Vertical variations in the concentration and community structure of airborne microbes in PM2.5

Unveiling the overlooked microbial niches thriving on building exteriors

Rapid urbanization in the Asia-Pacific region is expected to place two-thirds of its population in concrete-dominated urban landscapes by 2050. While diverse architectural facades define the unique appearance of these urban systems. There remains a significant gap in our understanding of the composition, assembly, and ecological potential of microbial communities on building exteriors. Here, we examined bacterial and protistan communities on building surfaces along an urbanization gradient (urban, suburban and rural regions), investigating their spatial patterns and the driving factors behind their presence. A total of 55 bacterial and protist phyla were identified. The bacterial community was predominantly composed of Proteobacteria (33.7% to 67.5%). The protistan community exhibited a prevalence of Opisthokonta and Archaeplastida (17.5% to 82.1% and 1.8% to 61.2%, respectively). The composition and functionality of bacterial communities exhibited spatial patterns correlated with urbanization. In urban buildings, factors such as facade type, light exposure, and building height had comparatively less impact on bacterial composition compared to suburban and rural areas. The highest bacterial diversity and lowest Weighted Average Community Identity (WACI) were observed on suburban buildings, followed by rural buildings. In contrast, protists did not show spatial distribution characteristics related to facade type, light exposure, building height and urbanization level. The distinct spatial patterns of protists were primarily shaped by community diffusion and the bottom-up regulation exerted by bacterial communities. Together, our findings suggest that building exteriors serve as attachment points for local microbial metacommunities, offering unique habitats where bacteria and protists exhibit independent adaptive strategies closely tied to the overall ecological potential of the community.

Exploring the Microbial Community Structure in the Chicken House Environment by Metagenomic Analysis

The environmental conditions of chicken houses play an important role in the growth and development of these animals. The chicken house is an essential place for the formation of microbial aerosols. Microbial aerosol pollution and transmission can affect human and animal health. In this work, we continuously monitored fine particulate matter (PM2.5) in the chicken house environment for four weeks and studied the microbial community structure in the aerosols of the chicken house environment through metagenomic sequencing. Our results found that bacteria, fungi, viruses, and archaea were the main components of PM2.5 in the chicken house environment, accounting for 89.80%, 1.08%, 2.06%, and 0.49%, respectively. Conditional pathogens are a type of bacteria that poses significant harm to animals themselves and to farm workers. We screened ten common conditional pathogens and found that Staphylococcus had the highest relative abundance, while Clostridium contained the most microbial species, up to 456. Basidiomycetes and Ascomycota in fungi showed dramatic changes in relative abundance, and other indexes showed no significant difference. Virulence factors (VF) are also a class of molecules produced by pathogenic microbes that can cause host diseases. The top five virulence factors were found in four groups: FbpABC, HitABC, colibactin, acinetobactin, and capsule, many of which are used for the iron uptake system. In the PM2.5 samples, eight avian viruses were the most significant discoveries, namely Fowl aviadovirus E, Fowl aviadovirus D, Avian leukosis virus, Avian endogenous retrovirus EAV-HP, Avian dependent parvovirus 1, Fowl adenovus, Fowl aviadovirus B, and Avian sarcoma virus. The above results significantly improve our understanding of the microbial composition of PM2.5 in chicken houses, filling a gap on virus composition; they also indicate a potential threat to poultry and to human health. This work provides an important theoretical basis for animal house environmental monitoring and protection.

How dominant the load of bioaerosols in PM2.5 and PM10: a comprehensive study in the IGP during winter

The winter period is most ideal for studying near-surface aerosols in the Indo-Gangetic plains (IGP) of India, since this period is inundated with significantly higher concentrations of aerosols across the unique geographical domain because of shallow atmospheric boundary layer. This study focuses on analysing the concentration of the biotic component of aerosols (bioaerosols) in a central location of the IGP and estimating their dominance in ambient particulate matter (PM) from 2021 to 2023. Observations showed that bioaerosol concentrations also increased significantly with the increasing concentrations of PM2.5 and PM10, suggesting that bioaerosols are a dominant component of the total aerosol load in the atmosphere. The total microbe's concentration (collectively fungi and bacteria) was found to be 94 to 226 cfu m-3 in PM2.5 and 167 to 375 cfu m-3 in PM10 where bacteria contributed 81.12 and 79.99%, respectively. The contribution of fungal spores in PM2.5 and PM10 remained as 18.88 and 20.01%, respectively, in the total microbes in the respective particulate matter. In the bioaerosols, fungi, namely Aspergillus, Cladosporium, and Penicillium, were dominant, and bacteria, namely E. coli, Mammaliicoccus and Enterobacter, were prevalent in both the PM size regimes. The most prominent microbial presence was observed when the temperature ranged between 16 and 20°C and relative humidity between 80 and 85%. The outcomes of the present study will be useful for further research on the health effect of the bioaerosols in the IGP.

