Distribution of bacterial concentration and viability in atmospheric aerosols under various weather conditions in the coastal region of China

Characteristics of airborne bacteria over inland and coastal atmosphere influenced by systemic air mass in northern China

Regional aerosol pollution frequently occurs in winter and spring in northern China. Here, we surveyed four air pollution, categorized as episodes influenced by northerly or southerly air mass, and discussed the bacterial communities in inland and coastal cities. Influenced by northerly airmass, the predominant bacterial phyla were Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria both in the inland and coastal cities. The opportunistic pathogen in the genus Staphylococcus was predominant, and the relative proportion increased with the intensification of air pollution. Gut bacteria of the genus Lactobacillus and aquatic bacteria of the family Flavobacteriaceae were enriched in the coastal city. Influenced by southerly air mass, combined with the transmission of dust air masses in the northwest, air pollution in spring showed obvious sand dust characteristics. The prevalence of the members from the phylum Cyanobacteria was markedly greater in inland city compared to the coastal city, especially in dust samples. This indicated the possibility of soil Cyanobacteria members, subsequently being transported from terrestrial to coastal areas via dust movements. The bacterial community dynamics was intimately linked to meteorological factors and air pollutants. In both cities, pathogenic bacteria predominate in haze pollution influenced by northernly air masses, while a higher proportion of soil bacteria originating from natural sources predominate in southern air mass samples. The impact of varying air masses was particularly pronounced in inland city. Meteorological factors instigated by seasonal changes-especially the transition of wind direction from winter to spring, accompanied by elevated wind speeds and rising temperatures-play a pivotal role in shaping bacterial community structure. This study examined the sea-land variations in bacterial communities transported by systemic air masses during typical air pollution events. These insights lay the groundwork for future research into the distribution, sources, and health risks of bioaerosols during air pollution.

Contrasting Effects of Atmospheric Particulate Matter Deposition on Free-Living and Particle-Associated Bacteria in the South China Sea

Atmospheric particulate matter (PM) deposition has become an important nutrient source in marine ecosystems, increasing particulate organic carbon and resource heterogeneity. However, their effects on marine bacterial communities remain unclear. In this study, by conducting on-board microcosm experiments with anthropogenic East Asian PM in the oligotrophic South China Sea, the response of particle-associated (PA) bacteria was investigated and compared with its free-living (FL) counterparts. Results showed that PM input increased nutrient heterogeneity, shifting bacterial community composition and lifestyle. Copiotrophic PA bacteria became more abundant and contributed a disproportionately higher percentage to total bacterial production despite a decline in total bacterial abundance. FL bacteria showed increased diversity, shifting from oligotrophs to copiotrophs, while PA bacteria displayed reduced diversity and nondirectional compositional changes, suggesting their distinct assembly mechanisms in response to external nutrient inputs. Metagenomic analysis further revealed that PM drives a shift toward a copiotrophic, particle-attached lifestyle with upregulated pathways for chemotaxis, motility, and biofilm formation. Notably, PM addition also increased the relative abundance of oil-degrading taxa. These findings reveal the complexity of microbial responses to environmental perturbations and underscore the need to consider unique ecological niches and bacterial lifestyles.

Expanding the focus of the One Health concept: links between the Earth-system processes of the planetary boundaries framework and antibiotic resistance

The scientific community warns that our impact on planet Earth is so acute that we are crossing several of the planetary boundaries that demarcate the safe operating space for humankind. Besides, there is mounting evidence of serious effects on people's health derived from the ongoing environmental degradation. Regarding human health, the spread of antibiotic resistant bacteria is one of the most critical public health issues worldwide. Relevantly, antibiotic resistance has been claimed to be the quintessential One Health issue. The One Health concept links human, animal, and environmental health, but it is frequently only focused on the risk of zoonotic pathogens to public health or, to a lesser extent, the impact of contaminants on human health, i.e., adverse effects on human health coming from the other two One Health "compartments". It is recurrently claimed that antibiotic resistance must be approached from a One Health perspective, but such statement often only refers to the connection between the use of antibiotics in veterinary practice and the antibiotic resistance crisis, or the impact of contaminants (antibiotics, heavy metals, disinfectants, etc.) on antibiotic resistance. Nonetheless, the nine Earth-system processes considered in the planetary boundaries framework can be directly or indirectly linked to antibiotic resistance. Here, some of the main links between those processes and the dissemination of antibiotic resistance are described. The ultimate goal is to expand the focus of the One Health concept by pointing out the links between critical Earth-system processes and the One Health quintessential issue, i.e., antibiotic resistance.

