Resolving the abundance and air-sea fluxes of airborne microorganisms in the North Atlantic Ocean

The immunostimulatory activity of sea spray aerosols: bacteria and endotoxins activate TLR4, TLR2/6, NF-κB and IRF in human cells

Frequent exposure to sea spray aerosols (SSA) containing marine microorganisms and bioactive compounds may influence human health. However, little is known about potential immunostimulation by SSA exposure. This study focuses on the effects of marine bacteria and endotoxins in SSA on several receptors and transcription factors known to play a key role in the human innate immune system. SSA samples were collected in the field (Ostend, Belgium) or generated in the lab using a marine aerosol reference tank (MART). Samples were characterized by their sodium contents, total bacterial counts, and endotoxin concentrations. Human reporter cells were exposed to SSA to investigate the activation of toll-like receptor 4 (TLR4) in HEK-Blue hTLR4 cells and TLR2/6 in HEK-Blue hTLR2/6 cells, as well as the activation of nuclear factor kappa B (NF-κB) and interferon regulatory factors (IRF) in THP1-Dual monocytes. These responses were then correlated to the total bacterial counts and endotoxin concentrations to explore dose-effect relationships. Field SSA contained from 3.0 × 103 to 6.0 × 105 bacteria/m3 air (averaging 2.0 ± 1.9 × 105 bacteria/m3 air) and an endotoxin concentration ranging from 7 to 1217 EU/m3 air (averaging 389 ± 434 EU/m3 air). In contrast, MART SSA exhibited elevated levels of total bacterial count (from 2.0 × 105 to 2.4 × 106, averaging 7.3 ± 5.5 × 105 cells/m3 air) and endotoxin concentration from 536 to 2191 (averaging 1310 ± 513 EU/m3 air). SSA samples differentially activated TLR4, TLR2/6, NF-κB and IRF. These immune responses correlated dose-dependently with the total bacterial counts, endotoxin levels, or both. This study sheds light on the immunostimulatory potential of SSA and its underlying mechanisms, highlighting the need for further research to deepen our understanding of the health implications of SSA exposure.

A critical review on bioaerosols-dispersal of crop pathogenic microorganisms and their impact on crop yield

Bioaerosols are potential sources of pathogenic microorganisms that can cause devastating outbreaks of global crop diseases. Various microorganisms, insects and viroids are known to cause severe crop diseases impeding global agro-economy. Such losses threaten global food security, as it is estimated that almost 821 million people are underfed due to global crisis in food production. It is estimated that global population would reach 10 billion by 2050. Hence, it is imperative to substantially increase global food production to about 60% more than the existing levels. To meet the increasing demand, it is essential to control crop diseases and increase yield. Better understanding of the dispersive nature of bioaerosols, seasonal variations, regional diversity and load would enable in formulating improved strategies to control disease severity, onset and spread. Further, insights on regional and global bioaerosol composition and dissemination would help in predicting and preventing endemic and epidemic outbreaks of crop diseases. Advanced knowledge of the factors influencing disease onset and progress, mechanism of pathogen attachment and penetration, dispersal of pathogens, life cycle and the mode of infection, aid the development and implementation of species-specific and region-specific preventive strategies to control crop diseases. Intriguingly, development of R gene-mediated resistant varieties has shown promising results in controlling crop diseases. Forthcoming studies on the development of an appropriately stacked R gene with a wide range of resistance to crop diseases would enable proper management and yield. The article reviews various aspects of pathogenic bioaerosols, pathogen invasion and infestation, crop diseases and yield.

Planetary Protection Knowledge Gap Closure Enabling Crewed Missions to Mars

As focus for exploration of Mars transitions from current robotic explorers to development of crewed missions, it remains important to protect the integrity of scientific investigations at Mars, as well as protect the Earth's biosphere from any potential harmful effects from returned martian material. This is the discipline of planetary protection, and the Committee on Space Research (COSPAR) maintains the consensus international policy and guidelines on how this is implemented. Based on National Aeronautics and Space Administration (NASA) and European Space Agency (ESA) studies that began in 2001, COSPAR adopted principles and guidelines for human missions to Mars in 2008. At that point, it was clear that to move from those qualitative provisions, a great deal of work and interaction with spacecraft designers would be necessary to generate meaningful quantitative recommendations that could embody the intent of the Outer Space Treaty (Article IX) in the design of such missions. Beginning in 2016, COSPAR then sponsored a multiyear interdisciplinary meeting series to address planetary protection "knowledge gaps" (KGs) with the intent of adapting and extending the current robotic mission-focused Planetary Protection Policy to support the design and implementation of crewed and hybrid exploration missions. This article describes the outcome of the interdisciplinary COSPAR meeting series, to describe and address these KGs, as well as identify potential paths to gap closure. It includes the background scientific basis for each topic area and knowledge updates since the meeting series ended. In particular, credible solutions for KG closure are described for the three topic areas of (1) microbial monitoring of spacecraft and crew health; (2) natural transport (and survival) of terrestrial microbial contamination at Mars, and (3) the technology and operation of spacecraft systems for contamination control. The article includes a KG data table on these topic areas, which is intended to be a point of departure for making future progress in developing an end-to-end planetary protection requirements implementation solution for a crewed mission to Mars. Overall, the workshop series has provided evidence of the feasibility of planetary protection implementation for a crewed Mars mission, given (1) the establishment of needed zoning, emission, transport, and survival parameters for terrestrial biological contamination and (2) the creation of an accepted risk-based compliance approach for adoption by spacefaring actors including national space agencies and commercial/nongovernment organizations.

Bioaerosols in the atmosphere: A comprehensive review on detection methods, concentration and influencing factors

In the past few decades, especially since the outbreak of the coronavirus disease (COVID-19), the effects of atmospheric bioaerosols on human health, the environment, and climate have received great attention. To evaluate the impacts of bioaerosols quantitatively, it is crucial to determine the types of bioaerosols in the atmosphere and their spatial-temporal distribution. We provide a concise summary of the online and offline observation strategies employed by the global research community to sample and analyze atmospheric bioaerosols. In addition, the quantitative distribution of bioaerosols is described by considering the atmospheric bioaerosols concentrations at various time scales (daily and seasonal changes, for example), under various weather, and different underlying surfaces. Finally, a comprehensive summary of the reasons for the spatiotemporal distribution of bioaerosols is discussed, including differences in emission sources, the impact process of meteorological factors and environmental factors. This review of information on the latest research progress contributes to the emergence of further observation strategies that determine the quantitative dynamics of public health and ecological effects of bioaerosols.