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 characteristics of nano-micron calcite particles/common bacteria complex and its interfacial interaction

Based on the composite pollution of atmospheric microbial aerosol, this paper selects the calcite/bacteria complex as the research object which was prepared by calcite particles and two common strains of bacteria (Escherichia coli, Staphylococcus aureus) in the solution system. The morphology, particle size, surface potential, and surface groups of the complex were explored by modern analysis and testing methods, with an emphasis on the interfacial interaction between calcite and bacteria. The SEM, TEM, and CLSM results showed that the morphology of the complex could be divided into three types: bacteria adhering to the surface or edge of micro-CaCO₃, bacteria aggregating with nano-CaCO₃, and single nano-CaCO₃ wrapping bacteria. The complex's particle size was about 2.07 ~ 192.4 times larger than the original mineral particles, and the nano-CaCO₃/bacteria complex's particle size variation was caused by the fact that nano-CaCO₃ has agglomeration in solution. The surface potential of the micro-CaCO₃/bacteria complex (isoelectric point pH = 3.0) lies between micro-CaCO₃ and bacteria, while the surface potential of the nano-CaCO₃/bacteria complex (isoelectric point pH = 2.0) approaches the nano-CaCO₃. The complex's surface groups were based primarily on the infrared characteristics of calcite particles, accompanied by the infrared characteristics of bacteria, displaying the interfacial interaction from the protein, polysaccharides, and phosphodiester groups of bacteria. The interfacial action of the micro-CaCO₃/bacteria complex is mainly driven by electrostatic attraction and hydrogen bonding force, while the nano-CaCO₃/bacteria complex is guided by surface complexation and hydrogen bonding force. The increase in the β-fold/α-helix ratio of the calcite/S. aureus complex indicated that the secondary structure of bacterial surface proteins was more stable and the hydrogen bond effect was strong than the calcite/E. coli complex. The findings are expected to provide basic data for the mechanism research of atmospheric composite particles closer to the real environment.

Differences in microbial community composition and factors affecting different particulate matter during autumn in three cities of Xinjiang, China

Environmental pollution has become an issue of increasing concern in China, owing to the country's rapid economic development. Atmospheric particulate matter (PM) is known to be an important parameter in air quality monitoring; further, bioaerosol forms a crucial component of PM. As the climatic environments in the north and south of Xinjiang, China, are significantly different, here, atmospheric PM samples collected from three cities, Shihezi, Yining, and Tumushuk, located in different directions, were analysed for a better understanding of the spatial distribution patterns of microbial community composition of Xinjiang. The16s rDNA and 18 s rDNA were used to locate bacteria and fungi in PM_2.5, PM₁₀, and total suspended particulate matter (TSP) at the species level and genus level, and the microbial communities with the top 15 abundances were selected for analysis. The reports indicate that the most abundant group in Shihezi and Yining was Cenchrus_americanus, which belongs to Proteobacteria. The remaining 14 dominant species had their own distribution pattern in each city. The most dominant strain in Tumushuk was Bacillus_taeanensis, but this strain was not detected in Yining and Shihezi. Similarly, the most predominant fungus in Tumushuk (Microdorylaimus_miser under Myriophyllum) was not detected in the other two cities. The analysis of the effect of environmental impact factors on bacteria and fungi revealed that the impact factors such as temperature, humidity, and wind speed had a greater effect on microorganisms, while O₃ had a negative correlation with most microorganisms, owing to its toxicity. Overall, the results of this study show that short-range transported air masses have a greater impact on local pollutants and microorganisms.