Impact of variations in airborne microbiota on pneumonia infection: An exploratory study

BACKGROUND

Previous studies showed airborne bacteria affect pneumonia incidence, but specific impacts of bacterial communities on Klebsiella pneumoniae infection were unknown.

METHODS

Five different ratios of bacterial community structures were randomly generated. Mice were divided into control, artificial bacterial community exposure, and corresponding Klebsiella pneumoniae challenge groups. Changes in body weight, blood parameters, pulmonary pathology, inflammatory factors, metabolomics, and fecal microbiota were analyzed.

RESULTS

Different bacterial community exposures had varying degrees of influence on body weight, complete blood count, inflammatory factors, alveolar lavage fluid and plasma metabolome, as well as intestinal microbiota at baseline and after infection. Metabolomic analysis showed that microbial exposure affected both bronchoalveolar lavage fluid and plasma metabolomes, suggesting systemic effects of microbial exposure on the organism. Differences in the structure of artificial microbiota had inconsistent effects on both the baseline state and the post-infection state, hinting at crosstalk between microbial exposure and Klebsiella pneumoniae infection. KEGG pathway analysis unveiled possible molecular mechanisms underlying the overall impact of microbial exposure on the lungs and the body as a whole. In the intestinal microbiota, differences were found in composition at the phylum and genus levels. Spearman correlation analysis established potential correlations between intestinal microbiota and differential metabolites, suggesting a potential link within the lung-gut axis.

CONCLUSION

This study demonstrated the significant and systemic impact of air microbiota structure differences on health. Future research should explore the underlying mechanisms to enhance our understanding of the air-environment-health relationship and identify interventions for improving public health strategies.

Insights into bioaerosol contamination in the process of mineralized refuse mining: Microbial aerosolization behavior and potential pathogenicity

The landfill mining process is a main source of anthropogenic bioaerosol release, posing potential risks to the health of occupationally exposed personnel and nearby residents. In this study, microbial aerosolization behavior and potential pathogenicity during the landfill mining process were systematically investigated. The highest concentration of bacterial aerosols was measured in the refuse mining area, with a value of 5968 ± 1608 CFU/m3, while the highest concentration of fungal aerosols was 1196 ± 370 CFU/m3 in the refuse screening area. The bacterial and fungal aerosols were distributed primarily in the particle size ranges of 4.7-7.0 µm and > 7.0 µm, respectively. The pathogenic microbes Arthrobacter, Bacillus, Arthrobotrys and Aspergillus had high bioaerosol aerosolization capacities, with aerosolization indices of 100-329, 31-62, 2-14 and 1-11, respectively, when released from mineralized refuse. There are more than 100 types of pathogenic bacteria in bioaerosols. The microorganisms Lysobacter, Luteimonas and Mycolicibacterium, which carry virulence factor genes (VFGs) (pilG, Rv0440, pilT, etc.), can spread VFGs, aggravate bioaerosol pollution, and threaten the health of workers and nearby residents. This research will help further the understanding of bioaerosol contamination behaviors and potential pathogenicity risks from landfill mining activities.

