Biogeochemical cycling and microbial diversity in the thrombolitic microbialites of Highborne Cay,Bahamas

Thrombolites are unlaminated carbonate build‐ups that are formed via the metabolic activities of complex microbial mat communities. The thrombolitic mats of Highborne Cay, Bahamas develop in close proximity (1–2 m) to accreting laminated stromatolites, providing an ideal opportunity for biogeochemical and molecular comparisons of these two distinctive microbialite ecosystems. In this study, we provide the first comprehensive characterization of the biogeochemical activities and microbial diversity of the Highborne Cay thrombolitic mats. Morphological and molecular analyses reveal two dominant mat types associated with the thrombolite deposits, both of which are dominated by bacteria from the taxa Cyanobacteria and Alphaproteobacteria. Diel cycling of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) were measured in all thrombolitic mat types. DO production varied between thrombolitic types and one morphotype, referred to in this study as ‘button mats’, produced the highest levels among all mat types, including the adjacent stromatolites. Characterization of thrombolite bacterial communities revealed a high bacterial diversity, roughly equivalent to that of the nearby stromatolites, and a low eukaryotic diversity. Extensive phylogenetic overlap between thrombolitic and stromatolitic microbial communities was observed, although thrombolite‐specific cyanobacterial populations were detected. In particular, the button mats were dominated by a calcified, filamentous cyanobacterium identified via morphology and 16S rRNA gene sequencing as Dichothrix sp. The distinctive microbial communities and chemical cycling patterns within the thrombolitic mats provide novel insight into the biogeochemical processes related to the lithifying mats in this system, and provide data relevant to understanding microbially induced carbonate biomineralization.     

Overview of biopolymer-induced mineralization: What goes on in biofilms?

Bacteria are associated with mineralization and dissolution processes, some of which may enhance or compromise the physical stability of engineered structures. Examples include stabilization of sediment dikes, bioplugging, biogrouting, and self-healing of concrete and limestone structures. In contrast to ‘biologically controlled’ precipitation (e.g. shells) of eukaryote organisms, microbial precipitation primarily results from two major processes: (1) ‘biologically induced’ precipitation, where microbial activities generate biogeochemical conditions that facilitate precipitation; and (2) ‘biologically influenced’ precipitation, where passive interactions of extracellular biopolymers and the geochemical environment drive precipitation. A common location for such biopolymers is the microbial ‘biofilm’ (i.e. cells surrounded within a matrix of extracellular polymeric substances (EPS)). EPS biofilms occur commonly in both natural environments and many engineered surfaces. Emerging evidence now suggests that EPS inhibit, alter or enhance precipitation of calcium carbonate. Functional groups on EPS serve as initial nucleation sites, while other moieties function to control extent and types (e.g. crystals vs. amorphous organominerals) of precipitation. Understanding how to control, or even manipulate, precipitation/dissolution processes within the confines of EPS matrices will influence long-term structural integrities of materials. The present overview explores properties of EPS, and their potentially destructive (dissolution) and constructive (precipitation) effects on precipitation. Initial insight is offered for understanding how biopolymers might be controlled for applied purposes.     

GeoChip-based analysis of the functional gene diversity and metabolic potential of microbial communities in acid mine drainage

Acid mine drainage (AMD) is an extreme environment, usually with low pH and high concentrations of metals. Although the phylogenetic diversity of AMD microbial communities has been examined extensively, little is known about their functional gene diversity and metabolic potential. In this study, a comprehensive functional gene array (GeoChip 2.0) was used to analyze the functional diversity, composition, structure, and metabolic potential of AMD microbial communities from three copper mines in China. GeoChip data indicated that these microbial communities were functionally diverse as measured by the number of genes detected, gene overlapping, unique genes, and various diversity indices. Almost all key functional gene categories targeted by GeoChip 2.0 were detected in the AMD microbial communities, including carbon fixation, carbon degradation, methane generation, nitrogen fixation, nitrification, denitrification, ammonification, nitrogen reduction, sulfur metabolism, metal resistance, and organic contaminant degradation, which suggested that the functional gene diversity was higher than was previously thought. Mantel test results indicated that AMD microbial communities are shaped largely by surrounding environmental factors (e.g., S, Mg, and Cu). Functional genes (e.g., narG and norB) and several key functional processes (e.g., methane generation, ammonification, denitrification, sulfite reduction, and organic contaminant degradation) were significantly (P < 0.10) correlated with environmental variables. This study presents an overview of functional gene diversity and the structure of AMD microbial communities and also provides insights into our understanding of metabolic potential in AMD ecosystems.     

