Effect of Dust Storms on the Atmospheric Microbiome in the Eastern Mediterranean

Aerosol sources and transport paths co-control the atmospheric bacterial diversity over the coastal East China Sea

Airborne bacteria along with chemical composition of aerosols were investigated during five sampling seasons at an offshore island of the East China Sea. Bacterial diversity was the lowest in spring, the highest in winter, and similar between the autumns of 2019 and 2020, suggesting remarkably seasonal variation but little interannual change. Geodermatophilus (Actinobacteria) was the indicator genus of mineral dust (MD) showed higher proportion in spring than in other seasons. Mastigocladopsis_PCC-10914 (Cyanobacteria) as the indicator of sea salt (SS) demonstrated the highest percentages in both autumns, when the air masses mainly passed over the ocean prior to the sampling site. The higher proportions of soil-derived genera Rubellimicrobium and Craurococcus (both Proteobacteria) and extremophile Chroococcidiopsis_SAG_2023 (Cyanobacteria) were found in summer and winter, respectively. Our study explores the linkage between aerosol source and transport path and bacterial composition, which has implication to understanding of land-sea transmission of bacterial taxa.

A Clean and Health-Care-Focused Way to Reduce Indoor Airborne Bacteria in Calf House with Long-Wave Ultraviolet

Long-term exposure to a relatively high concentration of airborne bacteria emitted from intensive livestock houses could potentially threaten the health and welfare of animals and workers. There is a dual effect of air sterilization and promotion of vitamin D synthesis for the specific bands of ultraviolet light. This study investigated the potential use of A-band ultraviolet (UVA) tubes as a clean and safe way of reducing airborne bacteria and improving calf health. The composition and emission characteristics of airborne bacteria were investigated and used to determine the correct operating regime of UVA tubes in calf houses. Intermittent exceedances of indoor airborne bacteria were observed in closed calf houses. The measured emission intensity of airborne bacteria was 1.13 ± 0.09 × 107 CFU h-1 per calf. Proteobacteria were the dominant microbial species in the air inside and outside calf houses. After UVA radiation, the indoor culturable airborne bacteria decreased in all particle size ranges of the Anderson sampler, and it showed the highest reduction rate in the size range of 3.3-4.7 μm. The results of this study would enrich the knowledge of the source characteristics of the airborne bacteria in intensive livestock farming and contribute to the environmental control of cattle in intensive livestock production.

Seasonal variability of airborne mold concentrations as related to dust in a coastal urban area in the Eastern Mediterranean

Recent studies have demonstrated that the amount of specific airborne mold types and their concentrations increase during dust events. This study investigates the seasonal variation of airborne mold concentrations before, during, and after the dust transport in an eastern Mediterranean coastal area, Izmir city, Turkey. A total of 136 airborne mold samples were collected between September 2020 and May 2021. Two different culture media, namely Potato Dextrose Agar (PDA) and Malt-Extract Agar (MEA), were used for enumeration and genus-based identification of the airborne mold. In addition to culture media, the influences of air temperature, relative humidity, and particulate matter equal to or less than 10 µm (PM10) were also investigated seasonally. The HYSPLIT trajectory model and web-based simulation results were mainly used to determine dusty days. The mean total mold concentrations (TMC) on dusty days (543 Colony Forming Unit (CFU)/m3 on PDA and 668 CFU/m3 on MEA) were approximately 2-2.5 times higher than those on non-dusty days (288 CFU/m3 on PDA and 254 CFU/m3 on MEA) for both culture media. TMC levels showed seasonal variations (p < 0.001), indicating that meteorological parameters influenced mold concentrations and compositions. Some mold genera, including Cladosporium sp., Chrysosporium sp., Aspergillus sp., Bipolaris sp., Alternaria sp., and yeast, were found higher during dusty days than non-dusty days. Thus, dust event impacts levels and types of airborne molds and has implications for regions where long-range dust transport widely occurs.

Microbial composition of Saharan dust plumes deposited as red rain in Granada (Southern Spain)

During durst storms, also biological material is transported from arid areas such as the Sahara Desert. In the present work, rain samples containing significant amounts of mineral dust have been collected in Granada during different red rain episodes. Biological features (bacteria, biofilm, pollen grain and fungal spore) as well as size-particle distribution and mineralogical composition were studied by SEM. Nanobacteria were observed for the first time in red rain samples. A preliminary metabarcoding analysis was performed on three red rain samples. Here, Bacillota made up 18 % and Pseudomonadota 23 % of the whole prokaryotic community. The fungal community was characterized by a high abundance of Ascomycota and, dependent on the origin, the presence of Chytridiomycota. By means of 16S rRNA sequencing, 18 cultivable microorganisms were identified. In general, members of the phyla Pseudomonadota and Bacillota made up the majority of taxa. Some species, such as Peribacillus frigoritolerans and Bacillus halotolerans were isolated during three different red rain episodes. Generally, red rain carries a wide variety of microorganisms, being their ecosystem and health effects largely unknown.

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.

The soil-microbe-plant resistome: A focus on the source-pathway-receptor continuum

The One World, One Health concept implies that antibiotic resistance (AR) in the soil-microbe-plant resistome is intricately linked to the human resistome. However, the literature is mainly confined to sources and types of AR in soils or microbes, but comprehensive reviews tracking AR in the soil-microbe-plant resistome are limited. The present review applies the source-pathway-receptor concept to understand the sources, behaviour, and health hazards of the soil-microbe-plant resistome. The results showed that the soil-microbe-plant system harbours various antibiotic-resistance genes (ARGs), antibiotic-resistant bacteria (ARB), and mobile genetic elements (MGEs). Anthropogenic sources and drivers include soil application of solid waste, wastewater, biosolids, and industrial waste. Water-, wind-, and human-driven processes and horizontal gene transfer circulate AR in the soil-microbe-plant resistome. The AR in bulk soil, soil components that include soil microorganisms, soil meso- and macro-organisms, and possible mechanisms of AR transfer to soil components and ultimately to plants are discussed. The health risks of the soil-microbe-plant resistome are less studied, but potential impacts include (1) the transfer of AR to previously susceptible organisms and other resistomes, including the human resistome. Overall, the study tracks the behaviour and health risks of AR in the soil-plant system. Future research should focus on (1) ecological risks of AR at different levels of biological organization, (2) partitioning of AR among various phases of the soil-plant system, (3) physico-chemical parameters controlling the fate of AR, and (4) increasing research from low-income regions particularly Africa as most of the available literature is from developed countries.

The phytomicrobiome: solving plant stress tolerance under climate change

With extraordinary global climate changes, increased episodes of extreme conditions result in continuous but complex interaction of environmental variables with plant life. Exploring natural phytomicrobiome species can provide a crucial resource of beneficial microbes that can improve plant growth and productivity through nutrient uptake, secondary metabolite production, and resistance against pathogenicity and abiotic stresses. The phytomicrobiome composition, diversity, and function strongly depend on the plant's genotype and climatic conditions. Currently, most studies have focused on elucidating microbial community abundance and diversity in the phytomicrobiome, covering bacterial communities. However, least is known about understanding the holistic phytomicrobiome composition and how they interact and function in stress conditions. This review identifies several gaps and essential questions that could enhance understanding of the complex interaction of microbiome, plant, and climate change. Utilizing eco-friendly approaches of naturally occurring synthetic microbial communities that enhance plant stress tolerance and leave fewer carbon-foot prints has been emphasized. However, understanding the mechanisms involved in stress signaling and responses by phytomicrobiome species under spatial and temporal climate changes is extremely important. Furthermore, the bacterial and fungal biome have been studied extensively, but the holistic interactome with archaea, viruses, oomycetes, protozoa, algae, and nematodes has seldom been studied. The inter-kingdom diversity, function, and potential role in improving environmental stress responses of plants are considerably important. In addition, much remains to be understood across organismal and ecosystem-level responses under dynamic and complex climate change conditions.