Seasonal and spatial variations in concentration, diversity, and antibiotic resistance of ambient bioaerosols in an arid region

The airborne microbiome significantly influences human health and atmospheric processes within Earth's troposphere and is a crucial focus for scientific research. This study aimed to analyze the composition, diversity, distribution, and spatiotemporal characteristics of airborne microbes in Qatar's ambient air. Air samples were collected using a sampler from ten geographically or functionally distinct locations during a period of one year. Spatial and seasonal variations significantly impacted microbial concentrations, with the highest average concentrations observed at 514 ± 77 CFU/m3 for bacteria over the dry-hot summer season and 134 ± 31 CFU/m3 for fungi over the mild winter season. Bacterial concentrations were notably high in 80% of the locations during the dry-hot summer sampling period, while fungal concentrations peaked in 70% of the locations during winter. The microbial diversity analysis revealed several health-significant bacteria including the genera Chryseobacterium, Pseudomonas, Pantoea, Proteus, Myroides, Yersinia, Pasteurella, Ochrobactrum, Vibrio, and fungal strains relating to the genera Aspergillus, Rhizopus Fusarium, and Penicillium. Detailed biochemical and microscopic analyses were employed to identify culturable species. The strongest antibiotic resistance (ABR) was observed during the humid-hot summer season, with widespread resistance to Metronidazole. Health risk assessments based on these findings indicated potential risks associated with exposure to high concentrations of specific bioaerosols. This study provides essential baseline data on the natural background concentrations of bioaerosols in Qatar, offering insights for air quality assessments and forming a basis for public health policy recommendations, particularly in arid regions.

Bioaerosol emission and exposure risk from a wastewater treatment plant in winter and spring

The potential health risks posed by bioaerosols containing pathogens originating from wastewater treatment plants (WWTPs) have gaining intensive attention. This study designated sampling locations within a WWTP situated in Xi'an, a major city in northwest China. The airborne bacterial concentration, taxonomic composition, and the associated health risks were analyzed in the aeration tanks with bottom microporous aeration system. The Anaerobic-Anoxic-Oxic (AAO) tank emitted significantly higher culturable bacteria (1.58×104 CFU m-3 in spring, 6.69×103 CFU m-3 in winter) compared to Double-ditch (DE) oxidation ditch and aerated grit chamber (AGC) chamber, aligning with 16S rDNA quantification results. The bacterial concentrations are higher in spring than that in winter, with the AAO tank posing the highest exposure risk during the spring season. The dominant genera in the air samples include Cutibacterium, Lawsonella, Acinetobacter, Pseudomonas, and Aeromonas. Among the identified genus, 139 bacterial genera were identified as potential human pathogens like Neisseria, Moraxella, Haemophilus, Escherichia-Shigella and Streptococcus. These pathogens further elevate exposure risks from WWTP bioaerosols. This study provides relevant information on the seasonal health risk variations tied to bioaerosol emissions from diverse aeration tanks with bottom microporous aeration system in the mega city of northwest China, emphasizing the imperative to enhance the management and control measures for bioaerosols originating from the AAO tank.

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

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

Aerosolized Cyanobacterial Harmful Algal Bloom Toxins: Microcystin Congeners Quantified in the Atmosphere

Cyanobacterial harmful algal blooms (cHABs) have the potential to adversely affect public health through the production of toxins such as microcystins, which consist of numerous molecularly distinct congeners. Microcystins have been observed in the atmosphere after emission from freshwater lakes, but little is known about the health effects of inhaling microcystins and the factors contributing to microcystin aerosolization. This study quantified total microcystin concentrations in water and aerosol samples collected around Grand Lake St. Marys (GLSM), Ohio. Microcystin concentrations in water samples collected on the same day ranged from 13 to 23 μg/L, dominated by the d-Asp3-MC-RR congener. In particulate matter <2.5 μm (PM2.5), microcystin concentrations up to 156 pg/m3 were detected; the microcystins were composed primarily of d-Asp3-MC-RR, with additional congeners (d-Asp3-MC-HtyR and d-Asp3-MC-LR) observed in a sample collected prior to a storm event. The PM size fraction containing the highest aerosolized MC concentration ranged from 0.44 to 2.5 μm. Analysis of total bacteria by qPCR targeting 16S rDNA revealed concentrations up to 9.4 × 104 gc/m3 in aerosol samples (≤3 μm), while a marker specific to cyanobacteria was not detected in any aerosol samples. Concentrations of aerosolized microcystins varied even when concentrations in water were relatively constant, demonstrating the importance of meteorological conditions (wind speed and direction) and aerosol generation mechanism(s) (wave breaking, spillway, and aeration systems) when evaluating inhalation exposure to microcystins and subsequent impacts on human health.

