Population dependent alteration in urban airborne bacterial communities enriched with pathogens: A study over Delhi, India

Urban airborne bacteria demand more attention due to their diversity and ability to adapt in different ambient conditions, causing significant impact on human health. Current study investigates weather-dependent composition, diversity, and variability of urban airborne bacterial loading over Delhi, the most polluted metropolitan city in India. Simultaneous winter-time airborne bacterial samples are collected under different weather conditions, namely typical winter (TW), haze (HZ), rain (RN), and seasonal transition (ST) from winter to summer, over high and low populated region (HPR and LPR, respectively). Maximum bacterial diversity with highest cell count (13.1±1.4×10 5 m -3 ) is noticed on HZ, followed by ST, TW, and RN. Winter haze could be responsible for proliferation of unique bacteria possibly due to abundance of nutrients in air. About 20% increase in bacterial loading is recorded over HPR due to stronger emissions from human activities. 10% bacterial genera are independent of spatial and temporal variation, representing urban background bacterial population. Beta diversities analysis revealed three distinct clusters, each corresponding to HZ, RN, and ST, due to significant variations in weather and air pollution. Ambient meteorology plays a major role in shaping bacterial diversity, contributing upto 60%, while urban air pollution accounted for 20%. Among meteorological parameters, temperature is most influential and positively correlated with bacterial diversity, while RH and wind speed are negatively correlated. Airborne pathogens like Acinetobacter and Corynebacterium , associated with respiratory diseases and skin infections, are in higher abundance in RN and warmer ST days. Present findings highlight public health risks posed by airborne pathogens over Delhi. • Airborne bacterial cell numbers are strongly influenced by weather conditions • Ambient temperature plays leading role in alteration of airborne bacterial loading • Air pollution impacts more on airborne bacterial diversity in high populated region • Urban atmosphere enriched with pathogens targets skin and respiratory organs • Human pathogens are abundant over high populated areas within urban regions