Investigation on meteorological dependency of airborne bacterial communities enriched with pathogens over Eastern Himalayas

Airborne bacteria have a significant role in structural variation of atmospheric microorganisms with limited knowledge about their composition and geographical distribution, which demands high attention to understand their effect on human health and climate change, as their substantial temporal variation depends on local meteorological conditions. Current study presents composition, diversity, and variability of airborne bacterial loading over the Eastern Himalayas in India. A long-term airborne bacterial sampling is carried out within Bose Institute campus, situated at Darjeeling (27.03°N, 88.26°E, 2200m amsl) from January 2022 to September 2023. Samples are collected for eight hours duration, three times a day at 15m above the ground over sampling site. Illumina NextSeq platform is used to analyze V3-V4 regions of 16S rRNA gene in airborne bacterial samples using bacterium-specific primers. Total 88 samples are being investigated and categorized into four groups according to seasons: winter (temperature = 7±3ºC, relative humidity (RH) = 88±7%), pre-monsoon (15±2ºC, 87±10%), monsoon (17±1ºC, 97±3%), and post-monsoon (13±4ºC, 91±8%). About one-fourth (349 bacterial genera) population of airborne bacterial genera are present throughout the year, implying as background of Eastern Himalayan atmosphere. Human pathogens like Aeromonas, hydrophila, Acinetobacter lwoffii, Staphylococcus aureus, and Staphylococcus epidermis, responsible for gastroenteritis, endocarditis, respiratory, skin, and urinary tract infections are dominating in the atmosphere over Eastern Himalayas. Airborne bacterial loading varies significantly during different seasons with maximum concentration during pre-monsoon (Total cell count = 4.6±2.1 cells.m^-3, OTUs = 597±343, Genera = 189±76, Shannon diversity index = 4.1±1.0), followed by post-monsoon (4.2±1.6 cells.m^-3, 492±299, 171±65, 4.1±0.5), monsoon (3.8±1.3 cells.m^-3, 332±171, 122±58, 3.4±1.0), and winter (3.6±1.7 cells.m^-3, 239±87, 105±37, 3.4±0.8). Two distinct groups of beta diversities have been noticed over Eastern Himalayas during pre-monsoon & monsoon and post-monsoon & winter seasons, indicating similar bacterial populations. Eastern Himalayan airborne bacteria exhibit a strong dependency on temperature (r= -0.90, p<0.001) during seasonal changes from winter to pre-monsoon and post-monsoon to winter. Wind (r= 0.80, p<0.01) plays a significant role in the diversity of pre-monsoon season by transporting desert dust from western India, having highly diverse bacteria, and introducing unique pathogenic bacteria responsible for respiratory and skin infections over Eastern Himalayas.