Aeromicrobiology: A global review of the cycling and relationships of bioaerosols with the atmosphere

Airborne microorganisms and biological matter (bioaerosols) play a key role in global biogeochemical cycling, human and crop health trends, and climate patterns. Their presence in the atmosphere is controlled by three main stages: emission, transport, and deposition. Aerial survival rates of bioaerosols are increased through adaptations such as ultra-violet radiation and desiccation resistance or association with particulate matter. Current research into modern concerns such as climate change, global gene transfer, and pathogenicity often neglects to consider atmospheric involvement. This comprehensive review outlines the transpiring of bioaerosols across taxa in the atmosphere, with significant focus on their interactions with environmental elements including abiotic factors (e.g., atmospheric composition, water cycle, and pollution) and events (e.g., dust storms, hurricanes, and wildfires). The aim of this review is to increase understanding and shed light on needed research regarding the interplay between global atmospheric phenomena and the aeromicrobiome. The abundantly documented bacteria and fungi are discussed in context of their cycling and human health impacts. Gaps in knowledge regarding airborne viral community, the challenges and importance of studying their composition, concentrations and survival in the air are addressed, along with understudied plant pathogenic oomycetes, and archaea cycling. Key methodologies in sampling, collection, and processing are described to provide an up-to-date picture of ameliorations in the field. We propose optimization to microbiological methods, commonly used in soil and water analysis, that adjust them to the context of aerobiology, along with other directions towards novel and necessary advancements. This review offers new perspectives into aeromicrobiology and calls for advancements in global-scale bioremediation, insights into ecology, climate change impacts, and pathogenicity transmittance.

Aerosolization flux, bio-products, and dispersal capacities in the freshwater microalga Limnomonas gaiensis (Chlorophyceae)

Little is known on the spreading capacities of Limnomonas gaiensis across freshwater lakes in Northern Europe. In this study, we show that the species could successfully be aerosolized from water sources by bubble bursting (2-40 particles.cm-3), irrespectively of its density in the water source or of the jet velocity used to simulate wave breaking. The species viability was impacted by both water turbulences and aerosolization. The survival rate of emitted cells was low, strain-specific, and differently impacted by bubble busting processes. The entity "microalga and bionts" could produce ethanol, and actively nucleate ice (principally ≤-18 °C) mediated soluble ice nucleation active proteins, thereby potentially impacting smog and cloud formation. Moreover, smallest strains could better cope with applied stressors. Survival to short-term exposure to temperatures down to -21 °C and freezing events further suggest that L. gaiensis could be air dispersed and contribute to their deposition.

Will "Air Eutrophication" Increase the Risk of Ecological Threat to Public Health?

Aquatic eutrophication, often with anthropogenic causes, facilitates blooms of cyanobacteria including cyanotoxin producing species, which profoundly impact aquatic ecosystems and human health. An emerging concern is that aquatic eutrophication may interact with other environmental changes and thereby lead to unexpected cascading effects on terrestrial systems. Here, we synthesize recent evidence showing the possibility that accelerating eutrophication will spill over from aquatic ecosystems to the atmosphere via "air eutrophication", a novel concept that refers to a process promoting the growth of airborne algae, some of them with the capacity to produce toxic compounds for humans and other organisms. Being catalyzed by various anthropogenic forcings─including aquatic eutrophication, climate warming, air contamination, and artificial light at night─accelerated air eutrophication may be expected in the future, posing a potentially increasing risk of threat to public health and the environment. So far knowledge of this topic is sparse, and we therefore consider air eutrophication a potentially important research field and propose an agenda of cross-discipline research. As a contribution, we have calculated a tolerable daily intake of 17 ng m-3 day-1 for the nasal intake of microcystins by humans.

The COSPAR Planetary Protection Policy for robotic missions to Mars: A review of current scientific knowledge and future perspectives

Planetary protection guidance for martian exploration has become a notable point of discussion over the last decade. This is due to increased scientific interest in the habitability of the red planet with updated techniques, missions becoming more attainable by smaller space agencies, and both the private sector and governments engaging in activities to facilitate commercial opportunities and human-crewed missions. The international standards for planetary protection have been developed through consultation with the scientific community and the space agencies by the Committee on Space Research's (COSPAR) Panel on Planetary Protection, which provides guidance for compliance with the Outer Space Treaty of 1967. In 2021, the Panel evaluated recent scientific data and literature regarding the planetary protection requirements for Mars and the implications of this on the guidelines. In this paper, we discuss the COSPAR Planetary Protection Policy for Mars, review the new scientific findings and discuss the next steps required to enable the next generation of robotic missions to Mars.

Fog-Induced Alteration in Airborne Microbial Community: a Study over Central Indo-Gangetic Plain in India

Fog supports an increase in airborne microbial loading by providing water with nutrients and protecting it from harmful incoming solar radiation. To improve our present understanding of fog-induced alteration in an atmospheric microbial community, a study was conducted during 1 to 14 January 2021 for continuous investigation of airborne bacteria over a rural site, Arthauli (25.95°N, 85.10°E), in central Indo-Gangetic Plain (IGP) in India. An increase of 36% ± 0.4% in airborne bacterial loading was noticed under fog versus prefog conditions, and a decrease of 48% ± 0.4% was noticed under the postfog condition. Airborne bacterial loading had a strong correlation with RH (R2 = 0.56; P < 0.05), temperature (R2 = -0.55, P < 0.05), and wind speed (R2 = -0.52, P < 0.05). Unique types of bacteria, representing about 29% of the whole community, were detected only under foggy conditions, likely by a continuous supply of nutrients and water from a cold, calm, and humid atmosphere. As a result, no significant diurnal variation of bacterial loading was noticed on a foggy day, with a higher daily mean concentration of about (8.4 ± 1.7) × 105 cells · m-3 than that on a typical winter day [(6.3 ± 3.8) × 105 cells · m-3]. A typical winter day experienced about a 60% decrease in bacterial loading in the afternoon in comparison to that in the morning. A 3-day back-trajectory analysis suggests a slow movement of airmass along with the wind blowing from west to central IGP. Fog pauses wind movement, which reduces continuous transportation of urban sources while increasing airborne bacteria from local sources. The abundances of Gp6 (14.8% ± 8.6%), Anaeromyxobacter (7.1% ± 2.8%), and Gp7 (6.8 ± 2.6%) have been observed to increase due to occurrences of fog over central IGP. IMPORTANCE Fog was investigated in the present study as a cause of alteration in the airborne microbial community. Occurrences of fog were responsible for an increase in airborne microbial loading (36%) over central IGP in India due to the easy availability of nutrients and water in the air and dimming of harmful solar radiation. More than 90% of unique bacteria were detected under fog (64%) and postfog (28%) conditions. A few bacteria, like Gp18 (0.5% ± 0.3%), Alicyclobacillus (0.5% ± 0.1%), Sinomonas (0.4% ± 0.2%), and Phenylobacterium (0.4% ± 0.2%), were detected only under foggy conditions. A strong correlation between meteorological parameters and bacterial loading was found in the current research work. The present study provides additional support toward a new direction in interdisciplinary science for the detailed investigations of the effects of meteorological conditions on airborne bacteria and their implications for society.

