bab1c13e_ling_BioPerl_on_Unix___BioPerl__Description
[Env. Variable] BLASTDATADIR or BLASTDB [Description] 
If one does not want to locate the data dir within the same dir as where the BLASTDIR variable points, a BLASTDATADIR or BLASTDB variable can be set to point to a dir where BLAST database indexes are located.
Installing BioPerl on Unix - BioPerl
Description