Diversity of planktonic and attached bacterial communities in a phenol-contaminated sandstone aquifer

Enhancing in situ biodegradation in groundwater using pump and treat remediation: a proof of concept and modelling analysis of controlling variables

A remediation approach which uses pump and treatment (PAT) to enhance the biodegradation of organic contaminants by increasing dispersive mixing between plumes and groundwater was evaluated for a phenol-contaminated aquifer, using a reactive transport model which simulates kinetic reactions between an electron donor (ED) in the plume and electron acceptor (EA) in the groundwater. The influence of system design and operation was examined in six modelling scenarios. Injection or extraction of groundwater increases biodegradation above no action and the location, pumping rate, and distance between well(s) are important variables which influence biodegradation. An increase in pumping rate, distance of the wells from the plume centreline, and changing the flow direction increase dispersive mixing between the plume and groundwater. This increases plume spreading and the plume fringe interface, providing a greater flux of dissolved EAs for biodegradation. In general, injection of groundwater containing natural EAs enhances biodegradation more than extraction. The enhancement of biodegradation is sensitive to the relative fluxes of ED and EA, as controlled by the arrangement of the wells. In the best performing scenario, biodegradation was enhanced by 128%, compared with no action.

Microalgae Inoculation Significantly Shapes the Structure, Alters the Assembly Process, and Enhances the Stability of Bacterial Communities in Shrimp-Rearing Water

Intensive shrimp farming may lead to adverse environmental consequences due to discharged water effluent. Inoculation of microalgae can moderate the adverse effect of shrimp-farming water. However, how bacterial communities with different lifestyles (free-living (FL) and particle-attached (PA)) respond to microalgal inoculation is unclear. In the present study, we investigated the effects of two microalgae (Nannochloropsis oculata and Thalassiosira weissflogii) alone or in combination in regulating microbial communities in shrimp-farmed water and their potential applications. PERMANOVA revealed significant differences among treatments in terms of time and lifestyle. Community diversity analysis showed that PA bacteria responded more sensitively to different microalgal treatments than FL bacteria. Redundancy analysis (RDA) indicated that the bacterial community was majorly influenced by environmental factors, compared to microalgal direct influence. Moreover, the neutral model analysis and the average variation degree (AVD) index indicated that the addition of microalgae affected the bacterial community structure and stability during the stochastic process, and the PA bacterial community was the most stable with the addition of T. weissflogii. Therefore, the present study revealed the effects of microalgae and nutrient salts on bacterial communities in shrimp aquaculture water by adding microalgae to control the process of community change. This study is important for understanding the microbial community assembly and interpreting complex interactions among zoo-, phyto-, and bacterioplankton in shrimp aquaculture ecosystems. Additionally, these findings may contribute to the sustainable development of shrimp aquaculture and ecosystem conservation.

Insight into bacterial community profiles of oil shale and sandstone in ordos basin by culture-dependent and culture-independent methods

To promote the exploitation of unconventional oil resources by indigenous microorganisms, the bacterial community profiles of oil shale and sandstone in Ordos Basin were investigated using Illumina Miseq sequencing combined with the culture-based method, which was performed and reported in this literature for the first time. A total of 601 operational taxonomic units (OTUs) were obtained from collected samples, the predominant phylum present in all samples was Proteobacteria (76.96%-93.07%). Discriminatory bacterial community profiles existed in those samples by culture-dependent and culture-independent methods, with variations not only in diversity indices but also in the abundance of bacteria at different genus levels. The dominant genera in cultured sandstone sample (SCB), uncultured sandstone sample (SUB), cultured shale sample (YCB), uncultured shale sample (YUB) were Enhydrobacter (71.62%), Acidovorax (42.44%), Pseudomonas (40.13%), Variovorax (70.02%), respectively. Both sample sources and culturing methods were the principal factors affecting the variation, while the communities' structures were favored primarily by culture-dependent or culture-independent approaches. The high abundance of hydrocarbon degradation-related genes was exhibited in YCB, which reveals a great potential for utilization of the culture-dependent method in shale oil exploitation. This study provided guidance for the exploitation of shale oil and sandstone oil by artificial utilization of indigenous bacteria.

