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Smoke from wildland fires contains more diverse, viable microbes than typical ambient air, yet little is known about the sources and sinks of smoke‐borne microorganisms. Data from molecular‐based surveys suggest that smoke‐borne microorganisms originate from material associated with the vegetation and underlying soils that becomes aerosolized during combustion, however, the sources of microbes in smoke have not yet been experimentally assessed. To elucidate this link, we studied high‐intensity forest fires in the Fishlake National Forest, Utah, USA and applied source‐sink modeling to assemblages of 16S ribosomal RNA (rRNA) gene sequences recovered from samples of smoke, vegetation, and soil. Our results suggest that 70% of the bacterial taxa in smoke originated from the local aspen (Populus tremuloides) (33%) and soil (37%) communities. In comparison, 42% of bacteria in air sampled prior to the fires could be attributed to these terrestrial sources. When the bacterial assemblages in smoke were modeled as sources to the local communities, they contributed an average of 25% to the terrestrial sinks versus an estimated contribution of <4% from ambient air. Our results provide support for the role of wildland fire in bacterial dispersal and the working hypothesis that smoke is an environmental reservoir of microbes for receiving ecosystems. Plain Language Summary: Microbes (bacteria and fungi) have been detected in wildland fire smoke using DNA technology and have been successfully cultured. Many of these organisms are associated with vegetation and soil, so it has been assumed that the microbes originate in the materials that are combusted during a fire, including vegetation and litter. This study uses DNA collected from vegetation, soil, air collected on a clear day, and wildland fire smoke at the same location to measure the connection between bacteria encountered on the surface and in the air. In addition to an inventory of the bacteria that are common to the surface and the atmosphere, we also used modeling to estimate the source communities that contributed to the suite of bacteria that were detected in each place. We found close relationships between surface sources and smoke and a much weaker exchange between clear air and the surface. These results provide more evidence for wildland fire smoke as a mechanism for transporting bacteria between ecosystems. Key Points: Most bacterial taxa in wildland fire smoke can be traced to local surface vegetation and soil communitiesThe bacterial assemblage in ambient air was mostly derived from unknown sourcesLocal terrestrial communities are more closely linked to smoke‐borne bacteria than those in ambient air, implicating smoke as a biological dispersal agent [ABSTRACT FROM AUTHOR]

During the 2018–2019 Antarctic field season, the Subglacial Antarctic Lakes Scientific Access project team cleanly accessed Mercer Subglacial Lake, West Antarctica, to sample water and sediments beneath 1087 m of overlying ice. A multicorer was successful in sampling the sediment–water interface, with 4 deployments retrieving 10 cores between 0.3 and 0.4 m in length. Gravity coring was also successful, retrieving cores of 0.97 and 1.78 m in glacial diamict. However, sediment cores retrieved by the gravity cores were shorter than the core barrel penetration (as measured by mud streaks on the outside of the coring system), indicating that the system can likely be improved. This manuscript describes the design, implementation, successes, and lessons learned while coring sediments in a subglacial lake. [ABSTRACT FROM AUTHOR]

Previous studies have identified regions where the occurrence of rainfall significantly increases or decreases the probability for subsequent rainfall over periods that range from a few days to several weeks. These observable phenomena are termed "rainfall feedback" (RF). To better understand the land--atmosphere interactions involved in RF, the behavior of RF patterns was analyzed using data from 1849 to 2016 at ~3000 sites in the contiguous United States. We also considered changes in major land-use types and applied a geographically weighted regression model technique for analyzing the predictors of RF. This approach identified non-linear and spatially nonstationary relationships between RF, climate, land use, and land type. RF patterns in certain regions of the United States are predictable by modeling variables associated with climate, season, and land use. The model outputs also demonstrate the extent to which the effect of precipitation, temperature, and land use on RF depend on season and location. Specifically, major changes were observed for land use associated with agriculture in the western United States, which had negative and positive influences on RF in summer and winter, respectively. In contrast, developed land in the eastern United States correlated with positive RF values in summer but with negative ones in winter. We discuss how changes in climate and land use would be expected to affect land-- atmosphere interactions, as well as the possible role that physical mechanisms and rain-enhanced bioaerosol emissions may play in the spatiotemporal changes observed for historical patterns of rainfall frequency in the United States. [ABSTRACT FROM AUTHOR]