Exopolymeric substances of sulfate-reducing bacteria: Interactions with calcium at alkaline pH and implication for formation of carbonate minerals

Sulfate‐reducing bacteria (SRB) have been recognized as key players in the precipitation of calcium carbonate in lithifying microbial communities. These bacteria increase the alkalinity by reducing sulfate ions, and consuming organic acids. SRB also produce copious amounts of exopolymeric substances (EPS). All of these processes influence the morphology and mineralogy of the carbonate minerals. Interactions of EPS with metals, calcium in particular, are believed to be the main processes through which the extracellular matrix controls the precipitation of the carbonate minerals. SRB exopolymers were purified from lithifying mat and type cultures, and their potential role in CaCO₃ precipitation was determined from acid‐base titrations and calcium‐binding experiments. Major EPS characteristics were established using infrared spectroscopy and gas chromatography to characterize the chemical functional groups and the sugar monomers composition. Our results demonstrate that all of the three SRB strains tested were able to produce large amounts of EPS. This EPS exhibited three main buffering capacities, which correspond to carboxylic acids (pK_a = 3.0), sulfur‐containing groups (thiols, sulfonic and sulfinic acids – pK_a = 7.0–7.1) and amino groups (pK_a = 8.4–9.2). The calcium‐binding capacity of these exopolymers in solution at pH 9.0 ranged from 0.12g_Ca g_EPS^?1–0.15 g_Ca g_EPS^?1. These results suggest that SRB could play a critical role in the formation of CaCO₃ in lithifying microbial mats. The unusually high sulfur content, which has not been reported for EPS before, indicates a possible strong interaction with iron. In addition to changing the saturation index through metabolic activity, our results imply that SRB affect the rock record through EPS production and its effect on the CaCO₃ precipitation. Furthermore, EPS produced by SRB may account for the incorporation of metals (e.g. Sr, Fe, Mg) associated with carbonate minerals in the rock record.     

Microbial functional diversity covaries with permafrost thaw‐induced environmental heterogeneity in tundra soil

Permafrost soil in high latitude tundra is one of the largest terrestrial carbon (C) stocks and is highly sensitive to climate warming. Understanding microbial responses to warming‐induced environmental changes is critical to evaluating their influences on soil biogeochemical cycles. In this study, a functional gene array (i.e., geochip 4.2) was used to analyze the functional capacities of soil microbial communities collected from a naturally degrading permafrost region in Central Alaska. Varied thaw history was reported to be the main driver of soil and plant differences across a gradient of minimally, moderately, and extensively thawed sites. Compared with the minimally thawed site, the number of detected functional gene probes across the 15–65 cm depth profile at the moderately and extensively thawed sites decreased by 25% and 5%, while the community functional gene β‐diversity increased by 34% and 45%, respectively, revealing decreased functional gene richness but increased community heterogeneity along the thaw progression. Particularly, the moderately thawed site contained microbial communities with the highest abundances of many genes involved in prokaryotic C degradation, ammonification, and nitrification processes, but lower abundances of fungal C decomposition and anaerobic‐related genes. Significant correlations were observed between functional gene abundance and vascular plant primary productivity, suggesting that plant growth and species composition could be co‐evolving traits together with microbial community composition. Altogether, this study reveals the complex responses of microbial functional potentials to thaw‐related soil and plant changes and provides information on potential microbially mediated biogeochemical cycles in tundra ecosystems.     

