Survival, biofilm formation, and growth potential of environmental and enteric escherichia coli strains in drinking water microcosms

E. coli is the most commonly used indicator for faecal contamination in a drinking water distribution system (WDS). The assumption is that E. coli are of enteric origin and cannot persist for long outside their host, therefore acting as indicators of recent contamination events. This study investigates the fate of E. coli in drinking water; specifically addressing survival, biofilm formation under shear stress, and regrowth in a series of laboratory-controlled experiments. We show the extended persistence of three E. coli strains (two enteric and one soil isolate) in sterile and non-sterile drinking water microcosms, at 8 and 17°C, with T90 values ranging from 17.4 ± 1.8 to 149 ± 67.7 days, using standard plate counts and a series of (RT)-Q-PCR assays targeting 16S rRNA, tuf, uidA, and rodA genes and transcripts. Furthermore, each strain was capable of attaching to a surface and replicating to form biofilm in the presence of nutrients under a range of shear stress values (0.6, 2.0, and 4.4 dyn cm-2; BioFlux, Fluxion); however, cell numbers did not increase when drinking water was flowed over (t-test; p > 0.05). Finally, E. coli regrowth within drinking water microcosms containing PE-100 pipe-wall material was not observed in the biofilm or water phase using a combination of culturing and Q-PCR methods for E. coli. The results of this work highlight that when E. coli enters drinking water it has the potential to survive and attach to surfaces but that regrowth within drinking water or biofilm is unlikely

Organic micropollutant removal in full-scale rapid sand filters used for drinking water treatment in The Netherlands and Belgium

Biological treatment processes have the potential to remove organic micropollutants (OMPs) during water treatment. The OMP removal capacity of conventional drinking water treatment processes such as rapid sand filters (RSFs), however, has not been studied in detail. We investigated OMP removal and transformation product (TP) formation in seven full-scale RSFs all treating surface water, using high-resolution mass spectrometry based quantitative suspect and non-target screening (NTS). Additionally, we studied the microbial communities with 16S rRNA gene amplicon sequencing (NGS) in both influent and effluent waters as well as the filter medium, and integrated these data to comprehensively assess the processes that affect OMP removal. In the RSF influent, 9 to 30 of the 127 target OMPs were detected. The removal efficiencies ranged from 0 to 93%. A data-driven workflow was established to monitor TPs, based on the combination of NTS feature intensity profiles between influent and effluent samples and the prediction of biotic TPs. The workflow identified 10 TPs, including molecular structure. Microbial community composition analysis showed similar community composition in the influent and effluent of most RSFs, but different from the filter medium, implying that specific microorganisms proliferate in the RSFs. Some of these are able to perform typical processes in water treatment such as nitrification and iron oxidation. However, there was no clear relationship between OMP removal efficiency and microbial community composition. The innovative combination of quantitative analyses, NTS and NGS allowed to characterize real scale biological water treatments, emphasizing the potential of bio-stimulation applications in drinking water treatment. © 2020 The Author

Efficient chemical and microbial removal of iron and manganese in a rapid sand filter and impact of regular backwash

Aeration followed by rapid sand filtration is a common method in drinking water treatment to remove iron (Fe) and manganese (Mn) from anoxic groundwater. To ensure the successful removal of Fe and Mn within a single filter, several factors such as raw water characteristics, backwash procedures and chemical and microbial interactions with the filter medium need to be considered. Here, we assess the characteristics of a single medium rapid sand filter with highly efficient removal of Fe and Mn. Using synchrotron X-ray spectroscopy, we show that formation of ferrihydrite-type Fe oxides in the top of the filter (0–50 cm) accounts for >95 % of the removal of dissolved Fe2+ in the filter. Birnessite-type Mn- oxides, which are thought to be biogenic, form over a wider depth interval (0–110 cm). Results of 16S rRNA gene amplicon sequencing indicate a corresponding distinct vertical stratification of the microbial community, with potential iron-oxidizing Gallionella, Leptothrix and Sideroxydans dominating in the upper part of the filter, and nitrifiers being more prevalent deeper in the filter. Besides Fe and Mn-oxide, Fe-flocs and bacteriological hollow sheets form in the upper part of the filter. Both the Fe-flocs, hollow Fe-sheets and part of the Fe and Mn coatings are removed through backwashing, thereby reducing the pressure difference measured over the filter medium linked to clogging of pores (from 14 kPa to 1.5 kPa) and ensuring continued water flow. Backwashing removes part of the Gallionella, but this does not negatively impact the filter performance. Strikingly, SEM imaging with EDS mapping revealed alternating layers of Fe and Mn-oxides on the coated grains throughout the filter. This indicates slow mixing of the filter medium between the upper 30 cm and the rest of the filter during backwashing. Slow mixing likely contributes to continued success of the filter by ensuring homogeneous filter bed growth, while still allowing for stratification of the microbial community

Influence of filter age on Fe, Mn and NH4+ removal in dual media rapid sand filters used for drinking water production

