Microbial ecology of hot and cold desert edaphic communities

Philosophiae Doctor - PhDThis thesis presents significant advances into the microbial ecology of hypolithic communities in two hyperarid deserts. Deserts account for one fifth of the Earths total surface area. These zones differ substantially in terms of climate, geomorphology, hydrology and vegetation. Desert biomes are, however, generally depauperate with particularly with respect to macroorganisms. Hypoliths, photosynthetic microbial assemblages associated with quartz rocks, are widely distributed in hot and cold desert environs where they may represent a large fraction of the standing biomass and mediate key ecosystem processes, including nutrient cycling. However, important questions regarding their (i) development (ii) community structure and assembly patterns and (iii) functional structure remain unaddressed. Here, molecular tools (T-RFLP, clone libraries and pyrosequencing) and multivariate data analyses were used to address these questions. This study presents evidence of species recruitment in the development of hypolithic communities in the Namib Desert. Hypolithic bacterial communities were compared at a fine scale (10 m radius). Multivariate analysis of T-RFLP-derived data showed that hypolithic and open soil communities were structurally distinct. Applying the ecological concept of ‘indicator species’, 6 and 9 indicator lineages were identified for hypoliths and soil, respectively. Hypolithic communities were dominated by cyanobacteria affiliated to Pleurocapsales, whereas actinobacteria were prevalent in the open soil. These results are consistent with the concept of species sorting and suggest that the underside of the quartz rocks provide conditions suitable for the development of discrete and demonstrably different microbial assemblages.However, strong evidence for neutral assembly processes was found, as almost 90% of the taxa present in the hypoliths were also detected in the open soil. All together, these results suggest that hypolithons do not develop independently from microbial communities found in the surrounding soil, but selectively recruit from local populations.The bacterial community structure and assembly patterns in hypolithons from Miers Valley (Antarctica) were investigated. Previous studies in this valley have identified three morphologically distinct hypolithic community types: cyanobacteria dominated(Type I), fungus dominated (Type II) and moss dominated (Type III). The bacterial composition of surface soils and hypolithic communities were shown to be clearly and robustly distinct, using T-RFLP analysis. Moreover, the bacterial assemblages were similar in Type II and Type III hypolithons and clearly distinct from those foundin Type I. Using16S ribosomal RNA gene (rRNA) 454 pyrosequencing,Proteobacteria were shown to be the most important bacterial component of all three types of hypolithic communities. As expected, Cyanobacteria dominated Type I hypolithons, whereas Actinobacteria dominated Types II and III hypolithons. Using a probabilistic dissimilarity metric and random sampling, deterministic processes were demonstrated to be relatively more important in shaping the structure of the bacterial community found in Type II and Type III hypolithons. Taken together, these results suggest that hypolithic development favors a sequential pathway with Type II hypolithons serving as an intermediate development state between Type I and Type In a more in depth analysis of the diversity patterns of key nutrient cycling genes in Antarctic Miers Valley edaphic communities, genes coding for carbon fixation (greenand red-like cbbL), nitrogen fixation (nifH), nitrification (amoA) and denitrification(nirK and nirS), were targeted. Multivariate analysis (PERMANOVA) showed that hypolithic and open soil communities were functionally distinct. Type I hypoliths were functionally more diverse than soils, suggesting higher potential for enzymatic activities. Taxonomic structure (derived from 16S rRNA data) showed congruence with functional traits (genes involved in C and N cycling). Redundancy analysis suggested that chemical variables (S, F, and NO3) were important structuring forces in the different communities. Taken together, the results suggest that stochastic processes such as dispersion cannot override the influence of environmental factors on functional diversity patterns

