Bacterial and Archaeal nitrifiers in deep water layer of an oligotrophic subalpine lake

Nitrification plays an important role in the nitrogen cycle and it consists in the conversion of ammonia into nitrite and then nitrate operated by two different groups of microorganisms: ammonia-oxidising bacteria (AOB) and nitrite-oxidising bacteria (NOB). In particular the oxidation of ammonia by AOB was until recently considered the rate-limiting step. Starting from 2005 with the discovery of Archaea with nitrification activity, our understanding of the nitrogen cycle and the microorganisms involved is dramatically changing. In this study, we focussed on the abundance of ammonia-oxidising Bacteria and Archaea in the deep-water layers of an oligotrophic subalpine lake (Lake Maggiore, Northern Italy). Based on sequence analysis of 16S rRNA genes and the functional genes amo, codifying for the ammonia-monooxygenase enzymes, the relative presence and importance of both ammonia-oxidising Bacteria and Archaea in deep waters have been assessed, confirming the emerging hypothesis of their spatial niche differentiation. We found a different vertical distribution of Bacteria and Archaea and here we will discuss the interaction with chemical and other limnological parameters.