Hexavalent chromate bioreduction by a magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1 and the effect of magnetosome synthesis.

Magnetotactic bacteria (MTB) are receiving attention for heavy metal biotreatment due to their potential for biosorption with heavy metals and the capability of the magnetic recovery. In this study, we investigated the characteristics of Cr(VI) bioreduction and biosorption by an MTB isolate, Magnetospirillum gryphiswaldense MSR-1, which has a higher growth rate and wider reflexivity in culture conditions. Our results demonstrated that the MSR-1 strain could remove Cr(VI) up to the concentration of 40 mg L-1 and with an optimal activity at neutral pH conditions. The magnetosome synthesis existed regulatory mechanisms between Cr(VI) reduction and cell division. The addition of 10 mg L-1 Cr(VI) significantly inhibited cell growth, but the magnetosome-deficient strain, B17316, showed an average specific growth rate of 0.062 h-1 at the same dosage. Cr(VI) reduction examined by the heat-inactivated and resting cells demonstrated that the main mechanism for MSR-1 strain to reduce Cr(VI) was chromate reductase and adsorption, and magnetosome synthesis would enhance the chromate reductase activity. Finally, our results elucidated that the chromate reductase distributes diversely in multiple subcellular components of the MSR-1 cells, including extracellular, membrane-associated, and intracellular cytoplasmic activity; and expression of the membrane-associated chromate reductase was increased after the cells were pre-exposed by Cr(VI).

Experimental validation of stability and applicability of Start Growth Time method for high-throughput bacterial ecotoxicity assessment.

Ecotoxicity assessments based on bacteria as model organisms are widely used for routine toxicity screening because it has the advantages of time-saving, high sensitivity, cost-effectiveness, and less ethical responsibility. Determination of ecotoxicity effect via bacterial growth can avoid the restriction of model bacteria selection and unique equipment requirements, but traditional viable cell count methods are relatively labor- and time-intensive. The Start Growth Time method (SGT) is a high-throughput and time-conserving method to determine the amount of viable bacterial cells. However, its usability and stability for ecotoxicity assessment are rarely studied. This study confirmed its applicability in terms of bacterial types (gram-positive and gram-negative), growth phases (middle exponential and early stationary phases), and simultaneous existence of dead cells (adjustment by flow cytometry). Our results verified that the stability of establishing SGT correlation is independent of the bacterial type and dead-cell portion. Moreover, we only observed the effect of growth phases on the slope value of established SGT correlation in Shewanella oneidensis, which suggests that preparing inoculum for the SGT method should be consistent in keeping its stability. Our results also elucidate that the SGT values and the live cell percentages meet the non-linear exponential correlation with high correlation coefficients from 0.97 to 0.99 for all the examined bacteria. The non-linear exponential correlation facilitates the application of the SGT method in the ecotoxicity assessment. Finally, applying the exponential SGT correlation to evaluate the ecotoxicity effect of copper ions on E. coli was experimentally validated. The SGT-based method would require about 6 to 7 h to finish the assessment and obtain an estimated EC50 at 2.27 ± 0.04 mM. This study demonstrates that the exponential SGT correlation can be a high-throughput, time-conversing, and wide-applicable method for bacterial ecotoxicity assessment.

Effect of the coexistence of endosulfan on the lindane biodegradation by Novosphingobium barchaimii and microbial enrichment cultures.

Organochlorine pesticides, especially lindane and endosulfan, have been demonstrated to be both biodegradable and frequently coexistent, but their inhibitory effect has never been studied. In this study, we investigated the effect of endosulfan coexistence on lindane degradation to a lindane-degrading isolate, Novosphingobium barchaimii strain LL02, and mixed enrichment cultures from two different inocula. Our results of the lindane degradation batch experiments demonstrated that endosulfan concentration above 20 mg L-1 causes significant inhibition to the lindane degradation efficiency of the strain LL02. Besides, the acidic conditions at pH 5.0 to 6.0 further decreased its lindane degradation rate constants by 57% compared to the neutral and alkaline conditions. For the mixed microbial cultures, the lindane degradation efficiency in the lindane/endosulfan co-contamination conditions decreased by 35.7%-50.7% compared to the lindane alone conditions. From our 16S rRNA amplicon sequencing results through the PacBio platform, most of the predominant bacteria in the lindane-enriched cultures were depressed in the lindane/endosulfan-enriched cultures. Moreover, bacteria of Burkholderia australis, Chujaibacter soli, Flavitalea flava, and one Rhodanobacteraceae bacterium were relatively highly abundant in the co-contamination enrichment cultures, suggesting their potential for lindane degradation under the endosulfan stress. Our results demonstrated that endosulfan coexistence causes inhibitory impacts on lindane biodegradation toward both lindane-degrading bacteria and mixed microbial cultures. The coexistence of multiple organochlorine pesticides on the biodegradation efficiencies should be carefully considered when applying bioremediation to remove organochlorine pesticide contamination.

