Researching the Anammox Genome

​Anammox (anaerobic ammonia oxidation) has received much attention in the past 10 years as it allows for lower utility costs over the more common practice of aerobic ammonia removal (nitrification). The reactions are as follows:

While the first step in ammonia removal is the same in both, the second step is biological short-cut that simplifies by converting nitrite and ammonia directly into nitrogen gas – thereby avoiding the denitrification step needed to meet modern total nitrogen permits.

While very successful anammox based systems have been constructed, we still do not really know much about the organisms that power the anammox process. So far what we know is:

• The microbes have a long generation time (slow growing)
• Grow in mixed culture with other organisms
• Form granules similar to that found in anaerobic digesters
• Possess an anammoxosome (membrane structure that actually does the conversion)

Data on the organisms is difficult to obtain as they are not readily cultured on standard microbiological media and the slow rate of growth. Over the past few years, researchers have evaluated anammox unit samples under various enrichment scenarios that make variation in the microbial populations. This involves varying any one or more environmental conditions or inputs to see what happens to the population as a whole. The testing then involves taking samples for metagenomics testing to determine what DNA is present in the biomass – thereby determining the organisms present and what relative frequency.
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The results of the results of the DNA sequencing have made the anammox puzzle even more interesting. Instead of typical bacteria, the anammox granules have a very unusual genome. They do not have many genes considered essential for bacteria. The researchers have called anammox populations the equivalent of “Microbial Dark Matter” – where much is yet to be learned.