| Author: | Zhao, Jue |
| Title: | Global airborne bacteria and antibiotic resistome from natural distribution to anthropogenic impacts : community structure, biogeography, driving mechanism, and human health |
| Advisors: | Li, Xiang-dong (CEE) |
| Degree: | Ph.D. |
| Year: | 2023 |
| Subject: | Air -- Microbiology Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xvii, 276 pages : color illustrations |
| Language: | English |
| Abstract: | Air pollution has become one of the top environmental issues across the globe, particularly bioaerosols, playing a crucial role in the interactions between ecosystems, climate, and public health. Airborne bacteria and potentially hazardous components therein, such as antibiotic resistance genes (ARGs), are part of the bioaerosols. It is imperative to identify their biogeographic patterns, driving mechanisms, source contributions, and potential impact on human health. However, a gap remains in the understanding of these key interactions with regard to the systematic surveillance of airborne bacterial community and quantified antibiotic resistance (AMR) risk at a global scale. To address this scientific challenge, the present PhD study used the 16S rRNA gene dataset and metagenomic dataset in the global atmosphere to establish the first atlas of global airborne bacteria from background sites and urban areas with a wide geographic and altitudinal range. The data obtained in this study revealed the maximum microbial richness in the intermediate latitudinal regions and dynamic airborne bacterial community structure by encompassing the bacterial community among the three largest ecosystems on the Earth’s surface (i.e., atmospheric, oceanic, and terrestrial systems). Among the thousands of bacteria detected in the global atmosphere, the core set (n=24) and key taxa (n=19) were identified and confirmed to impact the entire complex community network of interconnected bacteria. Both the uniform latitudinal bacterial diversity pattern and similarities in compositions and inferred functions of key taxa across various ecosystems suggested their potential linkages. Thereby, the Earth’s bacterial co-occurrence network involving 23 habitats indicated the importance of airborne bacteria to the planetary microbiomes and the great contributions from surface environments to airborne bacteria compositions (46.25%). Anthropogenic activities also affected the airborne bacterial community structure and corresponding phenotypes via reduced environmental filtering effects and elevated human-related source contributions. Notably, the higher abundance and diversity of airborne pathogens in urban areas indicated a higher exposure risk of pathogens in densely populated regions. In terms of driving mechanisms, although airborne bacterial communities assembled in more stochastic processes (72.4%), the deterministic processes, such as biotic interactions and environmental filtering, showed significant impacts on global airborne bacterial community structure. Both biotic and abiotic factors could influence the structure and distribution of global airborne bacterial communities; however, the most determinant mechanism was the environmental filtering process. Even though atmosphere is a highly dynamic and flowing ecosystem, its bacterial community was discovered to be largely affected by local environments, particularly for the source contributions and air pollutants from human activities, indicating that global climate change and impacted air quality may cause alterations of airborne bacterial abundance, community structure, and diversity. To further explore the exposure risks in urban air, the airborne AMR was investigated at a global scale, especially for the estimation of quantified ARG-related health risks. The differentia in the composition and abundance of airborne ARGs and pathogens (carrying ARGs) between urban and background areas illustrated the anthropogenic impacts on airborne AMR exposure risks: the ARGs associated with major urban sources (e.g., wastewater treatment plants (WWTPs), hospitals, and landfills) contributed more than 30% of the urban airborne ARGs in total, which could lead to a higher risk rank of airborne ARGs in urban areas than background areas, while the abundance of urban indicator ARGs was largely affected by antibiotic consumptions, particularly aminoglycoside, tetracycline, and beta-lactam, raising the importance of the appropriate use of these drugs. The signatures of ARGs and mobile genetic elements (MGEs) co-occurrence were much more frequent in urban air, exhibiting the higher mobility of airborne AMRs. A genome-resolved “panorama” of AMR was also revealed, and humans were found to inhale more potential antibiotic-resistant pathogens daily (averagely 789.75 ± 586.80 cells) in cities than in background areas (105.6 ± 82.05 cells). Furthermore, the Staphylococcus aureus genome identified in the MAGs generated from the global urban air samples showed close genetic relatedness to those strains of Methicillin-resistant Staphylococcus aureus (MRSA) isolated from nosocomial infections and was shown to carry mecC, which suggested airborne transmission as a possible route in the prevalent community acquisition of MRSA and other types of resistant infections alike. The higher proportion of horizontally transferred ARGs in urban air also provided early warning for the rapid spread of AMR, and their dissemination from sources to human inhalation contributed to predicting future threats and improving public health management. To sum up, this integrated study conducted comprehensive research on the bacterial (pathogenic) community, ARGs profiles, and AMR risks in the global atmosphere with quantitative estimations of source contributions, shaping mechanisms, and related potential health risks. These findings will provide key reference for predicting the evolution of airborne bacteria (and pathogens) and ARGs in a changing climate condition and highlights the urgent need to involve biological parameters, such as airborne microbiome and AMR, in the current and future air quality standards on public health. |
| Rights: | All rights reserved |
| Access: | open access |
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