Study on long-range transport of dust-associated airborne bacteria over Eastern Himalayas in India

Transboundary movement of atmospheric microorganisms through dust transportation plays a pivotal role in influencing human health, agricultural productivity, and climate dynamics by participating in cloud condensation processes. Present study investigates long-range transported atmospheric bacteria along with dust particlesover Darjeeling (27°03′N, 88°26′E), a high-altitude region (2.2 km amsl) in the Eastern Himalayas, India. 27 samples are collected in winter (Temp: 6.2± 1.5°C; RH: 85.2 ± 9.6%) and summer 2022 (Temp: 16 ± 1.5°C; RH: 93.5 ± 6.5%). Total bacterial cell count is found tobe increased by 24 ± 0.4% in summer compared to that in winter. Concurrently, particle number concentrations, measured using a Scanning Mobility Particle Sizer (SMPS) within the size range of 8-350 nm, showed 70% increasein summer, with modal size shifting from 110 nm to 150 nm.Satellite observations from MODIS on-board Aqua, Terra, and OMI on-board Aura reveal an increase in Aerosol Optical Depth (AOD) from 0.4 in winter to 0.7 in summer, alongside decline in Angstrom Exponent from 1.6 to 0.3, indication of coarser aerosol abundances. Aerosol Index also rises from 0.8 to 2.1, indicating dust dominance. CALIPSO data identifies a 1 km thick dust layer within 2 to 3 km altitude above the Eastern Himalayas. Air mass back-trajectory analysis suggests dust particles travel at an altitude of 2 to 3 km from the Thar Desert to Eastern Himalayas.Seasonal shifts in microbial communities are evident, with higher Shannon diversity in summer (4.4 ± 0.8) compared to winter (2.3 ± 0.6). Beta diversity analyses confirm distinct community compositions in summer that is due to transport of unique bacteria attached with desert dust. In summer, predominant bacterial genera included Flavobacterium (5.4 ± 3.6%), Nocardioides (4.2 ± 3%), and Corynebacterium (4.2 ± 1.4%), while Corynebacterium (2.4 ± 0.5%), Acinetobacter (1.8 ± 0.9%), and Massilia (1.3 ± 0.3%) in winter. Notably, pathogenic genera such as Afipia and Clostridium, linked to human and animal infections, are detected with dust exclusively in summer.Presentresult highlights the role of transported dust-associated microbes in altering the airborne bacterial composition in the Himalayas, providing critical insights into the sources and biodiversity changes over the Eastern Himalayas in India.