A new fluorescence-based methodology for studying bioaerosol scavenging processes using a hyperspectral LIF-LIDAR remote sensing system

This paper presents a novel experimental approach to in-situ study of atmospheric phenomena such as nucleation scavenging by biological seeds, bio-droplet dehydration, and bioaerosol's particle scavenging by raindrops. Our methodology is based on the analysis of the dynamical changes of fluorescence signal. We use a remote sensing system based on a homebuilt hyperspectral laser induced fluorescence (LIF) Lidar to measure the transient back-fluorescence and backscattering signals. The spectral line shape of the transient fluorescence associated with an aerosolized tryptophan solution was first analyzed in the laboratory. It then used to study bioaerosol phase transitions between wet and dry conditions. The experiments were first conducted in a dynamic aerosol cell where we repetitively create and monitor the droplets containing bioaerosol cloud starting from its early formation till its total evaporation. The LIF-Lidar was used to simultaneously measure back-fluorescence, scattering and transmission. These measurements were synchronized with the generation of droplets containing bioaerosol and with the monitoring of aerosol's size distribution and ambient conditions. A novel optical receiver design was used to simultaneously detect both back-fluorescence polarization components. Results showed that along with droplet's evaporation process, bioaerosol's fluorescence spectrum exhibit a blue shift, known as the dynamic Stokes-shifts, of ∼2000 cm^-1 and an increase in its fluorescence anisotropy. To the best of our knowledge, this is the first report of fluorescence Stokes-shifts and anisotropy within microdroplets containing a biological solution due to wet-dry phase transitions. This method was also used to quantify scavenging of biological particle by raindrops from 100 m. It shows that valuable information can be derived from analyzing the fluorescence spectrum of bioaerosol within a cloud and demonstrate the potential of a LIF-LIDAR remote system to perform in-situ studies of scavenging processes.

Climate change and human health in the Eastern Mediterranean and Middle East: Literature review, research priorities and policy suggestions

Human health is linked to climatic factors in complex ways, and climate change can have profound direct and indirect impacts on the health status of any given region. Susceptibility to climate change is modulated by biological, ecological and socio-political factors such as age, gender, geographic location, socio-economic status, occupation, health status and housing conditions, among other. In the Eastern Mediterranean and Middle East (EMME), climatic factors known to affect human health include extreme heat, water shortages and air pollution. Furthermore, the epidemiology of vector-borne diseases (VBDs) and the health consequences of population displacement are also influenced by climate change in this region. To inform future policies for adaptation and mitigation measures, and based on an extensive review of the available knowledge, we recommend several research priorities for the region. These include the generation of more empirical evidence on exposure-response functions involving climate change and specific health outcomes, the development of appropriate methodologies to evaluate the physical and psychological effects of climate change on vulnerable populations, determining how climate change alters the ecological determinants of human health, improving our understanding of the effects of long-term exposure to heat stress and air pollution, and evaluating the interactions between adaptation and mitigation strategies. Because national boundaries do not limit most climate-related factors expected to impact human health, we propose that adaptation/mitigation policies must have a regional scope, and therefore require collaborative efforts among EMME nations. Policy suggestions include a decisive region-wide decarbonisation, the integration of environmentally driven morbidity and mortality data throughout the region, advancing the development and widespread use of affordable technologies for the production and management of drinking water by non-traditional means, the development of comprehensive strategies to improve the health status of displaced populations, and fostering regional networks for monitoring and controlling the spread of infectious diseases and disease vectors.

The Relationship Between Dust Sources and Airborne Bacteria in the Southwest of Iran

The biological agents are carried from deserts and dried lands to long distances by high dust volumes. Their adverse effects can be reduced by specifying and controlling dust sources and their related biological agents. Thus, the current work examined the relationship between the bacteria in air and soil samples by taking samples from the soil surface of two dust sources, as well as from air samples during spring from Khorramshahr and Abadan cities. The dust event is the most influential factor on airborne bacteria. There is an insignificant negative (-0.06), insignificant positive (0.14), and weak positive (0.24) correlation between airborne bacteria and UV radiation, relative humidity, and temperature, respectively. After preparing a 16S ribosomal DNA (rDNA) clone library from the soil and air samples, operational taxonomic unit picking and taxonomic assignment were conducted using QIIME Virtual Box. In the present work, Bacillus was the dominant species. The relationship between dust sources and air samples was determined by principal component analysis. Bacteria in the Hoor-Al-Azim dust source and airborne bacteria on dusty and non-dusty days showed a more significant correlation compared to bacteria in the Shadegan dust source. Source Tracker software was used to estimate the contribution of dust sources. The primary source of dust was associated with the dried areas of Hoor-Al-Azim on the non-dusty and dusty days. Finally, the long transport of airborne bacteria was assessed by moderate resolution imaging spectroradiometer (MODIS) and the back trajectory model of Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) data. The research findings can help decision-makers prioritize dust sources to control the adverse effects of dust.

Simultaneous monitoring of SARS-CoV-2 and bacterial profiles from the air of hospital environments with COVID-19-affected patients

The SARS-CoV-2 presence and the bacterial community profile in air samples collected at the Intensive Care Unit (ICU) of the Operational Unit of Infectious Diseases of Santa Caterina Novella Hospital in Galatina (Lecce, Italy) have been evaluated in this study. Air samplings were performed in different rooms of the ICU ward with and without COVID-19 patients. No sample was found positive to SARS-CoV-2, according to Allplex 2019-nCoV Assay. The airborne bacterial community profiles determined by the 16S rRNA gene metabarcoding approach up to the species level were characterized by richness and biodiversity indices, Spearman correlation coefficients, and Principal Coordinate Analysis. Pathogenic and non-pathogenic bacterial species, also detected in outdoor air samples, were found in all collected indoor samples. Staphylococcus pettenkoferi, Corynebacterium tuberculostearicum, and others coagulase-negative staphylococci, detected at high relative abundances in all the patients' rooms, were the most abundant pathogenic species. The highest mean relative abundance of S. pettenkoferi and C. tuberculostearicum suggested that they were likely the main pathogens of COVID-19 patients at the ICU ward of this study. The identification of nosocomial pathogens representing potential patients' risks in ICU COVID-19 rooms and the still controversial airborne transmission of the SARS-CoV-2 are the main contributions of this study.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10453-022-09754-7.

Critical review of antibiotic resistance genes in the atmosphere

We conducted a critical review to establish what is known about the sources, characteristics, and dissemination of ARGs in the atmosphere. We identified 52 papers that reported direct measurements of bacterial ARGs in air samples and met other inclusion criteria. The settings of the studies fell into the following categories: urban, rural, hospital, industrial, wastewater treatment plants (WWTPs), composting and landfill sites, and indoor environments. Certain genes were commonly studied and generally abundant: sul1, intI1, β-lactam ARGs, and tetracycline ARGs. Abundances of total ARGs varied by season and setting, with air in urban areas having higher ARG abundance than rural areas during the summer and vice versa during the winter. There was greater consistency in the types and abundances of ARGs throughout the seasons in urban areas. Human activity within indoor environments was also linked to increased ARG content (abundance, diversity, and concentration) in the air. Several studies found that human exposure to ARGs through inhalation was comparable to exposure through drinking water or ingesting soil. Detection of ARGs in air is a developing field, and differences in sampling and analysis methods reflect the many possible approaches to studying ARGs in air and make direct comparisons between studies difficult. Methodologies need to be standardized to facilitate identification of the dominant ARGs in the air, determine their major sources, and quantify the role of atmospheric transport in dissemination of ARGs in the environment. With such knowledge we can develop better policies and guidelines to limit the spread of antimicrobial resistance.

