and bacterial community stability after inoculation: Unite resistance or individual collapse

Bacillus is the classic inoculant in rice straw composting. However, there has been no in-depth study of the mechanism promoting the degradation of lignocellulose and the change of indigenous bacterial communities after Bacillus inoculation. Moreover, the stability of bacterial communities is a significant challenge in achieving the efficacy of inoculation. In this study, the ecological succession and yield-resource acquisition-stress tolerance (Y-A-S) framework were combined with Redundancy analysis (RDA) and changes in relative abundance, Bacillus was found to be a pioneer bacterium that adopts a resource acquisition-stress tolerance strategy. The structural equation model (SEM) revealed that in addition to exerting a degradation effect, Bacillus inoculation could also indirectly affect lignocellulose degradation by changing the bacterial community. Random forest model and network analysis indicated a change in bacterial communities after inoculation, and bacteria with more complex relationships and weaker decomposition ability were key to the stability of bacterial communities.

Microbiome Structure and Function in Woodchip Bioreactors for Nitrate Removal in Agricultural Drainage Water

Woodchip bioreactors are increasingly used to remove nitrate (NO₃^–) from agricultural drainage water in order to protect aquatic ecosystems from excess nitrogen. Nitrate removal in woodchip bioreactors is based on microbial processes, but the microbiomes and their role in bioreactor efficiency are generally poorly characterized. Using metagenomic analyses, we characterized the microbiomes from 3 full-scale bioreactors in Denmark, which had been operating for 4–7 years. The microbiomes were dominated by Proteobacteria and especially the genus Pseudomonas, which is consistent with heterotrophic denitrification as the main pathway of NO₃^– reduction. This was supported by functional gene analyses, showing the presence of the full suite of denitrification genes from NO₃^– reductases to nitrous oxide reductases. Genes encoding for dissimilatory NO₃^– reduction to ammonium were found only in minor proportions. In addition to NO₃^– reducers, the bioreactors harbored distinct functional groups, such as lignocellulose degrading fungi and bacteria, dissimilatory sulfate reducers and methanogens. Further, all bioreactors harbored genera of heterotrophic iron reducers and anaerobic iron oxidizers (Acidovorax) indicating a potential for iron-mediated denitrification. Ecological indices of species diversity showed high similarity between the bioreactors and between the different positions along the flow path, indicating that the woodchip resource niche was important in shaping the microbiome. This trait may be favorable for the development of common microbiological strategies to increase the NO₃^– removal from agricultural drainage water.

Functional trait relationships demonstrate life strategies in terrestrial prokaryotes

Functional, physiological traits are the underlying drivers of niche differentiation. A common framework related to niches occupied by terrestrial prokaryotes is based on copiotrophy or oligotrophy, where resource investment is primarily in either rapid growth or stress tolerance, respectively. A quantitative trait-based approach sought relationships between taxa, traits and niche in terrestrial prokaryotes. With 175 taxa from 11 Phyla and 35 Families (n = 5 per Family), traits were considered as discrete counts of shared genome-encoded proteins. Trait composition strongly supported non-random functional distributions as preferential clustering of related taxa via unweighted pair-group method with arithmetic mean. Trait similarity between taxa increased as taxonomic rank decreased. A suite of Random Forest models identified traits significantly enriched or depleted in taxonomic groups. These traits conveyed functions related to rapid growth, nutrient acquisition and stress tolerance consistent with their presence in copiotroph-oligotroph niches. Hierarchical clustering of traits identified a clade of competitive, copiotrophic Families resilient to oxidative stress versus glycosyltransferase-enriched oligotrophic Families resistant to antimicrobials and environmental stress. However, the formation of five clades suggested a more nuanced view to describe niche differentiation in terrestrial systems is necessary. We suggest considering traits involved in both resource investment and acquisition when predicting niche.

Phylogenetic Core Groups: a promising concept in search of a consistent methodological framework : Comment to ``A conceptual framework for the phylogenetically-constrained assembly of microbial communities''

In this comment, we analyse the conceptual framework proposed by Aguirre de Cárcer (Microbiome 7:142, 2019), introducing the novel concept of Phylogenetic Core Groups (PCGs). This notion aims to complement the traditional classification in operational taxonomic units (OTUs), widely used in microbial ecology, to provide a more intrinsic taxonomical classification which avoids the use of pre-determined thresholds. However, to introduce this concept, the author frames his proposal in a wider theoretical framework based on a conceptualization of selection that we argue is a tautology. This blurs the subsequent formulation of an assembly principle for microbial communities, favouring that some contradictory examples introduced to support the framework appear aligned in their conclusions. And more importantly, under this framework and its derived methodology, it is not possible to infer PCGs from data in a consistent way. We reanalyse the proposal to identify its logical and methodological flaws and, through the analysis of synthetic scenarios, we propose a number of methodological refinements to contribute towards the determination of PCGs in a consistent way. We hope our analysis will promote the exploration of PCGs as a potentially valuable tool, helping to bridge the gap between environmental conditions and community composition in microbial ecology. Video Abstract.