Distribution of ETBE-degrading microorganisms and functional capability in groundwater, and implications for characterising aquifer ETBE biodegradation potential

Microbes in aquifers are present suspended in groundwater or attached to the aquifer sediment. Groundwater is often sampled at gasoline ether oxygenate (GEO)-impacted sites to assess the potential biodegradation of organic constituents. However, the distribution of GEO-degrading microorganisms between the groundwater and aquifer sediment must be understood to interpret this potential. In this study, the distribution of ethyl tert-butyl ether (ETBE)-degrading organisms and ETBE biodegradation potential was investigated in laboratory microcosm studies and mixed groundwater-aquifer sediment samples obtained from pumped monitoring wells at ETBE-impacted sites. ETBE biodegradation potential (as determined by quantification of the ethB gene) was detected predominantly in the attached microbial communities and was below detection limit in the groundwater communities. The copy number of ethB genes varied with borehole purge volume at the field sites. Members of the Comamonadaceae and Gammaproteobacteria families were identified as responders for ETBE biodegradation. However, the detection of the ethB gene is a more appropriate function-based indicator of ETBE biodegradation potential than taxonomic analysis of the microbial community. The study shows that a mixed groundwater-aquifer sediment (slurry) sample collected from monitoring wells after minimal purging can be used to assess the aquifer ETBE biodegradation potential at ETBE-release sites using this function-based concept.

Long-term dynamic changes in attached and planktonic microbial communities in a contaminated aquifer

Biodegradation is responsible for most contaminant removal in plumes of organic compounds and is fastest at the plume fringe where microbial cell numbers and activity are highest. As the plume migrates from the source, groundwater containing the contaminants and planktonic microbial community encounters uncontaminated substrata on which an attached community subsequently develops. While attached microbial communities are important for biodegradation, the time needed for their establishment, their relationship with the planktonic community and the processes controlling their development are not well understood. We compare the dynamics of development of attached microbial communities on sterile substrata in the field and laboratory microcosms, sampled simultaneously at intervals over two years. We show that attached microbial cell numbers increased rapidly and stabilised after similar periods of incubation (∼100 days) in both field and microcosm experiments. These timescales were similar even though variation in the contaminant source evident in the field was absent in microcosm studies, implying that this period was an emergent property of the attached microbial community. 16S rRNA gene sequencing showed that attached and planktonic communities differed markedly, with many attached organisms strongly preferring attachment. Successional processes were evident, both in community diversity indices and from community network analysis. Community development was governed by both deterministic and stochastic processes and was related to the predilection of community members for different lifestyles and the geochemical environment.

Biogeochemical Alteration of an Aquifer Soil during In Situ Chemical Oxidation by Hydrogen Peroxide and Peroxymonosulfate

In this study, the effects of in situ chemical oxidation (ISCO) on the biogeochemical properties of an aquifer soil were evaluated. Microcosms packed with an aquifer soil were investigated for 4 months in two phases including oxidant exposure (phase I) and biostimulation involving acetate addition (phase II). The geochemical and microbial alterations from different concentrations (0.2 and 50 mM) of hydrogen peroxide (HP) and peroxymonosulfate (PMS) were assessed. The 50 mM PMS-treated sample exhibited the most significant geochemical changes, characterized by the decrease in pH and the presence of more crystalline phases. Microbial activity decreased for all ISCO-treated microcosms compared to the controls; particularly, the activity was severely inhibited at high PMS concentration exposure. The soil microbial community structures were shifted after the ISCO treatment, with the high PMS causing the most distinct changes. Microbes such as the Azotobacter chroococcum and Gerobacter spp. increased during phase II of the ISCO treatment, indicating these bacterial communities can promote organic degradation despite the oxidants exposure. The HP (low and high concentrations) and low concentration PMS exposure temporarily impacted the microbial activity, with recovery after some duration, whereas the microbial activity was less recovered after the high concentration PMS exposure. These results suggest that the use of HP and low concentration PMS are suitable ISCO strategies for aquifer soil bioattenuation.