Infectious Diseases Associated with Desert Dust Outbreaks: A Systematic Review

Background: Desert dust outbreaks and dust storms are the major source of particulate matter globally and pose a major threat to human health. We investigated the microorganisms transported with desert dust particles and evaluated their potential impact on human health. Methods: A systematic review of all reports on the association between non-anthropogenic desert dust pollution, dust microorganisms and human health is conducted. Results: In total, 51 articles were included in this review. The affected regions studied were Asia (32/51, 62.7%) followed by Europe (9/51, 17.6%), America (6/51, 11.8%), Africa (4/51, 7.8%) and Australia (1/51, 2.0%). The Sahara Desert was the most frequent source of dust, followed by Asian and American deserts. In 39/51 studies the dust-related microbiome was analyzed, while, in 12/51 reports, the association of desert dust with infectious disease outbreaks was examined. Pathogenic and opportunistic agents were isolated from dust in 24/39 (61.5%) and 29/39 (74.4%) of the studies, respectively. A significant association of dust events with infectious disease outbreaks was found in 10/12 (83.3%) reports. The infectious diseases that were mostly investigated with dust outbreaks were pneumonia, respiratory tract infections, COVID-19, pulmonary tuberculosis and coccidioidomycosis. Conclusions: Desert dust outbreaks are vehicles of a significant number of pathogenic or opportunistic microorganisms and limited data indicate an association between dust events and infectious disease outbreaks. Further research is required to strengthen the correlation between dust events and infectious diseases and subsequently guide preventive public health measures.

Changes in Ambient Bacterial Community in Northern Taiwan during Long-Range Transport: Asian Dust Storm and Frontal Pollution

Long-range transport (LRT) can carry air pollutants to downwind areas. However, studies about the impacts of LRT on bacterial communities are few. This study investigated the influence of Asian dust storms (ADS) and frontal pollution (FP) on bacterial communities in ambient air using next-generation sequencing (NGS) and Terminal Restriction Fragment Length Polymorphism (T-RFLP). Air samples were collected at Cape Fugui (CF) and National Taiwan University (NTU) in northern Taiwan before (or background days), during, and after LRTs from November 2013 to March 2015. The richness, H index, and evenness increased during FPs and then decreased after FPs. During and after ADS and FP, the prevalence of the phylum Proteobacteria decreased, but that of Firmicutes increased. The dominant class of Proteobacteria changed from Alphaproteobacteria on background days to Betaproteobacteria during LRTs. At the genus level, the high abundance of Ralstonia and Bacillus during FP and Clostridium during ADS were detected at both locations. Additionally, Ralstonia was dominant at CF during ADS. In conclusion, FP and ADS both changed the bacterial community. The indicator genus was Clostridium and Ralstonia for ADS as well as Bacillus and Ralstonia for FP. Given the potential health threats posed by the bioaerosols transported, people should avoid outdoor activities during LRTs.

Effect of inlet-outlet configurations on the cross-transmission of airborne bacteria between animal production buildings

Cross-transmission of airborne pathogens between buildings facilitates the spread of both human and animal diseases. Rational spatial arrangement of buildings and air inlet-outlet design are well-established preventive measures, but the effectiveness of current configurations for mitigating pathogens cross-transmission is still under assessment. An intensive field study in a laying hen farm was conducted to elucidate the spatial distribution of airborne bacteria (AB) and the source of AB at the inlets under different wind regimes. We found higher concentrations of AB at the interspace and sidewall inlets of buildings with sidewall exhaust systems than at those with endwall exhaust systems. We observed significant differences in bacterial diversity and richness at the interspace and sidewall inlets between buildings with side exhaust systems and those with endwall exhaust systems. We further found that the AB emitted from buildings could translocate to the sidewall inlets of adjacent building to a greater extent between buildings with sidewall exhaust systems than between those with endwall exhaust systems. Our findings revealed that sidewall exhaust systems aggravate cross-transmission of AB between buildings, suggesting that endwall exhaust systems or other compensatory preventive measures combined with sidewall exhaust systems could be a better choice to suppress airborne cross-transmission.

Two-year systematic investigation reveals alterations induced on chemical and bacteriome profile of PM2.5 by African dust incursions to the Mediterranean atmosphere

PM_2.5 atmospheric samples were regularly collected between January 2013 and March 2015 at a central location of Eastern Mediterranean (Island of Crete) during African dust events (DES) and periods of absence of such episodes as controls (CS). The elemental composition and microbiome DES and CS were thoroughly investigated. Fifty-six major and trace elements were determined by inductively coupled plasma-mass spectrometry. Relative mass abundances (RMA) of major crustal elements and lanthanoids were higher in DES than in CS. Conversely in CS, RMAs were higher for most anthropogenic transition metals. Lanthanum-to-other lanthanoids concentration ratios for DES approached the corresponding reference values for continental crust and several African dust source regions, while in CS they exceeded these values. USEPA's UNMIX receptor model, applied in all PM_2.5 samples, established that African dust is the dominant contributing source (by 80%) followed by road dust/fuel oil emissions (17%) in the receptor area. Potential source contribution function (PSCF) identified dust hotspots in Tunisia, Libya and Egypt. The application of 16S rRNA gene amplicon sequencing revealed high variation of bacterial composition and diversity between DES and CS samples. Proteobacteria, Actinobacteria and Bacteroides were the most dominant in both DES and CS samples, representing ~88% of the total bacterial diversity. Cutibacterium, Tumebacillus and Sphingomonas dominated the CS samples, while Rhizobium and Brevundimonas were the most prevalent genera in DES. Mutual exclusion/co-occurrence network analysis indicated that Sphingomonas and Chryseobacterium exhibited the highest degrees of mutual exclusion in CS, while in DES the corresponding species were Brevundimonas, Delftia, Rubellimicrobium, Flavobacterium, Blastococcus, and Pseudarthrobacter. Some of these microorganisms are emerging global opportunistic pathogens and an increase in human exposure to them as a result of environmental changes, is inevitable.

Microbiome Variation Across Populations of Desert Halophyte Zygophyllum qatarensis

Microbial symbionts play a significant role in plant health and stress tolerance. However, few studies exist that address rare species of core-microbiome function during abiotic stress. In the current study, we compared the microbiome composition of succulent dwarf shrub halophyte Zygophyllum qatarensis Hadidi across desert populations. The results showed that rhizospheric and endosphere microbiome greatly varied due to soil texture (sandy and gravel). No specific bacterial amplicon sequence variants were observed in the core-microbiome of bulk soil and rhizosphere, however, bacterial genus Alcaligenes and fungal genus Acidea were abundantly distributed across root and shoot endospheres. We also analyzed major nutrients such as silicon (Si), magnesium, and calcium across different soil textures and Z. qatarensis populations. The results showed that the rhizosphere and root parts had significantly higher Si content than the bulk soil and shoot parts. The microbiome variation can be attributed to markedly higher Si - suggesting that selective microbes are contributing to the translocation of soluble Si to root. In conclusion, low core-microbiome species abundance might be due to the harsh growing conditions in the desert - making Z. qatarensis highly selective to associate with microbial communities. Utilizing rare microbial players from plant microbiomes may be vital for increasing crop stress tolerance and productivity during stresses.

Characteristics of airborne bacterial communities and antibiotic resistance genes under different air quality levels

Pathogenic bacteria and antibiotic resistance genes (ARGs) in bioaerosols are major threats to human health. In this study, the microbial community structure and ARG distribution characteristics of airborne bacteria in total suspended particulates (TSP) and PM_2.5 were investigated under different air quality levels in Xinxiang, Central China. The results revealed that with the deterioration of air quality, the concentrations of airborne bacteria in both TSP and PM_2.5 decreased; however, the relative amounts of pathogenic bacteria increased. The predominant genera in pathogenic bacteria of Bacillus, Sphingomonas, Corynebacterium, Rhodococcus, and Staphylococcus were identified in both TSP and PM_2.5. Although the airborne bacteria concentrations and absolute abundances of ARGs in TSP were higher than those in PM_2.5 under identical air quality conditions, the bacterial community structure and relative amounts of pathogenic bacteria were similar. In addition, the relationship between environmental factors of ions, metal elements, and meteorological parameters and the community structures of airborne bacteria and pathogenic bacteria were also analyzed. The effects of soluble ions and metal elements on several dominant genera of total bacteria and pathogenic bacteria differed, probably due to the strong tolerance of pathogenic bacteria to harsh atmospheric environments Different subtypes of ARGs showed various distribution characteristics with variations in air quality. The deterioration of air quality can inhibit the dissemination of ARGs, as the minimum values of all ARGs and class 1 integrase intI1 were observed under Severely Polluted conditions. This study provides a comprehensive understanding of the effect of air pollution levels on the airborne bacteria community composition and ARG distribution.

