Distribution, activity, and diversity of heterotrophic nitrifiers originating from East Pacific deep-sea hydrothermal vents

Nitrifiers (bacteria, n = 160) were enriched and isolated from samples of hydrothermal waters, sediments, invertebrate tissues, and chimney rocks collected from two East Pacific deep-sea hydrothermal vents (2000 m): the 13 degrees N site and the Guaymas Basin. They were nitrite producers and seemed be widely and uniformly distributed in various parts of hydrothermal ecosystem. These bacteria grew and nitrified better heterotrophically than autotrophically and they possessed characteristics of heterotrophic nitrifiers. All were aerobic, mesophilic gram-negative rods with a unfermentative metabolism and 88% were nitrate reducers or denitrifiers. They were characterized by a high physiological and nutritional diversity, and because of their ability to ammonify, nitrify, and reduce nitrate, they could largely contribute to the nitrogen cycle in hydrothermal sites.