Browsing by Author "Cowan, Don A."

Now showing 1 - 8 of 8
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    Contribution of soil bacteria to the atmosphere across biomes
    (2023) Archer, Stephen D. J.; Lee, Kevin C.; Caruso, Tancredi; Alcami, Antonio; Araya, Jonathan G.; Cary, S. Craig; Cowan, Don A.; Etchebehere, Claudia; Gantsetseg, Batdelger; Gomez-Silva, Benito; Hartery, Sean; Hogg, Ian D.; Kansour, Mayada K.; Lawrence, Timothy; Lee, Charles K.; Lee, Patrick K. H.; Leopold, Matthias; Leung, Marcus H. Y.; Maki, Teruya; Mckay, Christopher P.; Al Mailem, Dina M.; Ramond, Jean-Baptiste; Rastrojo, Alberto; Santl-Temkiv, Tina; Sun, Henry J.; Tong, Xinzhao; Vandenbrink, Bryan; Warren-Rhodes, Kimberley A.; Pointing, Stephen B.
    The dispersion of microorganisms through the atmosphere is a continual and essential process that underpins biogeography and ecosystem development and function. Despite the ubiquity of atmospheric microorganisms globally, specific knowledge of the determinants of atmospheric microbial diversity at any given location remains unresolved. Here we describe bacterial diversity in the atmospheric boundary layer and underlying soil at twelve globally distributed locations encompassing all major biomes, and characterise the contribution of local and distant soils to the observed atmospheric community. Across biomes the diversity of bacteria in the atmosphere was negatively correlated with mean annual precipitation but positively correlated to mean annual temperature. We identified distinct non-randomly assembled atmosphere and soil communities from each location, and some broad trends persisted across biomes including the enrichment of desiccation and UV tolerant taxa in the atmospheric community. Source tracking revealed that local soils were more influential than distant soil sources in determining observed diversity in the atmosphere, with more emissive semi-arid and arid biomes contributing most to signatures from distant soil. Our findings highlight complexities in the atmospheric microbiota that are relevant to understanding regional and global ecosystem connectivity.
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    Documenting the diversity of the Namibian Ju|'hoansi intestinal microbiome
    (2024) Truter, Mia; Koopman, Jessica E.; Jordaan, Karen; Tsamkxao, Leon Oma; Cowan, Don A.; Underdown, Simon J.; Ramond, Jean-Baptiste; Rifkin, Riaan F.
    We investigate the bacterial and fungal composition and functionality of the Ju|'hoansi intestinal microbiome (IM). The Ju|'hoansi are a hunter-gatherer community residing in northeastern Namibia. They formerly subsisted by hunting and gathering but have been increasingly exposed to industrial dietary sources, medicines, and lifestyle features. They present an opportunity to study the evolution of the human IM in situ, from a predominantly hunter-gatherer to an increasingly Western urban-forager-farmer lifestyle. Their bacterial IM resembles that of typical hunter-gatherers, being enriched for genera such as Prevotella, Blautia, Faecalibacterium, Succinivibrio, and Treponema. Fungal IM inhabitants include animal pathogens and plant saprotrophs such as Fusarium, Issatchenkia, and Panellus. Our results suggest that diet and culture exert a greater influence on Ju|'hoansi IM composition than age, self-identified biological sex, and medical history. The Ju|'hoansi exhibit a unique core IM composition that diverges from the core IMs of other populations.
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    Functional redundancy buffers the effect of poly-extreme environmental conditions on southern African dryland soil microbial communities
    (2024) Sauma-Sánchez, Tomás; Alcorta Loyola, Jaime Andrés; Tamayo Leiva, Javier Alejandro; Diez Moreno, Beatriz; Bezuidenhout, Hugo; Cowan, Don A.; Ramond, Jean-Baptiste
    Drylands' poly-extreme conditions limit edaphic microbial diversity and functionality. Furthermore, climate change exacerbates soil desiccation and salinity in most drylands. To better understand the potential effects of these changes on dryland microbial communities, we evaluated their taxonomic and functional diversities in two Southern African dryland soils with contrasting aridity and salinity. Fungal community structure was significantly influenced by aridity and salinity, while Bacteria and Archaea only by salinity. Deterministic homogeneous selection was significantly more important for bacterial and archaeal communities' assembly in hyperarid and saline soils when compared to those from arid soils. This suggests that niche partitioning drives bacterial and archaeal communities' assembly under the most extreme conditions. Conversely, stochastic dispersal limitations drove the assembly of fungal communities. Hyperarid and saline soil communities exhibited similar potential functional capacities, demonstrating a disconnect between microbial structure and function. Structure variations could be functionally compensated by different taxa with similar functions, as implied by the high levels of functional redundancy. Consequently, while environmental selective pressures shape the dryland microbial community assembly and structures, they do not influence their potential functionality. This suggests that they are functionally stable and that they could be functional even under harsher conditions, such as those expected with climate change., Salinity and aridity shape the assembly and structures, but not the potential functionality, of microbial communities from Southern African dryland soils.
