The coagulation process for enveloped and non-enveloped virus removal in turbid water: Removal efficiencies, mechanisms and its application to SARS-CoV-2 Omicron BA.2.

The coagulation process has a high potential as a treatment method that can handle pathogenic viruses including emerging enveloped viruses in drinking water treatment process which can lower infection risk through drinking water consumption. In this study, a surrogate enveloped virus, bacteriophage Փ6, and surrogate non-enveloped viruses, including bacteriophage MS-2, T4, ՓX174, were used to evaluate removal efficiencies and mechanisms by the conventional coagulation process with alum, poly­aluminum chloride, and ferric chloride at pH 5, 7, and 9 in turbid water. Also, treatability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a recent virus of global concern by coagulation was evaluated as SARS-CoV-2 can presence in drinking water sources. It was observed that an increase in the coagulant dose enhanced the removal efficiency of turbidity and viruses, and the condition that provided the highest removal efficiency of enveloped and non-enveloped viruses was 50 mg/L of coagulants at pH 5. In addition, the coagulation process was more effective for enveloped virus removal than for the non-enveloped viruses, and it demonstrated reduction of SARS-CoV-2 Omicron BA.2 over 0.83-log with alum. According to culture- and molecular-based assays (qPCR and CDDP-qPCR), the virus removal mechanisms were floc adsorption and coagulant inactivation. Through inactivation with coagulants, coagulants caused capsid destruction, followed by genome damage in non-enveloped viruses; however, damage to a lipid envelope is suggested to contribute to a great extend for enveloped virus inactivation. We demonstrated that conventional coagulation is a promising method for controlling emerging and re-emerging viruses in drinking water.

Bioaugmentation of Thauera mechernichensis TL1 for enhanced polyhydroxyalkanoate production in mixed microbial consortia for wastewater treatment.

Polyhydroxyalkanoate (PHA) is a fully biodegradable bioplastic. To foster a circular economy, the integration of PHA production into wastewater treatment facilities can be accomplished using mixed microbial consortia. The effectiveness of this approach relies greatly on the enrichment of PHA-accumulating microorganisms. Hence, our study focused on bioaugmenting Thauera mechernichensis TL1 into mixed microbial consortia with the aim of enriching PHA-accumulating microorganisms and enhancing PHA production. Three sequencing batch reactors-SBRctrl, SBR2.5%, and SBR25%-were operated under feast/famine conditions. SBR2.5% and SBR25% were bioaugmented with T. mechernichensis TL1 at 2.5%w/w of mixed liquor volatile suspended solids (MLVSS) and 25%w/w MLVSS, respectively, while SBRctrl was not bioaugmented. SBR2.5% and SBR25% achieved maximum PHA accumulation capacities of 56.3 %gPHA/g mixed liquor suspended solids (MLSS) and 50.2 %gPHA/gMLSS, respectively, which were higher than the 25.4 %gPHA/gMLSS achieved by SBRctrl. The results of quantitative polymerase chain reaction targeting the 16S rRNA gene specific to T. mechernichensis showed higher abundances of T. mechernichensis in SBR2.5% and SBR25% compared with SBRctrl in the 3rd, 17th, and 31st cycles. Fluorescence in situ hybridization, together with fluorescent staining of PHA with Nile blue A, confirmed PHA accumulation in Thauera spp. The study demonstrated that bioaugmentation of T. mechernichensis TL1 at 2.5%w/w MLVSS is an effective strategy to enhance PHA accumulation and facilitate the enrichment of PHA-accumulating microorganisms in mixed microbial consortia. The findings could contribute to the advancement of PHA production from wastewater, enabling the transformation of wastewater treatment plants into water and resource recovery facilities.

Comparative genomic analyses of pathogenic bacteria and viruses and antimicrobial resistance genes in an urban transportation canal.

