The Effect of Spring Water Geochemistry on Copper Proteins in Tengchong Hot Springs, China

Copper (Cu) is an essential trace metal cofactor for a variety of proteins; however, excess Cu is toxic to most organisms. Cu homeostasis is maintained by a complex machinery of Cu binding proteins that control the uptake, transport, sequestration, and efflux of Cu ions. Despite the importance of Cu binding proteins in electron transfer, substrate oxidation, superoxide dismutation, and denitrification, little information exists about microbial Cu utilization in extreme environments, where the geochemical conditions may affect Cu bioavailability. Using metagenomic data from 9 hot springs in Tengchong, China, which range in temperature from 42°C to 96°C and in pH from 2.3 to 9, the effects of pH, temperature, and spring geochemistry on the distribution of Cu binding domains of proteins and oxidoreductases were studied. Dissolved Cu and Cu binding domains were detected across all temperature and pH gradients. Cu binding domains of cytochrome c oxidase subunits, heavy-metal-associated domains, and nitrous oxide reductase were detected at all sites. DoxB, a quinol oxidase, and other quinol oxidase subunits were the dominant Cu binding oxidoreductase subunits present at low-pH and high-temperature sites, whereas cbb₃-type cytochrome c oxidase subunits were dominant at high-pH and high-temperature sites. Additionally, aa₃-type cytochrome c oxidase was more prominent than cbb₃-type cytochrome c oxidase under circumneutral-pH conditions. This suggests that the type of cytochrome c oxidase pathway and the Cu proteins employed by microbes to carry out important functions such as energy acquisition and efflux of excess Cu are affected by the physicochemical conditions of the springs.IMPORTANCE Copper is present in a variety of proteins and is required to carry out essential functions by all organisms. However, in hot spring environments, copper availability may be limited due to the high temperatures and the wide range in pH. The significance of our research is in relating the physicochemical environment to the distribution of copper proteins across hot spring environments, which provides increased understanding of primary functions and adaptions in these environments.