Many microbes use nitrate in the environment for growth. Nitrate can be converted to ammonium and used in molecules such as proteins, or used as a terminal electron acceptor to make energy.
A new report in Frontiers in Microbiology sheds light on how the deep-sea hydrothermal vent bacterium Nautilia profundicola strain AmH carries out these functions.
Normally, genes encoding the enzymes required for nitrate reduction to ammonium are easily recognized in complete genome sequences. The genome of N. profundicola does not encode any recognizable nitrite reductases, enzymes that are necessary for the second step in the reduction of nitrate to ammonium.
Three research groups from the USA predicted and then experimentally tested a new pathway for nitrate reduction to ammonium. The novel aspect of this pathway is that hydroxylamine, a potent mutagen, appears to be a free intermediate between nitrite and ammonium.
The key module in the pathway is a quinone-reactive protein coupled to a hydroxylamine dehydrogenase enzyme that works in reverse. Hydroxylamine dehydrogenase shares ancestry with certain nitrite reductases and the nitrite-reducing type may represent an evolutionary precursor of the variants that oxidize hydroxylamine to nitrite.
This enzyme complex is also found in other ε-proteobacteria, including some pathogenic Campylobacteria.
URL: http://www.frontiersin.org/Evolutionary_and_Genomic_Microbiology/10.3389/fmicb.2013.00180/abstract