Distribution characteristics and potential risks of bioaerosols during scattered farming

In most economically underdeveloped areas, scattered farming and human‒livestock cohabitation are common. However, production of bioaerosols and their potential harm in these areas have not been previously researched. In this study, bioaerosol characteristics were analyzed in scattered farming areas in rural Northwest China. The highest bacteria, fungi, and Enterobacteria concentrations were 125609 ± 467 CFU/m³, 25175 ± 10305 CFU/m³, and 4167 ± 592 CFU/m³, respectively. Most bioaerosols had particle sizes >3.3 μm. A total of 71 bacterial genera and 16 fungal genera of potential pathogens were identified, including zoonotic potential pathogenic genera. Moreover, our findings showed that the scattered farming pattern of human‒animal cohabitation can affect the indoor air environment in the surrounding area, leading to chronic respiratory diseases in the occupants. Therefore, relevant government departments and farmers should enhance their awareness of bioaerosol risks and consider measures that may be taken to reduce them.

Comprehensive insights into advances in ambient bioaerosols sampling, analysis and factors influencing bioaerosols composition

While the study of bioaerosols has a long history, it has garnered heightened interest in the past few years, focusing on both culture-dependent and independent sampling and analysis approaches. Observations have been made regarding the seasonal fluctuations in microbial communities and their connection to particular ambient atmospheric factors. The study of airborne microbial communities is important in public health and atmospheric processes. Nevertheless, the establishment of standardized protocols for evaluating airborne microbial communities and utilizing microbial taxonomy as a means to identify distinct bioaerosols sources and seasonal patterns remains relatively unexplored. This article discusses the challenges and limitations of ambient bioaerosols sampling and analysis, including the lack of standardized methods and the heterogeneity of sources. Future prospects in the field of bioaerosols, including the use of high-throughput sequencing technologies, omics studies, spectroscopy and fluorescence-based monitoring to provide comprehensive incite on metabolic capacity, and activity are also presented. Furthermore, the review highlights the factors that affect bioaerosols composition, including seasonality, atmospheric conditions, and pollution levels. Overall, this review provides a valuable resource for researchers, policymakers, and stakeholders interested in understanding and managing bioaerosols in various environments.

Bioinspired artificial spider silk photocatalyst for the high-efficiency capture and inactivation of bacteria aerosols

Bioaerosol can cause the spread of disease, and therefore, capture and inactivation of bioaerosols is desirable. However, filtration systems can easily become blocked, and are often unable to inactivate the bioaerosol once it is captured. Herein, we reported a bioinspired artificial spider silk (ASS) photocatalyst, consisting of a periodic spindle structure of TiO2 on nylon fiber that can efficiently capture and concentrate airborne bacteria, followed by photocatalytic inactivation in situ, without a power-supply exhaust system. The ASS photocatalyst exhibits a higher capture capacity than the nylon fiber substrate and a photocatalytic inactivation efficiency of 99.99% obtained under 4 h irradiation. We found that the capture capacity of the ASS photocatalyst can be mainly attributed to the synergistic effects of hydrophilicity, Laplace pressure differences caused by the size of the spindle knots and surface energy gradients induced by surface roughness. The bacteria captured by the ASS photocatalyst are inactivated by photocatalysis within droplets or at the air/photocatalyst interfaces. This strategy paves the way for constructing materials for bioaerosol purification.

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.

Number size distribution of bacterial aerosols in terrestrial and marine airflows at a coastal site of Japan