Characterization of airborne bacteria and fungi at a land-sea transition site in Southern China

Airborne microbe can have impact on regional to global climate as ice nuclei and cloud condensation nuclei. In coastal region, microbial aerosols are simultaneously contributed by terrestrial and marine sources under the influence of land-sea air exchange. We present a study on the characteristics of airborne bacteria and fungi, including their concentrations and communities, at a land-sea transition site in Southern China from December 2019 to December 2020. Seasonal variations of microbial communities were observed with evident profiles in summer, especially for fungal aerosols. The significant enhancement of Basidiomycota abundance in summer was contributed by local biogenic release under the influence of meteorological factors. Terrestrial sources are suggested as the dominant contributors to both bacterial and fungal aerosols rather than marine sources during the whole year period. Source-tracking analysis identified that marine contributions to airborne bacteria and fungi were 3.1-14.2 % and 4-24 %, respectively. It suggests that airborne fungi should be more suitable for long-range transport than airborne bacteria. This study improves the understanding of the conversional contribution of marine and terrestrial sources to airborne microbes in coastal region and the influencing environmental factors under land-sea exchange.

VEBA: a modular end-to-end suite for in silico recovery, clustering, and analysis of prokaryotic, microeukaryotic, and viral genomes from metagenomes

BACKGROUND

With the advent of metagenomics, the importance of microorganisms and how their interactions are relevant to ecosystem resilience, sustainability, and human health has become evident. Cataloging and preserving biodiversity is paramount not only for the Earth's natural systems but also for discovering solutions to challenges that we face as a growing civilization. Metagenomics pertains to the in silico study of all microorganisms within an ecological community in situ, however, many software suites recover only prokaryotes and have limited to no support for viruses and eukaryotes.

RESULTS

In this study, we introduce the Viral Eukaryotic Bacterial Archaeal (VEBA) open-source software suite developed to recover genomes from all domains. To our knowledge, VEBA is the first end-to-end metagenomics suite that can directly recover, quality assess, and classify prokaryotic, eukaryotic, and viral genomes from metagenomes. VEBA implements a novel iterative binning procedure and hybrid sample-specific/multi-sample framework that yields more genomes than any existing methodology alone. VEBA includes a consensus microeukaryotic database containing proteins from existing databases to optimize microeukaryotic gene modeling and taxonomic classification. VEBA also provides a unique clustering-based dereplication strategy allowing for sample-specific genomes and genes to be directly compared across non-overlapping biological samples. Finally, VEBA is the only pipeline that automates the detection of candidate phyla radiation bacteria and implements the appropriate genome quality assessments. VEBA's capabilities are demonstrated by reanalyzing 3 existing public datasets which recovered a total of 948 MAGs (458 prokaryotic, 8 eukaryotic, and 482 viral) including several uncharacterized organisms and organisms with no public genome representatives.

CONCLUSIONS

The VEBA software suite allows for the in silico recovery of microorganisms from all domains of life by integrating cutting edge algorithms in novel ways. VEBA fully integrates both end-to-end and task-specific metagenomic analysis in a modular architecture that minimizes dependencies and maximizes productivity. The contributions of VEBA to the metagenomics community includes seamless end-to-end metagenomics analysis but also provides users with the flexibility to perform specific analytical tasks. VEBA allows for the automation of several metagenomics steps and shows that new information can be recovered from existing datasets.

Characterization of atmospheric aerosols in the Antarctic region using Raman Spectroscopy and Scanning Electron Microscopy

The non-destructive spectroscopic characterization of airborne particulate matter (PM) was performed to gain better knowledge of the internal structures of atmospheric aerosols at the particle level in the Antarctic region, along with their potential sources. PM and soil samples were collected during the 2016-2017 austral summer season at the surroundings of the Spanish Antarctic Research Station "Gabriel de Castilla" (Deception Island, South Shetland Islands). PM was deposited in a low-volume sampler air filter. Raman spectroscopy (RS) and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS) were used to determine the elemental and molecular composition of the individual aerosol and soil particles. Filter spectra measured by these techniques revealed long-range atmospheric transport of organic compounds (polystyrene and bacteria), local single and cluster particles made of different kinds of black carbon (BC), exotic minerals (polyhalite, arcanite, niter, ammonium nitrate, syngenite and nitrogen, phosphorus, and potassium (NPK) fertilizer), and natural PM (sea salts, silicates, iron oxides, etc.). In addition to the filter samples, forsterite and plagioclase were discovered in the soil samples together with magnetite. This is the first report of the presence of a microplastic fiber in the Antarctic air. This fact, together with the presence of other pollutants, reflects that even pristine and remote regions are influenced by anthropogenic activities.

Ocean Aerobiology

Ocean aerobiology is defined here as the study of biological particles of marine origin, including living organisms, present in the atmosphere and their role in ecological, biogeochemical, and climate processes. Hundreds of trillions of microorganisms are exchanged between ocean and atmosphere daily. Within a few days, tropospheric transport potentially disperses microorganisms over continents and between oceans. There is a need to better identify and quantify marine aerobiota, characterize the time spans and distances of marine microorganisms’ atmospheric transport, and determine whether microorganisms acclimate to atmospheric conditions and remain viable, or even grow. Exploring the atmosphere as a microbial habitat is fundamental for understanding the consequences of dispersal and will expand our knowledge of biodiversity, biogeography, and ecosystem connectivity across different marine environments. Marine organic matter is chemically transformed in the atmosphere, including remineralization back to CO₂. The magnitude of these transformations is insignificant in the context of the annual marine carbon cycle, but may be a significant sink for marine recalcitrant organic matter over long (∼10⁴ years) timescales. In addition, organic matter in sea spray aerosol plays a significant role in the Earth’s radiative budget by scattering solar radiation, and indirectly by affecting cloud properties. Marine organic matter is generally a poor source of cloud condensation nuclei (CCN), but a significant source of ice nucleating particles (INPs), affecting the formation of mixed-phase and ice clouds. This review will show that marine biogenic aerosol plays an impactful, but poorly constrained, role in marine ecosystems, biogeochemical processes, and the Earth’s climate system. Further work is needed to characterize the connectivity and feedbacks between the atmosphere and ocean ecosystems in order to integrate this complexity into Earth System models, facilitating future climate and biogeochemical predictions.