Water commuting is a major urban transportation method in Thailand. However, urban boat commuters risk exposure to microbially contaminated bioaerosols or splash. We aimed to investigate the microbial community structures, identify bacterial and viral pathogens, and assess the abundance of antimicrobial resistance genes (ARGs) using next-generation sequencing (NGS) at 10 sampling sites along an 18 km transportation boat route in the Saen Saep Canal, which traverses cultural, commercial, and suburban land-based zones. The shotgun metagenomic (Illumina HiSeq) and 16S rRNA gene amplicon (V4 region) (Illumina MiSeq) sequencing platforms revealed diverse microbial clusters aligned with the zones, with explicit segregation between the cultural and suburban sites. The shotgun metagenomic sequencing further identified bacterial and viral pathogens, and ARGs. The predominant bacterial pathogens (>0.5 % relative abundance) were the Burkholderia cepacia complex, Arcobacter butzleri, Burkholderia vietnamiensis, Klebsiella pneumoniae, and the Enterobacter cloacae complex. The viruses (0.28 %-0.67 % abundance in all microbial sequences) comprised mainly vertebrate viruses and bacteriophages, with encephalomyocarditis virus (33.3 %-58.2 % abundance in viral sequences), hepatitis C virus genotype 1, human alphaherpesvirus 1, and human betaherpesvirus 6A among the human viral pathogens. The 15 ARG types contained 611 ARG subtypes, including those resistant to beta-lactam, which was the most diverse and abundant group (206 subtypes; 17.0 %-27.5 %), aminoglycoside (94 subtypes; 9.6 %-15.3 %), tetracycline (80 subtypes; 15.6 %-20.2 %), and macrolide (79 subtypes; 14.5 %-32.1 %). Interestingly, the abundance of ARGs associated with resistance to beta-lactam, trimethoprim, and sulphonamide, as well as A. butzleri and crAssphage, at the cultural sites was significantly different from the other sites (p < 0.05). We demonstrated the benefits of using NGS to deliver insights into microbial communities, and antimicrobial resistance, both of which pose a risk to human health. Using NGS may facilitate microbial risk mitigation and management for urban water commuters and proximal residents.

Influence of ammonia and NaCl on nitrifying community and activity: Implications for formulating nitrifying culture augmentation.

Bioaugmentation of nitrifying cultures can accelerate nitrification during startup and transition periods of recirculating aquaculture system (RAS) operations. To formulate nitrifying cultures for RASs, impacts of ammonia and salinity (NaCl) on culturing nitrifying microorganisms were comprehensively investigated by including currently known groups of nitrifying microorganisms (ammonia oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), comammox, Nitrospira, and Nitrobacter). By varying ammonia loading rate (ALRs of 1.6, 8, 20, 40, 60 and 150 mgN/L/d) of continuous-flow bioreactors fed with inorganic medium experimented for culture preparation, cultures containing distinct patterns of nitrifying communities were produced. Operating the reactors at the ALRs of ≤40 mgN/L/d, resulting in the effluent total ammonia nitrogen (TAN) and nitrite concentrations of ≤2.64 and ≤0.53 mgN/L, respectively, delivered the consortia consisting of a broad spectrum of substrate affinity nitrifying microorganisms. At the lower ranges of these ALRs (≤8 mgN/L/d), the most desirable consortia comprising comparable numbers of AOB, AOA, and comammox could be produced (the effluent TAN concentrations of ≤0.20 mgN/L), which would be resilient for applying in various RAS types. Enriching the cultures at the ALRs of ≥60 mgN/L/d allowed only the nitrifying microorganisms with low substrate affinity to dominate, incongruent with the consortia found in actual RASs. AOB were adaptable at all salinity studied (2, 15, and 30 g/L), while AOA and comammox were sensitive to elevated salinity (15 and 30 g/L, respectively). The ammonia removal rate of a culture prepared at 2 g/L salinity decreased largely when applied at 15 and 30 g/L. In contrast, those prepared at 15 and 30 g/L were more robust to different salinity. Separately preparing the cultures at different salinity for uses in freshwater-low salinity and brackish-marine RASs is recommended. The findings of this work enhance our understanding on how to formulate nitrifying culture augmentation for used in different RAS types.

Substrate loading rates conducive to nitritation in entrapped cell reactors: performance and microbial community structure.

