KO.background(genes, maps, size = -1, genomeName = "unknown", id.map = NULL, multiple.omics = FALSE, term.db = "unknown", instance.map = NULL);
a set of molecules with the kegg orthology/compound id mapping
the kegg maps model
the background gene size, default -1 or zero means auto calculation. [as integer]
the genome name that tagged with this background model. [as string]