Microbial diversity through an oceanographic lens: refining the concept of ocean provinces through trophic-level analysis and productivity-specific length scales

In the marine realm, microorganisms are responsible for the bulk of primary production, thereby sustaining marine life across all trophic levels. Longhurst provinces have distinct microbial fingerprints; however, little is known about how microbial diversity and primary productivity change at finer spatial scales. Here, we sampled the Atlantic Ocean from south to north (~50°S-50°N), every ~0.5° latitude. We conducted measurements of primary productivity, chlorophyll-a and relative abundance of 16S and 18S rRNA genes, alongside analyses of the physicochemical and hydrographic environment. We analysed the diversity of autotrophs, mixotrophs and heterotrophs, and noted distinct patterns among these guilds across provinces with high and low chlorophyll-a conditions. Eukaryotic autotrophs and prokaryotic heterotrophs showed a shared inter-province diversity pattern, distinct from the diversity pattern shared by mixotrophs, cyanobacteria and eukaryotic heterotrophs. Additionally, we calculated samplewise productivity-specific length scales, the potential horizontal displacement of microbial communities by surface currents to an intrinsic biological rate (here, specific primary productivity). This scale provides key context for our trophically disaggregated diversity analysis that we could relate to underlying oceanographic features. We integrate this element to provide more nuanced insights into the mosaic-like nature of microbial provincialism, linking diversity patterns to oceanographic transport through primary production.

Enzyme-Catalyzed Hydrolysis of Lipids in Immiscible Microdroplets Studied by Contained-Electrospray Ionization

Enzyme-catalyzed hydrolysis of lipids was monitored directly in immiscible microdroplet environments using contained-electrospray mass spectrometry. Aqueous solution of the lipase enzyme from Pseudomonas cepacia and the chloroform solution of the lipids were sprayed from separate capillaries, and the resultant droplets were merged within a reaction cavity that is included at the outlet of the contained-electrospray ionization source. By varying the length of the reaction cavity, the interaction time between the enzyme and its substrate was altered, enabling the quantification of reaction product as a function of time. Consequently, enhancement factors were estimated by comparing rate constants derived from the droplet experiment to rate constants calculated from solution-phase conditions. These experiments showed enhancement factors greater than 100 in favor of the droplet experiment. By using various lipid types, two possible mechanisms were identified to account for lipase reactivity in aerosols: in-droplet reactions for relatively highly soluble lipids and a droplet coalescence mechanism that allows interfacial reactions for the two immiscible systems.

The Effect of Abiotic Factors on Abundance and Photosynthetic Performance of Airborne Cyanobacteria and Microalgae Isolated from the Southern Baltic Sea Region

Cyanobacteria and microalgae present in the aquatic or terrestrial environment may be emitted into the air and transported along with air masses over long distances. As a result of staying in the atmosphere, these organisms may develop a greater tolerance to stressful factors, but this topic is still relatively unknown. The main aim was to show an autecological characteristic of some airborne microalgae and cyanobacteria strains by a factorial laboratory experiment approach, including changes in irradiance, temperature, and salinity conditions. The additional purpose of this work was also to present part of the Culture Collection of Baltic Algae (CCBA) collection, which consists of airborne algae (AA) isolated from the atmospheric air of the southern Baltic Sea region. Altogether, 61 strains of airborne cyanobacteria and microalgae from the southern Baltic Sea region were isolated from May 2018 to August 2020. Selected microorganisms were tested in controlled laboratory conditions to identify their response to different irradiance (10–190 µmol photons m⁻² s⁻¹), temperature (13–23 °C), and salinity conditions (0–36 PSU). The highest numbers of cells (above 30 × 10⁵ cell mL⁻¹) were recorded for cyanobacterium Nostoc sp., and for diatoms Nitzschia sp., Amphora sp., and Halamphora sp. We found that for cyanobacterium Nostoc sp. as well as for green alga Coccomyxa sp. the maximum cell concentrations were recorded at the salinity of 0 PSU. Moreover, cyanobacteria Planktolyngbya contorta, Pseudanabaena catenata, Leptolyngbya foveolarum, Gloeocapsa sp., and Rivularia sp. were able to grow only at a salinity of 0 PSU. On the other hand, in the range of 16–24 PSU, the highest cell numbers of examined diatoms have been identified. Our research provided that deposited airborne microalgae and cyanobacteria showed full colonization potential. The present experiment suggests that the adaptive abilities of microorganisms, in particular those producing toxins, may contribute to the spread in the future. Thus, it may increase human exposure to their negative health effects. Any distinctive adaptations of the genera give them an additional competitive advantage and a greater chance for territorial expansion.

Large Enrichment of Anthropogenic Organic Matter Degrading Bacteria in the Sea-Surface Microlayer at Coastal Livingston Island (Antarctica)

The composition of bacteria inhabiting the sea-surface microlayer (SML) is poorly characterized globally and yet undescribed for the Southern Ocean, despite their relevance for the biogeochemistry of the surface ocean. We report the abundances and diversity of bacteria inhabiting the SML and the subsurface waters (SSL) determined from a unique sample set from a polar coastal ecosystem (Livingston Island, Antarctica). From early to late austral summer (January–March 2018), we consistently found a higher abundance of bacteria in the SML than in the SSL. The SML was enriched in some Gammaproteobacteria genus such as Pseudoalteromonas, Pseudomonas, and Colwellia, known to degrade a wide range of semivolatile, hydrophobic, and surfactant-like organic pollutants. Hydrocarbons and other synthetic chemicals including surfactants, such as perfluoroalkyl substances (PFAS), reach remote marine environments by atmospheric transport and deposition and by oceanic currents, and are known to accumulate in the SML. Relative abundances of specific SML-enriched bacterial groups were significantly correlated to concentrations of PFASs, taken as a proxy of hydrophobic anthropogenic pollutants present in the SML and its stability. Our observations provide evidence for an important pollutant-bacteria interaction in the marine SML. Given that pollutant emissions have increased during the Anthropocene, our results point to the need to assess chemical pollution as a factor modulating marine microbiomes in the contemporaneous and future oceans.

The first characterization of airborne cyanobacteria and microalgae in the Adriatic Sea region

The presence of airborne cyanobacteria and microalgae as well as their negative impacts on human health have been documented by many researchers worldwide. However, studies on cyanobacteria and microalgae are few compared with those on bacteria and viruses. Research is especially lacking on the presence and taxonomic composition of cyanobacteria and microalgae near economically important water bodies with much tourism, such as the Adriatic Sea region. Here, we present the first characterization of the airborne cyanobacteria and microalgae in this area. Sampling conducted between 11^th and 15^th June 2017 revealed a total of 15 taxa of airborne cyanobacteria and microalgae. Inhalation of many of the detected taxa, including Synechocystis sp., Synechococcus sp., Bracteacoccus sp., Chlorella sp., Chlorococcum sp., Stichococcus sp., and Amphora sp., poses potential threats to human health. Aside from two green algae, all identified organisms were capable of producing harmful metabolites, including toxins. Moreover, we documented the presence of the cyanobacterium Snowella sp. and the green alga Tetrastrum sp., taxa that had not been previously documented in the atmosphere by other researchers. Our study shows that the Adriatic Sea region seems to be a productive location for future research on airborne cyanobacteria and microalgae in the context of their impacts on human health, especially during the peak of tourism activity.

