Project description:Nitrification, the oxidation of ammonia via nitrite to nitrate, has always been considered to be a two-step process catalysed by chemolithoautotrophic microorganisms oxidizing either ammonia or nitrite. No known nitrifier carries out both steps, although complete nitrification should be energetically advantageous. This functional separation has puzzled microbiologists for a century. Here we report on the discovery and cultivation of a completely nitrifying bacterium from the genus Nitrospira, a globally distributed group of nitrite oxidizers. The genome of this chemolithoautotrophic organism encodes the pathways both for ammonia and nitrite oxidation, which are concomitantly activated during growth by ammonia oxidation to nitrate. Genes affiliated with the phylogenetically distinct ammonia monooxygenase and hydroxylamine dehydrogenase genes of Nitrospira are present in many environments and were retrieved on Nitrospira contigs in new metagenomes from engineered systems. These findings fundamentally change our picture of nitrification and point to completely nitrifying Nitrospira as key components of nitrogen-cycling microbial communities.
Project description:Nitrospira are chemolithoautotrophic nitrite-oxidizing bacteria that catalyze the second step of nitrification in most oxic habitats and are important for excess nitrogen removal from sewage in wastewater treatment plants (WWTPs). To date, little is known about their diversity and ecological niche partitioning within complex communities. In this study, the fine-scale community structure and function of Nitrospira was analyzed in two full-scale WWTPs as model ecosystems. In Nitrospira-specific 16S rRNA clone libraries retrieved from each plant, closely related phylogenetic clusters (16S rRNA identities between clusters ranged from 95.8% to 99.6%) within Nitrospira lineages I and II were found. Newly designed probes for fluorescence in situ hybridization (FISH) allowed the specific detection of several of these clusters, whose coexistence in the WWTPs was shown for prolonged periods of several years. In situ ecophysiological analyses based on FISH, relative abundance and spatial arrangement quantification, as well as microautoradiography revealed functional differences of these Nitrospira clusters regarding the preferred nitrite concentration, the utilization of formate as substrate and the spatial coaggregation with ammonia-oxidizing bacteria as symbiotic partners. Amplicon pyrosequencing of the nxrB gene, which encodes subunit beta of nitrite oxidoreductase of Nitrospira, revealed in one of the WWTPs as many as 121 species-level nxrB operational taxonomic units with highly uneven relative abundances in the amplicon library. These results show a previously unrecognized high diversity of Nitrospira in engineered systems, which is at least partially linked to niche differentiation and may have important implications for process stability.
Project description:Nitrification, the oxidation of ammonia via nitrite to nitrate, has always been considered to be a two-step process catalysed by chemolithoautotrophic microorganisms oxidizing either ammonia or nitrite. No known nitrifier carries out both steps, although complete nitrification should be energetically advantageous. This functional separation has puzzled microbiologists for a century. Here we report on the discovery and cultivation of a completely nitrifying bacterium from the genus Nitrospira, a globally distributed group of nitrite oxidizers. The genome of this chemolithoautotrophic organism encodes the pathways both for ammonia and nitrite oxidation, which are concomitantly activated during growth by ammonia oxidation to nitrate. Genes affiliated with the phylogenetically distinct ammonia monooxygenase and hydroxylamine dehydrogenase genes of Nitrospira are present in many environments and were retrieved on Nitrospira-contigs in new metagenomes from engineered systems. These findings fundamentally change our picture of nitrification and point to completely nitrifying Nitrospira as key components of nitrogen-cycling microbial communities.
Project description:Wastewater treatment plants in temperate climate zones frequently undergo seasonal nitrification failure in the winter month yet maintain removal efficiency for other contaminants. We tested the hypothesis that nitrification failure can be correlated to shifts in the nitrifying microbial community. We monitored three parallel, full-scale sequencing batch reactors over the course of a year with respect to reactor performance, microbial community composition via 16S rRNA gene amplicon sequencing, and functional gene abundance using qPCR. All reactors demonstrated similar changes to their core microbiome, and only subtle variations among seasonal and transient taxa. We observed a decrease in species richness during the winter, with a slow recovery of the activated sludge community during spring. Despite the change in nitrification performance, ammonia monooxygenase gene abundances remained constant throughout the year, as did the relative sequence abundance of Nitrosomonadacae. This suggests that nitrification failure at colder temperatures might result from different reaction kinetics of nitrifying taxa, or that other organisms with strong seasonal shifts in population abundance, e.g. an uncultured lineage of Saprospiraceae, affect plant performance in the winter. This research is a comprehensive analysis of the seasonal microbial community dynamics in triplicate full-scale sequencing batch reactors and ultimately strengthens our basic understanding of the microbial ecology of activated sludge communities by revealing seasonal succession patterns of individual taxa that correlate with nutrient removal efficiency.
Project description:Nitrification, the oxidation of ammonia via nitrite to nitrate, has been considered to be a stepwise process mediated by two distinct functional groups of microorganisms. The identification of complete nitrifying Nitrospira challenged not only the paradigm of labor division in nitrification, it also raises fundamental questions regarding the environmental distribution, diversity, and ecological significance of complete nitrifiers compared to canonical nitrifying microorganisms. Recent genomic and physiological surveys identified factors controlling their ecology and niche specialization, which thus potentially regulate abundances and population dynamics of the different nitrifying guilds. This review summarizes the recently obtained insights into metabolic differences of the known nitrifiers and discusses these in light of potential functional adaptation and niche differentiation between canonical and complete nitrifiers.
Project description:Candidatus Saccharibacteria is a well-described candidate phylum that has not been successfully isolated. Nevertheless, its presence was suggested by 16S rRNA gene sequencing data, and it is frequently detected in natural environments and activated sludge. Because pure culture representatives of Candidatus Saccharibacteria are lacking, the specificity of primers for the determination of their abundance and diversity should be carefully evaluated. In this study, eight Candidatus Saccharibacteria-specific primers were selected from previous studies and evaluated for their coverage against a public database, annealing temperature of the combined primer sets, as well as their utilization to determine the detection frequencies and phylogenetic diversity by cloning analysis, and in quantification by quantitative polymerase chain reaction (PCR). Among the eight primers, four primers (TM7314F, TM7580F, TM7-910R, and TM7-1177R) showed high coverage. Cloning analysis showed that four primer sets (TM7314F and TM7-910R, TM7314F and TM7-1177R, TM7580F and TM7-910R, and TM7580F and TM7-1177R) yielded high detection frequencies for Candidatus Saccharibacteria in activated sludge from a wastewater treatment plant in Higashihiroshima City, Japan. Quantitative PCR results indicated that the primer set containing TM7314F and TM7-910R was superior for the specific detection of Candidatus Saccharibacteria in activated sludge.