Additive and competitive effects of bacteria and Mn oxides on arsenite oxidation kinetics

Efficacy of yellow gypsum application on mitigating arsenic bioavailability in groundnut and Boro-rice grown under arsenic contaminated soil

Agricultural soils naturally enriched with Arsenic (As) represent a significant global human health risk. In the present investigation, a series of pot experiments were conducted to study the efficacy of three levels of Yellow Gypsum (YG) application on bioavailability of As to kharif groundnut followed by boro-rice grown under 17 different levels of soil As contamination for two consecutive years. The results revealed that application of YG @ 60 kg ha-1 effectuated the lowest soil As content and the highest percent decline in soil extractable As at pegging (9.42 mg kg-1 and 9.81%) and harvesting (8.81 mg kg-1 and 11.85%) in groundnut, maximum tillering (7.52 mg kg-1 and 16.95%) and harvesting (6.77 mg kg-1 and 19.85%) in boro-rice respectively. It was also observed that irrespective of its level, the extractable As content of soil decreased significantly (P < 0.05) with increasing dosage of YG. Increase in YG dose effectuated a significant (P < 0.05) increasing trend and increase in As content in soil indicated a decreasing trend of Ca:As, Fe:As and S:As ratios which pointed out the potentiality of YG for reducing As bio-availability in contaminated soils and thus could be a good option for mitigating the risk of As contamination in food chain.

Remediation of arsenic-contaminated paddy field by a new iron oxidizing strain (Ochrobactrum sp.) and iron-modified biochar

Iron-oxidizing strain (FeOB) and iron modified biochars have been shown arsenic (As) remediation ability in the environment. However, due to the complicated soil environment, few field experiment has been conducted. The study was conducted to investigate the potential of iron modified biochar (BC-FeOS) and biomineralization by a new found FeOB to remediate As-contaminated paddy field. Compared with the control, the As contents of G_B (BC-FeOS), G_F (FeOB), G_FN (FeOB and nitrogen fertilizer), G_BF (BC-FeOS and FeOB) and G_BFN (BC-FeOS, FeOB and nitrogen fertilizer) treatments in pore water decreased by 36.53%-80.03% and the microbial richness of iron-oxidizing bacteria in these treatments increased in soils at the rice maturation stage. The concentrations of available As of G_B, G_F, G_FN, G_BF and G_BFN at the tillering stage were significantly decreased by 10.78%-55.48%. The concentrations of nonspecifically absorbed and specifically absorbed As fractions of G_B, G_F, G_FN, G_BF and G_BFN in soils were decreased and the amorphous and poorly crystalline hydrated Fe and Al oxide-bound fraction was increased. Moreover, the As contents of G_B, G_F, G_FN, G_BF and G_BFN in rice grains were significantly decreased (*P < 0.05) and the total As contents of G_FN, G_BF and G_BFN were lower than the standard limit of the National Standard for Food Safety (GB 2762-2017). Compared with the other treatments, G_BFN showed the greatest potential for the effective remediation of As-contaminated paddy fields.

Improved grain yield and lowered arsenic accumulation in rice plants by inoculation with arsenite-oxidizing Achromobacter xylosoxidans GD03

Arsenite is the predominant arsenic species in flooded paddy soil, and arsenite bioaccumulation in rice grains has been identified as a major problem in many Asian countries. Lowering arsenite level in rice plants and grain via accelerating arsenite oxidation is a potential strategy to help populations, who depended on rice consumption, to reduce the internal exposure level of arsenic. We herein isolated a strain, Achromobacter xylosoxidans GD03, with the high arsenite-oxidizing ability and plant growth-promoting traits. We observed that arsenite exposure could promote A. xylosoxidans GD03 to excrete indole-3-acetic acid and thus promoted rice growth. The pot culture experiments of Indica rice cultivar Guang You Ming 118 (GYM118) demonstrated that A. xylosoxidans GD03 inoculation of paddy soil (4.5-180 × 10⁸ CFU GD03/kg soil) significantly accelerated arsenite oxidation in flooded soil. The daily arsenic oxidation rate with GD03 inoculation was 1.5-3.3 times as that without strain GD03 inoculation within the whole growth period of Indica GYM118 in the presence of the native microflora. It thus led to a 34-69%, 43-74%, 24-76% and 35-57% decrease in arsenite concentration of the stems, leaves, bran and grain of Indica GYM118 respectively and a 59-96% increase in rice grain yield. The paddy soil inoculated with 40.0 mL/kg of A. xylosoxidans GD03 resulted in a lowest As(III) concentrations in all rice organs of Indica GYM118, which equivalent to only 24-50% of the As(III) concentrations in the group without GD03 inoculation. The results highlight that a highly arsenite-oxidizing bacterium could accelerate arsenite oxidation of paddy soil when facing competition with the native microflora, thus decrease arsenic toxicity and bioavailable soil arsenic.

