A UDB file is a database file that contains sequences and a k-mer index for those sequences. A UDB file is created using makeudb_usearch, makeudb_ublast or makeudb_utax.
The udb2fasta command can be used to convert the UDB file to FASTA.
See indexing options for a description of index parameters.
Information about a UDB file can be
obtained with the udbinfo and udbstats
commands.