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Combined effects of ZnO and TiO2 nanoparticles on functional gene expression of Nitrosomonas europaea

ABSTRACT: To further explore and differentiate the biotoxicity mechanisms of individual nanoparticles (NPs) and NP mixture on Nitrosomonas europaea (N. europaea, ATCC 19718) at genetic level, a genome-sequenced model ammonia oxidizing bacterium (AOB) commonly detected in the activated sludge of biological wastewater treatment plants, the induced whole-genome expressions were analyzed with the high throughput Microarray technique, after the dose-dependent changes of N. europaea’s physiological, metabolic and AMO enzyme activities in single and dual component NP systems was evaluated.

ORGANISM(S): Nitrosomonas europaea ATCC 19718 Nitrosomonas europaea

PROVIDER: GSE70121 | GEO | 2015/06/23

SECONDARY ACCESSION(S): PRJNA287672

REPOSITORIES: GEO

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Project description:Investigation of the whole genome gene expression level changes relative to exponential phase growth in Nitrosomonas europaea ATCC19718 after 12 hours ammonia starvation, 144 hours ammonia starvation, and 20 minutes following ammonia addition to starved cells. The ammonia monooxygenase of chemolithotrophic ammonia oxidizing bacteria (AOB) catalyzes the first step in ammonia oxidation by converting ammonia to hydroxylamine. The monooxygenase of Nitrosomonas europaea is encoded by two nearly identical operon copies (amoCAB1,2). Several AOB, including N. europaea, also posess a divergent monocistronic copy of amoC (amoC3) of unknown function. Previous work suggested a possible functional role for amoC3 in N. europaea during recovery from extended ammonia starvation as part of the σE- stress response regulon during the recovery of N. europaea from extended ammonia starvation, thus indicating its importance during the exit of cells from starvation. We here used global transcription analysis to show that expression of amoC3 is part of a general post-starvation cellular response system in N. europaea. We also found that amoC3 is required for efficient exit from prolonged ammonia starvation, as deleting this gene impaired growth at elevated temperatures and recovery following starvation under high oxygen tensions. Deletion of the σ32 global stress response regulator demonstrated that the heat shock regulon also plays a significant role in mediating the recovery of N. europaea from starvation. These findings provide the first described phenotype associated with the divergent AmoC3 subunit which appears to function as a stress responsive subunit capable of maintaining ammonia oxidation activity under stress conditions. A twelve chip study using total RNA recovered from four timepoints for each of three biological replicates of wild-type cultures of Nitrosomonas europaea ATCC 19718. Total RNA was obtained from each biological culture replicate during exponential growth, following 12 hours ammonia starvation, 144 hours ammonia starvations, and 20 minutes following ammonia addition to starved cells.

Project description:Wastewater treatment plants use a variety of bioreactor types and configurations to remove organic matter and nutrients. Little is known regarding the effects of different configurations and within-plant immigration on microbial community dynamics. Previously, we found that the structure of ammonia-oxidizing bacterial (AOB) communities in a full-scale dispersed growth activated sludge bioreactor correlated strongly with levels of NO2- entering the reactor from an upstream trickling filter (Wells et al 2009). Here, to further examine this puzzling association, we profile within-plant microbial biogeography (spatial variation) and test the hypothesis that substantial microbial immigration occurs along a transect (raw influent, trickling filter biofilm, trickling filter effluent, and activated sludge) at the same full-scale wastewater treatment plant. AOB amoA gene abundance increased >30-fold between influent and trickling filter effluent concomitant with NO2- production, indicating unexpected growth and activity of AOB within the trickling filter. Nitrosomonas europaea was the dominant AOB phylotype in trickling filter biofilm and effluent, while a distinct ‘Nitrosomonas-like’ lineage dominated in activated sludge. Prior time series indicated that this ‘Nitrosomonas-like’ lineage was dominant when NO2- levels in the trickling filter effluent (i.e., activated sludge influent) were low, while N. europaea became dominant in the activated sludge when NO2- levels were high. This is consistent with the hypothesis that NO2- production may co-occur with biofilm sloughing, releasing N. europaea from the trickling filter into the activated sludge bioreactor. Phylogenetic microarray (PhyloChip) analyses revealed significant spatial variation in taxonomic diversity, including a large excess of methanogens in the trickling filter relative to activated sludge and attenuation of Enterobacteriaceae across the transect, and demonstrated transport of a highly diverse microbial community via the trickling filter effluent to the activated sludge bioreactor. Our results provide compelling evidence that substantial immigration between coupled process units occurs and may exert significant influence over microbial community dynamics within staged bioreactors.

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Combined effects of ZnO and TiO2 nanoparticles on functional gene expression of Nitrosomonas europaea

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