The diversity of key anabolic genes in antarctic hypolithons

>Magister Scientiae - MScAntarctica is known for its pristine environments. A variety of unsuitable environmental conditions were once thought to render the continent unsuitable for sustaining life. However, metagenomic data have revealed a wealth of species diversity in a range of biotopes.Hypolithons, photosynthetic communities which live under translucent rocks in climatically extreme environments, are an important input source for both carbon (C) and nitrogen (N) in this hyperarid desert environment. Microbial contribution to biogeochemical cycling resulting in fixation of both C and N remains poorly understood. Moreover, there is a reported close interplay between both cycles, with nitrogen being reported to be a limiting factor in carbon assimilation.In this study the diversity of C and N fixing organisms was investigated by using the cbbL and nifH genes as phylogenetic and functional markers. High Molecular weight metagenomic DNA and RNA was extracted from hypolithons. PCR amplification was carried out using cbbL (800 bp for red-like, 1,100 bp for green-like) and nifH (360 bp) gene specific primers.Resultant PCR products were used to construct libraries which were screened for correct sized inserts. Restriction Fragment Length Polymorphism (RFLP) was used to de-replicate clones prior to sequencing. Phylogenetic positions from both clone libraries were established by aligning nucleotide sequences and constructing similarity trees using NJ clustering methods.BLASTn results indicated the presence of previously uncultured organisms which contain cbbL and nifH genes. BLASTn results were characterized by low percentages of maximum identity (typically <95%), a potential indicator of novel taxa. Sequences from respective libraries clustered with cyanobacteria such as Nostoc, Scytonema, and Tolypothrix and α-, β-, and γ-Proteobacteria such as Azotobacter, Agrobacterium and Mesorhizobium. Generally sequence results indicate a largely homogenous, being dominated by specific taxa. Each group may contain potential keystone species, essential for both biogeochemical cycling in oligotrophic environment

Phylogeny, classification and metagenomic bioprospecting of microbial acetyl xylan esterases

Acetyl xylan esterases (AcXEs), also termed xylan deacetylases, are broad specificity Carbohydrate-Active Enzymes (CAZymes) that hydrolyse ester bonds to liberate acetic acid from acetylated hemicellulose (typically polymeric xylan and xylooligosaccharides). They belong to eight families within the Carbohydrate Esterase (CE) class of the CAZy database. AcXE classification is largely based on sequence-dependent phylogenetic relationships, supported in some instances with substrate specificity data. However, some sequence-based predictions of AcXE-encoding gene identity have proved to be functionally incorrect. Such ambiguities can lead to mis-assignment of genes and enzymes during sequence data-mining, reinforcing the necessity for the experimental confirmation of the functional properties of putative AcXE-encoding gene products. Although one-third of all characterized CEs within CAZy families 1–7 and 16 are AcXEs, there is a need to expand the sequence database in order to strengthen the link between AcXE gene sequence and specificity. Currently, most AcXEs are derived from a limited range of (mostly microbial) sources and have been identified via culture-based bioprospecting methods, restricting current knowledge of AcXEs to data from relatively few microbial species. More recently, the successful identification of AcXEs via genome and metagenome mining has emphasised the huge potential of culture-independent bioprospecting strategies. We note, however, that the functional metagenomics approach is still hampered by screening bottlenecks. The most relevant recent reviews of AcXEs have focused primarily on the biochemical and functional properties of these enzymes. In this review, we focus on AcXE phylogeny, classification and the future of metagenomic bioprospecting for novel AcXEs.The South African Department of Science and Technology Biocatalysis Initiative, National Research Foundation (DAC, TPM), the University of Pretoria’s Genomics Research Institute (DAC) and Research Development Program (TPM). FAA was supported by funds from the Organisation for Women in Science in the Developing World (OWSD).http://www.elsevier.com/locate/emt2017-11-30hb2016Genetic

