For me, Bacteria are single celled microbes,, they don't have a nucleus and other bound organelles in their cell, the cell structure is simpler than that of the other organisms so, they are prokaryotes. Some bacteria have an extra circle of genetic material called plasmid. Bacteria classified into five group : spherical (cocci) , rod ( bacilli) , spiral ( spirilla), comma ( vibrios) or corkscrew (spirochaetes) ...