Deep‐water microbialites of the Mesoproterozoic Dismal Lakes Group: microbial growth,lithification, and implications for coniform stromatolites

Offshore facies of the Mesoproterozoic Sulky Formation, Dismal Lakes Group, arctic Canada, preserve microbialites with unusual morphology. These microbialites grew in water depths greater than several tens of meters and correlate with high‐relief conical stromatolites of the more proximal September Lake reef complex. The gross morphology of these microbial facies consists of ridge‐like vertical supports draped by concave‐upward, subhorizontal elements, resulting in tent‐shaped cuspate microbialites with substantial primary void space. Morphological and petrographic analyses suggest a model wherein penecontemporaneous upward growth of ridge elements and development of subhorizontal draping elements initially resulted in a buoyantly supported, unlithified microbial form. Lithification began via precipitation within organic elements during microbialite growth. Mineralization either stabilized or facilitated collapse of initially neutrally buoyant microbialite forms. Microbial structures and breccias were then further stabilized by precipitation of marine herringbone cement. During late‐stage diagenesis, remaining void space was occluded by ferroan dolomite cement. Cuspate microbialites are most similar to those found in offshore facies of Neoarchean carbonate platforms and to unlithified, buoyantly supported microbial mats in modern ice‐covered Antarctic lakes. We suggest that such unusual microbialite morphologies are a product of the interaction between motile and non‐motile communities under nutrient‐limiting conditions, followed by early lithification, which served to preserve the resultant microbial form. The presence of marine herringbone cement, commonly associated with high dissolved inorganic carbon (DIC), low O₂ conditions, also suggests growth in association with reducing environments at or near the seafloor or in conjunction with a geochemical interface. Predominance of coniform stromatolite forms in the Proterozoic—across a variety of depositional environments—may thus reflect a combination of heterogeneous nutrient distribution, potentially driven by variable redox conditions, and an elevated carbonate saturation state, which permits preservation of these unusual microbialite forms.     

Molecular indicators of microbial diversity in oolitic sands of Highborne Cay,Bahamas

Microbialites (stromatolites and thrombolites) are mineralized mat structures formed via the complex interactions of diverse microbial‐mat communities. At Highborne Cay, in the Bahamas, the carbonate component of these features is mostly comprised of ooids. These are small, spherical to ellipsoidal grains characterized by concentric layers of calcium carbonate and organic matter and these sand‐sized particles are incorporated with the aid of extra‐cellular polymeric substances (EPS), into the matrix of laminated stromatolites and clotted thrombolite mats. Here, we present a comparison of the bacterial diversity within oolitic sand samples and bacterial diversity previously reported in thrombolitic and stromatolitic mats of Highborne Cay based on analysis of clone libraries of small subunit ribosomal RNA gene fragments and lipid biomarkers. The 16S‐rRNA data indicate that the overall bacterial diversity within ooids is comparable to that found within thrombolites and stromatolites of Highborne Cay, and this significant overlap in taxonomic groups suggests that ooid sands may be a source for much of the bacterial diversity found in the local microbialites. Cyanobacteria were the most diverse taxonomic group detected, followed by Alphaproteobacteria, Gammaproteobacteria, Planctomyces, Deltaproteobacteria, and several other groups also found in mat structures. The distributions of intact polar lipids, the fatty acids derived from them, and bacteriohopanepolyols provide broad general support for the bacterial diversity identified through analysis of nucleic acid clone libraries.     