Aggregation Kinetics of Manganese Oxides Formed from permanganate activated by (Bi)sulfite: Dual Role of Ca2+ and MnII/III

Aqueous aggregation kinetics of manganese oxides, the solid products formed during water treatment and subsurface remediation with permanganate, are crucial for its application. In this study, manganese oxides nanoparticles were in situ formed in a permanganate/(bi)sulfite system, which was found to have excellent oxidation ability. Aggregation kinetics of such manganese oxides (i.e., MnO_x-1.5, MnO_x-2.5 and MnO_x-5; the number represents the molar ratio of (bi)sulfite to permanganate) were evaluated by employing time-resolved dynamic light scattering under various aquatic conditions. In NaNO₃ solution, the stability of manganese oxides decreased in the order of MnO_x-1.5 > MnO_x-2.5 > MnO_x-5, indicated by their critical coagulation concentrations (CCCs). X-ray photoelectron spectroscopy (XPS) and zeta potential measurements indicated that Mn^II/III were responsible for the decreased stability due to their charge neutralization effects. However, in Ca(NO₃)₂ solution, three manganese oxides had similar CCCs, probably due to the relatively great charge neutralization ability of Ca²⁺. Suwannee River fulvic acid (SRFA), through electrosteric interaction, suppressed the aggregation of MnO_x-1.5 in Ca(NO₃)₂ solution, but had no such effect in NaNO₃ solution. Comparatively, the stability of MnO_x-5 was markedly enhanced with SRFA in NaNO₃ solutions. It was proposed that Ca²⁺ and Mn^II/III could increase the adsorption of SRFA through charge neutralization and cation bridging. This study highlights the dual role, dependent on either presence or absence of SRFA, of Ca²⁺ and Mn^II/III in controlling the aggregation of manganese oxides nanoparticles.

Effect of supernatant water level on As removal in biological rapid sand filters

Current groundwater treatment facilities, mostly relying on aeration-filtration configurations, aim at the removal of iron (Fe), ammonia (NH₄ ⁺) and manganese (Mn). However, recently water companies expressed the ambition to also reduce arsenic (As) concentrations in these rapid sand filters. The aim of this study was to investigate the effect of the Fe oxidation state entering a biological filter bed on As removal. By varying supernatant water level, either Fe(II) or Fe(III) in the form of hydrous ferric oxides (HFO) could be stimulated to enter the filter bed at alkaline groundwater pH (7.6). The experimental pilot column filters showed that once the As(III) oxidation stabilised in the top layer of the filter sand, As removal reached its maximum (±75% at 120 cm supernatant level and 1.5 m/h filtration velocity). The increase in supernatant level from 5 to 120 cm resulted in additional HFO production prior to rapid filtration (1.5, 5 and 10 m/h), i.e. homogeneous Fe(II) oxidation and flocculation, and subsequently, HFO ending up deeper into the filter bed (120 cm filter depth). At a low supernatant water level of 5 cm, Fe(II) oxidised heterogeneously and was removed within the top 20 cm of the filter bed. Consequently, filters with high supernatant levels removed As to lower levels (by 20%) than in filters with low supernatant water levels. The benefits of Fe(II) oxidation prior to filtration for As removal was confirmed by comparing Fe(III) to Fe(II) additions in the supernatant water or in the filter bed. Overall it is concluded that in biological groundwater filters, the combination of a higher supernatant level and/or Fe(III) addition with biological As(III) oxidation in the top of the filter bed promotes As removal.