The use of different 16S rRNA gene variable regions in biogeographical studies

DATA AVAILABILITY STATEMENT : All Illumina sequences generated and analyzed in this study were deposited into the European Nucleotide Archive (accession number PRJEB55051).SUPPORTING INFORMATION 1 : FIGURE S1. Samples located in four inland areas of the Prince Charles Mountains (ME1 from Mount Rubin, ME2 and ME3 from Mawson Escarpment, MM1 and MM2 from Mount Menzies, LT1 and LT2 from Lake Terrasovoje), in the Reinbolt Hills (RH1), and in coastal sites in proximity of the Prince Charles Mountains (C1 and C2; see Table S1). Map was produced using MODIS mosaic (125 m) imagery distributed by Quantarctica (https://cmr.earthdata.nasa.gov/; https://www.npolar.no/quantarctica/). FIGURE S2. Pearson's pairwise correlations between Bray–Curtis dissimilarity matrices calculated on relative abundance taxonomic dataset (genus level; A), and between Jaccard dissimilarity matrices calculated on presence/absence taxonomic dataset (genus level; B). Correlations were calculated for all the variable region datasets (V1–V3, V3–V4, V4, V4–V5 and V8–V9), and the mixed datasets (Mix 1, Mix 2 and Mix 3) constituted by randomly picked samples from V1–V3, V3–V4, V4, V4–V5 and V8–V9 (Table S4). Pearson's correlation coefficients (r) are reported only in case of significant correlation (p < 0.05).SUPPORTING INFORMATION 2 : TABLE S1. Sample specifics. TABLE S2. Geochemical data. TABLE S3. Relative abundance (%) of the taxonomic domains Bacteria and Archaea in sample (i.e., ME1, ME2, ME3, MM1, MM2, LT1, LT2, RH1, C1 and C2) for each variable region dataset (i.e., V1–V3, V3–V4, V4, V4–V5 and V8–V9). TABLE S4. Composition of mixed communities. TABLE S5. Number of reads at each step of the 16S rRNA gene processing pipeline. *counts reported as read pairs. TABLE S6. Number and percentage of unknown amplicon sequence variants (ASVs) at genus level for each phylum. TABLE S7. Relative abundance associated to unknown amplicon sequence variants at genus-level for each phylum. TABLE S8. Pearson's correlations from pairwise comparisons of variable region datasets performed on number of genera (A), dominant genera (i.e., genera represented by a relative abundance higher than 1% in at least one sample) (B), rare genera (i.e., genera represented by a relative abundance lower than 0.1% in all samples (C), Shannon index (D) and unique genera (E).16S rRNA gene amplicon sequencing is routinely used in environmental surveys to identify microbial diversity and composition of the samples of interest. The dominant sequencing technology of the past decade (Illumina) is based on the sequencing of 16S rRNA hypervariable regions. Online sequence data repositories, which represent an invaluable resource for investigating microbial distributional patterns across spatial, environmental or temporal scales, contain amplicon datasets from diverse 16S rRNA gene variable regions. However, the utility of these sequence datasets is potentially reduced by the use of different 16S rRNA gene amplified regions. By comparing 10 Antarctic soil samples sequenced for five different 16S rRNA amplicons, we explore whether sequence data derived from diverse 16S rRNA variable regions can be validly used as a resource for biogeographical studies. Patterns of shared and unique taxa differed among samples as a result of variable taxonomic resolutions of the assessed 16S rRNA variable regions. However, our analyses also suggest that the use of multi-primer datasets for biogeographical studies of the domain Bacteria is a valid approach to explore bacterial biogeographical patterns due to the preservation of bacterial taxonomic and diversity patterns across different variable region datasets. We deem composite datasets useful for biogeographical studies.Australian Antarctic Division, Australian Research Council and NRF SANAP.http://wileyonlinelibrary.com/journal/emi4hj2023BiochemistryGeneticsMicrobiology and Plant Patholog

Microbial anhydrobiosis

The loss of cellular water (desiccation) and the resulting low cytosolic water activity are major stress factors for life. Numerous prokaryotic and eukaryotic taxa have evolved molecular and physiological adaptions to periods of low water availability or water-limited environments that occur across the terrestrial Earth. The changes within cells during the processes of desiccation and rehydration, from the activation (and inactivation) of biosynthetic pathways to the accumulation of compatible solutes, have been studied in considerable detail. However, relatively little is known on the metabolic status of organisms in the desiccated state; that is, in the sometimes extended periods between the drying and rewetting phases. During these periods, which can extend beyond decades and which we term ‘anhydrobiosis’, organismal survival could be dependent on a continued supply of energy to maintain the basal metabolic processes necessary for critical functions such as macromolecular repair. Here, we review the state of knowledge relating to the function of microorganisms during the anhydrobiotic state, highlighting substantial gaps in our understanding of qualitative and quantitative aspects of molecular and biochemical processes in desiccated cells.https://sfamjournals.onlinelibrary.wiley.com/journal/14622920hj2022BiochemistryGeneticsMicrobiology and Plant Patholog