GeoChip-based analysis of the functional gene diversity and metabolic potential of soil microbial communities of mangroves

Mangroves are unique and highly productive ecosystems and harbor very special microbial communities. Although the phylogenetic diversity of sediment microbial communities of mangrove habitats has been examined extensively, little is known regarding their functional gene diversity and metabolic potential. In this study, a high-throughput functional gene array (GeoChip 4.0) was used to analyze the functional diversity, composition, structure, and metabolic potential of microbial communities in mangrove habitats from mangrove national nature reserves in China. GeoChip data indicated that these microbial communities were functionally diverse as measured by the number of genes detected, unique genes, and various diversity indices. Almost all key functional gene categories targeted by GeoChip 4.0 were detected in the mangrove microbial communities, including carbon (C) fixation, C degradation, methane generation, nitrogen (N) fixation, nitrification, denitrification, ammonification, N reduction, sulfur (S) metabolism, metal resistance, antibiotic resistance, and organic contaminant degradation. Detrended correspondence analysis (DCA) of all detected genes showed that Spartina alterniflora (HH), an invasive species, did not harbor significantly different microbial communities from Aegiceras corniculatum (THY), a native species, but did differ from other species, Kenaelia candel (QQ), Aricennia marina (BGR), and mangrove-free mud flat (GT). Canonical correspondence analysis (CCA) results indicated the microbial community structure was largely shaped by surrounding environmental variables, such as total nitrogen (TN), total carbon (TC), pH, C/N ratio, and especially salinity. This study presents a comprehensive survey of functional gene diversity of soil microbial communities from different mangrove habitats/species and provides new insights into our understanding of the functional potential of microbial communities in mangrove ecosystems.     

湖泊硫循环微生物研究进展

湖泊是响应气候和环境变化的关键生态系统,是研究元素(如碳、氮和硫等)生物地球化学循环的热点环境。湖泊(尤其咸盐湖)具有硫酸盐含量高且含硫化合物种类丰富的特点,因而湖泊中硫元素生物地球化学循环过程非常活跃。微生物是驱动湖泊硫循环的重要推手。因此,研究湖泊中微生物参与的硫元素生物地球化学循环过程以及相关微生物类群构成,对于深入探索微生物在湖泊生态系统中的作用具有重要意义。本文综述了湖泊中驱动硫循环的微生物(硫氧化菌和硫酸盐还原菌)种群多样性、功能基因、代谢途径、硫氧化/硫酸盐还原速率及其对环境条件变化响应等方面的研究现状,并对未来湖泊微生物驱动的硫循环研究方向进行了展望。     

Potential role for microbial ureolysis in the rapid formation of carbonate tufa mounds

Modern carbonate tufa towers in the alkaline (~pH 9.5) Big Soda Lake (BSL), Nevada, exhibit rapid precipitation rates (exceeding 3 cm/year) and host diverse microbial communities. Geochemical indicators reveal that carbonate precipitation is, in part, promoted by the mixing of calcium-rich groundwater and carbonate-rich lake water, such that a microbial role for carbonate precipitation is unknown. Here, we characterize the BSL microbial communities and evaluate their potential effects on carbonate precipitation that may influence fast carbonate precipitation rates of the active tufa mounds of BSL. Small subunit rRNA gene surveys indicate a diverse microbial community living endolithically, in interior voids, and on tufa surfaces. Metagenomic DNA sequencing shows that genes associated with metabolisms that are capable of increasing carbonate saturation (e.g., photosynthesis, ureolysis, and bicarbonate transport) are abundant. Enzyme activity assays revealed that urease and carbonic anhydrase, two microbial enzymes that promote carbonate precipitation, are active in situ in BSL tufa biofilms, and urease also increased calcium carbonate precipitation rates in laboratory incubation analyses. We propose that, although BSL tufas form partially as a result of water mixing, tufa-inhabiting microbiota promote rapid carbonate authigenesis via ureolysis, and potentially via bicarbonate dehydration and CO₂ outgassing by carbonic anhydrase. Microbially induced calcium carbonate precipitation in BSL tufas may generate signatures preserved in the carbonate microfabric, such as stromatolitic layers, which could serve as models for developing potential biosignatures on Earth and elsewhere.     