Isolation of lindane- and endosulfan-degrading bacteria and dominance analysis in the microbial communities by culture-dependent and independent methods.

　　Bioremediation for lindane and endosulfan removal is a cost-effective approach, but its effectiveness depends on the ability to isolate degrading functionalized microorganisms. Researchers have isolated many lindane and endosulfan degrading bacteria from enrichment cultures based on culture-dependent methods during the past decades. However, it is unknown whether the isolated bacteria can reflect the indigenous predominant degraders in enriching cultures. In this study, we compared the culture-dependent method with selective medium isolation with culture-independent method (PacBio SMRT sequencing of full-length 16S rRNA amplicon) to analyze the bacterial communities from four distinct lindane (LA1 and LC1) and endosulfan (EA1 and EC1) enrichment cultures. From all the isolates we harvested from lindane (63 isolates) and endosulfan (61 isolates) enrichment cultures, their BLAST alignment can only match 5.49 % and 4.32 % of the bacterial operational taxonomic units (OTUs), respectively. Rhodanbacter lindaniclasticus and Pandoraea thiooxydans were the rarely seen potential degrading representatives that were simultaneously enriched and isolated. This study is the first comparative analysis of microbial communities from lindane and endosulfan enrichment culture using culture-dependent and culture-independent methods. Our results suggested that developing a target-specific and efficient microbial isolation method is necessary to harvest and study representative degrading bacteria in the community.

Evaluation of applying an alkaline green tea/ferrous iron system to lindane remediation impacts to soil and plant growth-promoting microbial community.

Application of in situ chemical oxidation or reduction (ISCO/ISCR) technologies for contaminated soil remediation and its subsequent impact on soil is gaining increased attention. Reductive reactivity, generated from green tea (GT) extract mixed with ferrous (Fe2+) ions under alkaline conditions (the alkaline GT/Fe2+ system), has been considered as a promising ISCR process; however, its impact on soil has never been studied. In this study, the impact of applying the alkaline GT/Fe2+ system on soil was evaluated by analyzing the variations of the soil microbial community, diversity, and richness using next-generation 16S rRNA amplicon sequencing while mimicking the lindane-contaminated soil remediation procedure. Lindane was reductively degraded by the alkaline GT/Fe2+ system with reaction rate constants of 0.014 to 0.057 µM/h depending on the lindane dosage. Environmental change to the alkaline condition significantly decreased the microbial diversity and richness, but the recovery of the influence was observed subsequently. Bacteria that mainly belong within the phylum Firmicutes, including Salipaludibacillus, Anaerobacillus, Bacillaceae, and Paenibacillaceae, were greatly enhanced due to the alkaline condition. Besides, the dominance of heterotrophic, iron-metabolic, lindane-catabolic, and facultative bacteria was observed in the other corresponding conditions. From the results of principal component analysis (PCA), although dominant microbes all shifted significantly at every lindane-existing condition, the set of optimal lindane treatment with the alkaline GT/Fe2+ system had a minimized effect on the plant growth-promoting bacteria (PGPB). Nitrogen-cycling-related PGPB is sensitive to all factors of the alkaline GT/Fe2+ system. However, the other types, including plant-growth-inducer producing, phosphate solubilizing, and siderophore producing PGPB, has less impact under the optimal treatment. Our results demonstrate that the alkaline GT/Fe2+ system is an effective and soil-ecosystem-friendly ISCR remediation technology for lindane contamination.

Assessment of green tea reductive degradation of halogenated solvents.