Full-length 16S rRNA gene sequencing and machine learning reveal the bacterial composition of inhalable particles from two different breeding stages in a piggery

Bacterial loading aggravates the harm of particulate matter (PM) to public health and ecological systems, especially in operations of concentrated animal production. This study aimed to explore the characteristics and influencing factors of bacterial components of inhalable particles at a piggery. The morphology and elemental composition of coarse particles (PM₁₀, aerodynamic diameter ≤ 10 µm) and fine particles (PM_2.5, aerodynamic diameter ≤ 2.5 µm) were analyzed. Full-length 16 S rRNA sequencing technology was used to identify bacterial components according to breeding stage, particle size, and diurnal rhythm. Machine learning (ML) algorithms were used to further explore the relationship between bacteria and the environment. The results showed that the morphology of particles in the piggery differed, and the morphologies of the suspected bacterial components were elliptical deposited particles. Full-length 16 S rRNA indicated that most of the airborne bacteria in the fattening and gestation houses were bacilli. The analysis of beta diversity and difference between samples showed that the relative abundance of some bacteria in PM_2.5 was significantly higher than that in PM₁₀ at the same pig house (P < 0.01). There were significant differences in the bacterial composition of inhalable particles between the fattening and gestation houses (P < 0.01). The aggregated boosted tree (ABT) model showed that PM_2.5 had a great influence on airborne bacteria among air pollutants. Fast expectation-maximization microbial source tracking (FEAST) showed that feces was a major potential source of airborne bacteria in pig houses (contribution 52.64-80.58 %). These results will provide a scientific basis for exploring the potential risks of airborne bacteria in a piggery to human and animal health.

Comparison of bacterial community structure in PM2.5 during hazy and non-hazy periods in Guilin, South China

In recent years, significant efforts have been made to study changes in the levels of air pollutants at regional and urban scales, and changes in bioaerosols during air pollution events have attracted increasing attention. In this study, the bacterial structure of PM_2.5 was analysed under different environmental conditions during hazy and non-hazy periods in Guilin. A total of 32 PM_2.5 samples were collected in December 2020 and July 2021, and the microbial community structures were analysed using high-throughput sequencing methods. The results show that air pollution and climate change alter the species distribution and community diversity of bacteria in PM_2.5, particularly Sphingomonas and Pseudomonas. The structure of the bacterial community composition is related to diurnal variation, vertical height, and urban area and their interactions with various environmental factors. This is a comprehensive study that characterises the variability of bacteria associated with PM_2.5 in a variety of environments, highlighting the impacts of environmental effects on the atmospheric microbial community. The results will contribute to our understanding of haze trends in China, particularly the relationship between bioaerosol communities and the urban environment.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10453-022-09777-0.

Global Meta-analysis of Airborne Bacterial Communities and Associations with Anthropogenic Activities

Airborne microbiome alterations, an emerging global health concern, have been linked to anthropogenic activities in numerous studies. However, these studies have not reached a consensus. To reveal general trends, we conducted a meta-analysis using 3226 air samples from 42 studies, including 29 samples of our own. We found that samples in anthropogenic activity-related categories showed increased microbial diversity, increased relative abundance of pathogens, increased co-occurrence network complexity, and decreased positive edge proportions in the network compared with the natural environment category. Most of the above conclusions were confirmed using the samples we collected in a particular period with restricted anthropogenic activities. Additionally, unlike most previous studies, we used 15 human-production process factors to quantitatively describe anthropogenic activities. We found that microbial richness was positively correlated with fine particulate matter concentration, NH₃ emissions, and agricultural land proportion and negatively correlated with the gross domestic product per capita. Airborne pathogens showed preferences for different factors, indicating potential health implications. SourceTracker analysis showed that the human body surface was a more likely source of airborne pathogens than other environments. Our results advance the understanding of relationships between anthropogenic activities and airborne bacteria and highlight the role of airborne pathogens in public health.

Internal Exposure and Distribution of Airborne Fine Particles in the Human Body: Methodology, Current Understandings, and Research Needs

Exposure to airborne fine particles (PM_2.5, particulate matter with aerodynamic diameter <2.5 μm) severely threatens global human health. Understanding the distribution and processes of inhaled PM_2.5 in the human body is crucial to clarify the causal links between PM_2.5 pollution and diseases. In contrast to extensive research on the emission and formation of PM_2.5 in the ambient environment, reports about the occurrence and fate of PM_2.5 in humans are still limited, although many studies have focused on the exposure and adverse effects of PM_2.5 with animal models. It has been shown that PM_2.5, especially ultrafine particles (UFPs), have the potential to go across different biological barriers and translocate into different human organs (i.e., blood circulation, brain, heart, pleural cavity, and placenta). In this Perspective, we summarize the factors affecting the internal exposure of PM_2.5 and the relevant analytical methodology and review current knowledge about the exposure pathways and distribution of PM_2.5 in humans. We also discuss the research challenges and call for more studies on the identification and characterization of key toxic species of PM_2.5, quantification of internal exposure doses in the general population, and further clarification of translocation, metabolism, and clearance pathways of PM_2.5 in the human body. In this way, it is possible to develop toxicity-based air quality standards instead of the currently used mass-based standards.