Ice shelves surround ∼ 75% of Antarctica's coastline and are highly sensitive to climate change; several have recently collapsed and others are predicted to in the near future. Marine waters beneath ice shelves harbor active ecosystems, while adjacent seas can be important areas of bottom water formation. Despite their oceanographic significance, logistical constraints have resulted in few opportunities to directly sample sub-ice shelf cavities. Here, we present the first data on microbial diversity and biogeochemistry beneath the McMurdo Ice Shelf (MIS) near Ross Island, Antarctica. Physicochemical profiles obtained via a 56 m deep borehole through the MIS revealed three vertically layered water masses (Antarctic Surface Water [AASW], Ice Shelf Water [ISW], and modified High Salinity Shelf Water [mHSSW]). Metabolically active, moderately diverse (Shannon diversity from 2.06 to 5.74) microbial communities were detected in the AASW and mHSSW. Heterotrophic bacterial production and dissolved organic matter concentrations were higher (12-37% and 24%, respectively) in mHSSW relative to AASW. Chemoautotrophic production was 5.3 nmol C L−1 d−1 and 6.0 nmol C L−1 d−1 in the AASW and mHSSW, respectively. Phytoplankton cells were more abundant and larger in the mHSSW sample relative to the AASW, which indicates sinking of phytoplankton produced in surface waters and, together with southerly flowing currents (0.09-0.16 m s−1), horizontal advection of phytoplankton from McMurdo Sound. Advected phytoplankton carbon together with in situ chemoautotrophic production provide important sources of organic matter and other reduced compounds to support ecosystem processes in the dark waters in the ice shelf cavity. [ABSTRACT FROM AUTHOR]

Snow overlays the majority of the Greenland Ice Sheet ( GrIS). However, there is very little information available on the microbiological assemblages that are associated with this vast and climate-sensitive landscape. In this study, the structure and diversity of snow microbial assemblages from two regions of the western GrIS ice margin were investigated through the sequencing of small subunit ribosomal RNA genes. The origins of the microbiota were investigated by examining correlations to molecular data obtained from marine, soil, freshwater and atmospheric environments and geochemical analytes measured in the snow. Snow was found to contain a diverse assemblage of bacteria ( A lphaproteobacteria, B etaproteobacteria and G ammaproteobacteria) and eukarya ( A lveolata, F ungi, S tramenopiles and C hloroplastida). Phylotypes related to archaeal T haumarchaeota and E uryarchaeota phyla were also identified. The snow microbial assemblages were more similar to communities characterized in soil than to those documented in marine ecosystems. Despite this, the chemical composition of snow samples was consistent with a marine contribution, and strong correlations existed between bacterial beta diversity and the concentration of Na+ and Cl−. These results suggest that surface snow from western regions of Greenland contains exogenous microbiota that were likely aerosolized from more distant soil sources, transported in the atmosphere and co-precipitated with the snow. [ABSTRACT FROM AUTHOR]

Although viable fungi have been recovered from a wide variety of icy environments, their metabolic capabilities under frozen conditions are still largely unknown. We investigated basidiomycetous yeasts isolated from an Antarctic ice core and showed that after freezing at a relatively slow rate (0.8°C min−1), the cells are excluded into veins of liquid at the triple junctions of ice crystals. These strains were capable of reproductive growth at −5°C under liquid conditions. Under frozen conditions, metabolic activity was assessed by measuring rates of [3H]leucine incorporation into the acid-insoluble macromolecular fraction, which decreased exponentially at temperatures between 15°C and −15°C and was inhibited by the protein synthesis inhibitor cycloheximide. Experiments at −5°C under frozen and liquid conditions revealed 2–3 orders of magnitude lower rates of endogenous metabolism in ice, likely due to the high salinity in the liquid fraction of the ice (equivalent of ≈ 1.4 mol l−1 of NaCl at −5°C). The mesophile Saccharomyces cerevisae also incorporated [3H]leucine at −5°C and −15°C, indicating that this activity is not exclusive to cold-adapted microorganisms. The ability of yeast cells to incorporate amino acid substrates into macromolecules and remain metabolically active under these conditions has implications for understanding the survival of Eukarya in icy environments. [ABSTRACT FROM AUTHOR]

Summary Ice that forms the bottom 18 m of a 308 m ice core drilled from the Guliya ice cap on the Qinghan-Tibetan plateau in Western China is over 750 000 years old and is the oldest glacial ice known to date. Fourteen bacterial isolates have been recovered from samples of this ice from ∼296 m below the surface (mbs). Based on 16S rDNA sequences, these are members of the α- and β-proteobacterial, actinobacterial and low-G + C Gram-positive bacterial lineages. 16S rDNA molecules have also been amplified directly, cloned and sequenced from the ice-core melt water. These originated from Pseudomonas and Acinetobacter γ-proteobacterial species. These results demonstrate that bacteria can be recovered from water ice that has frozen for time periods relevant to biological survival through terrestrial ice ages or during interplanetary transport. [ABSTRACT FROM AUTHOR]

