The effect of nitrate concentration on sulfide-driven autotrophic denitrification in marine sediment

The effect of nitrate concentration on denitrification rate, microbial community and byproduct accumulation in sulfide-driven autotrophic denitrification, one of the dominant processes during anoxic marine sediment remediation, was investigated in this study. Microorganisms which were phylogenetically closely related with Sulfurimonas denitrificans of ε-Proteobacteria and Thiohalomonas denitrificans of γ-Proteobacteria were the major autotrophic denitrifiers in this study. Nitrate concentration was demonstrated to have selective effect on denitrifying microbial community as revealed by denaturing gradient gel electrophoresis. Denitrifiers enriched at 30 mM NO3- have higher diversity than other two groups (10, and 80 mM NO3-) according to Shannon index. Denitrification showed zero-order reaction kinetics when nitrate concentration was higher than 4 mM. Neither absolute nitrate concentration nor overall nitrate/sulfide ratio acted as the determinant for denitrification byproduct (i.e. N2O and NO2-) accumulation. The limitation of sulfide due to low mass transfer might be the reason for the byproduct accumulation.

Research highlights
► Effect of [NO3-] on autotrophic denitrification in sediment was investigated.
► Denitrification show zero-order kinetics when [NO3-] > 4 mM.
► Sulfuromonas denitrificans and Thiohalomonas denitrificans   are the major denitrifier.
► Selection effects on denitrifiers by [NO3-] is confirmed by kinetics and DGGE.
► Limitation of sulfide due to low mass transfer leads to N2O accumulation.