In response to some
interesting questions from Lasse yesterday, I dug deeper and found that in addition to the ammonia-oxidizing microbes I've already reported, most samples also contain another less widely discussed group, the family Pirellulaceae, which also have ammonia-oxidizing activities.
These were more abundant in your biofilm sample (>2% of the community) than your water (0.5%), but still clearly present in the water. So at the DNA level we have evidence for two ammonia-oxidizing groups in your water: Cenarchaeaceae and Pirellulaceae. (Its still not clear from my reading whether the latter group can oxidize ammonia in aerobic conditions, but thats my only delay in adding it to the report)
I will be very interested to see if your measurements of ammonia metabolism support this.
Now you've really got me thinking. Can we do something similar for nitrite using BOD5? The reason I ask is that NOB are undetectable in a greater number of tanks than AOB/AOA. And as people have been discussing, other organisms (like algae and some animals) actively compete for ammonia. It would be interesting to test for nitrite oxidizing activity in your water, if its possible to do something analogous to the ammonia test.