"We propose to define subgenome as independent replicons that derive from the host genome having essential gene.It is discriminated from large-sized plasmids or second chromosomes often found in many bactria,based on their a prioi presence."
-------------------Mitsuhiro Itaya and Teruo Tanaka,Experimental surgery to create subgenome of Bacillus subtilis 168,PNAS(1997).Vol.94.pp5378-5382.