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    Hydrogen-Oxidizing Bacteria Are Abundant in Desert Soils and Strongly Stimulated by Hydration
    (2020) Jordaan, Karen; Lappan, Rachael; Dong, Xiyang; Aitkenhead, Ian J.; Bay, Sean K.; Chiri, Eleonora; Wieler, Nimrod; Meredith, Laura K.; Cowan, Don A.; Chown, Steven L.; Greening, Chris
    How the diverse bacterial communities inhabiting desert soils maintain energy and carbon needs is much debated. Traditionally, most bacteria are thought to persist by using organic carbon synthesized by photoautotrophs following transient hydration events. Recent studies focused on Antarctic desert soils have revealed, however, that some bacteria use atmospheric trace gases, such as hydrogen (H-2), to conserve energy and fix carbon independently of photosynthesis. In this study, we investigated whether atmospheric H-2 oxidation occurs in four nonpolar desert soils and compared this process to photosynthesis. To do so, we first profiled the distribution, expression, and activities of hydrogenases and photosystems in surface soils collected from the South Australian desert over a simulated hydrationdesiccation cycle. Hydrogenase-encoding sequences were abundant in the metagenomes and metatranscriptomes and were detected in actinobacterial, acidobacterial, and cyanobacterial metagenome-assembled genomes. Native dry soil samples mediated H-2 oxidation, but rates increased 950-fold following wetting. Oxygenic and anoxygenic phototrophs were also detected in the community but at lower abundances. Hydration significantly stimulated rates of photosynthetic carbon fixation and, to a lesser extent, dark carbon assimilation. Hydrogenase genes were also widespread in samples from three other climatically distinct deserts, the Namib, Gobi, and Mojave, and atmospheric H-2 oxidation was also greatly stimulated by hydration at these sites. Together, these findings highlight that H-2 is an important, hitherto-overlooked energy source supporting bacterial communities in desert soils. Contrary to our previous hypotheses, however, H-2 oxidation occurs simultaneously rather than alternately with photosynthesis in such ecosystems and may even be mediated by some photoautotrophs.
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    Multiple energy sources and metabolic strategies sustain microbial diversity in Antarctic desert soils
    (2021) Ortiz, Maximiliano; Leung, Pok Man; Shelley, Guy; Jirapanjawat, Thanavit; Nauer, Philipp A.; Van Goethem, Marc W.; Bay, Sean K.; Islam, Zahra F.; Jordaan, Karen; Vikram, Surendra; Chown, Steven L.; Hogg, Ian D.; Makhalanyane, Thulani P.; Grinter, Rhys; Cowan, Don A.; Greening, Chris
    Numerous diverse microorganisms reside in the cold desert soils of continental Antarctica, though we lack a holistic understanding of the metabolic processes that sustain them. Here, we profile the composition, capabilities, and activities of the microbial communities in 16 physicochemically diverse mountainous and glacial soils. We assembled 451 metagenome-assembled genomes from 18 microbial phyla and inferred through Bayesian divergence analysis that the dominant lineages present are likely native to Antarctica. In support of earlier findings, metagenomic analysis revealed that the most abundant and prevalent microorganisms are metabolically versatile aerobes that use atmospheric hydrogen to support aerobic respiration and sometimes carbon fixation. Surprisingly, however, hydrogen oxidation in this region was catalyzed primarily by a phylogenetically and structurally distinct enzyme, the group 1l [NiFe]-hydrogenase, encoded by nine bacterial phyla. Through gas chromatography, we provide evidence that both Antarctic soil communities and an axenic Bacteroidota isolate (Hymenobacter roseosalivarius) oxidize atmospheric hydrogen using this enzyme. Based on ex situ rates at environmentally representative temperatures, hydrogen oxidation is theoretically sufficient for soil communities to meet energy requirements and, through metabolic water production, sustain hydration. Diverse carbon monoxide oxidizers and abundant methanotrophs were also active in the soils. We also recovered genomes of microorganisms capable of oxidizing edaphic inorganic nitrogen, sulfur, and iron compounds and harvesting solar energy via microbial rhodopsins and conventional photosystems. Obligately symbiotic bacteria, including Patescibacteria, Chlamydiae, and predatory Bdellovibrionota, were also present. We conclude that microbial diversity in Antarctic soils reflects the coexistence of metabolically flexible mixotrophs with metabolically constrained specialists.
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    Temporal dynamics of microbial transcription in wetted hyperarid desert soils
    (2024) Leon-Sobrino, Carlos; Ramond, Jean-Baptiste; Coclet, Clement; Kapitango, Ritha-Meriam; Maggs-Kolling, Gillian; Cowan, Don A.