Assessing the relationship between airborne fungi and potential dust sources using a combined approach

Dust events impose negative socio-economic, health, and environmental impacts on vulnerable areas and reflect their sources' physiochemical and biological characteristics. This study aimed to assess the impact of two dust sources on the concentration and diversity of airborne fungi in one of the dustiest areas in the world. This study is the first attempt to investigate the relationship between dust sources fungal community and those in airborne dust. Also, the contribution of dust sources to airborne fungi was estimated. Air masses arriving at the study area were assessed using local wind rose and the HYSPLIT model. Sampling was carried out from airborne dust at the Arvand Free Zone as target areas and soil in the dried parts of the Hor al-Azim and Shadegan wetlands as source areas to explore the relationship between fungi in the dust sources and the downwind area. The samples were analyzed in the lab to extract DNA. The internal transcribed spacer (ITS) regions of the rDNA gene were amplified using the primers ITS1F and ITS4, and then PCR products were sent to the lab for sequencing. The raw DNA data were processed using the QIIME virtual box to pick operational taxonomic units and taxonomy assignments. The most common fungi at the genus level were in the order of Penicillium > Aspergillus > Alternaria > Fusarium > Paradendryphiella > Talaromyces. The similarity between air and soil fungal genera was investigated using richness and diversity indices, the phylogenetic tree, and principal component analysis. The results showed that the community structures of ambient fungi in the Hor al-Azim and Shadegan dust sources were more similar to those on dusty days than non-dusty days. The source tracker model was used to quantify the contributions of known dust sources to airborne fungi. The results showed that the main source of airborne fungi was Hor al-Azim on dusty and non-dusty days. This study's results can help managers identify and prioritize dust sources regarding fungal species.

Global dispersal and potential sources of antibiotic resistance genes in atmospheric remote depositions

Antibiotic resistance has become a major Global Health concern and a better understanding on the global spread mechanisms of antibiotic resistant bacteria (ARB) and intercontinental ARB exchange is needed. We measured atmospheric depositions of antibiotic resistance genes (ARGs) by quantitative (q)PCR in rain/snow collected fortnightly along 4 y. at a remote high mountain LTER (Long-Term Ecological Research) site located above the atmospheric boundary layer (free troposphere). Bacterial composition was characterized by 16S rRNA gene sequencing, and air mass provenances were determined by modelled back trajectories and rain/snow chemical composition. We hypothesize that the free troposphere may act as permanent reservoir and vector for ARB and ARGs global dispersal. We aimed to i) determine whether ARGs are long-range intercontinental and persistently dispersed through aerosols, ii) assess ARGs long-term atmospheric deposition dynamics in a remote high mountain area, and iii) unveil potential diffuse ARGs pollution sources. We showed that the ARGs sul1 (resistance to sulfonamides), tetO (resistance to tetracyclines), and intI1 (a proxy for horizontal gene transfer and anthropogenic pollution) were long-range and persistently dispersed in free troposphere aerosols. Major depositions of tetracyclines resistance matched with intensification of African dust outbreaks. Potential ARB mostly traced their origin back into agricultural soils. Our study unveils that air masses pathways are shaping ARGs intercontinental dispersal and global spread of antibiotic resistances, with potential predictability for interannual variability and remote deposition rates. Because climate regulates aerosolization and long-range air masses movement patterns, we call for a more careful evaluation of the connections between land use, climate change and ARB long-range intercontinental dispersal.

Seasonal disparities and source tracking of airborne antibiotic resistance genes in Handan, China

The transmission of airborne antibiotic resistance genes (ARGs) loaded on particle is a significant global public health concern. Up to date, the dispersal pattern of airborne ARGs remains unclear despite their critical role in multiregional transmission. In this study, airborne ARGs loaded on fine particulate matter (PM_2.5) and source tracking based on the airflow trajectories were performed by the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) model. The results show that the absolute abundance of ARG subtypes were generally twice times higher in the winter season than that in the summer season, which could be attributable to winter haze events with high particulate matter concentrations in Handan. Exogenous input from serious haze events and local release of ARGs loaded on PM_2.5 of air masses may cause higher levels of ARGs in the winter. Moreover, based on the positive correlation between the abundance of ARGs and PM_2.5 concentration, a source tracing model of airborne ARGs was proposed to the estimate of ARGs release and dissemination. This study highlights airborne ARGs transmission loaded on PM_2.5 of air masses, which facilitating the global spread of antibiotic resistance.

The air-borne antibiotic resistome: Occurrence, health risks, and future directions

Antibiotic resistance comprising of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is an emerging problem causing global human health risks. Several reviews exist on antibiotic resistance in various environmental compartments excluding the air-borne resistome. An increasing body of recent evidence exists on the air-borne resistome comprising of antibiotic resistance in air-borne bioaerosols from various environmental compartments. However, a comprehensive review on the sources, dissemination, behavior, fate, and human exposure and health risks of the air-borne resistome is still lacking. Therefore, the current review uses the source-pathway-receptor-impact-mitigation framework to investigate the air-borne resistome. The nature and sources of antibiotic resistance in the air-borne resistome are discussed. The dissemination pathways, and environmental and anthropogenic drivers accounting for the transfer of antibiotic resistance from sources to the receptors are highlighted. The human exposure and health risks posed by air-borne resistome are presented. A health risk assessment and mitigation strategy is discussed. Finally, future research directions including key knowledge gaps are summarized.

Agricultural practices drive biological loads, seasonal patterns and potential pathogens in the aerobiome of a mixed-land-use dryland

Air carries a diverse load of particulate microscopic biological matter in suspension, either aerosolized or aggregated with dust particles, the aerobiome, which is dispersed by winds from sources to sinks. The aerobiome is known to contain microbes, including pathogens, as well as debris or small-sized propagules from plants and animals, but its variability and composition has not been studied comprehensibly. To gain a dynamic insight into the aerobiome existing over a mixed-use dryland setting, we conducted a biologically comprehensive, year-long survey of its composition and dynamics for particles less than 10 μm in diameter based on quantitative analyses of DNA content coupled to genomic sequencing. Airborne biological loads were more dependent on seasonal events than on meteorological conditions and only weakly correlated with dust loads. Core aerobiome species could be understood as a mixture of high elevation (e.g. Microbacteriaceae, Micrococcaceae, Deinococci), and local plant and soil sources (e.g. Sphingomonas, Streptomyces, Acinetobacter). Despite the mixed used of the land surrounding the sampling site, taxa that contributed to high load events were largely traceable to proximal agricultural practices like cotton and livestock farming. This included not only the predominance of specific crop plant signals over those of native vegetation, but also that of their pathogens (bacterial, viral and eukaryotic). Faecal bacterial loads were also seasonally important, possibly sourced in intensive animal husbandry or manure fertilization activity, and this microbial load was enriched in tetracycline resistance genes. The presence of the native opportunistic pathogen, Coccidioides spp., by contrast, was detected only with highly sensitive techniques, and only rarely. We conclude that agricultural activity exerts a much stronger influence that the native vegetation as a mass loss factor to the land system and as an input to dryland aerobiomes, including in the dispersal of plant, animal and human pathogens and their genetic resistance characteristics.