Lake Vostok, the largest subglacial lake in Antarctica, is separated from the surface by ≈ 4 km of glacial ice. It has been isolated from direct surface input for at least 420 000 years, and the possibility of a novel environment and ecosystem therefore exists. Lake Vostok water has not been sampled, but an ice core has been recovered that extends into the ice accreted below glacial ice by freezing of Lake Vostok water. Here, we report the recovery of bacterial isolates belonging to the Brachybacteria, Methylobacterium, Paenibacillus and Sphingomonas lineages from a sample of melt water from this accretion ice that originated 3593 m below the surface. We have also amplified small-subunit ribosomal RNA-encoding DNA molecules (16S rDNAs) directly from this melt water that originated from α- and β-proteobacteria, low- and high-G+C Gram-positive bacteria and a member of the Cytophaga/Flavobacterium/Bacteroides lineage. [ABSTRACT FROM AUTHOR]

Although subglacial aquatic environments are widespread beneath the Antarctic ice sheet, subglacial biogeochemistry is not well understood, and the contribution of subglacial water to coastal ocean carbon and nutrient cycling remains poorly constrained. The Whillans Subglacial Lake (SLW) ecosystem is upstream from West Antarctica's Gould‐Siple Coast ~800 m beneath the surface of the Whillans Ice Stream. SLW hosts an active microbial ecosystem and is part of an active hydrological system that drains into the marine cavity beneath the adjacent Ross Ice Shelf. Here we examine sources and sinks for organic matter in the lake and estimate the freshwater carbon and nutrient delivery from discharges into the coastal embayment. Fluorescence‐based characterization of dissolved organic matter revealed microbially driven differences between sediment pore waters and lake water, with an increasing contribution from relict humic‐like dissolved organic matter with sediment depth. Mass balance calculations indicated that the pool of dissolved organic carbon in the SLW water column could be produced in 4.8 to 11.9 yr, which is a time frame similar to that of the lakes' fill‐drain cycle. Based on these estimates, subglacial lake water discharged at the Siple Coast could supply an average of 5,400% more than the heterotrophic carbon demand within Siple Coast embayments (6.5% for the entire Ross Ice Shelf cavity). Our results suggest that subglacial discharge represents a heretofore unappreciated source of microbially processed dissolved organic carbon and other nutrients to the Southern Ocean. Plain Language Summary: Antarctica's thick ice sheets cover a continent rich with liquid water. These subglacial aquatic environments are home to microbial ecosystems that process organic matter and nutrients important for all life. At the same time, subglacial water in Antarctica actively flows between basins and from subglacial basins to the edge of the continent where it mixes with seawater in coastal areas covered by ice shelves. The waters under these ice shelves are cold, dark, and contain low concentrations of organic carbon and nutrients. We used data from Whillans Subglacial Lake, which lies 800 m beneath the ice of West Antarctica, to understand the sources, sinks, and accumulation of organic matter in Antarctic subglacial aquatic environments. We then combined data from the same lake with data on subglacial hydrology in the region to determine whether inputs of subglacial organic matter and nutrients could be important in supporting life in the dark waters beneath the adjacent ice shelf. We found that the input of fresh water from the Antarctic continent to the surrounding ocean can meet the microbial demand for organic carbon and nutrients under the ice shelf. This work has implications for our understanding of Antarctica's influence on biology in the Southern Ocean. Key Points: A mass balance shows that dissolved organic carbon accumulation in Whillans Subglacial Lake is under hydrological and biological controlDifferences between the character of the water column and sediment porewater dissolved organic matter imply biological processingSubglacial outflows have the potential to subsidize biological activity under the world's largest ice shelf [ABSTRACT FROM AUTHOR]