Phylogenetic Structure and Metabolic Properties of Microbial Communities in Arsenic-Rich Waters of Geothermal Origin

Arsenic (As) is a toxic element released in aquatic environments by geogenic processes or anthropic activities. To counteract its toxicity, several microorganisms have developed mechanisms to tolerate and utilize it for respiratory metabolism. However, still little is known about identity and physiological properties of microorganisms exposed to natural high levels of As and the role they play in As transformation and mobilization processes. This work aims to explore the phylogenetic composition and functional properties of aquatic microbial communities in As-rich freshwater environments of geothermal origin and to elucidate the key microbial functional groups that directly or indirectly may influence As-transformations across a natural range of geogenic arsenic contamination. Distinct bacterial communities in terms of composition and metabolisms were found. Members of Proteobacteria, affiliated to Alpha- and Betaproteobacteria were mainly retrieved in groundwaters and surface waters, whereas Gammaproteobacteria were the main component in thermal waters. Most of the OTUs from thermal waters were only distantly related to 16S rRNA gene sequences of known taxa, indicating the occurrence of bacterial biodiversity so far unexplored. Nitrate and sulfate reduction and heterotrophic As(III)-oxidization were found as main metabolic traits of the microbial cultivable fraction in such environments. No growth of autotrophic As(III)-oxidizers, autotrophic and heterotrophic As(V)-reducers, Fe-reducers and oxidizers, Mn-reducers and sulfide oxidizers was observed. The ars genes, involved in As(V) detoxifying reduction, were found in all samples whereas aioA [As(III) oxidase] and arrA genes [As(V) respiratory reductase] were not found. Overall, we found that As detoxification processes prevailed over As metabolic processes, concomitantly with the intriguing occurrence of novel thermophiles able to tolerate high levels of As.

Hotspots for selected metal elements and microbes accumulation and the corresponding water quality deterioration potential in an unchlorinated drinking water distribution system

Biofilm formation, loose deposit accumulation and water quality deterioration in drinking water distribution systems have been widely reported. However, the accumulation and distribution of harbored elements and microbes in the different niches (loose deposits, PVC-U biofilm, and HDPE biofilm) and their corresponding potential contribution to water quality deterioration remain unknown. This precludes an in-depth understanding of water quality deterioration and the development of proactive management strategies. The present study quantitatively evaluated the distribution of elements, ATP, Aeromonas spp., and bacterial communities in distribution pipes (PVC-U, D = 110 mm, loose deposit and biofilm niches) and household connection pipes (HDPE, D = 32 mm, HDPE biofilm niches) at ten locations in an unchlorinated distribution system. The results show that loose deposits in PVC-U pipes, acting as sinks, constitute a hotspot (highest total amount per meter pipe) for elements, ATP, and target bacteria groups (e.g., Aeromonas spp., Mycobacterium spp., and Legionella spp.). When drinking water distribution system niches with harbored elements and microbes become sources in the event of disturbances, the highest quality deterioration potential (QDP) is that of HDPE biofilm; this can be attributed to its high surface-to-volume ratio. 16s rRNA analysis demonstrates that, at the genus level, the bacterial communities in the water, loose deposits, PVC-U biofilm, and HDPE biofilm were dominated, respectively, by Polaromonas spp. (2-23%), Nitrosipra spp. (1-47%), Flavobacterium spp. (1-36%), and Flavobacterium spp. (5-67%). The combined results of elemental composition and bacterial community analyses indicate that different dominant bio-chemical processes might occur within the different niches-for example, iron-arsenic oxidizing in loose deposits, bio-calumniation in PVC-U biofilm, and methane oxidizing in HDPE biofilm. The release of 20% loose deposits, 20% PVC-U biofilm and 10% HDPE biofilm will cause significant changes of water bacterial community.

