Who inhabits the built environment? A microbiological point of view on the principal bacteria colonizing our urban areas

Abstract

Modern lifestyle greatly influences human well-being. Indeed, nowadays people are centered in the cities and this trend is growing with the ever-increasing population. The main habitat for modern humans is defined as the built environment (BE). The modulation of life quality in the BE is primarily mediated by a biodiversity of microbes. They derive from different sources, such as soil, water, air, pets, and humans. Humans are the main source and vector of bacterial diversity in the BE leaving a characteristic microbial fingerprint on the surfaces and spaces. This review, focusing on articles published from the early 2000s, delves into bacterial populations present in indoor and outdoor urban environments, exploring the characteristics of primary bacterial niches in the BE and their native habitats. It elucidates bacterial interconnections within this context and among themselves, shedding light on pathways for adaptation and survival across diverse environmental conditions. Given the limitations of culture-based methods, emphasis is placed on culture-independent approaches, particularly high-throughput techniques to elucidate the genetic and -omic features of BE bacteria. By elucidating these microbiota profiles, the review aims to contribute to understanding the implications for human health and the assessment of urban environmental quality in modern cities.

Keywords: environmental niches; human health; human microbiota; microbial community; microbiomes; omic approaches; urban cities.

Figure 1

Main disciplines enable the evaluation of the built environment concept and quality and assess potential interventions for human health and well-being. The built environment assessment is based on different fields of study: urban planning, transportation, nutritional science which cooperates with behavioral (psychology), social, and environmental science, physical activity, epidemiology and public health, and economics.

Figure 2

Representation of the microbiota distribution at the phylum level in a built environment localized in a typical modern city. The principal built environment places are marked, and square boxes represent different inner environments, for example offices, household kitchen and the indoor of an old building. Each colored dot represents a bacterial phylum, and their distribution approximates bacteria retrieved in the different compartments accordingly to the updated literature.

Figure 3

Timeline journey into the hidden properties of the microbiomes of the built environment at the global level from culture-based methods toward molecular-independent techniques and multidisciplinary approaches.

Figure 4

Principal bacterial genera that belong to the natural environments (A) and human habitats (B) are distributed in diverse native niches. The main niches are plant-associated environments, water systems, soil, animals, and air and particles in (A) and different human compartments (B): lungs, stomach, male and female reproductive tracts, skin, oral cavity, small intestine, and colon.