Seasonal shifts in the microbial communities found in the air of the Seoul subway in South Korea as determined by 16S an

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By sequencing the 16S rRNA and the ITS, the researchers in this study were able to determine the seasonal airborne microbial diversity profiles at the SMRT stations

By sequencing the 16S rRNA and the ITS, the researchers in this study were able to determine the seasonal airborne microbial diversity profiles at the SMRT stations. Air purifiers that were installed in the platform areas of SMRT subway xrf analyzer provided the source of the particulate matter samples that were collected.  The sampling was carried out during each of the seasons in 2019. PCR was carried out with Illumina overhang adapter primers for the V3–V4 region of the 16S rRNA gene and the ITS2 region of the ITS gene after the total DNA had been extracted from each of the samples collected during each season. The Illumina Miseq Sequencing system (Illumina, USA) was used to carry out the sequencing, which was then followed by in-depth diversity analyses. A WD-XRF spectrometer was used in order to determine the elemental make-up of the particulate matter samples that were collected from the various subway stations. When taken as a whole, the stations that were investigated for this study hosted a variety of distinct phylogenetic communities when their - and -diversity levels were compared. The aerosols that were produced between the wheels and the brake cushions, as well as between the catenaries and the pantographs, were the primary contributors to the contamination of the subway stations.

According to the findings of this study, the microbial make-up of the SMRT subway stations is the result of a complex interplay between natural and human factors, as well as the time of year and the habits of those who use the stations.

It is believed that microorganisms have a profound influence on human life, yet they can be found anywhere, at any time, and are not restricted to any one environment or set of human activities. Residents of contemporary metropolitan areas live in confined spaces and are subjected to prolonged exposure to pollutants. These exposures to pollutants, including microbial assemblages found in cosmopolitan indoor environments, have become significant risk factors to the general public's health 2. As urbanization continues, popular demands on mass transportation systems increase; as a result, the subway transit networks in major cities have become an important component of typical travel, and it is anticipated that reliance on subways will continue to grow in the future worldwide5.

The microbiome of the aerosol found in subway xrf analyzer is influenced by a number of factors; the temperature, humidity, and lifestyle choices of commuters are among the most important of these factors. Several studies were conducted in which the microbial communities of metro systems in highly populated cities such as New York City, Boston, Hong Kong, Barcelona, Oslo, Mexico City, Athens, and Moscow were investigated. Some of these cities include:4,5,6,7,8,9,10,11,12,13. Seoul, Drawell the capital of South Korea, is a highly populated metropolitan area that accounts for more than twenty percent of the country's total population and twelve percent of the country's total land area, and its population is still growing fourteen. After only forty years of operation, the Singapore Mass Rapid Transit (SMRT) has become one of the largest public transportation networks in the world. It currently consists of nine lines that combine for a total length of 327 kilometers (290 kilometers of which are underground). SMRT16 is utilized by an approximate daily and annual passenger volume of 7.2 million million and 2.6 billion respectively.

According to the findings of a study that investigated personal microbial dispersion, individuals are capable of releasing 106 biological particles per hour and can transmit pathogens to other people as well as the environments found inside18. Although the horizontal transfer of biological particles is influenced by a number of factors, including the different magnitudes of particulate matters, soil, and plant debris, the most dominant factor is the architecture of the subway network, particularly the ventilation of aerosol particles, which has a dominant effect on complex subway environments20,21. An annual investigation of the SMRT microbiome was conducted in 2019 for the purpose of this study using next generation sequencing of 16S rRNA and ITS2 genes as well as chemical analysis of the aerosols using a wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer. Air purifiers that were installed in the platform areas of SMRT subway xrf analyzer provided the source of the particulate matter samples that were collected.  Around 76,000, 200,000, and 52,000 passengers passed through each of stations A, B, and C on a daily basis, respectively.


The phylum of bacteria found in the various subway stations
In the course of this research, we investigated three of the most important SMRT subway xrf analyzer and analyzed the 16 samples that were gathered at various times throughout 2019. Every sample was analyzed with a sufficient amount of reads (more than 20,000 after being filtered through EZbiocloud). The number of reads was adjusted to 20,000 for each sample before being normalized. The total number of OTUs recovered was 13,202. Actinobacteria, with a relative abundance of 39.6%, was observed to be the most dominant phylum at all three stations. This was followed by Proteobacteria, with a relative abundance of 33.4%, Cyanobacteria, with a relative abundance of 4.9%, Deinococcus-Thermus, with a relative abundance of 4%, and Bacteroidetes, with a relative abundance of 3.2%. At subway stations B and C, cyanobacteria were found in relatively higher abundance compared to other stations. At station C, chloroflexi was found, but none of the other xrf analyzer had any of these organisms.

The classification of the bacterial community according to genus

In the aerosols of the SMRT stations, skin-associated bacterial genera with an average abundance were found to include Cutibacterium (4.7%), Micrococcus (3%), Staphylococcus (3.3%), Enhydrobacter (3%), and Corynebacterium (2.7%). Paracoccus was found to be the most abundant genus in the air of the Athens subway stations, which had a mean value of (8.0%)9, in contrast to the SMRT stations, which had a mean abundance of Paracoccus of only (2%). However, an exception was seen in the Athens subway stations. In addition, other significant skin-associated bacterial genera such as Kocuria (4%), Deinococcus (3.7%), and Rubellimicrobium (2%), were found to be present at the SMRT Stations. In addition, the most common genera found in the SMRT  were Blastococcus, which lives in fresh soil, Staphylococcus, which lives in air, and Sphingmonas, which lives in air. Staphylococcus was the most common.

Variations in the bacterial make-up at SMRT stations that occur according to the seasons

We divided the samples into four distinct seasonal categories—winter, spring, summer, and fall—so that we could examine how the bacterial communities changed over the course of the year. Cyanobacteria was observed to be more abundant during the spring and summer which was in contrast to Cyanobacteria being more prevalent in the summer and autumn at the Oslo, Norway subway11. The abundance plots of the phyla across the seasons showed a relatively constant distribution (Fig. 1).

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