TABLE 1.

Normalized metadata format of the MSE 2 database

Metadata	Content
Project metadata
Project ID	The unique identifier of this project/study in the MSE 2 database
Project title	The project name and description in the MSE 2 database
Institute	The original producer of the study
Principal investigator	The original principal investigator of the study
Publication title	The paper’s title of the study, if applicable
Publication journal	The journal’s name of the paper, if applicable
Source	Link to the data source page, if applicable
Sequence type	Sequence type, 16S rRNA gene amplicon, and/or WGS
Date	Publishing date of the study/paper
Sample metadata
Sample metadata	Content
Project ID	The project ID to which the sample belonged
Sample ID	The unique ID of this sample in the MSE 2 database, initialed by its project ID
Habitat domain	Unified into 3 categories: human associated, animal associated, and environment
Habitat type	Unified into 22 categories (Table S1) to further explain the habitat domain
Habitat details	Detailed information of the habitat
Sampling site	Detailed sampling site information
Sampling product	The sampling material and product
Date	Sampling/publishing date of the sample
Country/region	Sampling country/region of the sample
Gender	Host gender of a human-associated habitat sample, if applicable
Age	Host age of a human-associated habitat sample, if applicable
Description	Additional description of sampling information, e.g., host health status, etc.
Amplicon sequence type	Amplicon marker and region, if applicable, e.g., 16S V4
Amplicon sequencing platform	Sequencing platform for amplicon sequences, if applicable
WGS	If the sample has WGS shotgun sequences
WGS platform	Sequencing platform for WGS, if applicable
Function	If the sample has functional annotation
NSTI	The nearest sequenced taxon index to quantify the accuracy of function profiles predicted from amplicons