Abstract
The desire to understand and distinguish the relative growth and activity of ammonia oxidising archaea (AOA) and ammonia oxidising bacteria (AOB) in soil nitrification has increased the search for selective inhibitors of these two groups. This study aimed to investigate the potency and specificity of simvastatin as a specific AOA inhibitor in pure cultures and in soil and to determine the effect of AOA inhibition on both ammonia oxidation activity and growth of AOB, under the hypothesis that AOB growth is higher when competition for NH4+ from AOA is removed. Simvastatin selectively inhibited pure cultures of all tested AOA at concentrations of 8–100 μM. In soil microcosms incubated for 21 days with low and high NH4+ concentrations, AOA but not AOB were selectively inhibited by simvastatin in both acidic (pH 4.5) and near-neutral (pH 6.5) soils. Additionally, growth of AOB significantly increased at both NH4+ concentrations following inhibition of AOA by simvastatin, suggesting that competition for substrate between AOA and AOB is a key factor restraining AOB growth in NH4+-limited soils. Simvastatin can therefore be used as a selective AOA inhibitor to investigate kinetic characteristics of AOB in soils and to study competition between AOA and AOB in complex environments.
Highlights
Ammonia oxidising archaea (AOA) and bacteria (AOB) and more recently discovered complete ammonia oxidisers perform the initial step of nitrification
Inhibition of ammonia oxidation activity of four AOA and three ammonia oxidising bacteria (AOB) isolates by simvastatin was determined by calculating the proportional decrease in maximum specific growth rate in medium supplemented with a series of simvastatin concentrations
N. sinensis was completely inhibited by simvastatin at a concentration of 8 μM (Fig. 1), with no detectable in creases in nitrite concentration after incubation of simvastatin-amended cultures for 17 and 11 days, respectively
Summary
Ammonia oxidising archaea (AOA) and bacteria (AOB) and more recently discovered complete ammonia oxidisers (comammox) perform the initial step of nitrification (oxidation of ammonia to nitrite). There is evidence that AOA and AOB have different preferences for ammonia source and concentration, with AOA being favoured when NH4þ is generated by mineralisation of organic N, while AOB prefer supply of high concentrations of inorganic NH4þ (Di et al, 2009; Hink et al, 2018; Ho€fferle et al, 2010; Levi cnik-Ho€fferle et al, 2012; Stopni sek et al, 2010; Verhamme et al, 2011) This was previously explained by higher ammonia affinity and sensitivity of AOA compared to AOB (Prosser and Nicol, 2012), but recent studies have challenged this theory following the isolation of several Ca. Nitrosocosmicus strains of AOA (Jung et al, 2016; Lehtovirta-Morley et al, 2016a; Sauder et al, 2017) that can grow at high ammonium concentrations, similar to those supporting growth of typical soil AOB. These findings suggest that both AOA and AOB are able to grow at both low and high NH4þ con centrations, while competition for ammonia may be the major factor differentiating growth of AOA and AOB in soil
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
