Genomics

The Depolluting Bacterium Speaks Out

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© H. Raguet/CNRS Photothèque

At the Genoscope, DNA sequences are assembled. Each red and green box corresponds to a sequence.

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The genome of Kuenenia stuttgartiensis has been sequenced, quite an achievement for the Genoscope's¹ Metabolic Genomic team² and their collaborators from the Universities of Nijmegen ( Netherlands), Munich (Germany), and Vienna (Austria). “It took us almost four years to piece together this genome and to identify its metabolic potential,” says CNRS researcher Denis Le Paslier. This species is an anammox bacterium, one of the tiny organisms that make up most of the air we breathe. In marine ecosystems, anammox bacteria actively contribute to the nitrogen cycle, a chemical that constitutes 78% of the air. Moreover, this result marks a huge step for the field of wastewater treatment.

Why? Because Kuenenia stuttgartiensis is the prototype of the anammox– anaerobic ammonium oxidation –bacteria, which transform ammonium into nitrogen in the absence of oxygen. Their utilization for ammonium removal from wastewater, in comparison with the conventional method of nitrification/denitrification, could present several advantages. The procedure is simpler, quicker, and the costs are cut by 90%, notably by an economy of energy. “As the anammox reaction is done under anaerobic conditions,” explains Le Paslier, “the supply of oxygen to the basin–which is very expensive–can be reduced. It's even better if there is no oxygen at all.” An experimental system is currently being tested in Rotterdam.

Like the majority of bacteria from the environment, Kuenenia could not be isolated. The French team extracted DNA from a complex community of bacteria cultivated for one year in a bioreactor in the Netherlands. “The sample they sent us looked like red chewing-gum!” remembers Le Paslier.

The genome sequence has revealed interesting features. For example, it carries the genetic blueprint of hydrazine metabolism and ladderane biosynthesis. These lipids compose the membrane of the anammoxosomes. This bacterium organelle confines highly toxic anammox reaction intermediates such as nitric oxide and hydrazine (rocket fuel).

And, last but not least, the DNA analysis has settled the controversy surrounding the evolutionary origin of Planctomycetes. This poorly understood group, that includes the anammox bacteria, shares a common ancestor with the intracellular parasite Chlamydiae.

Samantha Maguire