Influence of seasonal variability and meteorological factors on airborne bioaerosols in a high-altitude environment of Ooty, Western Ghats: Insights into bacterial dynamics

Bioaerosols, comprising viable and non-viable biological particles, significantly influence atmospheric processes, climate modulation and human health. This study investigates the impact of climatic and atmospheric conditions on bioaerosol composition and microbial dynamics at high altitudes of Western Ghats, specifically at the ISRO ARFI Environmental Observatory in Ooty, Tamil Nadu, situated at 2520 meters above sea level. Bioaerosol samples were collected using a high-volume respirable dust sampler with a flow rate of 1.4 m³/min over an 8-hour sampling period. Microbial enumeration was conducted through culture-based methods, including spread plate, streak plate and slant culture techniques on nutrient agar, Rose Bengal agar and Ken Knights agar media. Results revealed seasonal variations in bacterial colony-forming units (CFU), with peak concentrations recorded during the post-monsoon and winter months (October–January). CFU counts ranged from 50 to 169 CFU/m³, with the highest values observed in the central portion of the filter (169 ± 24.64 CFU/m³) and lower values in the peripheral region (134 ± 14.03 CFU/m³). Morphological characterisation and Gram staining of bacterial colonies indicated a diverse microbial population, with a predominance of Gram-positive rod-shaped bacteria. The study further highlighted that bacterial density was highest during February–May (134 ± 14.03 CFU/m³) and lowest between June–September (50 ± 10.72 CFU/m³), suggesting strong correlations with temperature, humidity and UV radiation. The findings underscore the sensitivity of bioaerosol populations to altitude-related environmental stressors, aligning with previous studies that report reduced microbial diversity at higher elevations. This study enhances the understanding of airborne microbial ecology and provides a basis for future research employing molecular techniques, such as 16S rRNA sequencing, to elucidate microbial community dynamics. These insights are crucial for assessing bioaerosol contributions to atmospheric chemistry, air quality and potential public health implications.