Effects of synthetic iron and aluminium oxide surface charge and hydrophobicity on the formation of bacterial biofilm

In this research, bacterial cell attachments to hematite, goethite and aluminium hydroxide were investigated. The aim was to study the effects of these minerals' hydrophobicity and pH-dependent surface charge on the extent of biofilm formation using six genetically diverse bacterial strains: Rhodococcus spp. (RC92 & RC291), Pseudomonas spp. (Pse1 & Pse2) and Sphingomonas spp. (Sph1 & Sph2), which had been previously isolated from contaminated environments. The surfaces were prepared in a way that was compatible with the naturally occurring coating process in aquifers: deposition of colloidal particles from the aqueous phase. The biofilms were evaluated using a novel, in situ and non-invasive technique developed for this purpose. A manufactured polystyrene 12-well plate was used as the reference surface to be coated with synthesized minerals by deposition of their suspended particles through evaporation. Planktonic phase growth indicates that it is independent of the surface charge and hydrophobicity of the studied surfaces. The hydrophobic similarities failed to predict biofilm proliferation. Two of the three hydrophilic strains formed extensive biofilms on the minerals. The third one, Sph2, showed anomalies in contrast to the expected electrostatic attraction between the minerals and the cell surface. Further research showed how the solution's ionic strength affects Sph2 surface potential and shapes the extent of its biofilm formation; reducing the ionic strength from ≈200 mM to ≈20 mM led to a tenfold increase in the number of cells attached to hematite. This study provides a technique to evaluate biofilm formation on metal-oxide surfaces, under well-controlled conditions, using a simple yet reliable method. The findings also highlight that cell numbers in the planktonic phase do not necessarily show the extent of cell attachment, and thorough physicochemical characterization of bacterial strains, substrata and the aquifer medium is fundamental to successfully implementing any bioremediation projects.

Polyphasic analysis of an Azoarcus-Leptothrix-dominated bacterial biofilm developed on stainless steel surface in a gasoline-contaminated hypoxic groundwater

Pump and treat systems are widely used for hydrocarbon-contaminated groundwater remediation. Although biofouling (formation of clogging biofilms on pump surfaces) is a common problem in these systems, scarce information is available regarding the phylogenetic and functional complexity of such biofilms. Extensive information about the taxa and species as well as metabolic potential of a bacterial biofilm developed on the stainless steel surface of a pump submerged in a gasoline-contaminated hypoxic groundwater is presented. Results shed light on a complex network of interconnected hydrocarbon-degrading chemoorganotrophic and chemolitotrophic bacteria. It was found that besides the well-known hydrocarbon-degrading aerobic/facultative anaerobic biofilm-forming organisms (e.g., Azoarcus, Leptothrix, Acidovorax, Thauera, Pseudomonas, etc.), representatives of Fe(2+)-and Mn(2+)-oxidizing (Thiobacillus, Sideroxydans, Gallionella, Rhodopseudomonas, etc.) as well as of Fe(3+)- and Mn(4+)-respiring (Rhodoferax, Geobacter, Magnetospirillum, Sulfurimonas, etc.) bacteria were present in the biofilm. The predominance of β-Proteobacteria within the biofilm bacterial community in phylogenetic and functional point of view was revealed. Investigation of meta-cleavage dioxygenase and benzylsuccinate synthase (bssA) genes indicated that within the biofilm, Azoarcus, Leptothrix, Zoogloea, and Thauera species are most probably involved in intrinsic biodegradation of aromatic hydrocarbons. Polyphasic analysis of the biofilm shed light on the fact that subsurface microbial accretions might be reservoirs of novel putatively hydrocarbon-degrading bacterial species. Moreover, clogging biofilms besides their detrimental effects might supplement the efficiency of pump and treat systems.

