Abstract: The current invention provides new Gram negative polypeptides exhibiting lipid A 3-O-deacylase activity and are capable of modifying and/or detoxifying gram negative LPS. The present invention also provides Gram negative bacteria, Gram negative bacterial lipopolysaccharides (LPS) and compositions comprising LPS, which are provided with or treated with a 3-O-deacylase activity according to the invention and which may be used for pharmaceutical and/or veterinary purposes, in particular for the preparation of whole cell or acellular vaccines against pathogenic Gram negatives such as Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica.