Biology subjects

Corbera-Rubio, F.

Publications and source records attributed to Corbera-Rubio, F..

5 recordsLinked to original sources

bioRxiv2024

A difficult coexistence: resolving the iron-induced nitrification delay in groundwater filters

Rapid sand filters (RSF) are an established and widely applied technology for the removal of dissolved iron (Fe2+) and ammonium (NH +) in groundwater treatment. Most often, biological NH + oxidation is delayed and starts only upon complete Fe2+ depletion. However, the mechanism(s) responsible for the inhibition of NH + oxidation by Fe2+ or its oxidation (by)products remains elusive, hindering further process control and optimization. We used batch assays, lab-scale columns, and full-scale filter characterizations to resolve the individual impact of the main Fe2+ oxidizing mechanisms and the resulting products on biological NH + oxidation. Modelling of the obtained datasets allowed to quantitatively assess the hydraulic implications of Fe2+ oxidation. Dissolved Fe2+ and the reactive oxygen species formed as byproducts during Fe2+ oxidation had no direct effect on nitrification. The Fe3+ oxides on the sand grain coating, commonly assumed to be the main cause for inhibited nitrification, seemed instead to enhance nitrification by providing additional surface area for biofilm growth. Modelling allowed to exclude mass transfer limitations induced by accumulation of iron flocs and consequent filter clogging as the cause for delayed nitrification. We unequivocally identify the inhibition of NH +oxidizing organisms by the Fe3+ flocs generated during Fe2+ oxidation as the main cause for the commonly observed nitrification delay. The addition of Fe3+ flocs inhibited NH + oxidation both in batch and column tests, and the removal of Fe3+ flocs by backwashing completely re-established the NH + removal capacity, suggesting that the inhibition is reversible. In conclusion, our findings not only identify the iron form that causes the inhibition, albeit the biological mechanism remains to be identified, but also highlight the ecological importance of iron cycling in nitrifying environments. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/581000v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@65ca28org.highwire.dtl.DTLVardef@bb3da3org.highwire.dtl.DTLVardef@cbd32dorg.highwire.dtl.DTLVardef@1956207_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightO_LIDissolved Fe2+ and reactive oxygen species do not affect NH + oxidation C_LIO_LIFe oxide coating aids sand grain colonization by NH +-oxidizing bacteria C_LIO_LIFe3+ flocs inhibit NH + oxidation by reducing the nitrifying capacity of AOB C_LIO_LIChanges in transport patterns due to clogging do not play a major role in NH + oxidation C_LIO_LIThe inhibition of NH4+ oxidation is reversible and reduced by backwashing C_LI

microbiology↗

bioRxiv2024

Shifting to biology promotes highly efficient iron removal in groundwater filters

Rapid sand filters are established and widely applied technologies for groundwater treatment. Conventionally, intensive aeration is employed to provide oxygen for the oxidation and removal of the main groundwater contaminants. While effective, intensive aeration promotes flocculent iron removal, which results in iron flocs that rapidly clog the filter. In this study, we operated two parallel full-scale sand filters at different aeration intensities to resolve the relative contribution of homogeneous, heterogeneous and biological iron removal pathways, and identify their operational controls. Our results show that mild aeration in the LOW filter (5 mg/L O2pH 6.9) promoted biological iron removal and enabled iron oxidation at twice the rate compared to the intensively aerated HIGH filter (>10mg/L O2,pH 7.4). ESEM images showed distinctive twisted stalk-like Fe solids, biosignatures of Gallionella ferruginea, both in the LOW filter sand coatings as well as in its backwash solids. In accordance, 10 times higher DNA copy numbers of G. ferruginea were found in the LOW filter effluent. Clogging by biogenic FeOx was slower than by chemical FeOx flocs, resulting in lower backwash frequencies and yielding four times more water per run. Ultimately, our results reveal that biological Fe2+ oxidation can be actively controlled and favoured over competing physico-chemical routes. The resulting operational benefits are only starting to be appreciated, with the counterintuitive higher oxidation rates and water yields at lower aeration regimes, and the production of more compact and practically valuable FeOx solids being of outmost interest.

microbiology↗

bioRxiv2023

"Candidatus Siderophilus nitratireducens": a psychrophilic, nap-dependent nitrate-reducing iron oxidizer within the new order Siderophiliales