    Rainfall is rare in hyperarid deserts but, when it occurs, it triggers large biological responses essential for the long-term maintenance of the ecosystem. In drylands, microbes play major roles in nutrient cycling, but their responses to short-lived opportunity windows are poorly understood. Due to its ephemeral nature, mRNA is ideally suited to study microbiome dynamics upon abrupt changes in the environment. We analyzed microbial community transcriptomes after simulated rainfall in a Namib Desert soil over 7 days. Using total mRNA from dry and watered plots we infer short-term functional responses in the microbiome. A rapid two-phase cycle of activation and return to basal state was completed in a short period. Motility systems activated immediately, whereas competition-toxicity increased in parallel to predator taxa and the drying of soils. Carbon fixation systems were downregulated, and reactivated upon return to a near-dry state. The chaperone HSP20 was markedly regulated by watering across all major bacteria, suggesting a particularly important role in adaptation to desiccated ecosystems. We show that transcriptomes provide consistent and high resolution information on microbiome processes in a low-biomass environment, revealing shared patterns across taxa. We propose a structured dispersal-predation dynamic as a central driver of desert microbial responses to rainfall.
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    The plant rhizosheath-root niche is an edaphic "mini-oasis" in hyperarid deserts with enhanced microbial competition
    (2022) Marasco, Ramona; Fusi, Marco; Ramond, Jean-Baptiste; Van Goethem, Marc W.; Seferji, Kholoud; Maggs-Koelling, Gillian; Cowan, Don A.; Daffonchio, Daniele
    Plants have evolved unique morphological and developmental adaptations to cope with the abiotic stresses imposed by (hyper)arid environments. Such adaptations include the formation of rhizosheath-root system in which mutualistic plant-soil microbiome associations are established: the plant provides a nutrient-rich and shielded environment to microorganisms, which in return improve plant-fitness through plant growth promoting services. We hypothesized that the rhizosheath-root systems represent refuge niches and resource islands for the desert edaphic microbial communities. As a corollary, we posited that microorganisms compete intensively to colonize such "oasis" and only those beneficial microorganisms improving host fitness are preferentially selected by plant. Our results show that the belowground rhizosheath-root micro-environment is largely more hospitable than the surrounding gravel plain soil with higher nutrient and humidity contents, and cooler temperatures. By combining metabarcoding and shotgun metagenomics, we demonstrated that edaphic microbial biomass and community stability increased from the non-vegetated soils to the rhizosheath-root system. Concomitantly, non-vegetated soil communities favored autotrophy lifestyle while those associated with the plant niches were mainly heterotrophs and enriched in microbial plant growth promoting capacities. An intense inter-taxon microbial competition is involved in the colonization and homeostasis of the rhizosheath zone, as documented by significant enrichment of antibiotic resistance genes and CRISPR-Cas motifs. Altogether, our results demonstrate that rhizosheath-root systems are "edaphic mini-oases" and microbial diversity hotspots in hyperarid deserts. However, to colonize such refuge niches, the desert soil microorganisms compete intensively and are therefore prepared to outcompete potential rivals.
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    With a pinch of salt: metagenomic insights into Namib Desert salt pan microbial mats and halites reveal functionally adapted and competitive communities
    (2023) Martinez-Alvarez, Laura; Ramond, Jean-Baptiste; Vikram, Surendra; Leon-Sobrino, Carlos; Maggs-Kolling, Gillian; Cowan, Don A.
    Salt pans or playas, which are saline-rich springs surrounded by halite evaporates in arid environments, have played an essential role in landscape erosion during the formation of the Namib Desert and are numerous in its central region. In this study, we used shotgun metagenomics to investigate the phylogenetic and functional capacities of the microbial communities from two salt pans (namely, Eisefeld and Hosabes) located in central Namib Desert, located in Southwest Africa. We studied the source and sink sediment mat communities of the saline streams, as well as those from two halites (crystallized structures on the stream margins). The microbial assemblages and potential functions were distinct in both niches. Independently from their localization (Eisfeld vs Hosabes and source vs sink), the sediment mat communities were dominated by members of the Alpha- and Gamma-proteobacteria classes, while halites were Archaea dominated and also contained high abundances of the extremely halophilic bacterium Salinibacter sp. (phylum Bacteroidota). Photoheterotrophy and chemoheterotrophy were the principal lifestyles in both niches, with halite communities having a reduced diversity of metabolic pathways. Intense microbial-virus interactions in both niches were implied by the widespread detection of CRISPR-Cas defense systems. We identified a putatively novel clade of type II CRISPR-Cas systems, as well as novel candidate viral lineages of the class Caudoviricetes and of Halobacteriales-infecting haloviruses. Putative gene transfer agent-like sequences within the Alphaproteobacteria were identified in the sediment mat communities. These horizontal gene transfer elements have the potential to drive genome plasticity and evolution of the Alphaproteobacteria in the Namib Desert salt pan microbiomes.IMPORTANCEThe hyperarid Namib Desert is one of the oldest deserts on Earth. It contains multiple clusters of playas which are saline-rich springs surrounded by halite evaporites. Playas are of great ecological importance, and their indigenous (poly)extremophilic microorganisms are potentially involved in the precipitation of minerals such as carbonates and sulfates and have been of great biotechnological importance. While there has been a considerable amount of microbial ecology research performed on various Namib Desert edaphic microbiomes, little is known about the microbial communities inhabiting its multiple playas. In this work, we provide a comprehensive taxonomic and functional potential characterization of the microbial, including viral, communities of sediment mats and halites from two distant salt pans of the Namib Desert, contributing toward a better understanding of the ecology of this biome.