This study aimed to elucidate the boundaries of ammonia and organic loading rates that allow for nitritation in continuous flow phosphorylated-polyvinyl alcohol entrapped cell reactors and to clarify the community structure of microorganisms involving nitrogen transformation in the gel bead matrices. At operating bulk dissolved oxygen concentration of 2 mg/L, nitritation was accomplished when the total ammonia nitrogen (TAN) loading rate was ≥ 0.3 kgN/m3/d. At TAN loading rates of ≤ 0.2 kgN/m3 /d, complete oxidation of ammonia to nitrate took place. Nitritation performance dropped with increased chemical oxygen demand (COD) loading rates indicating limitation of nitritation reactor operation at some COD loading conditions. 16S rRNA gene amplicon sequencing revealed that the uncultured Cytophagaceae bacterium, Arenimonas, Truepera, Nitrosomonas, Comamonas, unclassified Soil Crenarchaeotic Group, and uncultured Chitinophagaceae bacterium were highly abundant taxa in the reactors' gel bead matrices. qPCR with specific primers targeting amoA genes demonstrated the coexistence of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea, and Comammox in the gel bead matrices. AOB was likely the main functioning ammonia-oxidizing microorganisms due to the amoA gene being of highest abundance in most of the studied conditions. Nitrite-oxidizing microorganisms presented in less relative abundance than ammonia-oxidizing microorganisms, with Nitrobacter rather than Nitrospira dominating in the group. Results obtained from this study are expected to further the application of nitritation entrapped cell reactors to real wastewater treatment processes.

Chicken manure-based bioponics: Effects of acetic acid supplementation on nitrogen and phosphorus recoveries and microbial communities.

Bioponics has the potential to recover nutrients from organic waste streams, such as chicken manure and digestate with high volatile fatty acid (VFA) contents through crop production. Acetic acid, a dominant VFA, was supplemented weekly (0, 500, 1000, and 1500 mg/L) in a chicken manure-based bioponic system, and its effect on the performance of bioponics (e.g., plant yield and nitrogen and phosphorus availabilities) was examined. Microbial communities were analyzed using 16S rRNA gene sequencing, and the functional gene abundances were predicted using PICRUSt. Although acetic acid negatively affected plant yield, no significant difference (p > 0.05) was noted in the average nitrogen or phosphorus concentration. In terms of nutrient recovery, the bioponic systems still functioned well, although higher concentrations of acetic acid decreased plant yield and altered the bacterial communities in plant roots and chicken manure sediments. These data suggest that an acetic acid concentration of < 500 mg/L or a longer loading interval is recommended for the effective operation of chicken manure and digestate-based bioponics.

Development of reactive iron-coated natural filter media for treating antibiotic residual in swine wastewater: Mechanisms, intermediates and toxicity.

Degradation mechanisms, surface phenomena, and the influence of co-existing organic matter on heterogeneous Fenton-like reactions were investigated using low-cost natural materials, to remove three veterinary antibiotics. Zeolite rock, laterite rock, and pumice rock were modified by adding ferric chloride. Fenton-like reactions yielded more than 50 % of antibiotic removal at a neutral pH. The modified zeolite exhibited the highest antibiotic removal efficiency. The heterogeneous Fenton-like reaction could be indicated by the simultaneous detection of Fe(II) and Fe(III) on the surface of the modified zeolite. Leaching iron was also observed to reduce the antibiotics with homogeneous Fenton-like reaction. The co-existing organic matter expressed by the COD below 400 mg/L did not have a considerable adverse impact on antibiotic removal. An H2O2 concentration as low as 20 µM was sufficient to react with the modified zeolite and degraded more than 70 % of the antibiotics at a neutral pH. The modified zeolite could be reused at least three times, with a removal efficiency of at least 80 %. The antibiotic degradation efficiencies in real treated swine wastewater were above 75 %. Moreover, the degradation intermediates and bacterial inhibition after treatment were investigated.

Microbial community compositions and sulfate-reducing bacterial profiles in malodorous urban canal sediments.

Anthropogenically impacted urban canals represent distinct freshwater ecosystems that could shape microbial communities in underlying sediments; however, knowledge of the relationships between environmental factors and microbial community compositions and their functions in such an environment is limited. This study characterized the microbial community compositions of malodorous canal sediments at six locations along the Saen Saep Canal in Thailand. 16S rRNA gene amplicon sequencing (MiSeq, Illumina) revealed dominant genera classified as fermentative bacteria, methanogens, and sulfate-reducing bacteria (SRB), all of which emphasized anaerobic environments. SRB, as the primary producers of malodorous hydrogen sulfide, accounted for 8.2-30.4% of the total sequences. dsrB gene clone libraries further identified the SRB species. A constrained correspondence analysis demonstrated a spatial pattern of SRB that correlated with physicochemical parameters in which nitrate and sulfate in sediments were the most influencing factors. Overall, a better understanding of the SRB and other related microorganisms in canal sediments can assist in the future implementation of appropriate olfactory abatement and management methodologies in urban canals.

