Colonization kinetics and implantation follow-up of the sewage microbiome in an urban wastewater treatment plant.

The Seine-Morée wastewater treatment plant (SM_WWTP), with a capacity of 100,000 population-equivalents, was fed with raw domestic wastewater during all of its start-up phase. Its microbiome resulted from the spontaneous evolution of wastewater-borne microorganisms. This rare opportunity allowed us to analyze the sequential microbiota colonization and implantation follow up during the start-up phase of this WWTP by means of regular sampling carried out over 8 months until the establishment of a stable and functional ecosystem. During the study, biological nitrification-denitrification and dephosphatation occurred 68 days after the start-up of the WWTP, followed by flocs decantation 91 days later. High throughput sequencing of 18S and 16S rRNA genes was performed using Illumina's MiSeq and PGM Ion Torrent platforms respectively, generating 584,647 16S and 521,031 18S high-quality sequence rDNA reads. Analyses of 16S and 18S rDNA datasets show three colonization phases occurring concomitantly with nitrification, dephosphatation and floc development processes. Thus, we could define three microbiota profiles that sequentially colonized the SM_WWTP: the early colonizers, the late colonizers and the continuous spectrum population. Shannon and inverse Simpson diversity indices indicate that the highest microbiota diversity was reached at days 133 and 82 for prokaryotes and eukaryotes respectively; after that, the structure and complexity of the wastewater microbiome reached its functional stability. This study demonstrates that physicochemical parameters and microbial metabolic interactions are the main forces shaping microbial community structure, gradually building up and maintaining a functionally stable microbial ecosystem.

Uranium(VI) Scavenging by Amorphous Iron Phosphate Encrusting Sphaerotilus natans Filaments.

U(VI) sorption to iron oxyhydroxides, precipitation of phosphate minerals, as well as biosorption on bacterial biomass are among the most reported processes able to scavenge U(VI) under oxidizing conditions. Although phosphates significantly influence bacterially mediated as well as iron oxyhydroxide mediated scavenging of uranium, the sorption or coprecipitation of U(VI) with poorly crystalline nanosized iron phosphates has been scarcely documented, especially in the presence of microorganisms. Here we show that dissolved U(VI) can be bound to amorphous iron phosphate during their deposition on Sphaerotilus natans filamentous bacteria. Uranium LIII-edge EXAFS analysis reveals that the adsorbed uranyl ions share an equatorial oxygen atom with a phosphate tetrahedron of the amorphous iron phosphate, with a characteristic U-P distance of 3.6 Å. In addition, the uranyl ions are connected to FeO6 octahedra with U-Fe distances at ~3.4 Å and at ~4.0 Å. The shortest U-Fe distance corresponds to a bidentate edge-sharing complex often reported for uranyl adsorption onto iron oxyhydroxides, whereas the longest U-Fe and U-P distances can be interpreted as a bidentate corner-sharing complex, in which two adjacent equatorial oxygen atoms are shared with the vertices of a FeO6 octahedron and of a phosphate tetrahedron. Furthermore, based on these sorption reactions, we demonstrate the ability of an attached S. natans biofilm to remove uranium from solution without any filtration step.

Moderate oxygen depletion as a factor favouring the filamentous growth of Sphaerotilus natans.

Sphaerotilus natans is a neutrophilic iron-related sheath-forming filamentous microorganism that presents dual morphotype: single cells and ensheathed cells forming filaments. As S. natans has been proposed as a sorbent for inorganic pollutants and it is occasionally involved in bulking episodes, elucidating factors affecting its filamentous growth is of crucial interest. The purpose of this work was to evaluate the effect of dissolved oxygen (DO) as a factor affecting S. natans filamentation from single cells. A method to quantify S. natans in its filamentous and single-cell morphotypes, based on a differential filtration procedure coupled with quantitative real-time PCR, was developed here. Scanning Electron Microscopy was used to validate the filtration step. Under actively aerated conditions (DO maintained at 7.6 ± 0.1 mg l(-1)), S. natans grew mainly as single cells throughout the experiment, while a depletion in DO concentration (to ~3 mg l(-1)) induced its filamentous growth. Indeed, when oxygen was reduced the proportion of single cells diminished from 83.3 ± 5.9 to 14.3 ± 3.4% while the filaments increased from 16.7 ± 5.9 to 85.7 ± 3.4%. Our results suggest that oxygen plays a key role in S. natans filamentation and contribute to better understanding of the filamentous proliferation of this bacterium. In addition, the proposed method will be helpful to evaluate other factors favouring filamentous growth.

Impact of the repetition of oxygen deficiencies on the filamentous bacteria proliferation in activated sludge.

Cases of low stress can frequently occur in a wastewater treatment plant (WWTP). As they have no visible impact on the plant operation, they generally go unnoticed. Nevertheless, it would appear that an accumulation of such cases can result in serious operational problems. The impact of the repeated application of oxygen deficiency on the proliferation of the filamentous bacteria Sphaerotilus natans, Haliscomenobacter hydrossis, Eikelboom type 021N and Thiothrix spp has been studied on WWTP pilots. Two different oxygen deficiencies series were tested. Filamentous bacteria evolution in activated sludge was monitored using fluorescent in situ hybridization. For the weak deficiencies, no significant variation in the filamentous bacteria response level was recorded, whereas with more severe deficiencies the filamentous bacteria response increased considerably with the increase in stress number. From the results obtained, it would appear that there is an intensity and frequency threshold beyond which the filamentous bacteria response levels increase when the stress is applied in series. This "oxygen deficiencies repetition" appears to be an important factor in the appearance of bulking.