Size-differentiated concentration of bacterial aerosols is essential for investigating their dissemination via the atmosphere. In this study, the number size distribution of bacterial aerosols was measured at a coastal site in southwestern Japan (32.324°N, 129.993°E) using a size-segregated eight-stage (>11, 7.0-11, 4.7-7.0, 3.3-4.7, 2.1-3.3, 1.1-2.1, 0.65-1.1, and 0.43-0.65μm) sampler. The results showed that the distribution differed according to the source areas: terrestrial air, oceanic air, or a combination of the two. The distribution in the long-distance transported terrestrial air from the Asian continent was monomodal, with a peak of 3.3-4.7 μm. The distribution in local land breeze air was bimodal, with the peaks at 0.43-1.1 and 3.3-4.7 μm. A similar bimodal distribution was encountered when the local island air and long-distance transported terrestrial air mixed. In contrast, the size distribution did not show clear peaks in the air from either nearby or remote marine areas. According to the air mass backward trajectories, the further the distance the air moved in the 72 h before arriving at the site, the lower the concentration of total bacterial aerosols. The estimation of dry deposition fluxes of bacterial cells showed that the deposition was dominated by cells larger than 1.1 μm with a relative contribution from 70.5 % to 93.7 %, except for the local land breeze cases, where the contributions in the size ranges larger and smaller than 1.1 μm were similar. These results show the distinctive number size distributions and removal processes of bacterial aerosols in different types of air. In addition, they indicate that size-dependent characteristics of airborne bacteria should be considered when studying their activities and roles in the atmospheric environment.

Decrease of bioaerosols in westerlies from Chinese coast to the northwestern Pacific: Case data comparisons

The dissemination of bioaerosols in the westerly wind from the Asian continent to the northwestern Pacific constantly links the land and marine ecosystems. Several observation campaigns targeting bioaerosols were conducted in the coastal city Qingdao of China (QD), at a coast site of Kumamoto in southwestern Japan (KM), and in the northwestern Pacific (NP) between 2014 and 2016. We compared the concentration of bioaerosols in the range of 1.1-7.0 μm obtained in those campaigns to investigate their variation in the westerly wind. The substantial influence of westerlies on bioaerosol concentration was confirmed in the three areas. In the case of non-dust air, the arrival of the continental air led to a 29 % decrease of bioaerosols at KM while a 57 % increase at NP, indicating that the concentration in non-dust air was lower than the local level in the island air while higher than that in the remote marine air. In case of dust occurrence, bioaerosols in the air decreased with the distance from the Asian continent at KM and NP consecutively, and the arrival of the air caused a 2-fold increase at KM and a 1.7-fold increase at NP. The relative concentration increase rate of bioaerosols (IR_RC), defined as the ratio of the increment of bioaerosols caused by long-distance transported air to the local level in each area, decreased rapidly after the air left the continent in the dust cases, which is similar to the decrease of the dry deposition flux of dust reported in the literature. This result indicates that the reduction of bioaerosols in the dusty air was likely dominated by the removal of bioaerosols attached to dust particles.

Size distribution, community composition, and influencing factors of bioaerosols on haze and non-haze days in a megacity in Northwest China

Bioaerosols have become a major environmental concern in recent years. In this study, the diurnal variations and size distributions of bioaerosols, as well as airborne bacterial community compositions and their influencing factors on haze and non-haze days in Xi'an, China, were compared. The results indicated that the mean bacteria and fungi concentrations on non-haze days were 1.7 and 1.4 times of those on haze days, respectively, whereas the mean total airborne microbe (TAM) concentration was higher on haze days. Bacteria concentrations were the lowest in the afternoon, and the TAM concentration exhibited a bimodal distribution with two peaks coinciding with traffic rush hours. On haze days airborne fungi was mainly attached to PM_2.5, whereas bacteria and TAM were mainly distributed in coarse PM. The relative abundance of Chao1, Shannon and Simpson indices of bacterial communities were higher in the non-haze day samples, for the reason that high PM_2.5 levels with a large specific surface area may absorb more toxic and harmful substances on haze days, which should affect microbial growth. At the generic level, the relative abundance of Rhodococcus, Paracoccus, Acinetobacter, and Kocuria on haze days was higher than that on non-haze days, indicating a higher risk of contracting pathogenic pneumonia. The results of the redundancy analysis revealed that PM_2.5 and water-soluble inorganic ions (WSIIs, NO₃^-, SO₄²⁺, and NH₄⁺) strongly affected the bacterial communities on non-haze days, especially Acinetobacter. The atmospheric oxidation capacity (O_x) had a significant effect on bacterial communities during haze episodes, which were positively correlated with Paracoccus, Deinococcus, Sphingomonas, and Rubellimicrobium and were negatively correlated with Rhodococcus. These results provide valuable data to elucidate the formation and evolution of bioaerosol between haze and non-haze events and its potential threats to human health.