Identification of sulfate-reducing and methanogenic microbial taxa in anaerobic bioreactors from industrial wastewater treatment plants using next-generation sequencing and gene clone library analyses.

An understanding of microbial communities present in anaerobic bioreactors can strongly facilitate the development of approaches to control undesirable microorganisms, such as sulfate-reducing bacteria (SRB), in the system. In this study, overall microbial communities present in anaerobic bioreactors from seven industrial wastewater treatment plants (including food, pulp and paper industries) were investigated using 16S rRNA gene amplicon sequencing (MiSeq, Illumina). The dominant methanogens identified in the anaerobic bioreactors treating industrial wastewater were Methanobacterium and Methanosaeta; Methanospirillum was a predominant methanogen in the anaerobic sludge digester. Hydrogenotrophic and acetoclastic methanogens were detected at similar relative abundances in the anaerobic covered lagoons treating starch wastewater, whereas hydrogenotrophic methanogens were the predominant methanogens present in the sludge digester. SRB communities were further investigated using dsrB gene clone libraries. The results indicated the presence of SRB, such as uncultured Desulfobulbus sp., Syntrophobacter fumaroxidans, Syntrophorhabdus sp. PtaB.Bin027, and Desulfovibrio fructosivarans JJ. Incomplete-oxidizing SRB were the predominant SRB in all of the anaerobic bioreactors treating wastewater. In contrast, similar relative abundances of complete and incomplete-oxidizing SRB were observed in the sludge digester. The results of this study can further facilitate the development of SRB-controlling strategies to improve the efficiency of wastewater treatment.

Dissolved oxygen/free ammonia (DO/FA) ratio manipulation to gain distinct proportions of nitrogen species in effluent of entrapped-cell-based reactors.

Oxygen-limiting and/or free ammonia (FA)-accumulating conditions are two common operating strategies for partial nitrification in wastewater. Controlling either bulk dissolved oxygen (DO) or free ammonia (FA) concentration to maintain partial nitrification can be challenging due to the strong interdependency between these two parameters as substrates for ammonia oxidation. In this study, DO/FA ratio is proposed as a controlling parameter for partial nitrification by entrapped-cell-based reactors. At DO/FA >1.5, both ammonia and nitrite oxidation proceeded without inhibition leading to complete oxidation of ammonia to nitrate. An effluent containing nitrate as the main nitrogen species can be produced at these ratios. At a DO/FA ratio range of 0.2-1.5, ammonia oxidation proceeded without efficiency deterioration, while nitrite oxidation decreased with decreasing DO/FA ratio. At the ratios of 0.2-0.6, an effluent containing mainly nitrite can be generated. At DO/FA <0.2, both ammonia oxidation and nitrite oxidation were inhibited and the effluent with nearly equal molar of ammonia and nitrite was obtained. By controlling DO/FA ratio, effluents with different proportions of nitrogen species can be produced allowing the entrapped-cell-based system to be adaptable as an initial reactor for various nitrogen removal approaches.

Reduction of silver nanoparticle toxicity affecting ammonia oxidation using cell entrapment technique.