Green tea (GT) leaves can be brewed into a solution rich in polyphenols that serve as effective reducing agents, and the complexes formed by combining green tea with ferrous ion (GT/Fe(II)) can provide an elevated reduction potential. The dissociated GT polyphenols at alkaline pH can dramatically increase the formation of GT/Fe(II) complexes. This experimental work evaluated the reductive reactivity of alkaline GT solution and GT/Fe(II) complexes (at pH 10) on 14 halogenated volatile organic compounds (VOCs). Carbon tetrachloride (CT), with a highest carbon oxidation state (COS) of IV, was observed to be degradable by the alkaline GT solution, while all others proved ineffective. The GT/Fe(II) complexes are very reactive and capable of degrading halogenated methanes, ethanes, and ethenes, in which chemical structures exhibit zero or positive COS values, and the chlorine or bromine atom is bonded at the saturated carbon atom, such as CT, chloroform, bromoform, dibromomethane, 1,1,1-trichloroethane, and 1,1,1,2-tetrachloroethane. The linear free energy relationship (LFER) approach was used to determine the overall reduction potentials (EH0) of the alkaline GT solution and GT/Fe(II) complexes, which were found to be -0.131 V and -0.368 V, respectively. These findings demonstrated that GT/Fe(II) complexes exhibit the potential to remediate halogenated contaminants and the EH0 information obtained in this study may serve as a reference in determining probable reactivity that contributes to degradation of environmental contaminants.

Translocation of polybrominated diphenyl ethers from field-contaminated soils to an edible plant.

Polybrominated diphenyl ethers (PBDEs), recognised emerging contaminants, widely exist and persist in the environment. Samples were taken from a heavily contaminated farm in Taiwan located near a factory known to regularly use PBDEs. Sweet potato vines (Ipomoea batatas L., a commonly consumed vegetable in Asia) growing in the surrounding farmlands were found to contain a high concentration of PBDEs of 19.36 ng/g. The possibility of PBDEs translocation into sweet potato vines from soil samples was evaluated. To prevent the PBDEs from air through that factory, the pot experiments were performed in a greenhouse, which showed that the PBDEs concentration of 24 congeners (tri- through deca-BDE) in the sweet potato vine after 14-days cultivation was 29.90 ng/g, 40-times higher than that in the contaminated soil. After another 14-days, the PBDE concentration decreased to 12.30 ng/g as high-brominated PBDEs were transformed to medium- and/or low-brominated PBDEs in the sweet potato vine. The bioconcentration factor (BCF) values exceeded 20.0 for most of the deca-, nona-, and octa-BDEs but BCFs were below 18.9 for the rest of the medium- and low-brominated PBDEs. Our results demonstrate that high-brominated PBDEs can translocate into leafy vegetables from soils, and sweet potato vines tend to accumulate high-brominated PBDEs into their edible parts.

Partition uptake of a brominated diphenyl ether by the edible plant root of white radish (Raphanus sativus L.).

Polybrominated diphenyl ethers (PBDEs) are of a class of emerging contaminants. In this study, the accumulation of 4-bromodiphenyl ether (BDE-3) by different parts of a live white radish was investigated. Different cultural media (hydroponics, silica sand, and soil) were used to sustain the radish plant during its uptake and in-plant translocation of BDE-3. The results showed that BDE-3 can be translocated from the roots to the aboveground organs and the accumulated levels of BDE-3 in different parts of the white radish followed the order for the three types of cultivation: fibrous roots > peels > main roots > leaves. The results were analyzed by the aid of the partition-limited model for the plant uptake. The relevant partition coefficients (KOC and Kd) and uptake parameters of BDE-3 with plant components (Kpt and Klip) were obtained for analyzing the BDE-3 distribution. The partition-limited model offers a significant insight into the uptakes of BDE-3 by the various components of live white radishes. The types of cultivation affected the total sorption level, translocation factors (TFs), extent to equilibrium (αpt), and root concentration factors (RCFs).

Characterization of volatile organic compound adsorption on multiwall carbon nanotubes under different levels of relative humidity using linear solvation energy relationship.