Airborne bacteria structure and chemical composition relationships in winter and spring PM10 samples over southeastern Italy

The Redundancy Discrimination Analysis (RDA) and Spearman correlation coefficients were used to investigate relationships between airborne bacteria at the phylum and genus level and chemical species in winter and spring PM10 samples over Southeastern Italy. The identification of main chemical species/pollution sources that were related to and likely affected the bacterial community structure was the main goal of this work. The 16S rRNA gene metabarcoding approach was used to characterize airborne bacteria. Seventeen phyla and seventy-nine genera contributing each by mean within-sample relative abundance percentage > 0.01% were identified in PM10 samples, which were chemically characterized for 33 species, including ions, metals, OC, and EC (organic and elemental carbon, respectively). Chemical species were associated with six different pollution sources. A shift from winter to spring in both bacterial community structure and chemical species mass concentrations/sources and the relationships between them was observed. RDA triplots pointed out significant correlations for all tested bacterial phyla (genera) with other phyla (genera) and/or with chemical species, in contrast to correlation coefficient results, which showed that few phyla (genera) were significantly correlated with chemical species. More specifically, in winter Bacillus and Chryseobacterium were the only genera significantly correlated with chemical species likely associated with particles from soil-dust and anthropogenic pollution source, respectively. In spring, Enterobacter and Sphingomonas were the only genera significantly correlated with chemical species likely associated with particles from the anthropogenic pollution and the marine and soil-dust sources, respectively. The results of this study also showed that the correlation coefficients were the best tool to obtain unequivocal identifications of the correlations of phyla (genera) with chemical species. The seasonal changes of the PM10 chemical composition, the microbial community structure, and their relationships suggested that the seasonal changes of atmospheric particles may have likely contributed to seasonal changes of bacterial community in the atmosphere.

Airborne bacteria confirm the pristine nature of the Southern Ocean boundary layer

We found that the summer airborne bacterial community in the marine boundary layer over the Southern Ocean directly south of Australia is dominated by marine bacteria emitted in sea spray, originating primarily from the west in a zonal band at the latitude of collection. We found that airborne communities were more diverse to the north, and much less so toward Antarctica. These results imply that sea spray sources largely control the number concentrations of nuclei for liquid cloud droplets and limit ice nucleating particle concentrations to the low values expected in nascent sea spray. In the sampled region, the sources of summer cloud-active particles therefore are unlikely to have changed in direct response to perturbations in continental anthropogenic emissions.

Microorganisms are ubiquitous and highly diverse in the atmosphere. Despite the potential impacts of airborne bacteria found in the lower atmosphere over the Southern Ocean (SO) on the ecology of Antarctica and on marine cloud phase, no previous region-wide assessment of bioaerosols over the SO has been reported. We conducted bacterial profiling of boundary layer shipboard aerosol samples obtained during an Austral summer research voyage, spanning 42.8 to 66.5°S. Contrary to findings over global subtropical regions and the Northern Hemisphere, where transport of microorganisms from continents often controls airborne communities, the great majority of the bacteria detected in our samples were marine, based on taxonomy, back trajectories, and source tracking analysis. Further, the beta diversity of airborne bacterial communities varied with latitude and temperature, but not with other meteorological variables. Limited meridional airborne transport restricts southward community dispersal, isolating Antarctica and inhibiting microorganism and nutrient deposition from lower latitudes to these same regions. A consequence and implication for this region’s marine boundary layer and the clouds that overtop it is that it is truly pristine, free from continental and anthropogenic influences, with the ocean as the dominant source controlling low-level concentrations of cloud condensation nuclei and ice nucleating particles.

Temporal-spatial variations of fungal composition in PM2.5 and source tracking of airborne fungi in mountainous and urban regions

Fungi are ubiquitous in air and their composition is potentially important for human health. Exposure to fungal allergens has been considered as a significant risk factor due to the prevalence and severity of asthma in humans. However, temporal-spatial variations and potential sources of airborne fungi aerosol have been poorly understood. In this study, 48 PM_2.5 samples were collected at two sampling sites in Xi'an from April 2018 to January 2019. High-throughput sequencing technology was used to determine the diversity and abundance of fungal composition in all samples. Microbial samples were also collected from leaf-surface and soil to identify the potential sources of fungal aerosols. Results showed that the species richness of fungi in summer and autumn inclined to be higher than that in spring and winter in mountainous and urban regions. Airborne fungal species richness and diversity at Mt. Qinling sampling site were significantly higher compared to Yanta urban sampling site, except in winter. These variations in fungal composition were significantly related to season and location. The influence of atmospheric pollutants (PM_2.5, ozone, sulfur dioxide and carbon monoxide) on the richness and diversity of airborne fungal composition was higher than meteorological factors (temperature, relative humidity and wind speed). Moreover, it was observed that the leaf-surface was the primary local source of airborne fungi during all seasons at both sampling sites. Back trajectories arriving at both sampling sites showed that a considerable part of airborne fungi might have come from other regions by medium or long-range airflow. This study will provide an important reference for studying the source and temporal-spatial variations of fungal aerosols and further provide basic background data for human health exposure assessment.

Air mass source determines airborne microbial diversity at the ocean-atmosphere interface of the Great Barrier Reef marine ecosystem

The atmosphere is the least understood biome on Earth despite its critical role as a microbial transport medium. The influence of surface cover on composition of airborne microbial communities above marine systems is unclear. Here we report evidence for a dynamic microbial presence at the ocean-atmosphere interface of a major marine ecosystem, the Great Barrier Reef, and identify that recent air mass trajectory over an oceanic or continental surface associated with observed shifts in airborne bacterial and fungal diversity. Relative abundance of shared taxa between air and coral microbiomes varied between 2.2 and 8.8% and included those identified as part of the core coral microbiome. We propose that this variable source of atmospheric inputs may in part contribute to the diverse and transient nature of the coral microbiome.

The importance of cyanobacteria and microalgae present in aerosols to human health and the environment - Review study

Airborne microalgae and cyanobacteria are among the least studied organisms in aerobiology. While those of them living in freshwater and seawater are well recognized, those constituting the components of aerosols are rarely the focus of research. However, their presence has been noted by scientists from all over the world. The presence of these organisms is not indifferent to the environment as they participate in the formation of clouds and influence both the hydrological cycle and Earth's climate. Recent studies have concentrated mostly on the negative impact of airborne cyanobacteria and microalgae, as well as the toxic compounds they produce, on human health. This review focuses on measurement results published on those bioaerosols, combining the achievements of scientists from the last century with the latest reports and trends. Within it gaps in current knowledge are discussed, including the role of airborne organisms in the transport of harmful chemicals like PAHs and heavy metals. The current studies on which it is based emphasize the advantages and disadvantages of the measurement methods used in sampling and analysing. It also visualizes, in the form of maps, where research on bioaerosols has so far been conducted, while at the same time determining the share of organisms potentially dangerous to human health. In addition, we have also tried to recommend future research directions for both environmental and laboratory-based studies.