Occurrence of silver nanoparticles (AgNPs) in wastewater treatment systems could impact the ammonia oxidation (AO). This study investigated the reduction of AgNPs and dissociated silver ion (Ag+) toxicity on nitrifying sludge using cell entrapment technique. Three entrapment materials, including barium alginate (BA), polyvinyl alcohol (PVA), and a mixture of polyvinyl alcohol and barium alginate (PVA-BA), were applied. The BA beads provided the highest reduction of silver toxicity (up to 90%) and durability. Live/dead assays showed fatality of entrapped cells after exposure to AgNPs and Ag+. The maximum AO rate of the BA-entrapped cells was 5.6 mg-N/g-MLSS/h. The AO kinetics under the presence of silver followed an uncompetitive inhibition kinetic model. The experiments with AgNPs and Ag+ gave the apparent maximum AO rates of 4.2 and 4.8 mg-N/g-MLSS/h, respectively. The apparent half-saturation constants of the BA-entrapped cells under the presence of silver were 10.5 to 13.4 mg/L. Scanning electron microscopic observation coupled with energy-dispersive X-ray spectroscopy indicated no silver inside the beads. This elucidates that the silver toxicity can be reduced by preventing silver penetration through the porous material, leading to less microbial cell damage. This study revealed the potential of the entrapment technology for mitigating the effect of silver species on nitrification.

Partial nitrification in entrapped-cell-based reactors with two different cell-to-matrix ratios: performance, microenvironment, and microbial community.

In this study, we investigated the effect of different cell-to-matrix ratios (1% and 4%) on the partial nitrification of phosphorylated polyvinyl alcohol-entrapped-cell-based reactors and evaluated the microenvironment, microbial community, and microbial localization within the gel matrices. The results indicated that the reactor with a 1% cell-to-matrix ratio required 184 days of operation to reach partial nitrification that produced anaerobic ammonium oxidation-suitable effluent. In contrast, partial nitrification was achieved from the beginning of the operation of the reactor with the 4% cell-to-matrix ratio. The oxygen-limiting zone (dissolved oxygen = 0.5-1.5 mg L-1), where nitrite-oxidizing activity has been suggested to be suppressed and ammonia-oxidizing activity was reported to be maintained, occurred at 10-230 µm from the gel matrices surface. In addition, the layer of ammonia-oxidizing bacteria observed in this zone is likely to have played a role in obstructing oxygen penetration into the inner region of the gel matrices. The next-generation sequencing results indicated that members of the family Nitrosomonadaceae accounted for 16.4-20.7% of the relative abundance of bacteria at the family level, while members of the family Bradyrhizobiaceae, to which the genus Nitrobacter belongs, accounted for approximately 10% of the relative abundance of bacteria at the genus level in the gel matrices.

Incorporation of 13C-HCO3- by ammonia-oxidizing archaea and bacteria during ammonia oxidation of sludge from a municipal wastewater treatment plant.

Ammonia-oxidizing archaea (AOA) have recently been proposed as potential players for ammonia removal in wastewater treatment plants (WWTPs). However, there is little evidence directly showing the contribution of AOA to ammonia oxidation in these engineered systems. In this study, DNA-stable isotope probing (DNA-SIP) with labeled 13C-HCO3- was introduced to sludge from a municipal WWTP. Quantitative PCR demonstrated that AOA amoA genes outnumbered AOB amoA genes in this WWTP sludge. AOA amoA gene sequence analysis revealed that AOA present in this WWTP were specific to one subcluster within the group 1.1b Thaumarchaeota. When ammonia was supplied to DNA-SIP incubation, the DNA-SIP profiles demonstrated the incorporation of the 13C into AOA and AOB. However, the 13C was not found to be assimilated into both microorganisms in the incubation without ammonia. Specific primers were designed to target amoA genes of AOA belonging to the subcluster found in this WWTP. Applying the primers to DNA-SIP experiment revealed that AOA of this subcluter most likely utilized inorganic carbon during ammonia oxidation under the studied conditions.

Contribution of ammonia-oxidizing archaea and ammonia-oxidizing bacteria to ammonia oxidation in two nitrifying reactors.

In this study, two laboratory nitrifying reactors (NRI and NRII), which were seeded by sludge from different sources and operated under different operating conditions, were found to possess distinct dominant ammonia-oxidizing microorganisms. Ammonia-oxidizing archaeal (AOA) amoA genes outnumbered ammonia-oxidizing bacterial (AOB) amoA genes in reactor NRI, while only AOB amoA genes were detectable in reactor NRII. The AOA amoA gene sequences retrieved from NRI were characterized within the Nitrososphaera sister cluster of the group 1.1b Thaumarchaeota. Two inhibitors for ammonia oxidation, allylthiourea (ATU) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), were applied individually and as a mixture to observe the ammonia-oxidizing activity of both microorganisms in the reactors' sludge. The results indicated that AOA and AOB jointly oxidized ammonia in NRI, while AOB played the main role in ammonia oxidation in NRII. DNA-stable isotope probing with labeled 13C-HCO3- was performed on NRI sludge. Incorporation of 13C into AOA and AOB implied that both microorganisms may perform autotrophy during ammonia oxidation. Taken together, the results from this study provide direct evidence demonstrating the contribution of AOA and AOB to ammonia oxidation in the nitrifying reactors.