Characteristics of inhalable bioaerosols on foggy and hazy days and their deposition in the human respiratory tract

Atmospheric bioaerosols contain live and dead biological components that can enter the human respiratory tract (HRT) and affect human health. Here, the total microorganisms in a coastal megacity, Qingdao, were characterized on the basis of long-term observations from October 2013 to January 2021. Particular attention was given to the size dependence of inhalable bioaerosols in concentration and respiratory deposition in different populations on foggy and hazy days. Bioaerosol samples stained with 4,6-diamidino-2-phenylindole (DAPI) were selected to measure the total airborne microbe (TAM) concentrations with an epifluorescence microscope, while a multiple-path particle dosimetry model was employed to calculate respiratory deposition. The mean TAM concentrations in the particle size range of 0.65-1.1 μm (TAM_0.65-1.1) were 1.23, 2.02, 1.60 and 2.33 times those on sunny reference days relative to the corresponding values on days with slight, mild, moderate and severe levels of haze, respectively. The mean concentration of TAMs in the particle size range of 0.65-2.1 μm (TAM_0.65-2.1) on severely hazy days was (2.02 ± 3.28) × 10⁵ cells/m³, with a reduction of 4.16% relative to that on the reference days. The mean TAM_0.65-2.1 concentration changed from (1.50 ± 1.37) × 10⁵ cells/m³ to (1.76 ± 1.36) × 10⁵ cells/m³, with TAM_0.65-1.1 increasing from (7.91 ± 7.97) × 10⁴ cells/m³ to (1.76 ± 1.33) × 10⁵ cells/m³ on days with light fog days and medium fog, respectively. The modeling results showed that the majority of TAM_0.65-2.1 deposition occurred in the extrathoracic (ET) region, followed by the alveolar (AL) region. When different populations were examined separately, the deposition doses (DDs) in adult females and in children ranked at the minimum value (6.19 × 10³ cells/h) and maximum value (1.08 × 10⁴ cells/h), respectively. However, the inhalation risks on polluted days, such as hazy, foggy and mixed hazy-foggy (HF) days, were still below the threshold for adverse impacts on human health.

Kinetics and mechanism analysis on self-decay of airborne bacteria:biological and physical decay under different temperature

Bioaerosol as an important medium has aroused widespread concern on its potential hazards in disease transmission and environment biosafety. However, little is known about the duration and self-decay of airborne bacteria in the atmosphere environment. Further, the self-decay process is proposed to include biological-decay and physical-decay. At present, there are many reports on the bacteria apoptosis mechanism and airborne particle migration. However, few studies focus on self-decay during the physical movement of airborne bacteria. The present study investigated self-decay laws and efficiencies of airborne bacteria in the sealed reactor under room temperature (18 ± 2 °C, RT) and low temperature (3 ± 2 °C, LT). The self-decay rate constants of 0.0089, 0.0133, 0.0092, and 0.0122 min^-1 were obtained under RT-E. coli, LT-E. coli, RT-S. aureus and LT-S. aureus, respectively. There was no significant difference between the self-decay efficiency of gram-negative and gram-positive bacteria under the same conditions. Nevertheless, gram-negative bacteria were more sensitive to temperature change compared with gram-positive bacteria, where the self-decay efficiency of gram-negative under LT was 49% higher than that under RT, and the value of gram-positive was 32% at the same condition. Furthermore, the laws of biological-decay and physical-decay conformed to the first-order kinetic model by theoretical derivation. Biological-decay accounted for 59.5% at RT and 88.5% at LT among self-decay, which is mainly caused by energy absorption, environmental stress, and bacterial structure changes. Physical-decay mainly caused by gravity settlement accounting for 40% at RT and 10% at LT among self-decay, approximately. Meanwhile, the influence of environmental factors on self-decay was mainly reflected in the biological-decay process. Overall, it is of great significance for clarifying the changing laws of bioaerosol and controlling the transmission of airborne bacteria.