# Role of wind in alteration of hilltop airborne bacterial communities enriched with pathogens over the Eastern Himalayas in India

## TL;DR

This study shows how wind patterns and weather influence airborne bacteria, including potential pathogens, at a high-altitude site in the Eastern Himalayas.

## Contribution

First comprehensive seasonal assessment of airborne bacterial diversity in the Eastern Himalayas, linking wind patterns and health risks.

## Key findings

- Airborne bacterial abundance and diversity were highest in pre-monsoon due to continental wind transport and particulate matter.
- Wind speed, temperature, and PM2.5 showed strong positive correlations with bacterial populations.
- Opportunistic pathogens like Acinetobacter and Staphylococcus were found across all seasons, indicating potential health risks.

## Abstract

Airborne microorganisms play a significant role in atmospheric processes and public health, yet their variations over high-altitude regions are underexplored. To investigate the meteorological influence and role of transport patterns on airborne microorganisms, we analyzed DNA sequencing of bacterial population collected from ambient atmosphere during 2022–2023 over Darjeeling (27.03°N, 88.26°E; 2,200 m amsl), an Eastern Himalayan hilltop site, and categorized as winter (dry: cold, stable), pre-monsoon (semi-dry: warm, transitional), monsoon (wet: humid, rainy), and post-monsoon (semi-wet: cooler, cloudy) seasons. Back-trajectory analysis showed air masses from the western Indo-Gangetic Plain during pre-monsoon and from the Bay of Bengal during monsoon, while winter and post-monsoon air masses were predominantly regional hilly winds. Significant seasonal variability in airborne bacterial populations was noticed over the Eastern Himalayas, with highest abundance and diversity in pre-monsoon (cell count = 5.8 ± 1.9 × 105 m−3, operational taxonomic units = 597 ± 343, genera = 188 ± 76, Shannon = 4.1 ± 1.0) due to continental wind transport and particulate matter influx. About one-fourth of airborne bacterial genera were persistent in all seasons, representing background Himalayan hilltop airborne bacterial population. Unique season-specific genera are prominent in pre-monsoon (15%), followed by post-monsoon (7%), monsoon (6%), and winter (4%), indicating significant enrichment of airborne bacteria due to the influence of wind. Positive correlations with wind speed (r = 0.57, P < 0.05), temperature (r = 0.50, P < 0.05), and PM2.5 (r = 0.84, P < 0.001) indicate the role of meteorological parameters in shaping airborne bacterial population. Human pathogens like Acinetobacter, Staphylococcus, and Corynebacterium, responsible for gastroenteritis and respiratory, skin, and urinary tract infections, highlight potential health risks and the importance of integrating atmospheric biological data and meteorological modeling into public health strategies over Eastern Himalayan region.

Airborne microorganisms play an important role in atmospheric processes, ecosystem functioning, and human health. However, their dynamics in high-altitude regions are poorly characterized. The present study provides the first comprehensive seasonal assessment of Eastern Himalayan airborne bacterial diversity and abundance, revealing strong meteorological control, particularly wind patterns and particulate matter, on airborne bacterial loading and community composition. Identification of opportunistic pathogenic bacterial genera across all seasons raises concerns about potential health impacts, especially in regions where population density and tourism are increasing. Our findings also highlight continental transport of airborne bacteria from distant source regions like the Indo-Gangetic Plain, suggesting airborne bacterial influx. By integrating atmospheric biological data with air-mass back-trajectory simulation, the present study highlights valuable insights into how wind influences Himalayan airborne bacterial community. These insights are essential for developing airborne bacterial forecasting tools and public health strategies in vulnerable hilltop atmospheres that undergo rapid environmental change.