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Background: The processes that shape microbial biogeography are not well understood, and concepts that apply to macroorganisms, like dispersal barriers, may not affect microorganisms in the same predictable ways. To better understand how known macro-scale biogeographic processes can be applied at micro-scales, we examined seagrass associated microbiota on either side of Wallace's line to determine the influence of this cryptic dispersal boundary on the community structure of microorganisms. Communities were examined from twelve locations throughout Indonesia on either side of this theoretical line. Results: We found significant differences in microbial community structure on either side of this boundary (R2 = 0.09; P = 0.001), and identified seven microbial genera as differentially abundant on either side of the line, six of these were more abundant in the West, with the other more strongly associated with the East. Genera found to be differentially abundant had significantly smaller minimum cell dimensions (GLM: t923 = 59.50, P < 0.001) than the overall community. Conclusion: Despite the assumed excellent dispersal ability of microbes, we were able to detect significant differences in community structure on either side of this cryptic biogeographic boundary. Samples from the two closest islands on opposite sides of the line, Bali and Komodo, were more different from each other than either was to its most distant island on the same side. We suggest that limited dispersal across this barrier coupled with habitat differences are primarily responsible for the patterns observed. The cryptic processes that drive macroorganism community divergence across this region may also play a role in the bigeographic patterns of microbiota. [ABSTRACT FROM AUTHOR]

Mammalian gut microbial communities are frequently found to be host‐specific—microbial community compositions are more similar within than between host species—and some individual microbial taxa consistently associate with a single or small set of host species. The ecoevolutionary dynamics that result in this pattern of phylosymbiosis or host specificity have been proposed, but robust tests of the mechanisms driving these relationships are lacking. In this issue of Molecular Ecology, Mazel et al. (2023) combine large amplicon sequencing data sets with bacterial phenotypic traits to test whether microbial dispersal patterns contribute to the host specificity of the gut microbiome. They find that both transmission mode and oxygen tolerance are predictive of how specialized a microbe is. Horizontally transmitted, oxygen‐tolerant microbes are more likely to be generalists, and vertically transmitted anaerobes are more likely to be limited to a few host species. This creative use of publicly available data provides a roadmap for testing hypotheses about the mechanisms underlying phylosymbiosis. [ABSTRACT FROM AUTHOR]

Metacommunity theory dictates that a microbial community is supported both by local ecological processes and the dispersal of microbes between neighboring communities. Studies that apply this perspective to human-associated microbial communities are thus far limited to the gut microbiome. Yet, the skin serves as the primary barrier between the body and the external environment, suggesting frequent opportunities for microbial dispersal to the variable microbial communities that are housed across skin sites. This paper applies metacommunity theory to understand the dispersal of microbes to the skin from the physical and social environment, as well as between different skin sites on an individual's body. This includes highlighting the role of human behavior in driving microbial dispersal, as well as shaping physiological properties of skin that underscore local microbial community dynamics. By leveraging data from research on the skin microbiomes of amphibians and other animals, this paper provides recommendations for future research on the skin microbial metacommunity, including generating testable predictions about the ecological underpinnings of the skin microbiome. [ABSTRACT FROM AUTHOR]

Microbiomes are integral to viticulture and winemaking – collectively termed winegrowing – where diverse fungi and bacteria can exert positive and negative effects on grape health and wine quality. Wine is a fermented natural product, and the vineyard serves as a key point of entry for quality-modulating microbiota, particularly in wine fermentations that are conducted without the addition of exogenous yeasts. Thus, the sources and persistence of wine-relevant microbiota in vineyards critically impact its quality. Site-specific variations in microbiota within and between vineyards may contribute to regional wine characteristics. This includes distinctions in microbiomes and microbiota at the strain level, which can contribute to wine flavor and aroma, supporting the role of microbes in the accepted notion of terroir as a biological phenomenon. Little is known about the factors driving microbial biodiversity within and between vineyards, or those that influence annual assembly of the fruit microbiome. Fruit is a seasonally ephemeral, yet annually recurrent product of vineyards, and as such, understanding the sources of microbiota in vineyards is critical to the assessment of whether or not microbial terroir persists with inter-annual stability, and is a key factor in regional wine character, as stable as the geographic distances between vineyards. This review examines the potential sources and vectors of microbiota within vineyards, general rules governing plant microbiome assembly, and how these factors combine to influence plant-microbe interactions relevant to winemaking. [ABSTRACT FROM AUTHOR]

