Diversity and Abundance of Denitrifying Bacteria in the Sediment of a Eutrophic Estuary

The relationships between denitrifying microbial communities and their controlling factors are largely unknown in eutrophic estuaries sediment. This work showed that in Liaohe Estuary,nirS-type denitrifiers were consistently more abundant and diverse thannirK andnosZ-type denitrifiers, which probably means that they play an important role in nitrogen removal, particularly around nearshore stations. The dominant genera ofnirK,nirS andnosZ-type denitrifiers wereSinorhizobium,Pseudomonas, andAzospirillum. Salinity, nitrogen levels, and sediment grain size were the main factors affecting the denitrification process in this eutrophic estuary. These results provide more information about the dynamics of denitrifying microbiota in marine sediments. Summary:The relationships between denitrifying microbial communities and abundance in estuaries sediment and their controlling factors are largely unknown, especially in eutrophic estuaries. In this study, nitrite reductase genes (nirS,nirK) and nitrous oxide reductase genes (nosZ) were used as molecular markers, qPCR and illumina Miseq high-throughput sequencing technology were used to study the relative abundance of key functional microflora groups and major environmental impact factors in Liaohe Estuary. The results showed thatnirS-type denitrifiers were consistently more abundant and diverse thannirK andnosZ-type denitrifiers, which suggested thatnirS-type denitrifiers probably play an important role in nitrogen removal in Liaohe Estuary, particularly around nearshore stations. The dominant genera of the bacterial containingnirK,nirS andnosZ genes wereSinorhizobium,Pseudomonas, andAzospirillum,in whichSinorhizobiumandAzospirillumwere nitrogen-fixing bacteria, whilePseudomonaswas denitrogenation bacteria. The different dominant denitrifiers indicated that sedimentary denitrification was accomplished by cooperation of different denitrifying species rather than a single species. Salinity, NH4+, NO3-, NO(2)(-)and sediment grain size were regarded as determinants for the denitrification process in the sediment of the estuary. Overall, the results of this study suggest that a comprehensive analysis of different denitrifying functional genes may provide more information about the dynamics of denitrifying microbiota in marine sediments.

Automated summary

The relationships between denitrifying microbial communities and their controlling factors are largely unknown in eutrophic estuaries sediment. This study in the Liaohe Estuary showed that nirS-type denitrifiers were consistently more abundant and diverse than nirK and nosZ-type denitrifiers, likely playing a key role in nitrogen removal, especially at nearshore stations. The main factors affecting denitrification were salinity, nitrogen levels, and sediment grain size. These results provide valuable information about denitrifying microbiota dynamics in marine sediments.