Abundance and diversity of antibiotic resistance genes possibly released to ambient air by experiments in biology laboratories

Antibiotic resistance genes (ARG) have been considered as a global emerging threat to public health systems. As special locations where both antibiotics and ARGs are directly used, biology laboratories are poorly studied but potential important emission sources where not only the environmental stress is strong but also obtaining resistance is much easier comparing to other well studied hot spots including farms, hospitals, wastewater treatment plants and landfills where antibiotics but not ARGs are used or discharged. Therefore, in this study, 11 Swiss biology laboratories working on different fields and located in the city center, suburb and rural area were studied to reveal the abundance and diversity of airborne ARGs in them and their surrounding areas with Colony-forming units (CFU) cultivation and quantitative Polymerase Chain Reaction (qPCR). Most biology laboratories did not discharge significant amounts or varieties of ARGs and cultivable bacteria via air. No correlation was found between the number of CFUs and the abundance of 16S rRNA, but two clusters of correlated airborne ARGs, the animal husbandry related cluster, and city and hospital related cluster were identified in this study. Although most biology laboratories may not be the emission sources of a wide variety of airborne ARGs, the ARGs in the animal husbandry related cluster which are abundant in the animal laboratories and aadA1 which is abundant in the laboratories working on other eukaryocytes need to be furtherly studied to make sure if they are potential health risks for the researchers.

Size-Resolved Community Structure of Bacteria and Fungi Transported by Dust in the Middle East

The atmosphere plays an important role in transporting microorganisms on a global scale, yet the processes affecting the composition of the airborne microbiome, the aerobiome, are not fully outlined. Here we present the community compositions of bacteria and fungi obtained by DNA amplicon-sequencing of aerosol samples collected in a size-resolved manner during nine consecutive days in central Israel. The campaign captured dust events originating from the Sahara and the Arabian deserts, as well as days without dust ("clear days"). We found that the source of the aerosol was the main variable contributing to the composition of both fungal and bacterial communities. Significant differences were also observed between communities representing particles of different sizes. We show evidence for the significant transport of bacteria as cell-aggregates and/or via bacterial attachment to particles during dust events. Our findings further point to the mixing of local and transported bacterial communities, observed mostly in particles smaller than 0.6 μm in diameter, representing bacterial single cells. Fungal communities showed the highest dependence on the source of the aerosols, along with significant daily variability, and without significant mixing between sources, possibly due to their larger aerodynamic size and shorter atmospheric residence times. These results, obtained under highly varied atmospheric conditions, provide significant assurances to previously raised hypotheses and could set the course for future studies on aerobiome composition.

General decline in the diversity of the airborne microbiota under future climatic scenarios

Microorganisms attached to aerosols can travel intercontinental distances, survive, and further colonize remote environments. Airborne microbes are influenced by environmental and climatic patterns that are predicted to change in the near future, with unknown consequences. We developed a new predictive method that dynamically addressed the temporal evolution of biodiversity in response to environmental covariates, linked to future climatic scenarios of the IPCC (AR5). We fitted these models against a 7-year monitoring of airborne microbes, collected in wet depositions. We found that Bacteria were more influenced by climatic variables than by aerosols sources, while the opposite was detected for Eukarya. Also, model simulations showed a general decline in bacterial richness, idiosyncratic responses of Eukarya, and changes in seasonality, with higher intensity within the worst-case climatic scenario (RCP 8.5). Additionally, the model predicted lower richness for airborne potential eukaryotic (fungi) pathogens of plants and humans. Our work pioneers on the potential effects of environmental variability on the airborne microbiome under the uncertain context of climate change.

Seasonal changes dominate long-term variability of the urban air microbiome across space and time

Compared to soil or aquatic ecosystems, the atmosphere is still an underexplored environment for microbial diversity. In this study, we surveyed the composition, variability and sources of microbes (bacteria and fungi) in the near surface atmosphere of a highly populated area, spanning ~ 4,000 Km² around the city center of Madrid (Spain), in different seasonal periods along two years. We found a core of abundant bacterial genera robust across space and time, most of soil origin, while fungi were more sensitive to environmental conditions. Microbial communities showed clear seasonal patterns driven by variability of environmental factors, mainly temperature and accumulated rain, while local sources played a minor role. We also identified taxa in both groups characteristic of seasonal periods, but not of specific sampling sites or plant coverage. The present study suggests that the near surface atmosphere of urban environments contains an ecosystem stable across relatively large spatial and temporal scales, with a rather homogenous composition, modulated by climatic variations. As such, it contributes to our understanding of the long-term changes associated to the human exposome in the air of highly populated areas.

Characterization of long-range transported bioaerosols in the Central Mediterranean

Airborne bacteria were characterized over a 2-y period via high-throughput massive sequencing of 16S rRNA gene in aerosol samples collected at a background mountain European Monitoring and Evaluation Programme (EMEP) Network site (Monte Martano, Italy) located in the Central Mediterranean area. The air mass origin of nineteen samples was identified by air mass modelling and a detailed chemical analysis was performed. Four main origins (Saharan, North-western, North-eastern, and Regional) were identified, and distinct microbial communities were associated with these air masses. Samples featured a great bacterial diversity with Protobacteria being the most abundant phylum, and Sphingomonas followed by Acidovorax, Acinetobacter and Stenotrophomonas the most abundant genera of the dataset. Bacterial genera including potential human and animal pathogens were more abundant in European and in Regional samples compared to Saharan samples; this stressed the relevance of anthropic impact on bacterial populations transported by air masses that cross densely populated areas. The principal aerosol chemical characteristics and the airborne bacterial communities were correlated by cluster analysis, similarity tests and non-metric multidimensional scaling analysis, explaining most of the variability observed. However, the strong correlation between bacterial community structure and air mass origin hampered the possibility to disentangle the effects of variations in bacterial populations and in dust provenance on variations in chemical variables.

Multi-Scale Airborne Infectious Disease Transmission

Airborne disease transmission is central to many scientific disciplines including agriculture, veterinary biosafety, medicine, and public health. Legal and regulatory standards are in place to prevent agricultural, nosocomial, and community airborne disease transmission. However, the overall importance of the airborne pathway is underappreciated, e.g.,, US National Library of Medicine's Medical Subjects Headings (MESH) thesaurus lacks an airborne disease transmission indexing term. This has practical consequences as airborne precautions to control epidemic disease spread may not be taken when airborne transmission is important, but unrecognized. Publishing clearer practical methodological guidelines for surveillance studies and disease outbreak evaluations could help address this situation.To inform future work, this paper highlights selected, well-established airborne transmission events - largely cases replicated in multiple, independently conducted scientific studies. Methodologies include field experiments, modeling, epidemiology studies, disease outbreak investigations and mitigation studies. Collectively, this literature demonstrates that airborne viruses, bacteria, and fungal pathogens have the capability to cause disease in plants, animals, and humans over multiple distances - from near range (< 5 m) to continental (> 500 km) in scale. The plausibility and implications of undetected airborne disease transmission are discussed, including the notable underreporting of disease burden for several airborne transmitted diseases.

The Microbiome of Size-Fractionated Airborne Particles from the Sahara Region

Diverse airborne microbes affect human health and biodiversity, and the Sahara region of West Africa is a globally important source region for atmospheric dust. We collected size-fractionated (>10, 10-2.5, 2.5-1.0, 1.0-0.5, and <0.5 μm) atmospheric particles in Mali, West Africa and conducted the first cultivation-independent study of airborne microbes in this region using 16S rRNA gene sequencing. Abundant and diverse microbes were detected in all particle size fractions at levels higher than those previously hypothesized for desert regions. Average daily abundance was 1.94 × 10⁵ 16S rRNA copies/m³. Daily patterns in abundance for particles <0.5 μm differed significantly from other size fractions likely because they form mainly in the atmosphere and have limited surface resuspension. Particles >10 μm contained the greatest fraction of daily abundance (51-62%) and had significantly greater diversity than smaller particles. Greater bacterial abundance of particles >2.5 μm that are bigger than the average bacterium suggests that most airborne bacteria are present as aggregates or attached to particles rather than as free-floating cells. Particles >10 μm have very short atmospheric lifetimes and thus tend to have more localized origins. We confirmed the presence of several potential pathogens using polymerase chain reaction that are candidates for viability and strain testing in future studies. These species were detected on all particle sizes tested, including particles <2.5 μm that are expected to undergo long-range transport. Overall, our results suggest that the composition and sources of airborne microbes can be better discriminated by collecting size-fractionated samples.

