Rich microbial diversity in tropospheric samples above the planetary boundary layer confirms long-distance transport of potential human pathogens

Existence of viable human pathogens in air above the planetary boundary layer (PBL) susceptible of reaching far-distance regions has never been demonstrated. Now ten aircraft monitoring surveys conducted over Japan in 2014 confirm the existence of a vast diversity of microbial species between 1000-3000 m a.s.l. being dispersed through wind currents for distances up to 2000 Km. Use of atmospheric particle dispersion models and LIDAR data has enabled us to confirm that under very predominant wintertime atmospheric conditions, aerosolised particles are uplifted by seasonal strong winds from areas in NE China, travel near 2000 Km away from their source well above the PBL and subside over Japan in less than 2 days. The area in NE China is covered with vast amounts of frozen decaying organic material originating from massive cereal croplands. Characterisation of microbial species attached to those particles shows dominance of known human pathogens typically originating from sewage, pesticides, fertilisers or agricultural debris from decaying organic matter. A majority of fungal taxa (over 90% concentration at times) and/or bacterial taxa (up to 67%) found therein are known for their potential adverse effects on human health. Noticeably, for bacteria less of a 30% of the taxa appearing could be identified to the species level and an additional 30% at most only at the family level. Similar numbers for fungi appear. Over 390 different fungal genera and over 340 bacterial genera showed up in flight samples comprised in the 10 aircraft transects, showing a great resemblance between flight and surface origin. Overall diversity is similar in high-altitudes and the surface when entrainment of air develops. In our study, microbial viability has also been observed as well as transport of antimicrobial resistance genes (ARG) in the cultured flight bacteria. The former constitutes one of the first evidences of very far distant transport of ARG and adds to the current known mechanisms for ARG propagation.