Functional metagenomic analysis of dust-associated microbiomes above the Red Sea

Atmospheric transport is a major vector for the long-range transport of microbial communities, maintaining connectivity among them and delivering functionally important microbes, such as pathogens. Though the taxonomic diversity of aeolian microorganisms is well characterized, the genomic functional traits underpinning their survival during atmospheric transport are poorly characterized. Here we use functional metagenomics of dust samples collected on the Global Dust Belt to initiate a Gene Catalogue of Aeolian Microbiome (GCAM) and explore microbial genetic traits enabling a successful aeolian lifestyle in Aeolian microbial communities. The GCAM reported here, derived from ten aeolian microbial metagenomes, includes a total of 2,370,956 non-redundant coding DNA sequences, corresponding to a yield of ~31 × 10⁶ predicted genes per Tera base-pair of DNA sequenced for the aeolian samples sequenced. Two-thirds of the cataloged genes were assigned to bacteria, followed by eukaryotes (5.4%), archaea (1.1%), and viruses (0.69%). Genes encoding proteins involved in repairing UV-induced DNA damage and aerosolization of cells were ubiquitous across samples, and appear as fundamental requirements for the aeolian lifestyle, while genes coding for other important functions supporting the aeolian lifestyle (chemotaxis, aerotaxis, germination, thermal resistance, sporulation, and biofilm formation) varied among the communities sampled.

Aerosol Microbiome over the Mediterranean Sea Diversity and Abundance

Prokaryotic microbes can become aerosolized and deposited into new environments located thousands of kilometers away from their place of origin. The Mediterranean Sea is an oligotrophic to ultra-oligotrophic marginal sea, which neighbors northern Africa (a major source of natural aerosols) and Europe (a source of mostly anthropogenic aerosols). Previous studies demonstrated that airborne bacteria deposited during dust events over the Mediterranean Sea may significantly alter the ecology and function of the surface seawater layer, yet little is known about their abundance and diversity during ‘background’ non-storm conditions. Here, we describe the abundance and genetic diversity of airborne bacteria in 16 air samples collected over an East-West transect of the entire Mediterranean Sea during non-storm conditions in April 2011. The results show that airborne bacteria represent diverse groups with the most abundant bacteria from the Firmicutes (Bacilli and Clostridia) and Proteobacteria (Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria) phyla. Most of the bacteria in our samples have previously been observed in the air at other open ocean locations, in the air over the Mediterranean Sea during dust storms, and in the Mediterranean seawater. Airborne bacterial abundance ranged from 0.7 × 104 to 2.5 × 104 cells m−3 air, similar to abundances at other oceanic regimes. Our results demonstrate that airborne bacterial diversity is positively correlated with the mineral dust content in the aerosols and was spatially separated between major basins of the Mediterranean Sea. To our knowledge, this is the first comprehensive biogeographical dataset to assess the diversity and abundance of airborne microbes over the Mediterranean Sea. Our results shed light on the spatiotemporal distribution of airborne microbes and may have implications for dispersal and distribution of microbes (biogeography) in the ocean.

Airborne Prokaryote and Virus Abundance Over the Red Sea

Aeolian dust exerts a considerable influence on atmospheric and oceanic conditions negatively impacting human health, particularly in arid and semi-arid regions like Saudi Arabia. Aeolian dust is often characterized by its mineral and chemical composition; however, there is a microbiological component of natural aerosols that has received comparatively little attention. Moreover, the amount of materials suspended in the atmosphere is highly variable from day to day. Thus, understanding the variability of atmospheric dust loads and suspended microbes throughout the year is essential to clarify the possible effects of dust on the Red Sea ecosystem. Here, we present the first estimates of dust and microbial loads at a coastal site on the Red Sea over a 2-year period, supplemented with measurements from dust samples collected along the Red Sea basin in offshore waters. Weekly average dust loads from a coastal site on the Red Sea ranged from 4.6 to 646.11 μg m^-3, while the abundance of airborne prokaryotic cells and viral-like particles (VLPs) ranged from 77,967 to 1,203,792 cells m^-3 and from 69,615 to 3,104,758 particles m^-3, respectively. To the best of our knowledge, these are the first estimates of airborne microbial abundance in this region. The elevated concentrations of resuspended dust particles and suspended microbes found in the air indicate that airborne microbes may potentially have a large impact on human health and on the Red Sea ecosystem.

The Relationship between Air-Mass Trajectories and the Abundance of Dust-Borne Prokaryotes at the SE Mediterranean Sea

Airborne prokaryotes are transported along with dust/aerosols, yet very little attention is given to their temporal variability above the oceans and the factors that govern their abundance. We analyzed the abundance of autotrophic (cyanobacteria) and heterotopic airborne microbes in 34 sampling events between 2015–2018 at a coastal site in the SE Mediterranean Sea. We show that airborne autotrophic (0.2–7.6 cells × 103 m−3) and heterotrophic (0.2–30.6 cells × 103 m−3) abundances were affected by the origin and air mass trajectory, and the concentration of dust/aerosols in the air, while seasonality was not coherent. The averaged ratio between heterotrophic and autotrophic prokaryotes in marine-dominated trajectories was ~1.7 ± 0.6, significantly lower than for terrestrial routes (6.8 ± 6.1). Airborne prokaryotic abundances were linearly and positively correlated to the concentrations of total aerosol, while negatively correlated with the aerosol’s anthropogenic fraction (using Pb/Al or Cu/Al ratios as proxies). While aerosols may play a major role in dispersing terrestrial and marine airborne microbes in the SE Mediterranean Sea, the mechanisms involved in the dispersal and diversity of airborne microorganisms remain to be studied and should include standardization in collection and analysis protocols.

Bioaerosol biomonitoring: Sampling optimization for molecular microbial ecology

Bioaerosols (or biogenic aerosols) have largely been overlooked by molecular ecologists. However, this is rapidly changing as bioaerosols play key roles in public health, environmental chemistry and the dispersal ecology of microbes. Due to the low environmental concentrations of bioaerosols, collecting sufficient biomass for molecular methods is challenging. Currently, no standardized methods for bioaerosol collection for molecular ecology research exist. Each study requires a process of optimization, which greatly slows the advance of bioaerosol science. Here, we evaluated air filtration and liquid impingement for bioaerosol sampling across a range of environmental conditions. We also investigated the effect of sampling matrices, sample concentration strategies and sampling duration on DNA yield. Air filtration using polycarbonate filters gave the highest recovery, but due to the faster sampling rates possible with impingement, we recommend this method for fine -scale temporal/spatial ecological studies. To prevent bias for the recovery of Gram-positive bacteria, we found that the matrix for impingement should be phosphate-buffered saline. The optimal method for bioaerosol concentration from the liquid matrix was centrifugation. However, we also present a method using syringe filters for rapid in-field recovery of bioaerosols from impingement samples, without compromising microbial diversity for high -throughput sequencing approaches. Finally, we provide a resource that enables molecular ecologists to select the most appropriate sampling strategy for their specific research question.