Microbial Activity and Community Structure in PM2 .5 at Different Heights in Ground Boundary Layer of Beijing Atmosphere under Various Air Quality Levels

The outbreak of the COVID-19 epidemic is a reminder that aerosols have important health effects as a potential route for disease transmission. Biological components in aerosols (especially PM_2.5 ) may pose potential threats to humans as pathogens and allergens. Research on PM_2.5 and biological components currently focuses mainly on polluted conditions, with less emphasis on clean environments. Sampling has also been primarily based on a single point with a lack of data at different positions. In this study, a modified fluorescein diacetate hydrolysis method was used to measure microbial activity in PM_2.5 at different altitudes over a year in Beijing, China. A high-throughput sequencing method was used to study the microbial community. Results showed that microbial activity 1.5 m (0.0465 ng m^-3 ) above the ground was higher than 31.5 m (0.0348 ng m^-3 ). There was higher microbial activity at both heights during spring. Furthermore, a positive correlation was observed between microbial activity and relative abundance of dominant species. Microbial activity increased during autumn and winter increased alongside the pollution level, but in spring higher levels of microbial activity were observed in excellent or good weather conditions. The results from this study are valuable for further research regarding the biological components of atmospheric PM, the prevention of biological pollution, and establishing a comprehensive air quality evaluation system. This article is protected by copyright. All rights reserved.

Seasonal and vegetational variations of culturable bacteria concentrations in air from urban forest parks: a case study in Hunan, China

It is important to investigate the airborne bacterial air quality in urban forest parks as tree bacteriostasis practices are being increasingly advocated as measures to improve the air quality and public health in urban green spaces around the world. The aim of the study was to quantitatively investigate airborne culturable bacteria (ACB) concentration levels based on field measurements in every season in five selected forest communities and the uncovered space in an urban forest park, as well as the effects of several factors on the culturability of airborne bacteria. Results suggested that the airborne bacterial levels of all the forest communities reached the clean air quality standard with regard to the airborne bacteria content, with the highest concentration of ACB showing in the uncovered space (1658 ± 1298 CFU/m³) and the lowest showing in the mixed community (907 ± 567 CFU/m³). The temporal distribution analysis showed that the airborne bacteria were mostly concentrated in summer, as well as in the morning and afternoon. The bacteriostatic rates of the mixed community were significantly different with seasonal variation (p < 0.05). Spearman's correlations revealed that the concentration of ACB was significantly positively correlated with the season, wind speed (WS), temperature (T), ultraviolet light (UV), negative air ion (NAI), and total suspended particles (TSP) (p<0.05) but significantly negatively correlated with the forest community type (p < 0.05). Overall, the selection of tree species plays a key role in shaping the forest structure and improving air quality, and the urban forest highlights key priorities for future efforts toward a cleaner, healthier, and more diverse regional forest environment.

The decay of airborne bacteria and fungi in a constant temperature and humidity test chamber

Despite substantial research to profile the microbial characteristics in the atmosphere, the changing metabolism underpinning microbial successional dynamics remains ambiguous. Herein, we applied qPCR, high-throughput sequencing of the genes encoding 16S and ITS rRNA to render the bacterial/fungal dynamics of ambient PM_2.5 filters maintained at constant conditions of temperature (20 ± 2 °C) and humidity (50 ± 5%). The incubation experiments which lasted for 50 days aim to simulate a metabolic process of microbe in two types PM_2.5 (polluted and non-polluted). The results show that microbial community species in polluted PM_2.5 had faster decay rates, more bacterial diversity and less fungal community compared to the non-polluted ones. For bacteria, the proportion of anaerobic species is higher than aerobic ones, and their performance of contain mobile elements, form-biofilms, and pathogenic risks declined rapidly as times went by. Whereas for fungi, saprotroph species occupied about 70% of the population, resulting in a specified peak of abundance due to the adequacy nutrients supplied by the apoptosis cells. Combining the classified microbial species, we found stable community structure and the volatile ones related to the various metabolic survival strategies during different time. Without the input of peripheral environment, the health risks of airborne microbe descend to a healthy level after 20 days, implying their biologic effectiveness was about 20 days no matter the air is polluted or not. This study provided new insights into the different metabolic survival of airborne microorganisms in ideal and stable conditions.