Community Analysis and Recovery of Phenol-degrading Bacteria from Drinking Water Biofilters

Phenol is a ubiquitous organic contaminant in drinking water. Biodegradation plays an important role in the elimination of phenol pollution in the environment, but the information about phenol removal by drinking water biofilters is still lacking. Herein, we study an acclimated bacterial community that can degrade over 80% of 300 mg/L phenol within 3 days. PCR detection of genotypes involved in bacterial phenol degradation revealed that the degradation pathways contained the initial oxidative attack by phenol hydroxylase, and subsequent ring fission by catechol 1,2-dioxygenase. Based on the PCR denatured gradient gel electrophoresis (PCR-DGGE) profiles of bacteria from biological activated carbon (BAC), the predominant bacteria in drinking water biofilters including Delftia sp., Achromobacter sp., and Agrobacterium sp., which together comprised up to 50% of the total microorganisms. In addition, a shift in bacterial community structure was observed during phenol biodegradation. Furthermore, the most effective phenol-degrading strain DW-1 that correspond to the main band in denaturing gradient gel electrophoresis (DGGE) profile was isolated and identified as Acinetobacter sp., according to phylogenetic analyses of the 16S ribosomal ribonucleic acid (rRNA) gene sequences. The strain DW-1 also produced the most important enzyme, phenol hydroxylase, and it also exhibited a good ability to degrade phenol when immobilized on granular active carbon (GAC). This study indicates that the enrichment culture has great potential application for treatment of phenol-polluted drinking water sources, and the indigenous phenol-degrading microorganism could recover from drinking water biofilters as an efficient resource for phenol removal. Therefore, the aim of this study is to draw attention to recover native phenol-degrading bacteria from drinking water biofilters, and use these native microorganisms as phenolic water remediation in drinking water sources.

Biodegradation of phenolic compounds and their metabolites in contaminated groundwater using microbial fuel cells

This is the first study demonstrating the biodegradation of phenolic compounds and their organic metabolites in contaminated groundwater using bioelectrochemical systems (BESs). The phenols were biodegraded anaerobically via 4-hydroxybenzoic acid and 4-hydroxy-3-methylbenzoic acid, which were retained by electromigration in the anode chamber. Oxygen, nitrate, iron(III), sulfate and the electrode were electron acceptors for biodegradation. Electro-active bacteria attached to the anode, producing electricity (~1.8mW/m(2)), while utilizing acetate as an electron donor. Electricity generation started concurrently with iron reduction; the anode was an electron acceptor as thermodynamically favorable as iron(III). Acetate removal was enhanced by 40% in the presence of the anode. However, enhanced removal of phenols occurred only for a short time. Field-scale application of BESs for in situ bioremediation requires an understanding of the regulation and kinetics of biodegradation pathways of the parent compounds to relevant metabolites, and the syntrophic interactions and carbon flow in the microbial community.

Cytometric patterns reveal growth states of Shewanella putrefaciens

Bacterial growth is often difficult to estimate beyond classical cultivation approaches. Low cell numbers, particles or coloured and dense media may disturb reliable growth assessment. Further difficulties appear when cells are attached to surfaces and detachment is incomplete.

Therefore, flow cytometry was tested and used for analysis of bacterial growth on the single-cell level. Shewanella putrefaciens was cultivated as a model organism in planktonic or biofilm culture. Materials of smooth and rough surfaces were used for biofilm cultivation. Both aerobic and anaerobic as well as feast and famine conditions were applied. Visualization of growth was also done using Environmental Scanning and Phase Contrast Microscopy. Bioinformatic tools were applied for data interpretation.

Cytometric proliferation patterns based on distributions of DNA contents per cell corresponded distinctly to the various lifestyles, electron acceptors and substrates tested. Therefore, cell cycling profiles of S. putrefaciens were found to mirror growth conditions.

The cytometric patterns were consistently detectable with exception of some biofilm types whose resolution remained challenging. Corresponding heat maps proved to be useful for clear visualization of growth behaviour under all tested conditions. Therefore, flow cytometry in combination with bioinformatic tools proved to be powerful means to determine various growth states of S. putrefaciens, even in constrained environments. The approach is universal and will also be applicable for other bacterial species.