A mesoporous titanium glycolate with exceptional adsorption capacity to remove multiple heavy metal ions in water

A facile, green strategy is explored to obtain mesoporous titanium glycolate (Ti(OCH₂CH₂O)₂) via a one-pot hydrothermal reaction.

Effects of Manganese Oxide on Arsenic Reduction and Leaching from Contaminated Floodplain Soil

Reductive release of the potentially toxic metalloid As from Fe(III) (oxyhydr)oxides has been identified as an important process leading to elevated As porewater concentrations in soils and sediments. Despite the ubiquitous presence of Mn oxides in soils and their oxidizing power toward As(III), their impact on interrelated As, Fe, and Mn speciation under microbially reducing conditions remains largely unknown. For this reason, we employed a column setup and X-ray absorption spectroscopy to investigate the influence of increasing birnessite concentrations (molar soil Fe-to-Mn ratios: 4.8, 10.2, and 24.7) on As speciation and release from an As-contaminated floodplain soil (214 mg As/kg) under anoxic conditions. Our results show that birnessite additions significantly decreased As leaching. The reduction of both As and Fe was delayed, and As(III) accumulated in birnessite-rich column parts, indicating the passivation of birnessite and its transformation products toward As(III) oxidation and the precipitation of Fe(III)(oxyhydr)oxides. Microbial Mn reduction resulted in elevated soil pH values, which in turn lowered the microbial activity in the birnessite-enriched soil. We conclude that in Mn-oxide-rich soil environments undergoing redox fluctuations, the enhanced As adsorption to newly formed Fe(III) (oxyhydr)oxides under reducing conditions leads to a transient stabilization of As.

Arsenic redox transformation by Pseudomonas sp. HN-2 isolated from arsenic-contaminated soil in Hunan, China

A mesophilic, Gram-negative, arsenite[As(III)]-oxidizing and arsenate[As(V)]-reducing bacterial strain, Pseudomonas sp. HN-2, was isolated from an As-contaminated soil. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that the strain was closely related to Pseudomonas stutzeri. Under aerobic conditions, this strain oxidized 92.0% (61.4μmol/L) of arsenite to arsenate within 3hr of incubation. Reduction of As(V) to As(III) occurred in anoxic conditions. Pseudomonas sp. HN-2 is among the first soil bacteria shown to be capable of both aerobic As(III) oxidation and anoxic As(V) reduction. The strain, as an efficient As(III) oxidizer and As(V) reducer in Pseudomonas, has the potential to impact arsenic mobility in both anoxic and aerobic environments, and has potential application in As remediation processes.

The role of biogenic Fe-Mn oxides formed in situ for arsenic oxidation and adsorption in aquatic ecosystems

As(III&V), Mn(II), and Fe(II) may occur simultaneously in some groundwater and surface water. Studying their redox reactions and interactions is essential to unravel the biogeochemical cycles of these metal ions in aquatic ecosystems and to find effective methods to remove them simultaneously in drinking water treatment. Here, the formation of biogenic Fe-Mn oxides (BFMO, defined as a mixture of biogenic Mn oxide (BMO) and Fe oxide) as well as its oxidation and adsorption of As in a Fe(II)-Mn(II)-As(III&V)-Mn-oxidizing microbe (Pseudomonas sp. QJX-1) system were investigated. Batch experiments and structure characterization revealed that the BFMO was formed via a sequential precipitation of Fe oxide and BMO. The first formed Fe oxide was identified as FeOOH (lepidocrocite) and the latter formed BMO was identified as MnO2 (similar to hexagonal birnessite). In the BFMO mixture, the BMO part was mainly responsible for As(III) oxidation, and the Fe oxide part dominated As adsorption. Remarkably, the BMO could oxidize Fe(II) to form FeOOH, which may improve As adsorption. The optimum Mn(II)/Fe(II) ratio for As removal was approximately 1:3 (mol/mol). Taken together, in Fe(II)-Mn(II)-As(III&V)-Mn-oxidizing microbe ecosystems, the in situ formation of BFMO could eliminate or decrease Fe(II), Mn(II), and As(III&V) species simultaneously. Therefore, based on this study, new approaches may be developed for As removal from water containing high concentrations of Fe(II) and Mn(II).

