Filamentation is the anomalous (not normal) growth of certain bacteria, such as "E. coli", in which cells continue to elongate but do not divide (no septa formation). Bacterial filamentation is a defect in completing replication and is observed in bacteria responding to a various stresses. This may happen, for example, when there is extensive DNA damage through the SOS response system. Nutritional change may also cause bacterial filamentation.