Filamentous Giant Beggiatoaceae from the Guaymas Basin Are Capable of both Denitrification and Dissimilatory Nitrate Reduction to Ammonium

Abstract

Whether large sulfur bacteria of the family Beggiatoaceae reduce NO 3 − to N 2 via denitrification or to NH 4 + via DNRA has been debated in the literature for more than 25 years. We resolve this debate by showing that certain members of the Beggiatoaceae use both metabolic pathways. This is important for the ecological role of these bacteria, as N 2 production removes bioavailable nitrogen from the ecosystem, whereas NH 4 + production retains it. For this reason, the topic of environmental controls on the competition for NO 3 − between N 2 -producing and NH 4 + -producing bacteria is of great scientific interest. Recent experiments on the competition between these two types of microorganisms have demonstrated that the balance between electron donor and electron acceptor availability strongly influences the end product of NO 3 − reduction. Our results suggest that this is also the case at the even more fundamental level of enzyme system regulation within a single organism.