Bacteria are one-celled organisms with no visible organelles. They have their DNA distributed through their cytoplasm, as opposed to other eukarotic cells that have their DNA within a nucleus. Bacteria are easy to reproduce, meaning they are available as an inexhaustible supply. They are also simple in structure, making them an ideal candidate to study and work with. When trying something as intricate as DNA manipulation, it is best to start small. DNA strands can be quite lengthy and complicated, so starting small and working your way up is recommended. The isolation of specific gene sequences should be easier, as is the observation of the result of the genetic insertion. There are three things that can result as the effect of genetic engineering: 1) a beneficial trait, one that helps the organism survive, 2) a negative trait, one that either helps or causes the organism to die, and 3) nothing at all, because a lot of different codons all basically produce the same trait.
bacteria plays an important role in GE (genetic engenering). As we already know that bacteria genome is easy to manupulate and they can be mutatted easly. Moreover their frequency of multiplication is very high.
So we can mutate a bacterium (that is inserted our gene of interest to it ) and then trasfer it to the host.
one of the best example is Agrobacterium mediated infection. In which a agrobacterium are modified with the gene of our interest and transfer to the host plant.