Deep ocean microbial communities rely on the organic carbon produced in the sunlit ocean, yet it remains unknown whether surface processes determine the assembly and function of bathypelagic prokaryotes to a larger extent than deep‐sea physicochemical conditions. Here, we explored whether variations in surface phytoplankton assemblages across Atlantic, Pacific and Indian ocean stations can explain structural changes in bathypelagic (ca. 4,000 m) free‐living and particle‐attached prokaryotic communities (characterized through 16S rRNA gene sequencing), as well as changes in prokaryotic activity and dissolved organic matter (DOM) quality. We show that the spatial structuring of prokaryotic communities in the bathypelagic strongly followed variations in the abundances of surface dinoflagellates and ciliates, as well as gradients in surface primary productivity, but were less influenced by bathypelagic physicochemical conditions. Amino acid‐like DOM components in the bathypelagic reflected variations of those components in surface waters, and seemed to control bathypelagic prokaryotic activity. The imprint of surface conditions was more evident in bathypelagic than in shallower mesopelagic (200–1,000 m) communities, suggesting a direct connectivity through fast‐sinking particles that escape mesopelagic transformations. Finally, we identified a pool of endemic deep‐sea prokaryotic taxa (including potentially chemoautotrophic groups) that appear less connected to surface processes than those bathypelagic taxa with a widespread vertical distribution. Our results suggest that surface planktonic communities shape the spatial structure of the bathypelagic microbiome to a larger extent than the local physicochemical environment, likely through determining the nature of the sinking particles and the associated prokaryotes reaching bathypelagic waters. [ABSTRACT FROM AUTHOR]

Forest-to-agriculture conversion has been identified as a major threat to soil biodiversity and soil processes resilience, although the consequences of long-term land use change to microbial community assembly and ecological processes have been often neglected. Here, we combined metagenomic approach with a large environmental dataset, to (i) identify the microbial assembly patterns and, (ii) to evaluate the ecological processes governing microbial assembly, in bulk soil and soybean rhizosphere, along a long-term forest-to-agriculture conversion chronosequence, in Eastern Amazon. We hypothesized that (i) microbial communities in bulk soil and rhizosphere have different assembly patterns and (ii) the weight of the four ecological processes governing assembly differs between bulk soil and rhizosphere and along the chronosequence in the same fraction. Community assembly in bulk soil fitted most the zero-sum multinomial (ZSM) neutral-based model, regardless of time. Low to intermediate dispersal was observed. Decreasing influence of abiotic factors was counterbalanced by increasing influence of biotic factors, as the chronosequence advanced. Undominated ecological processes of dispersal limitation and variable selection governing community assembly were observed in this soil fraction. For soybean rhizosphere, community assembly fitted most the lognormal niche-based model in all chronosequence areas. High dispersal and an increasing influence of abiotic factors coupled with a decreasing influence of biotic factors were found along the chronosequence. Thus, we found a dominant role of dispersal process governing microbial assembly with a secondary effect of homogeneous selection process, mainly driven by decreasing aluminum and increased cations saturation in soil solution, due to long-term no-till cropping. Together, our results indicate that long-term no-till lead community abundances in bulk soil to be in a transient and conditional state, while for soybean rhizosphere, community abundances reach a periodic and permanent distribution state. Dominant dispersal process in rhizosphere, coupled with homogeneous selection, brings evidences that soybean root system selects microbial taxa via trade-offs in order to keep functional resilience of soil processes. [ABSTRACT FROM AUTHOR]