Biogeographic survey of soil bacterial communities across Antarctica

Background: Antarctica and its unique biodiversity are increasingly at risk from the effects of global climate change and other human influences. A significant recent element underpinning strategies for Antarctic conservation has been the development of a system of Antarctic Conservation Biogeographic Regions (ACBRs). The datasets supporting this classification are, however, dominated by eukaryotic taxa, with contributions from the bacterial domain restricted to Actinomycetota and Cyanobacteriota. Nevertheless, the ice-free areas of the Antarctic continent and the sub-Antarctic islands are dominated in terms of diversity by bacteria. Our study aims to generate a comprehensive phylogenetic dataset of Antarctic bacteria with wide geographical coverage on the continent and sub-Antarctic islands, to investigate whether bacterial diversity and distribution is reflected in the current ACBRs. Results: Soil bacterial diversity and community composition did not fully conform with the ACBR classification. Although 19% of the variability was explained by this classification, the largest differences in bacterial community composition were between the broader continental and maritime Antarctic regions, where a degree of structural overlapping within continental and maritime bacterial communities was apparent, not fully reflecting the division into separate ACBRs. Strong divergence in soil bacterial community composition was also apparent between the Antarctic/sub-Antarctic islands and the Antarctic mainland. Bacterial communities were partially shaped by bioclimatic conditions, with 28% of dominant genera showing habitat preferences connected to at least one of the bioclimatic variables included in our analyses. These genera were also reported as indicator taxa for the ACBRs. Conclusions: Overall, our data indicate that the current ACBR subdivision of the Antarctic continent does not fully reflect bacterial distribution and diversity in Antarctica. We observed considerable overlap in the structure of soil bacterial communities within the maritime Antarctic region and within the continental Antarctic region. Our results also suggest that bacterial communities might be impacted by regional climatic and other environmental changes. The dataset developed in this study provides a comprehensive baseline that will provide a valuable tool for biodiversity conservation efforts on the continent. Further studies are clearly required, and we emphasize the need for more extensive campaigns to systematically sample and characterize Antarctic and sub-Antarctic soil microbial communities. APsmQ8MphSAgg4BzZyqdNTVideo Abstrac

Long-read metagenomics of soil communities reveals phylum-specific secondary metabolite dynamics

Microbial biosynthetic gene clusters (BGCs) encoding secondary metabolites are thought to impact a plethora of biologically mediated environmental processes, yet their discovery and functional characterization in natural microbiomes remains challenging. Here we describe deep long-read sequencing and assembly of metagenomes from biological soil crusts, a group of soil communities that are rich in BGCs. Taking advantage of the unusually long assemblies produced by this approach, we recovered nearly 3,000 BGCs for analysis, including 712 full-length BGCs. Functional exploration through metatranscriptome analysis of a 3-day wetting experiment uncovered phylum-specific BGC expression upon activation from dormancy, elucidating distinct roles and complex phylogenetic and temporal dynamics in wetting processes. For example, a pronounced increase in BGC transcription occurs at night primarily in cyanobacteria, implicating BGCs in nutrient scavenging roles and niche competition. Taken together, our results demonstrate that long-read metagenomic sequencing combined with metatranscriptomic analysis provides a direct view into the functional dynamics of BGCs in environmental processes and suggests a central role of secondary metabolites in maintaining phylogenetically conserved niches within biocrusts.Supplementary Data 1 : Description: Raw metagenome and metatranscriptome statistics.Supplementary Data 2 : Description: Assembly statistics of short- and long-read metagenomes as well as metatranscriptomes.Supplementary Data 3 : Description: Each biosynthetic gene cluster identified from the assembled metagenomes in this study.Supplementary Data 4 : Description: Each biosynthetic gene cluster identified in the metatranscriptomic assemblies.Supplementary Data 5 : Description: The genes used to calculate transcription of biosynthetic gene clusters and core bacterial genes.Supplementary Data 6 : Description: DESeq2 analysis of significantly transcribed genes between day and night-time transcription.Supplementary Data 7 : Description: Transcriptional scores for cation-related genes.Supplementary Data 8 : Description: Average abundance pattern for each phylum through time.Supplementary Data 9 : Description: Taxonomic composition of metagenomes and metatranscriptomes using fulllength 16S rRNA.Supplementary Data 10 : Description: Normalized sequence data showing scores of transcription at each time point with BGC type and Phylum shownThis work was partially supported by funds provided by the Office of Science Early Career Research Program Office of Biological and Environmental Research, of the U.S. Department of Energy and by the U.S. Department of Energy Joint Genome Institute, a DOE Office of Science User Facility, supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory. We also wish to acknowledge Simon Roux, Emiley Eloe-Fadrosh and Eoin Brodie for their constructive feedback.https://www.nature.com/commsbioam2022BiochemistryGeneticsMicrobiology and Plant Patholog