Life-history strategies of soil microbial communities in an arid ecosystem

The overwhelming taxonomic diversity and metabolic complexity of microorganisms can be simplified by a life-history classification; copiotrophs grow faster and rely on resource availability, whereas oligotrophs efficiently exploit resource at the expense of growth rate. Here, we hypothesize that community-level traits inferred from metagenomic data can distinguish copiotrophic and oligotrophic microbial communities. Moreover, we hypothesize that oligotrophic microbial communities harbor more unannotated genes. To test these hypotheses, we conducted metagenomic analyses of soil samples collected from copiotrophic vegetated areas and from oligotrophic bare ground devoid of vegetation in an arid-hyperarid region of the Sonoran Desert, Arizona, USA. Results supported our hypotheses, as we found that multiple ecologically informed life-history traits including average 16S ribosomal RNA gene copy number, codon usage bias in ribosomal genes and predicted maximum growth rate were higher for microbial communities in vegetated than bare soils, and that oligotrophic microbial communities in bare soils harbored a higher proportion of genes that are unavailable in public reference databases. Collectively, our work demonstrates that life-history traits can distill complex microbial communities into ecologically coherent units and highlights that oligotrophic microbial communities serve as a rich source of novel functions.

Disentangling the Association of Corn Root Mycobiome With Plant Productivity and the Importance of Soil Physicochemical Balance in Shaping Their Relationship

Soil bacteria and fungi are integral parts of healthy ecosystem functioning in production agriculture. The effects of fungal abundance and diversity on crop productivity is poorly understood. We sampled 10 corn farms at the V10 growth stage across southwestern Ontario, Canada, using aerial infrared imaging to identify zones of low and high productive corn plants. Roots and soils were sampled from low and high yield zones and soil physical and chemical properties were measured in conjunction with assessment of the root mycobiome communities using Illumina MiSeq sequencing of 4 rRNA amplicons. Higher crop yields were associated with sites having greater fungal phylogenetic diversity and Fisher's α diversity. Indicator species associated with high and low yield sites within a farm could be identified but there were no shared fungal indicators of productivity differences across farms. Communities largely varied across locations despite crop genetics, demonstrating a major influence of soil texture and chemistry in shaping the mycobiome in a site-specific manner. Across all 4 primers, roots from high-yielding sites shared 35 major OTUs including Penicillium spp., Trichoderma, Chalara fungorum, and Gibellulopsis. Low-yielding sites shared 31 OTUs including Fusarium spp., Pythium, Setophoma terrestris, and Neonectria. Soil physical and chemical parameters that contributed to broad scale differences in yield and mycobiome diversity included: %clay, %sand, %phosphorus saturation, cation exchange capacity, aluminum, pH, iron, potassium, %moisture, organic matter, and chlorine. The results show the importance of physicochemical balance in shaping the relationship between root mycobiome and plant productivity.

Changes in Water Retention and Carbon Sequestration in the Huangshan UNESCO Global Geopark (China) from 2000 to 2015

Geopark ecosystem function assessments form an essential knowledge base for natural resource conservation and sustainable development. In this study, we evaluated changes in water retention and carbon sequestration in forests in the Huangshan United Nations Educational, Scientific, and Cultural Organization (UNESCO) Global Geopark (HUGG), China, from 2000 to 2015. We analyzed the relationship between these ecosystem functions and various controlling factors. The ecosystem functions in HUGG experienced significant changes during the study period. Water retention function increased slightly (0.15 m3 hm−2 year−1), while carbon sequestration increased sharply (25.57 g C m−2 year−1), with both showing increased spatial homogenization. Increased precipitation significantly enhanced the water retention function, whereas a temperature increase had a positive effect on the carbon sequestration. Both water retention and carbon sequestration decreased significantly with increased tourist disturbance. Pearson’s correlation coefficient and variance partitioning analysis identified the climate factors and tourist disturbance controlling water retention and carbon sequestration, respectively. The fitted structural equation model showed that climate factors had a greater total impact on water retention than tourist disturbance, while the total impact of climate factors on carbon sequestration was far less than that due to tourist disturbance. This study untangled the relationship between ecosystem functions (water retention and carbon sequestration) and influential factors in the HUGG and clarified that climate factors and tourist disturbance were determinants of changes in these ecosystem functions. The results from this study provide scientific foundations for the sustainable management of natural ecosystems in the HUGG and other geoparks.