Dormant endospores of anaerobic, thermophilic bacteria found in cold marine sediments offer a useful model for studying microbial biogeography, dispersal, and survival. The dormant endospore phenotype confers resistance to unfavorable environmental conditions, allowing dispersal to be isolated and studied independently of other factors such as environmental selection. To study the resilience of thermospores to conditions relevant for survival in extreme cold conditions, their viability following different freezing treatments was tested. Marine sediment was frozen at either −80°C or −20°C for 10 days prior to pasteurization and incubation at +50°C for 21 days to assess thermospore viability. Sulfate reduction commenced at +50°C following both freezing pretreatments indicating persistence of thermophilic endospores of sulfate-reducing bacteria. The onset of sulfate reduction at +50°C was delayed in −80°C pretreated microcosms, which exhibited more variability between triplicates, compared to −20°C pretreated microcosms and parallel controls that were not frozen in advance. Microbial communities were evaluated by 16S rRNA gene amplicon sequencing, revealing an increase in the relative sequence abundance of thermophilic endospore-forming Firmicutes in all microcosms. Different freezing pretreatments (−80°C and −20°C) did not appreciably influence the shift in overall bacterial community composition that occurred during the +50°C incubations. Communities that had been frozen prior to +50°C incubation showed an increase in the relative sequence abundance of operational taxonomic units (OTUs) affiliated with the class Bacilli , relative to unfrozen controls. These results show that freezing impacts but does not obliterate thermospore populations and their ability to germinate and grow under appropriate conditions. Indeed the majority of the thermospore OTUs detected in this study (21 of 22) could be observed following one or both freezing treatments. These results are important for assessing thermospore viability in frozen samples and following cold exposure such as the very low temperatures that would be encountered during panspermia. [ABSTRACT FROM AUTHOR]

Abstract: The effects of soil microbial communities upon hydrological processes in relation to water holding capacity, run-off and percolation were assessed using sterile and non-sterile microcosms subjected to simulated rainfall. The treatments comprised a non-sterile field soil, soil sterilised by gamma-irradiation and sterile soil re-inoculated with field soil. Microbial biomass C was determined by chloroform fumigation–extraction and community structure by phospholipid fatty acid (PLFA) analysis. These properties were measured at the top, middle and bottom regions of the sloped (12°) microcosms. The field soil treatment had a significantly greater water holding capacity than the sterilised treatments. There was no significant difference in mean volumes of run-off or percolate between the treatments, although our results suggest a trend to a lower probability of run-off losses from a soil with higher microbial biomass and a greater potential for percolation of water. In re-inoculated treatments, microbial biomass was greater at the bottom of the slopes after rainfall, suggesting that the nascent community was relatively mobile. This effect did not occur in the field soil, although the community profiles in the re-inoculated and field soils were significantly different between the tops and bottoms of slope after rainfall. The soil microbial communities observed before and after rainfall application were significantly different for all treatments. The microbial community profiles associated with the run-off and percolate were significantly different to those found in the soil and also those found in the rainwater prior to application. Run-off and percolate community profiles were similar to one another, suggesting a consistency in the phenotypic structure of the phase of the microbial communities that was “water mobile”. This may be of significance when considering how microbial populations and communities disperse, and in relation to microbial quality of surface and groundwaters. [Copyright &y& Elsevier]

• First complete aerial microbiome inventory through multi-primer metabarcoding. • Huge diversity of bacteria, fungi, protists and plant material in the air. • Microbiome contains many potential pathogens of plants and animals. • Many co-occuring taxa such as obligate insect parasites with host insects. • Predictable patterns of microbiome and pathogens depending on weather conditions. Air is a major conduit for the dispersal of organisms at the local and the global scale. Most research has focused on the dispersal of plants, vertebrates and human disease agents. However, the air represents a key dispersal medium also for bacteria, fungi and protists. Many of those represent potential pathogens of animals and plants and have until now gone largely unrecorded. Here we studied the turnover in composition of the entire aerobiome, the collective diversity of airborne microorganisms. For that we performed daily analyses of all prokaryotes and eukaryotes (including plants) using multi-marker high-throughput sequencing for a total of three weeks. We linked the resulting communities to local weather conditions, to assess determinants of aerobiome composition and distribution. We observed hundreds of microbial taxa, mostly belonging to spore-forming organisms including fungi, but also protists. Additionally, we detected many potential human- and plant-pathogens. Community composition fluctuated on a daily basis and was linked to concurrent weather conditions, particularly air pressure and temperature. Using network analyses, we identified taxonomically diverse groups of organisms with correlated temporal dynamics. In part, this was due to co-variation with environmental conditions, while we could also detect specific host-parasite interactions. This study provides the first full inventory of the aerobiome and identifies putative drivers of its dynamics in terms of taxon composition. This knowledge can help develop early warning systems against pathogens and improve our understanding of microbial dispersal. [ABSTRACT FROM AUTHOR]