Bacterial chromosomes are often circular but sometimes linear. Some bacteria have one chromosome, while others have more than one. Bactcrial DN A also exist as plasmids which are circular pieces of DNA that can be transmitted between bacteria. Plasmids often carry the genes for antibiotic resistance and can thus spread between different bacteria. Bacterial chromosomes initiate replication and one origin of replication. When linear, bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria.