The loss of oxygen in the oceans is considered one of the most important threats currently occurring in marine ecosystems. The occurrence of hypoxic and anoxic events in coastal waters are becoming increasingly frequent. Some basins and fjords have permanently or periodically anoxic waters, making them excellent locations for studies of pelagic oxic anoxic interfaces. The study of respiratory kinetics provides insight into the adaptation of the microbial community to decreasing levels of O2. Prokaryotes can use different types of terminal oxidases with a broad range of affinities for O2 during aerobic respiration thus modulating their affinity for O2. Here we explore the respiratory kinetics in natural communities in the seasonally anoxic water column of the Mariager Fjord, Denmark. We measured O2 consumption and CO2 production rates of water samples collected at different depths in the oxycline while exposing them to a wide range of O2 concentrations from full saturation to nanomolar levels. Maximum respiration rates ranged from 254 to 355 nM O2/h, being dependent of the temperature (from 14 to 17 deg). The half saturation constant (Km) decreased from values of 139 nM in oxic waters to 76 nM in the hypoxic layer, suggesting a dominant contribution of low affinity terminal oxidases in fully oxic waters and the adaptation of the community in low O2 waters with increasing use of high affinity terminal oxidases. Our data show the adaptation of the microbial community in water layers with low O2 levels, decreasing the apparent Km for increasing the respiration efficiency.

Primary Presenter: Irene Ramirez Hernandez, University of Cadiz (irene.ramirez@gm.uca.es)

Authors:

Irene Ramírez Hernández, University of Cadiz  (irene.ramirez@gm.uca.es)

Laura Bristow, University of Gothenburg  (laura.bristow@gu.se)

Bo Thamdrup, University of Southern Denmark  (bot@biology.sdu.dk)

Emilio García Robledo, University of Cadiz  (emilio.garcia@uca.es)

José Calderón Caro, University of Cadiz  (jose.calderon@gm.uca.es)

Julio Bohórquez Ferrando, University of Cadiz  (julio.bohorquez@gm.uca.es)