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The molecular mechanisms of microbial adaptation to repeated anoxic-aerobic cycling were investigated by integrating whole community gene expression (metatranscriptomics) and physiological responses, including the production of nitric (NO) and nitrous (N2O) oxides. Anoxic-aerobic cycling was imposed for 17 days in a lab-scale full-nitrification mixed culture system. Prior to cycling, NO and N2O levels were sustained at 0.097 ± 0.006 and 0.054 ± 0.019 ppmv, respectively. Once the anoxic-aerobic cycling was initiated, peak emissions were highest on the first day (9.8 and 1.3 ppmv, respectively). By the end of day 17, NO production returned to pre-cycling levels (a peak of 0.12 ± 0.007 ppmv), while N2O production reached a new baseline (a peak of 0.32 ± 0.05 ppmv), one order of magnitude higher than steady-state conditions. Concurrently, post-cycling transcription of norBQ and nosZ returned to pre-cycling levels after an initial 5.7- and 9.5-fold increase, while nirK remained significantly expressed (1.6-fold) for the duration of and after cycling conditions. The imbalance in nirK and nosZ mRNA abundance coupled with continuous conversion of NO to N2O might explain the elevated post-cycling baseline for N2O. Metatranscriptomic investigation notably indicated possible NO production by NOB under anoxic-aerobic cycling through a significant increase in nirK expression. Opposing effects on AOB (down-regulation) and NOB (up-regulation) CO2 fixation were observed, suggesting that nitrifying bacteria are differently impacted by anoxic-aerobic cycling. Genes encoding the terminal oxidase of the electron transport chain (ccoNP, coxBC) were the most significantly transcribed, highlighting a hitherto unexplored pathway to manage high electron fluxes resulting from increased ammonia oxidation rates, and leading to overall, increased NO and N2O production. In sum, this study identified underlying metabolic processes and mechanisms contributing to NO and N2O production through a systems-level interrogation, which revealed the differential ability of specific microbial groups to adapt to sustained operational conditions in engineered biological nitrogen removal processes.
Pubmed ID: 30574136
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Database of biological data related to a single initiative, originating from a single organization or from a consortium. A BioProject record provides users a single place to find links to the diverse data types generated for that project. It is a searchable collection of complete and incomplete (in-progress) large-scale sequencing, assembly, annotation, and mapping projects for cellular organisms. Submissions are supported by a web-based Submission Portal. The database facilitates organization and classification of project data submitted to NCBI, EBI and DDBJ databases that captures descriptive information about research projects that result in high volume submissions to archival databases, ties together related data across multiple archives and serves as a central portal by which to inform users of data availability. BioProject records link to corresponding data stored in archival repositories. The BioProject resource is a redesigned, expanded, replacement of the NCBI Genome Project resource. The redesign adds tracking of several data elements including more precise information about a project''''s scope, material, and objectives. Genome Project identifiers are retained in the BioProject as the ID value for a record, and an Accession number has been added. Database content is exchanged with other members of the International Nucleotide Sequence Database Collaboration (INSDC). BioProject is accessible via FTP.
View all literature mentionsSequence assembler and mapper for whole genome shotgun and EST/RNASeq sequencing data.
View all literature mentionsAn open-source software package for describing and comparing microbial communities. It incorporates the functionality of a number of computational tools, calculators, and visualization tools.
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