If you are like me, you have always believed that there were two types of bacteria involved in the nitrate cycle, Nitrosomonas ammonia-oxidizing bacteria (AOB) and Nitrobacter, responsible for converting nitrite to nitrate. Recent studies have found that while these bacteria are present in most aquarium filters, they are far from the whole story for eliminating ammonia. The predominant form belongs to the ammonia-oxidizing archaea (AOA), a group that did not even exist when I was studying microbial genetics in the 70’s! In studies of mature aquarium systems (home and public displays), the AOA were the predominant form in 85% of the filter systems. While all we really need to care about is having some type of bacteria converting the ammonia, these new discoveries will have ramifications on the bacterial starter cultures for the aquarium.

Speaking of these bacterial treatments, studies have also shown that a lot of the “assumed” liabilities of these products really do not exist. It was thought that the anaerobic conditions would kill the bacteria, but in truth, the bacteria simply go dormant and the bacterial predators are what actually die off! It was assumed that the high nitrite levels could kill the AOB (AOA) but studies showed that the AOB (AOA) bacteria actually recovered faster in the presence of nitrite than they did in fresh water. When starved of ammonia, the AOB (AOA) can use other sources, but keep producing the enzymes needed for ammonia digestion. Other heterotrophic bacteria switch off these genes and activate others to process new foods. This means when ammonia becomes available, the AOB (AOA) can immediately start to reproduce while the other bacteria need to convert back to their original gene activation. Also, while this would rarely occur in the home aquarium, in larger bodies of water, if the conditions become too intolerant for these bacteria, they can create a small nitrogen bubble and use it to float away to a new location! So much for simple single cell organisms!

About The Author Don Roberts

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