The global contribution of soil mosses to ecosystem services

Soil mosses are among the most widely distributed organisms on land. Experiments and observations suggest that they contribute to terrestrial soil biodiversity and function, yet their ecological contribution to soil has never been assessed globally under natural conditions. Here we conducted the most comprehensive global standardized field study to quantify how soil mosses influence 8 ecosystem services associated with 24 soil biodiversity and functional attributes across wide environmental gradients from all continents. We found that soil mosses are associated with greater carbon sequestration, pool sizes for key nutrients and organic matter decomposition rates but a lower proportion of soil-borne plant pathogens than unvegetated soils. Mosses are especially important for supporting multiple ecosystem services where vascular-plant cover is low. Globally, soil mosses potentially support 6.43 Gt more carbon in the soil layer than do bare soils. The amount of soil carbon associated with mosses is up to six times the annual global carbon emissions from any altered land use globally. The largest positive contribution of mosses to soils occurs under a high cover of mat and turf mosses, in less-productive ecosystems and on sandy and salty soils. Our results highlight the contribution of mosses to soil life and functions and the need to conserve these important organisms to support healthy soils.The study work associated with this paper was funded by a Large Research Grant from the British Ecological Society (no. LRB17\1019; MUSGONET). D.J.E. is supported by the Hermon Slade Foundation. M.D.-B. was supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-025483-I), a project from the Spanish Ministry of Science and Innovation for the I + D + i (PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033a) and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). E.G. is supported by the European Research Council grant agreement 647038 (BIODESERT). M.B. is supported by a Ramón y Cajal grant from Spanish Ministry of Science (RYC2021-031797-I). A.d.l.R is supported by the AEI project PID2019-105469RB-C22. L.W. and Jianyong Wang are supported by the Program for Introducing Talents to Universities (B16011) and the Ministry of Education Innovation Team Development Plan (2013-373). The contributions of T.G. and T.U.N. were supported by the Research Program in Forest Biology, Ecology and Technology (P4-0107) and the research projects J4-3098 and J4-4547 of the Slovenian Research Agency. The contribution of P.B.R. was supported by the NSF Biological Integration Institutes grant DBI-2021898. J. Durán and A. Rodríguez acknowledge support from the FCT (2020.03670.CEECIND and SFRH/BDP/108913/2015, respectively), as well as from the MCTES, FSE, UE and the CFE (UIDB/04004/2021) research unit financed by FCT/MCTES through national funds (PIDDAC)

Urban greenspaces and nearby natural areas support similar levels of soil ecosystem services

