Adaptive radiation of marine ammonia-oxidizing archaea

Abstract

We report here on the basic physiology of two new isolates of marine ammonia-oxidizing archaea (AOA) and their relationship to Nitrosopumilus maritimus, the first isolated representative of the marine AOA. Although all isolates are closely related members of the Group 1 clade, they exhibit strikingly different growth responses to differences in pH, salinity, temperature, and light. Notably, strain PS0 is capable of sustaining nearly 80% of ammonia oxidation activity at a pH as low as 5.9, challenging previous generalizations of marine AOA sensitivity to increases in ocean acidity. All strains showed only minor photoinhibition at 15 μE m-2 s-1, demonstrating the plausibility of an AOA origin of the primary nitrite maximum in the euphotic zone. Comparative analyses also provided direct physiological confirmation of a capacity to utilize fixed carbon and urea as carbon and energy sources, respectively. Together, these findings highlight a remarkable adaptive capacity of marine AOA and new understanding of the physiological basis for the remarkable ecological success reflected by their high oceanic abundance, and possible future success in a changing ocean.