Nitrate-Driven Trophic Association of Sulfur-Cycling Microorganisms in Tsunami-Deposited Marine Sediment Revealed by High-Sensitivity C-Bicarbonate Probing

Although denitrification-dependent chemolithotrophic sulfur oxidizers proliferated in tsunami-deposited marine sediment with nitrate amendment, their ecophysiological roles in biogeochemical carbon transfer are not addressed. We employed time-resolved high-sensitivity C-bicarbonate probing of rRNA to unveil the carbon fixation and resulting trophic relationship of the nitrate-amended sediment microorganisms. Nitrate reduction and sulfur oxidation co-occurred along with significant decreases in the CO and dissolved bicarbonate concentrations for the first 4 days of the incubation, during which the denitrification-dependent sulfur-oxidizing chemolithotrophs, i.e., the sp. HDS01 and sp. HDS22 relatives, and the sulfate-reducing heterotrophs, i.e., the spp. and relatives, actively incorporated C. These indicated that the sulfur oxidizers and sulfate reducers were tightly associated with each other through the direct carbon transfer. Relatives of the fermentative and the hydrolytic , in addition to various sulfur-cycling microorganisms, significantly assimilated C at day 14. Although the incorporation of C was not detected, a syntrophic volatile-fatty-acid oxidizer and hydrogenotrophic methanogens significantly expressed their 16S rRNA molecules at day 21, indicating the metabolic activation of these final decomposers under the latter nutrient-limited conditions. The results demonstrated the nitrate-driven trophic association of sulfur-cycling microorganisms and the subsequent microbial activation and diversification, triggering the restoration of the marine ecosystem function.