NaCl-amendment assay targeting airborne bacteria in tropospheric bioaerosols transported by westerly wind over Noto Peninsula

Abstract

Bioaerosol particles including bacteria, fungi and virus are originated from marine and terrestrial environments. The airborne microorganisms are transported for long-distance through the free troposphere and are thought to influence the downwind ecosystems and human life. However, microbial communities in the free troposphere have not been understood in detail because the direct sampling of microbial cells at high altitude requires sophisticated sampling techniques. In this study, for the investigation of microbial species compositions in the free troposphere, air sampling using an aircraft was performed over the Noto Peninsula in Japan, where the tropospheric winds carry aerosol particles from continental areas. Two air samples were collected at 3000 m on March 27th, 2010, when air mass was carried from the Gobi Desert to Japan area.Microorganisms from one air sample grew in culture media containing up to 15% NaCl, suggesting that halotolerant bacteria maintain their viabilities in the free troposphere. DGGE analysis revealed that the amended cultures were dominated by Bacillus subtilis, and the isolates obtained from the amended cultures were identical to B. subtilis.Furthermore, the 16S rDNA clone library (culture independent survey) of the other air sample grew was composed of three phylotypes belonging to Firmicutes, Bacteroidetes, and Proteobacteria with the sequences of Firmicutes phylotype corresponding to that of the cultured B. subtilis sequence. Microscopic observation using FISH method indicated that B. subtilis particles occupied 80% of total eubacterial particles on the mineral particles. The halotolerant bacteria identical to B. subtilis would dominate at high altitudes over Noto Peninsula where the prevailing westerly wind was blowing.2

About the Biodiversity of the Air Microbiome

“…However, other studies showed a high proportion of the Bacteroidetes phylum members in bioaerosols in the air above Japan after dust storms in Asia [ 17 , 66 ], as well as in the air above eastern Australia [ 67 ]. The composition of the bacterial microbiome in the upper troposphere above the Noto Peninsula in Japan was quite specific, where it was demonstrated (although using fluorescence in situ hybridization) that 80% of all eubacteria on mineral aerosol particles were represented by Bacillus subtilis belonging to the phylum Firmicutes [ 68 ].…”

“…Однако другими исследованиями показано высокое содержание представителей Bacteroidetes в биоаэрозоле над Японией после пылевых бурь в Азии [17,66], а также в воздухе над восточной Австралией [67]. Весьма специфичным был состав бактериобиома в высоких слоях тропосферы над полуостровом Ното в Японии, где (правда, методом флуоресцентной гибридизации in situ) показано, что 80% всех эубактерий на минеральных частицах аэрозоля были представлены Bacillus subtilis, относящейся к фирмикутам [68].…”

Airborne bacterial community associated with fine particulate matter (PM2.5) under different air quality indices in Temuco city, southern Chile

“…Unstable compositions at vertical atmospheric height during a polluted sampling day have been reported (Bai et al 2020); thus, the influence of environmental factors on the composition of airborne bacterial communities requires exploration under particular or specific meteorological conditions. In this sense, DNA fingerprint methods such as PCR-DGGE have proven to be particularly useful as a first approach for continuous, cheaper and rapid comparison analysis of airborne bacterial community analyses based on universal 16S rRNA genes (Tanaka et al 2015;Qi et al 2018;Maki et al 2013).…”