Insights into the Profile of the Human Expiratory Microbiota and Its Associations with Indoor Microbiotas

Microorganisms
residing in the human respiratory tract can be exhaled,
and they constitute a part of environmental microbiotas. However,
the expiratory microbiota community and its associations with environmental
microbiotas remain poorly understood. Here, expiratory bacteria and
fungi and the corresponding microbiotas from the living environments
were characterized by DNA amplicon sequencing of residents’
exhaled breath condensate (EBC) and environmental samples collected
from 14 residences in Nanjing, China. The microbiotas of EBC samples,
with a substantial heterogeneity, were found to be as diverse as those
of skin, floor dust, and airborne microbiotas. Model fitting results
demonstrated the role of stochastic processes in the assembly of the
expiratory microbiota. Using a fast expectation–maximization
algorithm, microbial community analysis revealed that expiratory microbiotas
were differentially associated with other types of microbiotas in
a type-dependent and residence-specific manner. Importantly, the expiratory
bacteria showed a composition similarity with airborne bacteria in
the bathroom and kitchen environments with an average of 12.60%, while
the expiratory fungi showed a 53.99% composition similarity with the
floor dust fungi. These differential patterns indicate different relationships
between expiratory microbiotas and the airborne microbiotas and floor
dust microbiotas. The results here illustrated for the first time
the associations between expiratory microbiotas and indoor microbiotas,
showing a potential microbial exchange between the respiratory tract
and indoor environment. Thus, improved hygiene and ventilation practices
can be implemented to optimize the indoor microbial exposome, especially
in indoor bathrooms and kitchens.