Novelty statement
Nitrate amendment has been extensively used in microbial bioremediation to help exhaust the reductant pollutants in anaerobic habitats, but very few studies focused on the microbial dynamics. Previously we treated sulfide-rich river sediments for a week and identified enriched functional genes involved in nitrogen and sulfur cycles. In this study, we extended the observation to a month and focused on how nitrate amendment affected microbial community assembly.
The first finding was as predicted that elevated nitrate led to a taxonomic convergence at denitrifiers (Thiobacillus andLuteimonas ), and a functional convergence at denitrification and sulfide oxidation. The resulting communities had significantly decreased biodiversity and became highly fragile to environmental perturbations. With so abundant organic carbon present in subject sediments however, the most enriched denitrifiers were obligate chemolithotrophs. In addition, when looking into the microbial interactive networks, the keystone taxa consisted of neither the most abundant taxa nor the best metabolic competitors, but those performing interspecies cross-feeding, e.g. syntrophic bacteria and methanogens.