元蛋白质组学在微生物功能研究中的应用

后基因组时代,仅依靠基因组方法来研究原位微生物群落的功能已远远不够,在这种背景下元蛋白质组学研究逐渐兴起。应用元蛋白质组学技术可大规模研究原位微生物群落的蛋白质表达,分析生态系统中微生物的功能,寻找新的功能基因和代谢通路,为微生物群体的基因和功能多样性研究提供数据。同时,还可鉴定与微生物功能相关的蛋白质,这些蛋白质未来可以作为生物标记物为环境可持续发展铺路。综述了元蛋白质组学的发展概况及其在微生物功能研究中的重大作用,强调了元蛋白质组学方法在分析新功能基因及其相关基因,揭示微生物多样性与微生物群体功能之间的关系等方面起到的作用,并对其应用前景进行了展望。     

New insights into relationships between active and dormant organisms,phylogenetic diversity and ecosystem productivity

Marine microbes make up a key part of ocean food webs and drive ocean chemistry through a range of metabolic processes. A fundamental question in ecology is whether the diversity of organisms in a community shapes the ecological functions of that community. While there is substantial evidence to support a positive link between diversity and ecological productivity for macro‐organisms in terrestrial environments, this relationship has not previously been verified for marine microbial communities. One factor complicating the understanding of this relationship is that many marine microbes are dormant and are easily dispersed by ocean currents, making it difficult to ensure that the organisms found in a given environmental sample accurately reflect processes occurring in that environment. Another complication is that, due to microbes great range of genotypic and phenotypic variability, communities with distantly related species may have greater range of metabolic functions than communities have the same richness and evenness, but in which the species present are more closely related to each other. In this issue of Molecular Ecology, Galand et al. (2015) provide compelling evidence that the most metabolically active communities are those in which the nondormant portion of the microbial community has the highest phylogenetic diversity. They also illustrate that focusing on the active portion of the community allows for detection of temporal patterns in community structure that would not be otherwise evident. The authors’ point out that the presence of many dormant organisms that do not contribute to ecosystem functioning is a feature that makes microbial ecosystems fundamentally different from macro‐ecosystems and that this difference needs to be accounted for in microbial ecology theory.     

Microbial influence on dolomite and authigenic clay mineralisation in dolocrete profiles of NW Australia

Dolomite (CaMg(CO₃)₂) precipitation is kinetically inhibited at surface temperatures and pressures. Experimental studies have demonstrated that microbial extracellular polymeric substances (EPS) as well as certain clay minerals may catalyse dolomite precipitation. However, the combined association of EPS with clay minerals and dolomite and their occurrence in the natural environment are not well documented. We investigated the mineral and textural associations within groundwater dolocrete profiles from arid northwest Australia. Microbial EPS is a site of nucleation for both dolomite and authigenic clay minerals in this Late Miocene to Pliocene dolocrete. Dolomite crystals are commonly encased in EPS alveolar structures, which have been mineralised by various clay minerals, including montmorillonite, trioctahedral smectite and palygorskite-sepiolite. Observations of microbial microstructures and their association with minerals resemble textures documented in various lacustrine and marine microbialites, indicating that similar mineralisation processes may have occurred to form these dolocretes. EPS may attract and bind cations that concentrate to form the initial particles for mineral nucleation. The dolomite developed as nanocrystals, likely via a disordered precursor, which coalesced to form larger micritic crystal aggregates and rhombic crystals. Spheroidal dolomite textures, commonly with hollow cores, are also present and may reflect the mineralisation of a biofilm surrounding coccoid bacterial cells. Dolomite formation within an Mg-clay matrix is also observed, more commonly within a shallow pedogenic horizon. The ability of the negatively charged surfaces of clay and EPS to bind and dewater Mg²⁺, as well as the slow diffusion of ions through a viscous clay or EPS matrix, may promote the incorporation of Mg²⁺ into the mineral and overcome the kinetic effects to allow disordered dolomite nucleation and its later growth. The results of this study show that the precipitation of clay and carbonate minerals in alkaline environments may be closely associated and can develop from the same initial amorphous Ca–Mg–Si-rich matrix within EPS. The abundance of EPS preserved within the profiles is evidence of past microbial activity. Local fluctuations in chemistry, such as small increases in alkalinity, associated with the degradation of EPS or microbial activity, were likely important for both clay and dolomite formation. Groundwater environments may be important and hitherto understudied settings for microbially influenced mineralisation and for low-temperature dolomite precipitation.     

