why do bacteria in a biofilm have different characteristics than free-floating bacteria
Biofilm Bacteria living in a biofilm usually have significantly different properties from free-floating bacteria of the same species, as the dense and protected environment of the film allows them to cooperate and interact in various ways.[34] One benefit of this environment is increased resistance to detergents and antibiotics, as the dense extracellular matrix and the outer layer of cells protect the interior of the community. In some cases antibiotic resistance can be increased a thousandfold.[35] Lateral gene transfer is often facilitated within bacterial and archaeal biofilms[36] and leads to a more stable biofilm structure.[37] Extracellular DNA is a major structural component of many different microbial biofilms.[38] Enzymatic degradation of extracellular DNA can weaken the biofilm structure and release microbial cells from the surface.
Bacterial cell structure Unlike eukaryotes, the bacterial DNA is not enclosed inside of a membrane-bound nucleus but instead resides inside the bacterial cytoplasm. This means that the transfer of cellular information through the processes of translation, transcription and DNA replication all occur within the same compartment and can interact with other cytoplasmic structures, most notably ribosomes. The bacterial DNA is not packaged using histones to form chromatin as in eukaryotes but instead exists as a highly compact supercoiled structure, the precise nature of which remains unclear.[4] Most bacterial chromosomes are circular although some examples of linear DNA exist (e.g. Borrelia burgdorferi). Along with chromosomal DNA, most bacteria also contain small independent pieces of DNA called plasmids that often encode for traits that are advantageous but not essential to their bacterial host. Plasmids can be easily gained or lost by a bacterium and can be transferred between bacteria as a form of horizontal gene transfer. So plasmids can be described as an extra chromosomal DNA in a bacterial cell.