Outdoor Atmospheric Microbial Diversity Is Associated With Urban Landscape Structure and Differs From Indoor-Transit Systems as Revealed by Mobile Monitoring and Three-Dimensional Spatial Analysis

Microbes are abundant inhabitants of the near-surface atmosphere in urban areas. The distribution of microbial communities may benefit or hinder human wellbeing and ecosystem function. Surveys of airborne microbial diversity are uncommon in both natural and built environments and those that investigate diversity are stationary in the city, thus missing continuous exposure to microbes that covary with three-dimensional urban structure. Individuals in cities are generally mobile and would be exposed to diverse urban structures outdoors and within indoor-transit systems in a day. We used mobile monitoring of microbial diversity and geographic information system spatial analysis, across Philadelphia, Pennsylvania, USA in outdoor and indoor-transit (subways and train cars) environments. This study identifies to the role of the three-dimensional urban landscape in structuring atmospheric microbiomes and employs mobile monitoring over ~1,920 kilometers to measure continuous biodiversity. We found more diverse communities outdoors that significantly differ from indoor-transit air in microbial community structure, function, likely source environment, and potentially pathogenic fraction of the community. Variation in the structure of the urban landscape was associated with diversity and function of the near-surface atmospheric microbiome in outdoor samples.

Abundance and composition of airborne archaea during springtime mixed dust and haze periods in Beijing, China

Archaea have an important role in the elemental biogeochemical cycle and human health. However, characteristics of airborne archaea affected by anthropogenic and natural processes are unclear. In this study, we investigated the abundance, structures, influencing factors and assembly processes of the archaeal communities in the air samples collected from Beijing in springtime using quantitative polymerase chain reaction (qPCR), high-throughput sequencing technology and statistical analysis. The concentrations of airborne archaea ranged from 10¹ to 10³ copies m^-3 (455 ± 211 copies m^-3), accounting for 0.67% of the total prokaryote (sum of archaea and bacteria). An increase in airborne archaea was seen when the air quality shifted from clean to slightly polluted conditions. Sandstorm dust imported a large number of archaea to the local atmosphere. Euryarchaeota, Thaumarchaeota and Crenarchaeota were the dominant phyla, revealing the primary role of soil in releasing archaea to the ambient environment. Dispersal-related neutral processes play an important role in shaping the structure of airborne archaeal assembly. Of all phyla, methanogenic Euryarchaeota were most abundant in the air parcels come from the south of Beijing. Air masses from the west of Beijing, which brought sandstorm to Beijing, carried large amounts of ammonia oxidizing archaea Nitrososphaera. The results demonstrate the importance of air mass sources and local weather conditions in shaping the local airborne archaea community.

Investigating the culturable atmospheric fungal and bacterial microbiome in West Texas: implication of dust storms and origins of the air parcels

Individuals often experience ailments such as allergies, asthma and respiratory tract infections throughout the year. Weather reports often include estimations of common allergens that can affect these individuals. To describe the local 'atmospheric microbiome' in Lubbock, Texas, USA, we examined the culturable fungal and bacterial microbiome present in the air on calm and dust storm days using internal transcribed spacer (ITS)-1 and 16S rRNA amplicon sequencing, respectively. While some types of airborne fungi were frequently present throughout the year, distinct differences were also observed between calm and dust storm days. We also observed the influence of the origin of air parcels and wind elevation of the air trajectory. The most abundant genera of fungi identified during the study period were Cryptococcus, Aureobasidium, Alternaria, Cladosporium and Filobasidium. This observation was not surprising considering the agricultural intensive environment of West Texas. Interestingly, Cladosporium, a common allergenic mold, was increased during days with dust storm events. The predominant bacterial genera observed were Bacillus, Pseudomonas, Psychrobacter, Massilia and Exiguobacterium. The relative abundance of the psychrophiles, Psychrobacter and Exiguobacterium, was surprising, given the semi-aridity of West Texas. Coupling our observations with back trajectories of the wind (Hybrid Single-Particle Lagrangian Integrated Trajectory models) demonstrated that dust storms, regional anthropogenic activity and origin of air parcels are important influences on the diversity and temporal presence of the atmospheric microbiome.

Monitoring antibiotic resistomes and bacterial microbiomes in the aerosols from fine, hazy, and dusty weather in Tianjin, China using a developed high-volume tandem liquid impinging sampler

Accurate quantification of the airborne antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is critically important to assess their health risks. However, the currently widely used high-volume filter sampler (HVFS) often causes the desiccation of the sample, interfering with subsequent bacterial culture. To overcome this limitation, a high-volume tandem liquid impinging sampler (HVTLIS) was developed and optimized to investigate the airborne bacterial microbiomes and antibiotic resistomes under different weathers in Tianjin, China. Results revealed that HVTLIS can capture significantly more diverse culturable bacteria, ARB, and ARGs than HVFS. Compared with fine and hazy weathers, dusty weather had significantly more diverse and abundant airborne bacteria, ARGs, and human opportunistic pathogens with the resistance to last-resort antibiotics of carbapenems and polymyxin B, implicating a potential human health threat of dusty bioaerosols. Intriguingly, we represented the first report of Saccharibacteria predominance in the bioaerosol, demonstrating that the potential advantage of HVTLIS in collecting airborne microbes.

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.

Links between airborne microbiome, meteorology, and chemical composition in northwestern Turkey

The composition of atmospheric aerosols is dynamic and influenced by their emission sources, organic and inorganic composition, transport pathways, chemical and physical processes, microorganisms' content and more. Characterization of such factors can improve the ability to evaluate air quality and health risks under different atmospheric scenarios. Here we investigate the microbial composition of the atmospheric particulate matter (<10 μm; PM₁₀), sampled in Bolu, Turkey, and the linkage to the chemical composition changes, and different environmental factors. We show distinct differences between aerosol composition of different sources and air-mass transport patterns, sampled in July-August 2017 and in February 2018. The summer samples had a typical northern component air mass trajectories and higher local wind speed. They were characterized by high PM₁₀ levels, marine and mineral dust tracers and high relative abundance of Ascomycota, suggesting long-range transport of the particles from remote sources. In contrast, samples collected in February were characterized by a dominant contribution of southern air masses, and low wind speed. They had low PM₁₀ values, higher relative abundance of antibiotic resistance genes and anthropogenic ions related to local industries and farming, suggesting a dominance of local sources. With the microbiome analyses reported here for the first time for this region, we show good agreement between airborne microbial composition, aerosol mass load, chemistry, and meteorology. These results allow better air quality evaluation and prediction capabilities.

Air Microbiome and Pollution: Composition and Potential Effects on Human Health, Including SARS Coronavirus Infection

Polluted air poses a significant threat to human health. Exposure to particulate matter (PM) and harmful gases contributes to cardiovascular and respiratory diseases, including allergies and obstructive lung disease. Air pollution may also be linked to cancer and reduced life expectancy. Uptake of PM has been shown to cause pathological changes in the intestinal microbiota in mice and humans. Less is known about the effects of pollution-associated microbiota on human health. Several recent studies described the microbiomes of urban and rural air samples, of the stratosphere and sand particles, which can be transported over long distances, as well as the air of indoor environments. Here, we summarize the current knowledge on airborne bacterial, viral, and fungal communities and discuss their potential consequences on human health. The current data suggest that bacterial pathogens are typically too sparse and short-lived in air to pose a significant risk for infecting healthy people. However, airborne fungal spores may exacerbate allergies and asthma. Little information is available on viruses including phages, and future studies are likely to detect known and novel viruses with a yet unknown impact on human health. Furthermore, varying experimental protocols have been employed in the recent microbiome and virome studies. Therefore, standardized methodologies will be required to allow for better comparisons between studies. Air pollution has been linked to more severe outcomes of SARS (severe acute respiratory syndrome) coronavirus (SARS-CoV) infections. This may have contributed to severe SARS-CoV-2 outbreaks, especially those in China, Northern Italy, Iran, and New York City.

