Concentration and transport of nitrate by the mat-forming sulphur bacterium Thioploca

MARINE species of Thioploca occur over 3,000 km along the continental shelf off Southern Peru and North and Central Chile 1–4 . These filamentous bacteria live in bundles surrounded by a common sheath and form thick mats on the sea floor under the oxygen-minimum zone in the upwelling region, at between 40 and 280 m water depth. The metabolism of this marine bacterium 5,6 remained a mystery until long after its discovery 1,7 . We report here that Thioploca cells are able to concentrate nitrate to up to 500 mM in a liquid vacuole that occupies >80% of the cell volume. Gliding filaments transport this nitrate 5–10 cm down into the sediment and reduce it, with concomitant oxidation of hydrogen sulphide, thereby coupling the nitrogen and sulphur cycles in the sediment.