The microbially mediated soil organic carbon loss under degenerative succession in an alpine meadow

Land‐cover change has long been recognized as having marked effect on the amount of soil organic carbon (SOC). However, the microbially mediated processes and mechanisms on SOC are still unclear. In this study, the soil samples in a degenerative succession from alpine meadow to alpine steppe meadow in the Qinghai–Tibetan Plateau were analysed using high‐throughput technologies, including Illumina sequencing and geochip functional gene arrays. The soil microbial community structure and diversity were significantly (p < .05) different between alpine meadow and alpine steppe meadow; the microbial ɑ‐diversity in alpine steppe meadow was significantly (p < .01) higher than in alpine meadow. Molecular ecological network analysis indicated that the microbial community structure in alpine steppe meadow was more complex and tighter than in the alpine meadow. The relative abundance of soil microbial labile carbon degradation genes (e.g., pectin and hemicellulose) was significantly higher in alpine steppe meadow than in alpine meadow, but the relative abundance of soil recalcitrant carbon degradation genes (e.g., chitin and lignin) showed the opposite tendency. The Biolog Ecoplate experiment showed that microbially mediated soil carbon utilization was more active in alpine steppe meadow than in alpine meadow. Consequently, more soil labile carbon might be decomposed in alpine steppe meadow than in alpine meadow. Therefore, the degenerative succession of alpine meadow because of climate change or anthropogenic activities would most likely decrease SOC and nutrients medicated by changing soil microbial community structure and their functional potentials for carbon decomposition.     

The influence of hydrogeological disturbance and mining on coal seam microbial communities

The microbial communities present in two underground coal mines in the Bowen Basin, Queensland, Australia, were investigated to deduce the effect of pumping and mining on subsurface methanogens and methanotrophs. The micro‐organisms in pumped water from the actively mined areas, as well as, pre‐ and post‐mining formation waters were analyzed using 16S rRNA gene amplicon sequencing. The methane stable isotope composition of Bowen Basin coal seam indicates that methanogenesis has occurred in the geological past. More recently at the mine site, changing groundwater flow dynamics and the introduction of oxygen in the subsurface has increased microbial biomass and diversity. Consistent with microbial communities found in other coal seam environments, pumped coal mine waters from the subsurface were dominated by bacteria belonging to the genera Pseudomonas and the family Rhodocyclaceae. These environments and bacterial communities supported a methanogen population, including Methanobacteriaceae, Methanococcaceae and Methanosaeta. However, one of the most ubiquitous micro‐organisms in anoxic coal mine waters belonged to the family ‘Candidatus Methanoperedenaceae’. As the Archaeal family ‘Candidatus Methanoperedenaceae’ has not been extensively defined, the one studied species in the family is capable of anaerobic methane oxidation coupled to nitrate reduction. This introduces the possibility that a methane cycle between archaeal methanogenesis and methanotrophy may exist in the anoxic waters of the coal seam after hydrogeological disturbance.     