Microbes in the atmosphere have broad ecological impacts, including the potential to trigger precipitation through species and strains that act as ice nucleation particles. To characterize spatiotemporal trends of microbial assemblages in precipitation we sequenced 16S (bacterial) and 18S (fungal) rRNA gene amplicon libraries collected from 72 precipitation events in three U.S. states (Idaho, Louisiana, and Virginia) over four seasons. We considered these data from the perspective of a novel metacommunity framework. In agreement with our heuristic, we found evidence for distinct mechanisms underlying the composition and diversity of bacterial and fungal assemblages in precipitation. Specifically, we determined that (1) bacterial operational taxonomic unit (OTU) composition of precipitation was strongly associated with macroscale drivers including season and high‐altitude characteristics of storms; (2) fungal OTU composition was strongly correlated with mesoscale drivers including particular spatial locations; (3) β‐diversity (heterogeneity of taxa among samples) for both bacteria and fungi was largely maintained by turnover of taxa; however, (4) bacterial assemblages had higher contributions to total β‐diversity from nestedness (i.e., lower richness assemblages were largely taxonomic subsets of richer assemblages), due to losses of taxa during dispersal, particularly among potential ice nucleation active bacteria; and (5) fungal assemblages had higher contributions to total β‐diversity from turnover due to OTU replacement. Spatiotemporal trends in precipitation‐borne metacommunities allowed delineation of a large number of statistically significant indicator taxa for particular sites and seasons, including trends for bacteria that are potentially ice nucleation active. Our findings advance understanding regarding the dispersion of aerosolized microbes via wet deposition, and the development of theory concerning potential assembly rules for bioaerosol assemblages. [ABSTRACT FROM AUTHOR]

We characterized trends of bacteria and fungi assemblages from 72 precipitation events in three US states over four seasons. We determined that (1) bacterial assemblages were associated with season and high-altitude characteristics of storms, whereas fungal assemblages were correlated with particular spatial locations; and (2) bacterial assemblages had higher contributions to total -diversity from nestedness, due to taxa losses during dispersal, particularly among potentially ice-nucleating bacteria, whereas fungal assemblages had higher contributions to total I - i diversity from taxa turnover. GLO:69VH/01jan20:bes21653-fig-0002.jpg PHOTO (COLOR): Precipitation sampling regimen for an approaching storm at the Kentland Farms properties of the Virginia Tech College of Agriculture and Life Sciences, Blacksburg Virginia. [Extracted from the article]

The east lobe of Lake Bonney, a permanently ice-covered lake in the McMurdo Dry Valleys, Antarctica, has a mid-depth maximum N2O concentration of 43.3 µmol N L-1 (>700,000% saturation with respect to air), representing one of the highest concentrations reported for a natural aquatic system. δ15N and δ18O measurements indicate that this is the most isotopically depleted N2O yet observed in a natural environment (minimum δ15N-N2O of -79.6% vs. air-N2; minimum δ18O-N2O of -4.7% vs. Vienna standard mean ocean water), providing new end points for these parameters in natural systems. The extremely depleted nitrogen and oxygen isotopes, together with nitrogen isotopic isomer data for N2O, imply that most of the N2O was produced via incomplete nitrification and has undergone virtually no subsequent consumption. However, molecular evidence provides little support for metabolically active nitrifying populations at depths where the maximal N2O concentrations occur and contemporary biogeochemical reactions cannot explain the extreme excesses of N2O in Lake Bonney. The gas appears to be a legacy of past biogeochemical conditions within the lake, an d in the absence of a significant sink and the presence of a highly stable water column, gradients in N2O produced by past microbial activity could persist in the cold saline waters of Lake Bonney for >104 years. [ABSTRACT FROM AUTHOR]

Subglacial Lake Vostok is located ∼4 km beneath the surface of the East Antarctic Ice Sheet and has been isolated from the atmosphere for >15 million yr. Concerns for environmental protection have prevented direct sampling of the lake water thus far. However, an ice core has been retrieved from above the lake in which the bottom ,85 m represents lake water that has accreted (i.e., frozen) to the bottom of the ice sheet. We measured selected constituents within the accretion ice core to predict geomicrobiological conditions within the surface waters of the lake. Bacterial density is two- to sevenfold higher in accretion ice than the overlying glacial ice, implying that Lake Vostok is a source of bacterial carbon beneath the ice sheet. Phylogenetic analysis of amplified small subunit ribosomal ribonucleic acid (rRNA) gene sequences in accretion ice formed over a deep portion of the lake revealed phylotypes that classify within the β-, χ-, and δ-Proteobacteria. Cellular, major ion, and dissolved organic carbon levels all decreased with depth in the accretion ice (depth is a proxy for increasing distance from the shoreline), implying a greater potential for biological activity in the shallow shoreline waters of the lake. Although the exact nature of the biology within Lake Vostok awaits direct sampling of the lake water, our data from the accretion ice support the working hypothesis that a sustained microbial ecosystem is present in this subglacial lake environment, despite high pressure, constant cold, low nutrient input, potentially high oxygen concentrations, and an absence of sunlight. [ABSTRACT FROM AUTHOR]