DATA AVAILABILITY : All the materials, raw data, and protocols used in the article are available upon request and without restriction, and all data will be made publicly available in a public repository (Figshare https://doi.org/10.6084/m9.figshare.24873135.v1) upon publication.Greenspaces are important for sustaining healthy urban environments and their human populations. Yet their capacity to support multiple ecosystem services simultaneously (multiservices) compared with nearby natural ecosystems remains virtually unknown. We conducted a global field survey in 56 urban areas to investigate the influence of urban greenspaces on 23 soil and plant attributes and compared them with nearby natural environments. We show that, in general, urban greenspaces and nearby natural areas support similar levels of soil multiservices, with only six of 23 attributes (available phosphorus, water holding capacity, water respiration, plant cover, arbuscular mycorrhizal fungi (AMF), and arachnid richness) significantly greater in greenspaces, and one (available ammonium) greater in natural areas. Further analyses showed that, although natural areas and urban greenspaces delivered a similar number of services at low (>25% threshold) and moderate (>50%) levels of functioning, natural systems supported significantly more functions at high (>75%) levels of functioning. Management practices (mowing) played an important role in explaining urban ecosystem services, but there were no effects of fertilisation or irrigation. Some services declined with increasing site size, for both greenspaces and natural areas. Our work highlights the fact that urban greenspaces are more similar to natural environments than previously reported and underscores the importance of managing urban greenspaces not only for their social and recreational values, but for supporting multiple ecosystem services on which soils and human well-being depends.Supported by a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (URBANFUN); the BES grant agreement No LRB17\1019 (MUSGONET); the Spanish Ministry of Science and Innovation for the I + D + i project PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033; a project of the Fondo Europeo de Desarrollo Regional (FEDER) and the Consejería de Transformación Económica, Industria, Conocimiento y Universidades of the Junta de Andalucía; the Hermon Slade Foundation; the National Natural Science Foundation of China; the Young Science and Technology Talent Support Project of Jilin Province; Young Elite Scientists Sponsorship Program by BAST; the Fundamental Research Funds for the Central Universities; a Ramón y Cajal grant from Spanish Ministry of Science and Innovation; FONDECYT; the EU’s H2020 research and innovation programme; FCT/MCTES through national funds (PIDDAC); the National Research Foundation of South Africa; the Slovenian Research Agency; the SERB, DST and Banaras Hindu University; the Program for Introducing Talents to Universities and the Ministry of Education Innovation Team Development Plan.https://www.nature.com/npjurbansustainhj2024BiochemistryGeneticsMicrobiology and Plant PathologySDG-15:Life on lan

Biogenic factors explain soil carbon in paired urban and natural ecosystems worldwide

DATA AVAILABILITY : The raw data associated with this study are available in https://figshare.com/s/1eadef6619e74a8f2904 (https://doi.org/10.6084/m9.figshare.21025615).Urban greenspaces support multiple nature-based services, many of which depend on the amount of soil carbon (C). Yet, the environmental drivers of soil C and its sensitivity to warming are still poorly understood globally. Here we use soil samples from 56 paired urban greenspaces and natural ecosystems worldwide and combine soil C concentration and size fractionation measures with metagenomics and warming incubations. We show that surface soils in urban and natural ecosystems sustain similar C concentrations that follow comparable negative relationships with temperature. Plant productivity’s contribution to explaining soil C was higher in natural ecosystems, while in urban ecosystems, the soil microbial biomass had the greatest explanatory power. Moreover, the soil microbiome supported a faster C mineralization rate with experimental warming in urban greenspaces compared with natural ecosystems. Consequently, urban management strategies should consider the soil microbiome to maintain soil C and related ecosystem services.This study was supported by a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (URBANFUN), and by BES Grant. Unión Europea NextGeneration; the Spanish Ministry of Science and Innovation funded by MCIN/AEI/10.13039/501100011033; a project of the Fondo Europeo de Desarrollo Regional (FEDER) and the Consejería de Transformación Económica, Industria, Conocimiento y Universidades of the Junta de Andalucía (FEDER Andalucía 2014-2020 Objetivo temático ‘01 - Refuerzo de la investigación, el desarrollo tecnológico y la innovación’); the Hermon Slade Foundation; the Science and Engineering Research Board (SERB); the Department of Science and Technology (DST), India; Banaras Hindu Univeristy; the FCT; the MCTES, FSE, UE and the CFE research unit financed by FCT/MCTES through national funds (PIDDAC).https://www.nature.com/nclimatehj2024BiochemistryGeneticsMicrobiology and Plant PathologySDG-15:Life on lan