Rapid sand filtration is a common method for removal of iron (Fe), manganese (Mn) and ammonium (NH4+) from anoxic groundwaters used for drinking water production. In this study, we combine geochemical and microbiological data to assess how filter age influences Fe, Mn and NH4+ removal in dual media filters, consisting of anthracite overlying quartz sand, that have been in operation for between ∼2 months and ∼11 years. We show that the depth where dissolved Fe and Mn removal occurs is reflected in the filter medium coatings, with ferrihydrite forming in the anthracite in the top of the filters ( 1 m). Removal of NH4+ occurs through nitrification in both the anthracite and sand and is the key driver of oxygen loss. Removal of Fe is independent of filter age and is always efficient (> 97% removal). In contrast, for Mn, the removal efficiency varies with filter age, ranging from 9 to 28% at ∼2–3 months after filter replacement to 100% after 8 months. After 11 years, removal reduces to 60–80%. The lack of Mn removal in the youngest filters (at 2–3 months) is likely the result of a relatively low abundance of mineral coatings that adsorb Mn2+ and provide surfaces for the establishment of a microbial community. 16S rRNA gene amplicon sequencing shows that Gallionella, which are known Fe2+ oxidizers, are present after 2 months, yet Fe2+ removal is mostly chemical. Efficient NH4+ removal (> 90%) establishes within 3 months of operation but leakage occurs upon high NH4+loading (> 160 µM). Two-step nitrification by Nitrosomonas and Candidatus Nitrotoga is likely the most important NH4+ removal mechanism in younger filters during ripening (2 months), after which complete ammonia oxidation by Nitrospira and canonical two-step nitrification occur simultaneously in older filters. Our results highlight the strong effect of filter age on especially Mn2+but also NH4+ removal. We show that ageing of filter medium leads to the development of thick coatings, which we hypothesize leads to preferential flow, and breakthrough of Mn2+. Use of age-specific flow rates may increase the contact time with the filter medium in older filters and improve Mn2+ and NH4+ removal

Use of 16S rRNA Gene Based Clone Libraries to Assess Microbial Communities Potentially Involved in Anaerobic Methane Oxidation in a Mediterranean Cold Seep

This study provides data on the diversities of bacterial and archaeal communities in an active methane seep at the Kazan mud volcano in the deep Eastern Mediterranean sea. Layers of varying depths in the Kazan sediments were investigated in terms of (1) chemical parameters and (2) DNA-based microbial population structures. The latter was accomplished by analyzing the sequences of directly amplified 16S rRNA genes, resulting in the phylogenetic analysis of the prokaryotic communities. Sequences of organisms potentially associated with processes such as anaerobic methane oxidation and sulfate reduction were thus identified. Overall, the sediment layers revealed the presence of sequences of quite diverse bacterial and archaeal communities, which varied considerably with depth. Dominant types revealed in these communities are known as key organisms involved in the following processes: (1) anaerobic methane oxidation and sulfate reduction, (2) sulfide oxidation, and (3) a range of (aerobic) heterotrophic processes. In the communities in the lowest sediment layer sampled (22–34 cm), sulfate-reducing bacteria and archaea of the ANME-2 cluster (likely involved in anaerobic methane oxidation) were prevalent, whereas heterotrophic organisms abounded in the top sediment layer (0–6 cm). Communities in the middle layer (6–22 cm) contained organisms that could be linked to either of the aforementioned processes. We discuss how these phylogeny (sequence)-based findings can support the ongoing molecular work aimed at unraveling both the functioning and the functional diversities of the communities under study

Phylogenetic and functional marker genes to study ammonia-oxidizing microorganisms (AOM) in the environment

The oxidation of ammonia plays a significant role in the transformation of fixed nitrogen in the global nitrogen cycle. Autotrophic ammonia oxidation is known in three groups of microorganisms. Aerobic ammonia-oxidizing bacteria and archaea convert ammonia into nitrite during nitrification. Anaerobic ammonia-oxidizing bacteria (anammox) oxidize ammonia using nitrite as electron acceptor and producing atmospheric dinitrogen. The isolation and cultivation of all three groups in the laboratory are quite problematic due to their slow growth rates, poor growth yields, unpredictable lag phases, and sensitivity to certain organic compounds. Culture-independent approaches have contributed importantly to our understanding of the diversity and distribution of these microorganisms in the environment. In this review, we present an overview of approaches that have been used for the molecular study of ammonia oxidizers and discuss their application in different environments

Amino acid absorption in the large intestine of humans and porcine models

Dietary protein quality has been recognized as a critical issue by international authorities because it can affect important functions of the body. To predict protein quality, the FAO introduced the Digestible Indispensable Amino Acid Score. This score depends on ileal amino acid (AA) digestibility; therefore, the assumption is made that AAs are not absorbed in nutritionally relevant amounts from the large intestine. This article reviews the evidence for this assumption by considering the role of themammalian large intestine in dietary protein and AA digestion and absorption,with particular reference to adult humans. Althoughmost dietary AAs and peptides are absorbed in the small intestine, substantial amounts can enter the large intestine. Nitrogen is absorbed in the large intestine, and a series of animal experiments indicate a potential small degree of AA absorption. In humans, colonocytes have the capacity for AA absorption because AA transporters are present in the large intestine. The absorption of nutritionally relevant amounts of dietary indispensable AAs and peptides in the human large intestine has not been convincingly demonstrated, however