The indoor environment - a potent source for intact human-associated anaerobes

People in westernized countries spend most of their time indoors. As interaction and exchange of microbes between the human body and its environment is crucial for a healthy human microbiome, the build environment (BE) might represent a potent source for commensal microbes. Especially anaerobic microbes are of interest, as acquisition routes of oxygen-sensitive microbes such as obligate or facultative anaerobes to the human microbiome are not sufficiently clarified yet. We sampled a total of ten bathroom floors and used propidium monoazide (PMA) to assess the viability of the collected prokaryotes. Quantitative and qualitative analysis revealed that most of the microbial taxa are of human origin, but less than 25% of the prokaryotic signatures originate from intact, and thus potentially living, cells with an apparent survival advantage for aerobic and stress resistant taxa. We could verify the presence of strictly anaerobic taxa - including methanogenic archaea - in PMA-treated samples, indicating a limited, but substantial capability of those taxa to survive in the BE. As methanogens are regarded as highly sensitive to aerobic conditions, oxygen tolerance experiments were performed with human isolates to validate their survival. We could confirm that human-associated methanogens are capable of surviving oxic conditions for at least 6h. In conclusion, we collected strong evidence supporting the notion that obligate anaerobic taxa are capable of surviving in the BE for a limited amount of time and thus, making the BE a potential source for anaerobic human commensals.