Municipal Solid Waste Treatment System Increases Ambient Airborne Bacteria and Antibiotic Resistance Genes

Landfill and incineration are the primary disposal practices for municipal solid waste (MSW) and have been considered as the critical reservoir of antibiotic resistance genes (ARGs). However, the possible transmission of ARGs from the municipal solid waste treatment system (MSWT system) to ambient air is still unclear. In this study, we collected inside and ambient air samples (PM₁₀ and PM_2.5) and potential source samples (leachate and solid waste) in the MSWT system. The results showed that the MSWT system contributed to the increased ambient airborne bacteria and associated ARGs. Forty-one antibiotic-resistant bacteria (ARB) harboring bla_TEM-1 were isolated, and the full-length nucleotide sequences of the bla_TEM-1 gene (harbored by identical bacillus) from air (downwind samples) were 100% identical with those in the leachate and solid waste, indicating that the MSWT system was the important source of disperse bacteria and associated ARGs in the ambient air. The daily intake (DI) burden level of ARGs via PM inhalation was comparable with that via ingestion of drinking water but lower than the DI level via ingestion of raw vegetables. The antibiotic-resistant opportunistic pathogen Bacillus cereus was isolated from air, with a relatively high DI level of Bacillus via inhalation (10⁴-10⁶ copies/day) in the MSWT system. This study highlights the key pathway of airborne ARGs to human exposure.

Metagenomic investigation of African dust events in the Caribbean

African dust from the Sahara and Sahel regions of Northern Africa is blown intercontinental distances and is the highest portion of atmospheric dust generated each year. During the Northern Hemisphere summer months (boreal summer), these dust events travel into the Caribbean and southern United States. While viability assays, microscopy and bacterial amplicon analyses have shown that dust-associated microbes may be diverse, the specific microbial taxa that are transported intercontinental distances with these dust events remain poorly characterized. To provide new insights into these issues, five metagenomes of Saharan dust events occurring in the Caribbean, collected in the summer months of 2002 and 2008, were analyzed. The data revealed that similar microbial composition existed between three out of the five of the distinct dust events and that fungi were a prominent feature of the metagenomes compared to other environmental samples. These results have implications for better understanding of microbial transport through the atmosphere and may implicate that the dust-associated microbial load transiting the Atlantic with Saharan dust is similar from year to year.

Airborne bacteria in the Central Mediterranean: Structure and role of meteorology and air mass transport

The 16S rRNA gene metabarcoding approach has been used to characterize the structure of the airborne bacterial community of PM10 samples, and investigate the dependence on meteorology, seasons, and long-range transported air masses. The PM10 samples were collected at a Central Mediterranean coastal site, away from large sources of local pollution. Proteobacteria, Cyanobacteria, Actinobacteria, Firmicutes, and Bacteroidetes, which were found in all samples, were the most abundant phyla. Calothrix, Pseudomonas, and Bacillus were the most abundant genera. The within-sample relative abundance (RA) of each phylum/genus varied from sample to sample. Calothrix was the most abundant genus during the advection of desert dust and Atlantic air masses, Pseudomonas was the most abundant genus when the advected air flows spent several hours over lands or close to lands affected by anthropogenic activities, before reaching the study site. The bacterial community richness and biodiversity of the PM10 samples on average increased from winter to spring, while the sample dissimilarity on average decreased from winter to spring. The spring meteorological conditions over the Mediterranean, which have likely contributed to maintain for longer time the bacterial community in the atmosphere, could have been responsible for the above results. The analysis of the presumptive species-level characterization of the airborne bacterial community has revealed that the abundance of human (opportunistic) pathogens was highly inhomogeneous among samples, without any significant change from winter to spring. We also found that the PM10 samples collected during the advection of desert dust and Atlantic air masses were on average the less enriched in human (opportunistic) pathogenic species.

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.

Water and sanitation: an essential battlefront in the war on antimicrobial resistance

Water and sanitation represent a key battlefront in combatting the spread of antimicrobial resistance (AMR). Basic water sanitation infrastructure is an essential first step towards protecting public health, thereby limiting the spread of pathogens and the need for antibiotics. AMR presents unique human health risks, meriting new risk assessment frameworks specifically adapted to water and sanitation-borne AMR. There are numerous exposure routes to AMR originating from human waste, each of which must be quantified for its relative risk to human health. Wastewater treatment plants play a vital role in centralized collection and treatment of human sewage, but there are numerous unresolved issues in terms of the microbial ecological processes occurring within them and the extent to which they attenuate or amplify AMR. Research is needed to advance understanding of the fate of resistant bacteria and antibiotic resistance genes in various waste management systems, depending on the local constraints and intended reuse applications. World Health Organization and national AMR action plans would benefit from a more holistic 'One Water' understanding. In this article we provide a framework for research, policy, practice and public engagement aimed at limiting the spread of AMR from water and sanitation in low-, medium- and high-income countries.

Scoping studies to establish the capability and utility of a real-time bioaerosol sensor to characterise emissions from environmental sources

A novel dual excitation wavelength based bioaerosol sensor with multiple fluorescence bands called Spectral Intensity Bioaerosol Sensor (SIBS) has been assessed across five contrasting outdoor environments. The mean concentrations of total and fluorescent particles across the sites were highly variable being the highest at the agricultural farm (2.6 cm^-3 and 0.48 cm^-3, respectively) and the composting site (2.32 cm^-3 and 0.46 cm^-3, respectively) and the lowest at the dairy farm (1.03 cm^-3 and 0.24 cm^-3, respectively) and the sewage treatment works (1.03 cm^-3 and 0.25 cm^-3, respectively). In contrast, the number-weighted fluorescent fraction was lowest at the agricultural site (0.18) in comparison to the other sites indicating high variability in nature and magnitude of emissions from environmental sources. The fluorescence emissions data demonstrated that the spectra at different sites were multimodal with intensity differences largely at wavelengths located in secondary emission peaks for λex 280 and λex 370. This finding suggests differences in the molecular composition of emissions at these sites which can help to identify distinct fluorescence signature of different environmental sources. Overall this study demonstrated that SIBS provides additional spectral information compared to existing instruments and capability to resolve spectrally integrated signals from relevant biological fluorophores could improve selectivity and thus enhance discrimination and classification strategies for real-time characterisation of bioaerosols from environmental sources. However, detailed lab-based measurements in conjunction with real-world studies and improved numerical methods are required to optimise and validate these highly resolved spectral signatures with respect to the diverse atmospherically relevant biological fluorophores.

Airborne bacteria and persistent organic pollutants associated with an intense Saharan dust event in the Central Mediterranean

In this paper, we present a comprehensive taxonomic survey of the bacterial community and accurate quantification of polycyclic aromatic hydrocarbons (PAHs) associated with an intense Saharan dust advection, which impacted Central Mediterranean area in the whole 2014-2015 period. This work is part of an intensive field campaign at the EMEP regional background site of Monte Martano (Central Italy), considered well representative of long-range transport in the Central Mediterranean area. 22 samples have been characterized in their provenance region and have been considered for the chemical and biological characterization. The event described in the present paper was exceptionally intense at the sampling site allowing a detailed evaluation of the dust load on a regional scale, an estimation of the impact of PAH based on the Toxic Equivalency Factor methodology and a thorough characterization of the airborne bacterial fraction performed by High Throughput Sequencing approach. Afterward, we cultured viable bacteria and evaluated several enzymatic activities and conducted UV survival tests. Principal findings include: (i) the striking evidence that, during the Saharan dust event, a highly diverse and abundant bacterial community was associated with PAH concentrations higher than the yearly mean; (ii) the tangible presence of cultivable microbes; (iii) the proof that the isolates recovered from Saharan dust had the potential to be metabolically active and that almost all of them were able to persist following UV radiation exposure. Comparisons of results for the present case study with mean values for the 2014-2015 experimental campaign are presented. The bacterial community and chemical speciation associated with the Saharan dust advection were specific and very different from those associated with other air masses. The particular case of North-Western Atlantic, which represents one of the most typical advection route reaching the sampling site is discussed in detail.

