Aims: The objective of the present work was to describe a new deep-sea, aerobic, mesophilic and heterotrophic bacterium, referenced as strain AT1214, able to produce polyhydroxyalkanoates (PHAs) under laboratory conditions. This bacterium was isolated from a shrimp collected nearby a hydrothermal vent located on the Mid-Atlantic Ridge. Methods and Results: This micro-organism, on the basis of the phenotypical features and genotypic investigations, can be clearly assigned to the Halomonas genus and the name of Halomonas profundus is proposed. Optimal growth occurred between 32 and 37 degrees C at a pH between 8 and 9 and at ionic strength between 20 and 30 g l(-1) of sea salts. The G + C content of DNA was 58.6%. This bacterium produced PHAs of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from different carbon sources. Conclusions: The bacterium H. profundus produces PHA of 3HB and 3HV monomers from different carbon sources. Significance and Impact of the Study: PHAs share physical and material properties that suggest them for application in various areas, and are considered as an alternative to nonbiodegradable plastics produced from fossil oils. In this study, we describe a new bacteria isolated from a deep-sea hydrothermal vent with the capability to produce polyesters of biotechnological interest.