Dependence of toxicity of silver nanoparticles on Pseudomonas putida biofilm structure.

Susceptibility of biofilms with different physical structures to silver nanoparticles (AgNPs) was studied. Biofilms of Pseudomonas putida KT2440 were formed in batch conditions under different carbon sources (glucose, glutamic acid, and citrate), glucose concentrations (5 and 50 mM), and incubation temperatures (25 and 30 °C). The biofilms were observed using confocal laser scanning microscopy for their physical characteristics (biomass amount, thickness, biomass volume, surface to volume ratio, and roughness coefficient). The biofilms forming under different growth conditions exhibited different physical structures. The biofilm thickness and the roughness coefficient were found negatively and positively correlated with the biofilm susceptibility to AgNPs, respectively. The effect of AgNPs on biofilms was low (1-log reduction of cell number) when the biofilms had high biomass amount, high thickness, high biomass volume, low surface to volume ratio, and low roughness coefficient. Furthermore, the extracellular polymeric substance (EPS) stripping process was applied to confirm the dependence of susceptibility to AgNPs on the structure of biofilm. After the EPS stripping process, the biofilms forming under different conditions showed reduction in thickness and biomass volume, and increases in surface to volume ratio and roughness coefficient, which led to more biofilm susceptibility to AgNPs. The results of this study suggest that controlling the growth conditions to alter the biofilm physical structure is a possible approach to reduce the impact of AgNPs on biofilms in engineered and natural systems.

Influence of silver nanoparticles and liberated silver ions on nitrifying sludge: ammonia oxidation inhibitory kinetics and mechanism.

Silver nanoparticles (AgNPs) are widely used in commercial products because of their excellent antimicrobial activity. Entrance of AgNPs and its released Ag ions (Ag+) into wastewater treatment plants could harm ammonia oxidation (AO) process resulting in environmental problems. This study investigated inhibitory kinetics and mechanism of AO from nitrifying sludge influenced by AgNPs and Ag+. The findings demonstrated that AgNPs and Ag+ adversely influenced on AO. Silver ions were more toxic to AO than AgNPs, which was indicated by the lower inhibitory constant (K i ) of 0.29 mg/L compared to that of AgNPs (K i of 73.5 mg/L). Over the experimental period of 60 h, AgNPs at 1, 10, and 100 mg/L released Ag+ in the average concentrations of 0.059, 0.171, and 0.503 mg/L, respectively. Silver nanoparticles of 1-100 mg/L inhibited AO by 45-74%, whereas Ag+ of 0.05-0.50 mg/L inhibited AO by 53-94%. This suggested that the AgNP toxicity mainly derived from the liberated Ag+. Scanning electron microscopy results revealed that AgNPs attached on microbial cell surfaces, and both AgNPs and Ag+ induced cell morphological change from rod shape to shorter rod shape. Transmission electron microscopy showed that AgNPs and Ag+ diminished the thickness of the outer layer and reduced the density of internal parts of the exposed microbial cells, which could be the reasons for the morphology change. Live/dead results also confirmed that AgNPs and Ag+ damaged membrane integrity of cells in the nitrifying sludge. This study suggested that the primary mechanism for toxicity of AgNPs was the liberation of Ag+ and then both of silver species caused cell death.

Differences in nitrite-oxidizing communities and kinetics in a brackish environment after enrichment at low and high nitrite concentrations.