The fate of arsenic adsorbed on iron oxides in the presence of arsenite-oxidizing bacteria

Arsenic (As) is a redox-active metalloid whose toxicity and mobility in soil depend on its oxidation state. Arsenite [As(III)] can be oxidized by microbes and adsorbed by minerals in the soil. However, the combined effects of these abiotic and biotic processes are not well understood. In this study, the fate of arsenic in the presence of an isolated As(III)-oxidizing bacterium (Pseudomonas sp. HN-1, 10(9) colony-forming units (CFUs)·ml(-1)) and three iron oxides (goethite, hematite, and magnetite at 1.6 g L(-1)) was determined using batch experiments. The total As adsorption by iron oxides was lower with bacteria present and was higher with iron oxides alone. The total As adsorption decreased by 78.6%, 36.0% and 79.7% for goethite, hematite and magnetite, respectively, due to the presence of bacteria. As(III) adsorbed on iron oxides could also be oxidized by Pseudomonas sp. HN-1, but the oxidation rate (1.3 μmol h(-1)) was much slower than the rate in the aqueous phase (96.2 μmol h(-1)). Therefore, the results of other studies with minerals only might overestimate the adsorptive capacity of solids in natural systems; the presence of minerals might hinder As(III) oxidation by microbes. Under aerobic conditions, in the presence of iron oxides and As(III)-oxidizing bacteria, arsenic is adsorbed onto iron oxides within the adsorption capacity, and As(V) is the primary form in the solid and aqueous phases.

Impact of Arsenite on the Bacterial Community Structure and Diversity in Soil

The impact of arsenite (As[III]) on the bacterial community structure and diversity in soil was determined by incubating soil slurries with 50, 500, and 5,000 μM As(III). As(III) was oxidized to arsenate (As[V]), and the microbial contribution to As(III) oxidation was 70–100%. PCR-denaturing gradient gel electrophoresis revealed that soil bacterial diversity decreased in the presence of As(III). Bacteria closely related to the family Bacillaceae were predominant in slurry spiked with 5,000 μM As(III). The population size of culturable As(III)-resistant bacteria was 37-fold higher in this slurry than in unspiked slurry (p < 0.01), indicating that high levels of As(III) stimulate the emergence of As(III)-resistant bacteria. As(III)-resistant bacteria isolated from slurry spiked with 5,000 μM As(III) were mainly affiliated with the genus Bacillus; however, no strains showed As(III)-oxidizing capacity. An As(III)-oxidizing bacterial community analysis based on As(III) oxidase gene (aioA) sequences demonstrated that diversity was the lowest in slurry spiked with 5,000 μM As(III). The deduced AioA sequences affiliated with Alphaproteobacteria accounted for 91–93% of all sequences in this slurry, among which those closely related to Bosea spp. were predominant (48–86%). These results suggest that exposure to high levels of As(III) has a significant impact on the composition and diversity of the soil bacterial community, including the As(III)-oxidizing bacterial community. Certain As(III)-oxidizing bacteria with strong As(III) resistance may be enriched under high As(III) levels, while more sensitive As(III) oxidizers are eliminated under these conditions.

A greener approach for impressive removal of As(iii)/As(v) from an ultra-low concentration using a highly efficient chitosan thiomer as a new adsorbent

Contamination of ground water with arsenic is a serious problem all over the world.

The influence of environmental conditions on kinetics of arsenite oxidation by manganese-oxides

BACKGROUND

Manganese-oxides are one of the most important minerals in soil due to their widespread distribution and high reactivity. Despite their invaluable role in cycling many redox sensitive elements, numerous unknowns remain about the reactivity of different manganese-oxide minerals under varying conditions in natural systems. By altering temperature, pH, and concentration of arsenite we were able to determine how manganese-oxide reactivity changes with simulated environmental conditions. The interaction between manganese-oxides and arsenic is particularly important because manganese can oxidize mobile and toxic arsenite into more easily sorbed and less toxic arsenate. This redox reaction is essential in understanding how to address the global issue of arsenic contamination in drinking water.

