Anaerobic sulfur oxidation in the absence of nitrate dominates microbial chemoautotrophy beneath the pelagic chemocline of the eastern Gotland Basin, Baltic Sea

摘要: Oxic-anoxic interfaces harbor significant numbers and activity of chemolithoautotrophic microorganisms, known to oxidize reduced sulfur or nitrogen species. However, measurements in situ distribution bulk carbon dioxide (CO(2)) assimilation rates active autotrophic microorganisms have challenged the common concept that aerobic denitrifying oxidizers are predominant autotrophs pelagic oxic-anoxic interfaces. Here, we provide a comparative investigation nutrient, sulfur, manganese chemistry, microbial biomass distribution, as well CO(2) fixation at redoxcline eastern Gotland Basin, Baltic Sea. Opposing gradients oxygen, nitrate, sulfide approached detection limits chemocline 204 m water depth. No overlap oxygen nitrate with was observed, whereas particulate detected down 220 m. More than 70% dark assimilation, totaling 9.3 mmol C m(-2) day(-1), found absence nitrite, could not be stimulated by their addition. Maximum up 1.1 mumol L(-1) day(-1) were surprisingly susceptible altered redox potential concentration. These results suggest novel redox-sensitive pathways oxidation account for fraction growth beneath chemoclines. A mechanism coupled sulfur-oxidizing sulfur-reducing is proposed.