Wind-driven spume droplet production and the transport of Pseudomonas syringae from aquatic environments

Natural aquatic environments such as oceans, lakes, and rivers are home to a tremendous diversity of microorganisms. Some may cross the air-water interface within droplets and become airborne, with the potential to impact the Earth’s radiation budget, precipitation processes, and spread of disease. Larger droplets are likely to return to the water or adjacent land, but smaller droplets may be suspended in the atmosphere for transport over long distances. Here, we report on a series of controlled laboratory experiments to quantify wind-driven droplet production from a freshwater source for low wind speeds. The rate of droplet production increased quadratically with wind speed above a critical value (10-m equivalent 5.7 m/s) where droplet production initiated. Droplet diameter and ejection speeds were fit by a gamma distribution. The droplet mass flux and momentum flux increased with wind speed. Two mechanisms of droplet production, bubble bursting and fragmentation, yielded different distributions for diameter, speed, and angle. At a wind speed of about 3.5 m/s, aqueous suspensions of the ice-nucleating bacterium Pseudomonas syringae were collected at rates of 283 cells m⁻² s⁻¹ at 5 cm above the water surface, and at 14 cells m⁻² s⁻¹ at 10 cm above the water surface. At a wind speed of about 4.0 m/s, aqueous suspensions of P. syringae were collected at rates of 509 cells m⁻² s⁻¹ at 5 cm above the water surface, and at 81 cells m⁻² s⁻¹ at 10 cm above the water surface. The potential for microbial flux into the atmosphere from aquatic environments was calculated using known concentrations of bacteria in natural freshwater systems. Up to 3.1 × 10⁴ cells m⁻² s⁻¹ of water surface were estimated to leave the water in potentially suspended droplets (diameters <100 µm). Understanding the sources and mechanisms for bacteria to aerosolize from freshwater aquatic sources may aid in designing management strategies for pathogenic bacteria, and could shed light on how bacteria are involved in mesoscale atmospheric processes.

Coordinated Sampling of Microorganisms Over Freshwater and Saltwater Environments Using an Unmanned Surface Vehicle (USV) and a Small Unmanned Aircraft System (sUAS)

Biological aerosols (bioaerosols) are ubiquitous in terrestrial and aquatic environments and may influence cloud formation and precipitation processes. Little is known about the aerosolization and transport of bioaerosols from aquatic environments. We designed and deployed a bioaerosol-sampling system onboard an unmanned surface vehicle (USV; a remotely operated boat) to collect microbes and monitor particle sizes in the atmosphere above a salt pond in Falmouth, MA, United States and a freshwater lake in Dublin, VA, United States. The bioaerosol-sampling system included a series of 3D-printed impingers, two different optical particle counters, and a weather station. A small unmanned aircraft system (sUAS; a remotely operated airplane) was used in a coordinated effort with the USV to collect microorganisms on agar media 50 m above the surface of the water. Samples from the USV and sUAS were cultured on selective media to estimate concentrations of culturable microorganisms (bacteria and fungi). Concentrations of microbes from the sUAS ranged from 6 to 9 CFU/m³ over saltwater, and 12 to 16 CFU/m³ over freshwater (over 10-min sampling intervals) at 50 m above ground level (AGL). Concentrations from the USV ranged from 0 (LOD) to 42,411 CFU/m³ over saltwater, and 0 (LOD) to 56,809 CFU/m³ over freshwater (over 30-min sampling intervals) in air near the water surface. Particle concentrations recorded onboard the USV ranged from 0 (LOD) to 288 μg/m³ for PM1, 1 to 290 μg/m³ for PM2.5, and 1 to 290 μg/m³ for PM10. A general trend of increasing concentration with an increase in particle size was recorded by each sensor. Through laboratory testing, the collection efficiency of the 3D-printed impingers was determined to be 75% for 1 μm beads and 99% for 3 μm beads. Additional laboratory tests were conducted to determine the accuracy of the miniaturized optical particle counters used onboard the USV. Future work aims to understand the distribution of bioaerosols above aquatic environments and their potential association with cloud formation and precipitation processes.

Taxon-specific aerosolization of bacteria and viruses in an experimental ocean-atmosphere mesocosm

Ocean-derived, airborne microbes play important roles in Earth’s climate system and human health, yet little is known about factors controlling their transfer from the ocean to the atmosphere. Here, we study microbiomes of isolated sea spray aerosol (SSA) collected in a unique ocean–atmosphere facility and demonstrate taxon-specific aerosolization of bacteria and viruses. These trends are conserved within taxonomic orders and classes, and temporal variation in aerosolization is similarly shared by related taxa. We observe enhanced transfer into SSA of Actinobacteria, certain Gammaproteobacteria, and lipid-enveloped viruses; conversely, Flavobacteriia, some Alphaproteobacteria, and Caudovirales are generally under-represented in SSA. Viruses do not transfer to SSA as efficiently as bacteria. The enrichment of mycolic acid-coated Corynebacteriales and lipid-enveloped viruses (inferred from genomic comparisons) suggests that hydrophobic properties increase transport to the sea surface and SSA. Our results identify taxa relevant to atmospheric processes and a framework to further elucidate aerosolization mechanisms influencing microbial and viral transport pathways.

Factors controlling the transfer of microbes from the ocean to the atmosphere are unclear. Here, Michaud et al. study this process in an enclosed ocean-atmosphere facility, and show that the degree of aerosolization of bacteria and viruses is taxon-specific.

Deposition rates of viruses and bacteria above the atmospheric boundary layer

Aerosolization of soil-dust and organic aggregates in sea spray facilitates the long-range transport of bacteria, and likely viruses across the free atmosphere. Although long-distance transport occurs, there are many uncertainties associated with their deposition rates. Here, we demonstrate that even in pristine environments, above the atmospheric boundary layer, the downward flux of viruses ranged from 0.26 × 10⁹ to >7 × 10⁹ m^-2 per day. These deposition rates were 9-461 times greater than the rates for bacteria, which ranged from 0.3 × 10⁷ to >8 × 10⁷ m^-2 per day. The highest relative deposition rates for viruses were associated with atmospheric transport from marine rather than terrestrial sources. Deposition rates of bacteria were significantly higher during rain events and Saharan dust intrusions, whereas, rainfall did not significantly influence virus deposition. Virus deposition rates were positively correlated with organic aerosols <0.7 μm, whereas, bacteria were primarily associated with organic aerosols >0.7 μm, implying that viruses could have longer residence times in the atmosphere and, consequently, will be dispersed further. These results provide an explanation for enigmatic observations that viruses with very high genetic identity can be found in very distant and different environments.