Global Ramifications of Dust and Sandstorm Microbiota

Dust and sandstorm events inject substantial quantities of foreign microorganisms into global ecosystems, with the ability to impact distant environments. The majority of these microorganisms originate from deserts and drylands where the soil is laden with highly stress-resistant microbes capable of thriving under extreme environmental conditions, and a substantial portion of them survive long journeys through the atmosphere. This large-scale transmission of highly resilient alien microbial contaminants raises concerns with regards to the invasion of sensitive and/or pristine sink environments, and to human health-concerns exacerbated by increases in the rate of desertification. Further increases in the transport of dust-associated microbiota could extend the spread of foreign microbes to new ecosystems, increase their load in present sink environments, disrupt ecosystem balance, and potentially introduce new pathogens. Our present understanding of these microorganisms, their phylogenic affiliations and functional significance, is insufficient to determine their impact. The purpose of this review is to provide an overview of available data regarding dust and sandstorm microbiota and their potential ramifications on human and ecosystem health. We conclude by discussing current gaps in dust and sandstorm microbiota research, and the need for collaborative studies involving high-resolution meta-omic approaches in conjunction with extensive ecological time-series studies to advance the field towards an improved and sufficient understanding of these invisible atmospheric travelers and their global ramifications.

Insights into microbial involvement in desert varnish formation retrieved from metagenomic analysis

Desert varnishes are dark rock coatings observed in arid environments and might resemble Mn-rich coatings found on Martian rocks. Their formation mechanism is not fully understood and the possible microbial involvement is under debate. In this study, we applied DNA metagenomic Shotgun sequencing of varnish and surrounding soil to evaluate the composition of the microbial community and its potential metabolic function. We found that the α diversity was lower in varnish compared to soil samples (p value < 0.05), suggesting distinct populations with significantly higher abundance of Actinobacteria, Proteobacteria and Cyanobacteria within the varnish. Additionally, we observed increased levels of transition metal metabolic processes in varnish compared to soil samples. Nevertheless, potentially relevant enzymes for varnish formation were detected at low to insignificant levels in both niches, indicating no current direct microbial involvement in Mn oxidation. This finding is supported by quantitative genomic analysis, elemental analysis, fluorescence imaging and scanning transmission X-ray microscopy. We thus conclude that the distinct microbial communities detected in desert varnish originate from settled Aeolian microbes, which colonized this nutrient-enriched niche, and discuss possible indirect contributions of microorganisms to the formation of desert varnish.

Metagenomic profiling of ARGs in airborne particulate matters during a severe smog event

Information is currently limited regarding the distribution of antibiotic resistance genes (ARGs) in smog and their correlations with airborne bacteria. This study characterized the diversity and abundance of ARGs in the particulate matters (PMs) of severe smog based on publicly available metagenomic data, and revealed the occurrence of 205 airborne ARG subtypes, including 31 dominant ones encoding resistance to 11 antibiotic types. Among the detectable ARGs, tetracycline, β-lactam and aminoglycoside resistance genes had the highest abundance, and smog and soil had similar composition characteristics of ARGs. During the smog event, the total abundance of airborne ARGs ranged from 4.90 to 38.07ppm in PM_2.5 samples, and from 7.61 to 38.49ppm in PM₁₀ samples, which were 1.6-7.7 times and 2.1-5.1 times of those in the non-smog day, respectively. The airborne ARGs showed complicated co-occurrence patterns, which were heavily influenced by the interaction of bacterial community, and physicochemical and meteorological factors. Lactobacillus and sulfonamide resistance gene sul1 were determined as keystones in the co-occurrence network of microbial taxa and airborne ARGs. The results may help to understand the distribution patterns of ARGs in smog for the potential health risk evaluation.

Meteorological factors had more impact on airborne bacterial communities than air pollutants

Airborne bacteria have gained increasing attention because they affect ecological balance and pose potential risks on human health. Recently, some studies have focused on the abundance and composition of airborne bacteria under heavy, hazy polluted weather in China, but they reached different conclusions about the comparisons with non-polluted days. In this study, we tested the hypothesis that meteorological factors could have a higher impact on shaping airborne bacterial communities than air pollutants by systematically monitoring the communities for 1year. Total suspended particles in Beijing were sampled for 20 consecutive days in each season of 2015. Bacterial abundance varied from 8.71×10³ to 2.14×10⁷ ribosomal operons per cubic meter according to the quantitative PCR analysis. There were relatively higher bacterial counts in spring and in autumn than in winter and summer. Airborne bacterial communities displayed a strong seasonality, according to the hierarchical cluster analysis. Only two exceptions overtook the seasonal trend, and both occurred in or after violent meteorological changes (sandstorm or rain). Aggregated boosted tree analysis performed on bacterial abundance showed that the dominant factors shaping bacterial communities were meteorological. They were air pressure in winter, air temperature and relative humidity in spring, RH in summer, and vapor pressure in autumn. Variation partition analysis on community structure showed that meteorological factors explained more variations than air pollutants. Therefore, both of the two models verified our hypothesis that the differences in airborne bacterial communities in polluted days or non-polluted days were mainly driven by the discrepancies of meteorological factors rather than by the presence of air pollutants.

Influence of seasonality, air mass origin and particulate matter chemical composition on airborne bacterial community structure in the Po Valley, Italy

The integration of chemical and biological data in aerosol studies represents a new challenge in atmospheric science. In this perspective it will be possible to gain a clearer and deeper comprehension of biogeochemical cycles in the atmosphere. In this view, this study aimed to investigate the relationships occurring between bacterial populations and PM chemical composition in one of the most polluted and urbanized areas in Europe: the Po Valley (Italy). Moreover, seasonality, long- and short-range transports were also evaluated to investigate the influence on airborne bacterial communities. PM samples were collected in two cities of the Po Valley (Milan and Venice) characterized by different meteorological conditions and atmospheric pollutant sources. Samples were analysed for water-soluble inorganic ions (WSIIs) and bacterial community structure. Chemical and biological data were jointly processed by using redundancy discriminate analysis (RDA), while the influence of atmospheric circulation was evaluated by using wind ground data and back-trajectories analysis. Results showed strong seasonal shifts of bacterial community structure in both cities, while a different behaviour was observed for air mass circulation at Milan ad Venice sites: long-range transport significantly affected bacterial populations in Milan whereas local ground wind had more influence in the Venice area. Moreover, difference in taxonomic composition can be mostly addressed to the characteristics of sampling sites. This evidence could suggest that, while PM composition is influenced by long-range transport, bacterial populations are affected, besides transport, by other factors (i.e., season and sampling site location). This perspective allow to better understand and explain airborne bacterial community behaviour.

Lessons from the Environmental Antibiotic Resistome

Antibiotic resistance is a global public health issue of growing proportions. All antibiotics are susceptible to resistance. The evidence is now clear that the environment is the single largest source and reservoir of resistance. Soil, aquatic, atmospheric, animal-associated, and built ecosystems are home to microbes that harbor antibiotic resistance elements and the means to mobilize them. The diversity and abundance of resistance in the environment is consistent with the ancient origins of antibiotics and a variety of studies support a long natural history of associated resistance. The implications are clear: Understanding the evolution of resistance in the environment, its diversity, and mechanisms is essential to the management of our existing and future antibiotic resources.