RESULTS

The reactivity of manganese-oxides in ascending order is random stacked birnessite, hexagonal birnessite, biogenic manganese-oxide, acid birnessite, and δ-MnO2. Increasing temperature raised the rate of oxidation. pH had a variable effect on the production of arsenate and mainly impacted the sorption of arsenate on δ-MnO2, which decreased with increasing pH. Acid birnessite oxidized the most arsenic at alkaline and acidic pHs, with decreased reactivity towards neutral pH. The δ-MnO2 showed a decline in reactivity with increasing arsenite concentration, while the acid birnessite had greater oxidation capacity under higher concentrations of arsenite. The batch reactions used in this study quantify the impact of environmental variances on different manganese-oxides' reactivity and provide insight to their roles in governing chemical cycles in the Critical Zone.

CONCLUSIONS

The reactivity of manganese-oxides investigated was closely linked to each mineral's crystallinity, surface area, and presence of vacancy sites. δ-MnO2 and acid birnessite are thought to be synthetic representatives of naturally occurring biogenic manganese-oxides; however, the biogenic manganese-oxide exhibited a lag time in oxidation compared to these two minerals. Reactivity was clearly linked to temperature, which provides important information on how these minerals react in the subsurface environment. The pH affected oxidation rate, which is essential in understanding how manganese-oxides react differently in the environment and their potential role in remediating contaminated areas. Moreover, the contrasting oxidative capacity of seemingly similar manganese-oxides under varying arsenite concentrations reinforces the importance of each manganese-oxide mineral's unique properties.

The diversity and abundance of As(III) oxidizers on root iron plaque is critical for arsenic bioavailability to rice

Iron plaque is a strong adsorbent on rice roots, acting as a barrier to prevent metal uptake by rice. However, the role of root iron plaque microbes in governing metal redox cycling and metal bioavailability is unknown. In this study, the microbial community structure on the iron plaque of rice roots from an arsenic-contaminated paddy soil was explored using high-throughput next-generation sequencing. The microbial composition and diversity of the root iron plaque were significantly different from those of the bulk and rhizosphere soils. Using the aoxB gene as an identifying marker, we determined that the arsenite-oxidizing microbiota on the iron plaque was dominated by Acidovorax and Hydrogenophaga-affiliated bacteria. More importantly, the abundance of arsenite-oxidizing bacteria (AsOB) on the root iron plaque was significantly negatively correlated with the arsenic concentration in the rice root, straw and grain, indicating that the microbes on the iron plaque, particularly the AsOB, were actively catalyzing arsenic transformation and greatly influencing metal uptake by rice. This exploratory research represents a preliminary examination of the microbial community structure of the root iron plaque formed under arsenic pollution and emphasizes the importance of the root iron plaque environment in arsenic biogeochemical cycling compared with the soil-rhizosphere biotope.

Impact of birnessite on arsenic and iron speciation during microbial reduction of arsenic-bearing ferrihydrite

Elevated solution concentrations of As in anoxic natural systems are usually accompanied by microbially mediated As(V), Mn(III/IV), and Fe(III) reduction. The microbially mediated reductive dissolution of Fe(III)-(oxyhydr)oxides mainly liberates sorbed As(V) which is subsequently reduced to As(III). Manganese oxides have been shown to rapidly oxidize As(III) and Fe(II) under oxic conditions, but their net effect on the microbially mediated reductive release of As and Fe is still poorly understood. Here, we investigated the microbial reduction of As(V)-bearing ferrihydrite (molar As/Fe: 0.05; Fe tot: 32.1 mM) by Shewanella sp. ANA-3 (10(8) cells/mL) in the presence of different concentrations of birnessite (Mn tot: 0, 0.9, 3.1 mM) at circumneutral pH over 397 h using wet-chemical analyses and X-ray absorption spectroscopy. Additional abiotic experiments were performed to explore the reactivity of birnessite toward As(III) and Fe(II) in the presence of Mn(II), Fe(II), ferrihydrite, or deactivated bacterial cells. Compared to the birnessite-free control, the highest birnessite concentration resulted in 78% less Fe and 47% less As reduction at the end of the biotic experiment. The abiotic oxidation of As(III) by birnessite (k initial = 0.68 ± 0.31/h) was inhibited by Mn(II) and ferrihydrite, and lowered by Fe(II) and bacterial cell material. In contrast, the oxidation of Fe(II) by birnessite proceeded equally fast under all conditions (k initial = 493 ± 2/h) and was significantly faster than the oxidation of As(III). We conclude that in the presence of birnessite, microbially produced Fe(II) is rapidly reoxidized and precipitates as As-sequestering ferrihydrite. Our findings imply that the ability of Mn-oxides to oxidize As(III) in water-logged soils and sediments is limited by the formation of ferrihydrite and surface passivation processes.

