Abstract
Biological nitrification and denitrification play significant roles in nitrogen-associated biogeochemical cycles. However, our understanding of the spatial scales at which microbial communities act and vary is limited. We used gene-specific metagenomic PCR to explore changes in nitrifying and denitrifying microbial communities within pristine lake and its branches, where the ammonium and dissolved organic carbon (DOC) concentrations form a gradient. The biomarkers hydroxylamine oxidoreductase and nitrite reductase genes indicated that strong relationships exist between the diversities and community structures of denitrifiers and ammonium gradients. It showed that the Nitrosomonas oligotropha cluster dominates the nitrifying bacteria in low-nutrition environments, while a new Nitrosomonas ureae cluster accounted for nearly 80% of the nitrifying bacteria in high-nitrogen environments. The distribution and diversity of nirS/K-dependent denitrifiers in the various habitats were similar, but predominantly affiliated with unknown clusters. Moreover, the abundance of all the hao genes dramatically outnumbered that of nir genes. The relative abundance of hao was clearly higher during eutrophication (13.60%) than during oligotrophy (5.23%), whereas that of nirS showed opposite tendencies. Overall, this study provides valuable comparative insights into the shifts in nitrifying and denitrifying microbial populations in lake environments with ammonium gradients, suggesting that unique dominant denitrifiers probably play an important role in the nitrogen cycle.
Highlights
IntroductionThe global biogeochemical nitrogen cycle has undergone dramatic changes in the past few decades
The global biogeochemical nitrogen cycle has undergone dramatic changes in the past few decades.In particular, anthropogenic processes, including agricultural, industrial, and domestic activities, have resulted in an unprecedented increase in environmental nitrogen release
In sample QL-H, the Proteobacteria were significantly affiliated with the Gammaproteobacteria (21.21%) and Betaproteobacteria (18.19%) clusters, whereas in the SR-W sample, they were more commonly associated with the Betaproteobacteria clusters, which were distributed on two distinct phylogenetic branches, and only one clone was clustered within the Alphaproteobacteria (Figure 1)
Summary
The global biogeochemical nitrogen cycle has undergone dramatic changes in the past few decades. Anthropogenic processes, including agricultural, industrial, and domestic activities, have resulted in an unprecedented increase in environmental nitrogen release. Overloading terrestrial ecosystems with ammonium, nitrate, and nitrite as the principal nitrogen pollutants has serious negative effects on human health, biodiversity, and water quality [1]. The coupled nitrification–denitrification and nitrification–anaerobic ammonium oxidation (anammox) processes mediated by environmental microorganisms are known to play important roles in the transformation and biogeochemical cycling of nitrogen, and probably contribute to the removal of up to 50% of the external dissolved inorganic. Sci. 2019, 9, 3229 nitrogen that enters the ecosphere [2,3]. Environmental conditions (i.e., carbon or nitrogen) can significantly influence the community structures and relative abundances of microorganisms [4]
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