Copper requirements and copper toxicity as niche-defining factors in the growth of terrestrial ammonia-oxidizing archaea and bacteria

Ammonia-oxidizing archaea (AOA) and bact eria (AOB) are critical for nitrogen cycling in the environment, but their copper requirements remain poorly understood. This study investigated copper requirements and toxicity thresholds for terrestrial AOA 'Ca. Nitrosocosmicus franklandianus' and Nitrosotalea sinensis, and the AOB Nitrosomonas europaea to understand the role of copper in their niche separation. Growth assays revealed significant differences between ammonia oxidisers in response to copper. Nitrosotalea sinensis exhibited the highest copper sensitivity, with full growth inhibition above 5 μM copper, while N. europaea demonstrated superior copper tolerance, withstanding up to 100 μM copper concentrations. Highest growth rates were observed at 50 nM copper for 'Ca. N. franklandianus' and at 10 nM for N. sinensis. Triethylenetetramine (TETA) provided protective effects against copper toxicity and enhanced the growth of both AOA strains by complexing inhibitory metals. Notably, hydroxylamine oxidation in AOA was inhibited by TETA, but it was not inhibited in AOB, indicating distinct differences in their metabolism. Cellular copper analysis confirmed that the amount of copper in cells differs between species. These findings demonstrate that copper availability and toxicity are important niche-differentiating factors for soil ammonia oxidisers. The differential copper sensitivities challenge current approaches using copper-chelating nitrification inhibitors.