Pyrosequencing reveals bacterial communities in unchlorinated drinking water distribution system: an integral study of bulk water, suspended solids, loose deposits, and pipe wall biofilm

The current understanding of drinking water distribution system (DWDS) microbiology is limited to pipe wall biofilm and bulk water; the contributions of particle-associated bacteria (from suspended solids and loose deposits) have long been neglected. Analyzing the composition and correlation of bacterial communities from different phases helped us to locate where most of the bacteria are and understand the interactions among these phases. In the present study, the bacteria from four critical phases of an unchlorinated DWDS, including bulk water, pipe wall biofilm, suspended solids, and loose deposits, were quantified and identified by adenosine triphosphate analysis and pyrosequencing, respectively. The results showed that the bulk water bacteria (including the contribution of suspended solids) contributed less than 2% of the total bacteria. The bacteria associated with loose deposits and pipe wall biofilm that accumulated in the DWDS accounted for over 98% of the total bacteria, and the contributions of bacteria in loose deposits and pipe wall biofilm were comparable. Depending on the amount of loose deposits, its contribution can be 7-fold higher than the pipe wall biofilm. Pyrosequencing revealed relatively stable bacterial communities in bulk water, pipe wall biofilm, and suspended solids throughout the distribution system; however, the communities present in loose deposits were dependent on the amount of loose deposits locally. Bacteria within the phases of suspended solids, loose deposits, and pipe wall biofilm were similar in phylogenetic composition. The bulk water bacteria (dominated by Polaromonas spp.) were clearly different from the bacteria from the other three phases (dominated by Sphingomonas spp.). This study highlighted that the integral DWDS ecology should include contributions from all of the four phases, especially the bacteria harbored by loose deposits. The accumulation of loose deposits and the aging process create variable microenvironments inside loose deposits structures for bacteria to grow. Moreover, loose deposits protect the associated bacteria from disinfectants, and due to their mobility, the associated bacteria reach taps easily.

ATR-FTIR spectroscopy study of the influence of pH and contact time on the adhesion of Shewanella putrefaciens bacterial cells to the surface of hematite

Attachment of live cells of Shewanella putrefaciens strain CN-32 to the surface of hematite (α-Fe(2)O(3)) was studied with in situ ATR-FTIR spectroscopy at variable pH (4.5-7.7) and contact times up to 24 h. The IR spectra indicate that phosphate based functional groups on the cell wall play an important role in mediating adhesion through formation of inner-sphere coordinative bonds to hematite surface sites. The inner-sphere attachment mode of microbial P groups varies with pH, involving either a change in protonation or in coordination to hematite surface sites as pH is modified. At all pH values, spectra collected during the early stages of adhesion show intense IR bands associated with reactive P-groups, suggestive of preferential coordination of P-moieties at the hematite surface. Spectra collected after longer sorption times show distinct frequencies from cell wall protein and carboxyl groups, indicating that bacterial adhesion occurring over longer time scales is to a lesser degree associated with preferential attachment of P-based bacterial functional groups to the hematite surface. The results of this study demonstrate that pH and reaction time influence cell-mineral interactions, implying that these parameters play an important role in determining cell mobility and biofilm formation in aqueous geochemical environments.