a character string specifying the database from which the genome
shall be retrieved: db = "refseq", db = "genbank",
db = "ensembl", db = "ensemblgenomes".
Default is db = "refseq".
# NOT RUN {# retrieve kingdoms available from refseqgetKingdoms(db = "refseq")
# retrieve kingdoms available from genbankgetKingdoms(db = "genbank")
# }