Nitrate leaching from agricultural soils is increasingly found in groundwater, a primary source of drinking water worldwide. This nitrate influx can potentially stimulate the biological oxidation of iron in anoxic groundwater reservoirs. Nitrate-reducing iron-oxidizing (NRFO) bacteria have been extensively studied in laboratory settings, yet their ecophysiology in natural environments remains largely unknown. To this end, we established a pilot-scale filter on nitrate-rich groundwater to elucidate the structure and metabolism of nitrate-reducing iron-oxidizing microbiomes under oligotrophic conditions mimicking natural groundwaters. The enriched community stoichiometrically removed iron and nitrate consistently with NRFO metabolism. Genome-resolved metagenomics revealed the underlying metabolic network between the dominant iron-dependent denitrifying autotrophs and the less abundant organoheterotrophs. The most abundant genome belonged to a new Candidate order, named Siderophiliales. This new species, "Candidatus Siderophilus nitratireducens", carries central genes to iron oxidation (cytochrome c cyc2), carbon fixation (rbc), and for the sole periplasmic nitrate reductase (nap). To our knowledge, this is the first report of nap-based lithoautotrophic growth, and we demonstrate that iron oxidation coupled to dissimilatory reduction of nitrate to nitrite is thermodynamically favourable under realistic Fe3+/Fe2+ and [Formula] concentration ratios. Ultimately, by bridging the gap between laboratory investigations and real-world conditions, this study provides insights into the intricate interplay between nitrate and iron in groundwater ecosystems, and expands our understanding of NRFOs taxonomic diversity and ecological role.

microbiology↗

bioRxiv2022

Microbiome, resistome and mobilome of chlorine-free drinking water treatment systems

Drinking water treatment plants (DWTPs) are designed to remove physical, chemical, and biological contaminants. However, until recently, the role of DWTPs in minimizing the cycling of antibiotic resistance determinants has got limited attention. In particular, the risk of selecting antibiotic-resistant bacteria (ARB) is largely overlooked in chlorine-free DWTPs where biological processes are applied. Here, we combined high-throughput quantitative PCR and metagenomics to analyze the abundance and dynamics of microbial communities, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs) across the treatment trains of two chlorine-free DWTPs involving dune-based and reservoir-based systems. The microbial diversity of the water being treated increased after all biological unit operations, namely rapid and slow sand filtration (SSF), and granular activated carbon filtration. Both DWTPs reduced the concentration of ARGs and MGEs in the water by about 2.5 log gene copies mL-1, despite their relative increase in the disinfection sub-units (SSF in dune-based and UV treatment in reservoir-based DWTPs). The total microbial concentration was also reduced (2.5 log units), and none of the DWTPs were enriched for antibiotic resistant bacteria. Our findings highlight the effectiveness of chlorine-free DWTPs in supplying safe drinking water while reducing the concentration of antibiotic resistance determinants. To the best of our knowledge, this is the first study that monitors the presence and dynamics of antibiotic resistance determinants in chlorine-free DWTPs.

microbiology↗

bioRxiv2022

Meta-omics profiling of full-scale groundwater rapid sand filters explains stratification of iron, ammonium and manganese removals

Rapid sand filters (RSF) are an established and widely applied technology for groundwater treatment. Yet, the underlying interwoven biological and physical-chemical reactions controlling the sequential removal of iron, ammonia and manganese remain poorly understood. To resolve the contribution and interactions between the individual reactions, we studied two full-scale drinking water treatment plant configurations, namely (i) one dual-media (anthracite and quartz sand) filter and (ii) two single-media (quartz sand) filters in series. In situ and ex situ activity tests were combined with mineral coating characterization and metagenome-guided metaproteomics along the depth of each filter. Both plants exhibited comparable performances and process compartmentalization, with most of ammonium and manganese removal occurring only after complete iron depletion. Within each compartment, the homogeneity of the media coating and genome-based microbial composition highlighted the effect of backwashing on filter media mixing. In stark contrast, intra-compartment contaminant removal was highly stratified following decreasing substrate availability along the filter height. This apparent and long-standing conflict was resolved by quantifying the expressed proteome at different filter heights, revealing a consistent stratification of proteins catalysing ammonia oxidation and protein-based relative abundances of nitrifying genera. This implies that microorganisms adapt their protein pool to the available nutrient load at a faster rate than the backwash mixing frequency. Ultimately, these results show the unique and complementary potential of metaproteomics to understand metabolic adaptations and interactions in highly dynamic ecosystems.

microbiology↗