"Curvibacter sp." is a Gram-negative curved rod-formed bacterium which is the main colonizer of the epithelial cell surfaces of the early branching metazoan "Hydra vulgaris". Sequencing the complete genome uncovered a circular chromosome (4.37 Mb), a plasmid (16.5 kb), and two operons coding each for an AHL (N-acyl-homoserine lactone) synthase ("curI1" and "curI2") and an AHL receptor ("curR1" and "curR2"). Moreover, a study showed that these host associated "Curvibacter" bacteria produce a broad spectrum of AHL, explaining the presence of those operons. As mentioned before, AHL are the quorum sensing molecules of Gram-negative bacteria, which means "Curvibacter" has a quorum sensing activity.