Comparative metagenomics of microbial communities inhabiting deep-sea hydrothermal vent chimneys with contrasting chemistries

Deep-sea hydrothermal vent chimneys harbor a high diversity of largely unknown microorganisms. Although the phylogenetic diversity of these microorganisms has been described previously, the adaptation and metabolic potential of the microbial communities is only beginning to be revealed. A pyrosequencing approach was used to directly obtain sequences from a fosmid library constructed from a black smoker chimney 4143-1 in the Mothra hydrothermal vent field at the Juan de Fuca Ridge. A total of 308 034 reads with an average sequence length of 227 bp were generated. Comparative genomic analyses of metagenomes from a variety of environments by two-way clustering of samples and functional gene categories demonstrated that the 4143-1 metagenome clustered most closely with that from a carbonate chimney from Lost City. Both are highly enriched in genes for mismatch repair and homologous recombination, suggesting that the microbial communities have evolved extensive DNA repair systems to cope with the extreme conditions that have potential deleterious effects on the genomes. As previously reported for the Lost City microbiome, the metagenome of chimney 4143-1 exhibited a high proportion of transposases, implying that horizontal gene transfer may be a common occurrence in the deep-sea vent chimney biosphere. In addition, genes for chemotaxis and flagellar assembly were highly enriched in the chimney metagenomes, reflecting the adaptation of the organisms to the highly dynamic conditions present within the chimney walls. Reconstruction of the metabolic pathways revealed that the microbial community in the wall of chimney 4143-1 was mainly fueled by sulfur oxidation, putatively coupled to nitrate reduction to perform inorganic carbon fixation through the Calvin–Benson–Bassham cycle. On the basis of the genomic organization of the key genes of the carbon fixation and sulfur oxidation pathways contained in the large genomic fragments, both obligate and facultative autotrophs appear to be present and contribute to biomass production.     

Microbial stabilization of sediments in a recent Salina, Lake Aghormi, Siwa Oasis, Egypt

Stabilization of sediments by microbial mats and biofilms were studied in detail in Lake Aghormi, Siwa Oasis, Egypt. The study has shown that microbial mat assemblages, particularly filamentous cyanobacteria, with their extracellular polymeric substances (EPS) are capable of effectively stabilizing sediments. The microbial mats in the siliciclastic environments of Lake Aghormi display distinctive sedimentary structures (microbially induced sedimentary structures), including multidirected ripple marks, microbial patches, petee structures, erosional remnants and pockets, and gas domes. Scanning electron microscopy study of the sediment surface colonized by cyanobacteria revealed that filamentous types are the most effective stabilizing organisms. Filamentous cyanobacteria and their EPS construct a network, interweave depositional grains of the sediment surface, envelope the particles, and glue them together. The studied biofilm is so thick forming a spider-web structure that totally coat the particles in such a way the morphology of the particles is masked.     

Differential sensitivity of total and active soil microbial communities to drought and forest management

Climate change will affect semiarid ecosystems through severe droughts that increase the competition for resources in plant and microbial communities. In these habitats, adaptations to climate change may consist of thinning—that reduces competition for resources through a decrease in tree density and the promotion of plant survival. We deciphered the functional and phylogenetic responses of the microbial community to 60 years of drought induced by rainfall exclusion and how forest management affects its resistance to drought, in a semiarid forest ecosystem dominated by Pinus halepensis Mill. A multiOMIC approach was applied to reveal novel, community‐based strategies in the face of climate change. The diversity and the composition of the total and active soil microbiome were evaluated by 16S rRNA gene (bacteria) and ITS (fungal) sequencing, and by metaproteomics. The microbial biomass was analyzed by phospholipid fatty acids (PLFAs), and the microbially mediated ecosystem multifunctionality was studied by the integration of soil enzyme activities related to the cycles of C, N, and P. The microbial biomass and ecosystem multifunctionality decreased in drought‐plots, as a consequence of the lower soil moisture and poorer plant development, but this decrease was more notable in unthinned plots. The structure and diversity of the total bacterial community was unaffected by drought at phylum and order level, but did so at genus level, and was influenced by seasonality. However, the total fungal community and the active microbial community were more sensitive to drought and were related to ecosystem multifunctionality. Thinning in plots without drought increased the active diversity while the total diversity was not affected. Thinning promoted the resistance of ecosystem multifunctionality to drought through changes in the active microbial community. The integration of total and active microbiome analyses avoids misinterpretations of the links between the soil microbial community and climate change.