Dynamic Regulation of Extracellular Superoxide Production by the Coccolithophore Emiliania huxleyi (CCMP 374).

ABSTRACT: In marine waters, ubiquitous reactive oxygen species (ROS) drive biogeochemical cycling of metals and carbon. Marine phytoplankton produce the ROS superoxide (O₂ ^-) extracellularly and can be a dominant source of O₂ ^- in natural aquatic systems. However, the cellular regulation, biological functioning, and broader ecological impacts of extracellular O₂ ^- production by marine phytoplankton remain mysterious. Here, we explored the regulation and potential roles of extracellular O₂ ^- production by a noncalcifying strain of the cosmopolitan coccolithophorid Emiliania huxleyi, a key species of marine phytoplankton that has not been examined for extracellular O₂ ^- production previously. Cell-normalized extracellular O₂ ^- production was the highest under presumably low-stress conditions during active proliferation and inversely related to cell density during exponential growth phase. Removal of extracellular O₂ ^- through addition of the O₂ ^- scavenger superoxide dismutase (SOD), however, increased growth rates, growth yields, cell biovolume, and photosynthetic efficiency (F_v/F_m ) indicating an overall physiological improvement. Thus, the presence of extracellular O₂ ^- does not directly stimulate E. huxleyi proliferation, as previously suggested for other phytoplankton, bacteria, fungi, and protists. Extracellular O₂ ^- production decreased in the dark, suggesting a connection with photosynthetic processes. Taken together, the tight regulation of this stress independent production of extracellular O₂ ^- by E. huxleyi suggests that it could be involved in fundamental photophysiological processes.

SUBMITTER: Plummer S 

PROVIDER: S-EPMC6640029 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature