Phyllosphere-associated microbiota in built environment: Do they have the potential to antagonize human pathogens?

Introduction
The plant microbiota is known to protect its host against invasion by plant pathogens. Recent studies have indicated that the microbiota of indoor plants is transmitted to the local built environment where it might fulfill yet unexplored functions. A better understanding of the interplay of such microbial communities with human pathogens might provide novel cues related to natural inhibition of them.
Objective
We studied the plant microbiota of two model indoor plants, Musa acuminata and Chlorophytum comosum, and their effect on human pathogens. The main objective was to identify mechanisms by which the microbiota of indoor plants inhibits human-pathogenic bacteria.
Methods
Microbial communities and functioning were investigated using a comprehensive set of experiments and methods combining amplicon and shotgun metagenomic analyses with results from interaction assays.
Results
A diverse microbial community was found to be present on Musa and Chlorophytum grown in different indoor environments; the datasets comprised 1,066 bacterial, 1,261 fungal, and 358 archaeal ASVs. Bacterial communities were specific for each plant species, whereas fungal and archaeal communities were primarily shaped by the built environment. Sphingomonas and Bacillus were found to be prevalent components of a ubiquitous core microbiome in the two model plants; they are well-known for antagonistic activity towards plant pathogens. Interaction assays indicated they can also antagonize opportunistic human pathogens. Moreover, the native plant microbiomes harbored broad spectrum of biosynthetic gene clusters, and in parallel, a variety of antimicrobial resistance genes. By conducting comparative metagenomic analyses between plants and abiotic surfaces, we found that the phyllosphere microbiota harbors features that are clearly distinguishable from the surrounding abiotic surfaces.
Conclusions
Naturally occurring phyllosphere bacteria can potentially act as a protective shield against opportunistic human pathogens. This knowledge and the underlying mechanisms can provide an important basis to establish a healthy microbiome in built environments.
Graphical abstract
Schematic visualization of the discovered implications of indoor-plant-associated bacteria as a defense line against opportunistic human pathogens. All relevant functions of the bacterial community confirmed in this study that serve to shield off pathogens. Methods and techniques that were implemented to analyze the respective functions are additionally highlighted.