OSM  - Determination of the intra- and interindividuality as well as the stability of the ocular surface microbiome and tear proteome in healthy individuals at baseline and after 2 and 8 months.
The human microbiome is composed of trillions of microbes in and on the human body. In 2007, the Human Microbiome Project characterized the microbiomes at five different body sites, including the skin, gastrointestinal tract, oral cavity, nasal passages, and urogenital tract in healthy human subjects. However, the surface of the eye has not been studied in the Human Microbiome Project. Despite the sparse colonization of the eye, recently we succeeded in characterization of the ocular surface microbiome (OSM) and found interactions with the tear proteome in humans. Since the ocular surface is continuously exposed to environmental factors and pathogens, an important role of its microbiome is the protection of the underlying tissue against colonization by pathogens. Moreover, we propose that the OSM may itself be associated with diseases such as dry eye disease. However, the key to understand the role of a dysbiosis in diseases is firstly to define the individuality of the ocular surface microbiome in healthy individuals.  Therefore, we aimed to determine the stability and the intra- and inter-individuality of the OSM and the tear proteome. For this aim, we collected conjunctival swabs and tears from the left and the right eye separately, as well as one swab from both lower lids from healthy individuals aged between 40 and 60 years (n = 29) at three time points (baseline, after 2 and 8 months). The OSM of these swabs were taxonomically and functionally characterized using the QIAamp Microbiome Kit for total DNA isolation and the Illumina NovaSeq 6000 platform for whole-metagenome shotgun sequencing. To characterize the tear proteome, the tear samples were analyzed by chromatography tandem mass spectrometry. The data between the left and right eye and between the conjunctiva and the lower lid was compared intra- and inter-individually using the multivariate association by linear models (MaAsLin) R package using default settings. The results will be presented on the DBMR Day of BioMedical Research 2022.   The results of this study will deepen our understanding about taxonomic composition and function of the OSM and its connection with the tear proteome. This knowledge will be an essential cornerstone for correct interpretation of further OSM research and may lead to new ideas about prevention, detection and targeted treatment of eye diseases.