Multiwall carbon nanotubes (MWCNTs) have been used as an adsorbent for evaluating the gas/solid partitioning of selected volatile organic compounds (VOCs). In this study, 15 VOCs were probed to determine their gas/solid partitioning coefficient (LogKd) using inverse gas chromatography at different relative humidity (RH) levels. Interactions between MWCNTs and VOCs were analyzed by regressing the observed LogKd with the linear solvation energy relationship (LSER). The results demonstrate that the MWCNT carbonyl and carboxyl groups provide high adsorption capacity for the VOCs (LogKd 3.72-5.24g/kg/g/L) because of the π-/n-electron pair interactions and hydrogen-bond acidity. The increasing RH gradually decreased the LogKd and shifted the interactions to dipolarity/polarizability, hydrogen-bond basicity, and cavity formation. The derived LSER equations provided adequate fits of LogKd, which is useful for VOC-removal processes and fate prediction of VOC contaminants by MWCNT adsorption in the environment.

Sorption equilibrium of emerging and traditional organic contaminants in leafy rape, Chinese mustard, lettuce and Chinese cabbage.

Emerging and petroleum contaminants could transfer into food chains by plant uptake, potentially causing food security problems. To build a prediction model, the sorption equilibrium and uptake kinetics of toluene, p-xylene, naphthalene, bisphenol A, and 4-bromo-diphenyl ether in some common leafy vegetables including leafy rape, Chinese mustard, lettuce and Chinese cabbage were examined. The kinetic experiments revealed that high sorption rates were observed for these plants that had high lipid contents. For two emerging contaminants with polar functional groups, their resulting isotherms were strongly linear (R(2) = 0.92 to 1.00), indicating that the sorption was dominated by partitioning. Moreover, regression correlation showed that log Klip, the lipid-water partition coefficient, and log Kow, the octanol-water coefficient, for these organic chemicals were strongly linear-related, following the equation: log Klip = 0.894 × log Kow+0.219 (R(2) = 0.953). The correlation equation allows the prediction of the sorption capacity of plant species for an organic compound when the plant composition and the log Kow of the chemical are determined. This improved model containing different organic chemicals with a wide range of log Kow (2.73-4.80) and including emerging contaminants was established, which shows further utilization for predicting the sorption of organic contaminants by plants.

Correlation between bio-hydrogen production and polyhydroxybutyrate (PHB) synthesis by Rhodopseudomonas palustris WP3-5.

The aim of this study was to determine the competition between H(2) production and polyhydroxybutyrate (PHB) accumulation of Rhodopseudomonas palustris WP3-5 when grown on six different substrates. From the results, strain WP3-5 can utilize acetate, propionate, malate, and lactate to produce H(2) but can only synthesize PHB on acetate and propionate. The substrate conversion efficiency (SCE) on acetate and propionate increased significantly after the maximum PHB content was achieved, illustrating a competition for reducing power when PHB synthesis occurred. However, when strain WP3-5 was cultivated at suboptimal pH values on acetate, the synthesized PHB prevented strain WP3-5 from the stress of the inappropriate pH and retained H(2) producing efficiency as at optimal pH value. Consequently, although PHB synthesis does compete with H(2) production in R. palustris WP3-5, it is still conducive to H(2) production when strain WP3-5 is in a stressful condition.

Correlation between fouling propensity of soluble extracellular polymeric substances and sludge metabolic activity altered by different starvation conditions.

Soluble extracellular polymeric substances (EPSs) cause membrane fouling in membrane bioreactors (MBRs), correlated with MBR sludge characteristics. Effects of F/M ratios on the evolution of soluble EPSs, fouling propensity of supernatants, and sludge metabolic activity were measured in this study in a two-period sequencing batch reactor (SBR). The experimental results show that fouling propensity was directly correlated with soluble-EPS concentration and composition. Sludge that had entirely lost active cells by long-term starvation released 64.4 ± 0.9 mg/L of humic acids, which caused a rapid increase in membrane resistance (40.67 ± 2.24 × 10(11) m(-1)) during fouling tests. During short-term starvation, induced by incubation at a normal to low F/M ratio of 0.05 d(-1), sludge can use previously secreted utilization-associated products (UAPs) to maintain endogenous respiration. Therefore, the strategies of accumulating sludge and prolonging sludge retention time in MBRs may create long-term starvation and promote membrane fouling.