Long-range transport of airborne microbes over the global tropical and subtropical ocean

The atmosphere plays a fundamental role in the transport of microbes across the planet but it is often neglected as a microbial habitat. Although the ocean represents two thirds of the Earth’s surface, there is little information on the atmospheric microbial load over the open ocean. Here we provide a global estimate of microbial loads and air-sea exchanges over the tropical and subtropical oceans based on the data collected along the Malaspina 2010 Circumnavigation Expedition. Total loads of airborne prokaryotes and eukaryotes were estimated at 2.2 × 10²¹ and 2.1 × 10²¹ cells, respectively. Overall 33–68% of these microorganisms could be traced to a marine origin, being transported thousands of kilometres before re-entering the ocean. Moreover, our results show a substantial load of terrestrial microbes transported over the oceans, with abundances declining exponentially with distance from land and indicate that islands may act as stepping stones facilitating the transoceanic transport of terrestrial microbes.

The extent to which the ocean acts as a sink and source of airborne particles to the atmosphere is unresolved. Here, the authors report high microbial loads over the tropical Atlantic, Pacific and Indian oceans and propose islands as stepping stones for the transoceanic transport of terrestrial microbes..

Bacterioplankton Biogeography of the Atlantic Ocean: A Case Study of the Distance-Decay Relationship

In order to determine the influence of geographical distance, depth, and Longhurstian province on bacterial community composition and compare it with the composition of photosynthetic micro-eukaryote communities, 382 samples from a depth-resolved latitudinal transect (51°S–47°N) from the epipelagic zone of the Atlantic ocean were analyzed by Illumina amplicon sequencing. In the upper 100 m of the ocean, community similarity decreased toward the equator for 6000 km, but subsequently increased again, reaching similarity values of 40–60% for samples that were separated by ~12,000 km, resulting in a U-shaped distance-decay curve. We conclude that adaptation to local conditions can override the linear distance-decay relationship in the upper epipelagial of the Atlantic Ocean which is apparently not restrained by barriers to dispersal, since the same taxa were shared between the most distant communities. The six Longhurstian provinces covered by the transect were comprised of distinct microbial communities; ~30% of variation in community composition could be explained by province. Bacterial communities belonging to the deeper layer of the epipelagic zone (140–200 m) lacked a distance-decay relationship altogether and showed little provincialism. Interestingly, those biogeographical patterns were consistently found for bacteria from three different size fractions of the plankton with different taxonomic composition, indicating conserved underlying mechanisms. Analysis of the chloroplast 16S rRNA gene sequences revealed that phytoplankton composition was strongly correlated with both free-living and particle associated bacterial community composition (R between 0.51 and 0.62, p < 0.002). The data show that biogeographical patterns commonly found in macroecology do not hold for marine bacterioplankton, most likely because dispersal and evolution occur at drastically different rates in bacteria.

Tools for the Microbiome: Nano and Beyond

The microbiome presents great opportunities for understanding and improving the world around us and elucidating the interactions that compose it. The microbiome also poses tremendous challenges for mapping and manipulating the entangled networks of interactions among myriad diverse organisms. Here, we describe the opportunities, technical needs, and potential approaches to address these challenges, based on recent and upcoming advances in measurement and control at the nanoscale and beyond. These technical needs will provide the basis for advancing the largely descriptive studies of the microbiome to the theoretical and mechanistic understandings that will underpin the discipline of microbiome engineering. We anticipate that the new tools and methods developed will also be more broadly useful in environmental monitoring, medicine, forensics, and other areas.

Airborne Microalgae: Insights, Opportunities, and Challenges

Airborne dispersal of microalgae has largely been a blind spot in environmental biological studies because of their low concentration in the atmosphere and the technical limitations in investigating microalgae from air samples. Recent studies show that airborne microalgae can survive air transportation and interact with the environment, possibly influencing their deposition rates. This minireview presents a summary of these studies and traces the possible route, step by step, from established ecosystems to new habitats through air transportation over a variety of geographic scales. Emission, transportation, deposition, and adaptation to atmospheric stress are discussed, as well as the consequences of their dispersal on health and the environment and state-of-the-art techniques to detect and model airborne microalga dispersal. More-detailed studies on the microalga atmospheric cycle, including, for instance, ice nucleation activity and transport simulations, are crucial for improving our understanding of microalga ecology, identifying microalga interactions with the environment, and preventing unwanted contamination events or invasions.

Seawater mesocosm experiments in the Arctic uncover differential transfer of marine bacteria to aerosols

Biogenic aerosols critically control atmospheric processes. However, although bacteria constitute major portions of living matter in seawater, bacterial aerosolization from oceanic surface layers remains poorly understood. We analysed bacterial diversity in seawater and experimentally generated aerosols from three Kongsfjorden sites, Svalbard. Construction of 16S rRNA gene clone libraries from paired seawater and aerosol samples resulted in 1294 sequences clustering into 149 bacterial and 34 phytoplankton operational taxonomic units (OTUs). Bacterial communities in aerosols differed greatly from corresponding seawater communities in three out of four experiments. Dominant populations of both seawater and aerosols were Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria. Across the entire dataset, most OTUs from seawater could also be found in aerosols; in each experiment, however, several OTUs were either selectively enriched in aerosols or little aerosolized. Notably, a SAR11 clade OTU was consistently abundant in the seawater, but was recorded in significantly lower proportions in aerosols. A strikingly high proportion of colony-forming bacteria were pigmented in aerosols compared with seawater, suggesting that selection during aerosolization contributes to explaining elevated proportions of pigmented bacteria frequently observed in atmospheric samples. Our findings imply that atmospheric processes could be considerably influenced by spatiotemporal variations in the aerosolization efficiency of different marine bacteria.

Infection of phytoplankton by aerosolized marine viruses

Marine viruses constitute a major ecological and evolutionary driving force in the marine ecosystems. However, their dispersal mechanisms remain underexplored. Here we follow the dynamics of Emiliania huxleyi viruses (EhV) that infect the ubiquitous, bloom-forming phytoplankton E. huxleyi and show that EhV are emitted to the atmosphere as primary marine aerosols. Using a laboratory-based setup, we showed that the dynamic of EhV aerial emission is strongly coupled to the host-virus dynamic in the culture media. In addition, we recovered EhV DNA from atmospheric samples collected over an E. huxleyi bloom in the North Atlantic, providing evidence for aerosolization of marine viruses in their natural environment. Decay rate analysis in the laboratory revealed that aerosolized viruses can remain infective under meteorological conditions prevailing during E. huxleyi blooms in the ocean, allowing potential dispersal and infectivity over hundreds of kilometers. Based on the combined laboratory and in situ findings, we propose that atmospheric transport of EhV is an effective transmission mechanism for spreading viral infection over large areas in the ocean. This transmission mechanism may also have an important ecological impact on the large-scale host-virus "arms race" during bloom succession and consequently the turnover of carbon in the ocean.