Nitrite accumulation in shrimp ponds can pose serious adverse effects to shrimp production and the environment. This study aims to develop an effective process for the enrichment of ready-to-use nitrite-oxidizing bacteria (NOB) inocula that would be appropriate for nitrite removal in brackish shrimp ponds. To achieve this objective, the effects of nitrite concentrations on NOB communities and nitrite oxidation kinetics in a brackish environment were investigated. Moving-bed biofilm sequencing batch reactors and continuous moving-bed biofilm reactors were used for the enrichment of NOB at various nitrite concentrations, using sediment from brackish shrimp ponds as seed inoculum. The results from NOB population analysis with quantitative polymerase chain reaction (qPCR) show that only Nitrospira were detected in the sediment from the shrimp ponds. After the enrichment, both Nitrospira and Nitrobacter coexisted in the reactors controlling effluent nitrite at 0.1 and 0.5 mg-NO2(-)-N/L. On the other hand, in the reactors controlling effluent nitrite at 3, 20, and 100 mg-NO2(-)-N/L, Nitrobacter outcompeted Nitrospira in many orders of magnitude. The half saturation coefficients (Ks) for nitrite oxidation of the enrichments at low nitrite concentrations (0.1 and 0.5 mg-NO2(-)-N/L) were in the range of 0.71-0.98 mg-NO2(-)-N/L. In contrast, the K(s) values of NOB enriched at high nitrite concentrations (3, 20, and 100 mg-NO2(-)-N/L) were much higher (8.36-12.20 mg-NO2(-)-N/L). The results suggest that the selection of nitrite concentrations for the enrichment of NOB inocula can significantly influence NOB populations and kinetics, which could affect the effectiveness of their applications in brackish shrimp ponds.

Survey of Microbial Diversity in Flood Areas during Thailand 2011 Flood Crisis Using High-Throughput Tagged Amplicon Pyrosequencing.

The Thailand flood crisis in 2011 was one of the largest recorded floods in modern history, causing enormous damage to the economy and ecological habitats of the country. In this study, bacterial and fungal diversity in sediments and waters collected from ten flood areas in Bangkok and its suburbs, covering residential and agricultural areas, were analyzed using high-throughput 454 pyrosequencing of 16S rRNA gene and internal transcribed spacer sequences. Analysis of microbial community showed differences in taxa distribution in water and sediment with variations in the diversity of saprophytic microbes and sulfate/nitrate reducers among sampling locations, suggesting differences in microbial activity in the habitats. Overall, Proteobacteria represented a major bacterial group in waters, while this group co-existed with Firmicutes, Bacteroidetes, and Actinobacteria in sediments. Anaeromyxobacter, Steroidobacter, and Geobacter were the dominant bacterial genera in sediments, while Sulfuricurvum, Thiovirga, and Hydrogenophaga predominated in waters. For fungi in sediments, Ascomycota, Glomeromycota, and Basidiomycota, particularly in genera Philipsia, Rozella, and Acaulospora, were most frequently detected. Chytridiomycota and Ascomycota were the major fungal phyla, and Rhizophlyctis and Mortierella were the most frequently detected fungal genera in water. Diversity of sulfate-reducing bacteria, related to odor problems, was further investigated using analysis of the dsrB gene which indicated the presence of sulfate-reducing bacteria of families Desulfobacteraceae, Desulfobulbaceae, Syntrobacteraceae, and Desulfoarculaceae in the flood sediments. The work provides an insight into the diversity and function of microbes related to biological processes in flood areas.

Effect of silver nanoparticles on Pseudomonas putida biofilms at different stages of maturity.

This study determined the effect of silver nanoparticles (AgNPs) on Pseudomonas putida KT2440 biofilms at different stages of maturity. Three biofilm stages (1-3, representing early to late stages of development) were identified from bacterial adenosine triphosphate (ATP) activity under static (96-well plate) and dynamic conditions (Center for Disease Control and Prevention biofilm reactor). Extracellular polymeric substance (EPS) levels, measured using crystal violet and total carbohydrate assays, and expression of the EPS-associated genes, csgA and alg8, supported the conclusion that biofilms at later stages were older than those at earlier stages. More mature biofilms (stages 2 and 3) showed little to no reduction in ATP activity following exposure to AgNPs. In contrast, the same treatment reduced ATP activity by more than 90% in the less mature stage 1 biofilms. Regardless of maturity, biofilms with EPS stripped off were more susceptible to AgNPs than controls with intact EPS, demonstrating that EPS is critical for biofilm tolerance of AgNPs. The findings from this study show that stage of maturity is an important factor to consider when studying effect of AgNPs on biofilms.