Achieving Long-Term Stability of Partial Nitrification and Autotrophic Denitrification in an MABR via Sulfide Dosing.

While partial nitrification (PN) has the potential to reduce energy for aeration, it has proven to be unstable when treating low-strength wastewater. This study introduces an innovative combined strategy incorporating a low rate of oxygen supply, pH control, and sulfide addition to selectively inhibit nitrite-oxidizing bacteria (NOB). This strategy led to a stable PN in a laboratory-scale membrane aerated biofilm reactor (MABR). Over a period of 260 days, the nitrite accumulation ratio exceeded 60% when treating synthetic sewage containing 50 mg NH4+-N/L. Through in situ activity testing and high-throughput sequencing, the combined strategy led to low levels of nitrite-oxidation activity (<5.5 mg N/m2 h), Nitrospira species (relative abundance <1%), and transcription of nitrite-oxidation genes (undetectable). The addition of sulfide led to simultaneous PN and autotrophic denitrification in the single-stage MABR, resulting in over 60% total inorganic nitrogen removal. Sulfur-based autotrophic denitrification consumed nitrite and inhibited NOB conversion of nitrite to nitrate. The combined strategy has potential to be applied in large-scale sewage treatment and deserves further exploration.

Novel Sulfate Reduction Coupled to Simultaneous Nitrification and Autotrophic Denitrification Process for Removing Nitrogen and Organics from Saline Wastewater.

Highly efficient sulfate reduction coupled to autotrophic denitrification plus nitrification is demonstrated by integrating an anaerobic membrane bioreactor (AnMBR) with a membrane aerated biofilm reactor (MABR). Concurrent chemical oxygen demand (COD) removal and sulfate reduction were accomplished in the AnMBR, while simultaneous nitrification and autotrophic denitrification were carried out in the MABR. Separate operation of the MABR achieved >90% total nitrogen (TN) removal when the N/S ratio was controlled at 0.4 gN/gS. The integrated AnMBR-MABR system efficiently resisted influent variability, realizing >95% COD removal in the AnMBR and >75% TN removal in the MABR when the influent COD/N ratio was above 4 gCOD/gN. Membrane fouling did not happen during ∼170 days of operation. Due to sulfide oxidation, a large amount of elemental sulfur (S0) accumulated in the MABR biofilm, where it served as an electron donor for denitrification. Microbial community analysis indicated that Nitrospira and Thiobacillus played key roles in nitrification and sulfide-driven denitrification, respectively, and that they occurred in different layers of the biofilm. This novel process offers advantages of a small land-area footprint, modular operation, and high efficiency electron-donor and oxygen utilizations, particularly for wastewater with a low COD/N ratio.

Multi-omics reveal various potential antimonate reductases from phylogenetically diverse microorganisms.

While previous work has demonstrated that antimonate (Sb(V)) can be bio-reduced with methane as the sole electron donor, the microorganisms responsible for Sb(V) reduction remain largely uncharacterized. Inspired by the recently reported Sb(V) reductase belonging to the dimethyl sulfoxide reductase (DMSOR) family, this study was undertaken to use metagenomics and metatranscriptomics to unravel whether any DMSOR family genes in the bioreactor had the potential for Sb(V) reduction. A search through metagenomic-assembled genomes recovered from the microbial community found that some DMSOR family genes, designated sbrA (Sb(V) reductase gene), were highly transcribed in four phylogenetically disparate assemblies. The putative catalytic subunits were found to be representatives of two distinct phylogenetic clades of reductases that were most closely related to periplasmic nitrate reductases and respiratory arsenate reductases, respectively. Putative operons containing sbrA possessed many other components, including genes encoding c-type cytochromes, response regulators, and ferredoxins, which together implement Sb(V) reduction. This predicted ability was confirmed by incubating the enrichment culture with 13C-labeled CH4 and Sb(V) in serum bottles, where Sb(V) was reduced coincident with the production of 13C-labeled CO2. Overall, these results increase our understanding of how Sb(V) can be bio-reduced in environments.

Formation of nanoscale Te0 and its effect on TeO32- reduction in CH4-based membrane biofilm reactor.

Formation and recovery of elemental tellurium (Te0) from wastewaters are required by increasing demands and scarce resources. Membrane biofilm reactor (MBfR) using gaseous electron donor has been reported as a low-cost and benign technique to reduce and recover metal (loids). In this study, we demonstrate the feasibility of nanoscale Te0 formation by tellurite (TeO32-) reduction in a CH4-based MBfR. Biogenic Te0 intensively attached on cell surface, within diameters ranging from 10 nm to 30 nm and the hexagonal nanostructure. Along with the Te0 formation, the TeO32- reduction was inhibited. After flushing, biofilm resumed the TeO32- reduction ability, suggesting that the formed nanoscale Te0 might inhibit the reduction by hindering substrate transfer of TeO32- to microbes. The 16S rRNA gene amplicon sequencing revealed that Thermomonas and Hyphomicrobium were possibly responsible for TeO32- reduction since they increased consecutively along with the experiment operation. The PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) analysis showed that the sulfite reductases were positively correlated with the TeO32- flux, indicating they were potential enzymes involved in reduction process. This study confirms the capability of CH4-based MBfR in tellurium reduction and formation, and provides more techniques for resources recovery and recycles.

Base substitution mutations in uridinediphosphate-dependent glycosyltransferase 76G1 gene of Stevia rebaudiana causes the low levels of rebaudioside A: mutations in UGT76G1, a key gene of steviol glycosides synthesis.

Steviol glycosides, extracted from the leaves of Stevia rebaudiana (Bert) Bertoni, are calorie-free sugar substitute of natural origin with intensely sweet (Boileau et al., 2012). Stevioside and rebaudioside A are the two main kinds of the diterpenic glycosides. We analyzed the concentration of stevioside and rebaudioside A in Stevia leaves of about 500 samples (hybrid progenies) and discovered a mutation plant "Z05" with very low levels of rebaudioside A. Because UGT76G1, a uridinediphosphate-dependent glycosyltransferases, is responsible for the conversion from stevioside to rebaudioside A (Richman et al., 2005), so mutation identification was done by sequencing the candidate gene, UGT76G1. In this study molecular analysis of two strains revealed a heterozygotic nonsense mutation of c.389T > G (p.L121X) in UGT76G1. Meanwhile, we found some amino acid substitutions significant change the protein structure. And the difference of enzyme activity between two strains proved the lack of functionality of UGT76G1 of the mutation "Z05". So the nonsense mutation and amino acid substitution mutation resulted in the low levels of rebaudioside A.

Organic acids on the growth, anatomical structure, biochemical parameters and heavy metal accumulation of Iris lactea var. chinensis seedling growing in Pb mine tailings.

The effect of citric acid (CA) and ethylene diamine tetraacetic acid (EDTA) on the growth, anatomical structure, physiological responses and lead (Pb) accumulation of Iris lactea var. chinensis seedling growing in Pb mine tailings for 30 days were studied. Results showed that the dry weights (DW) of roots decreased significantly under both levels of CA. The DWs of leaves and roots treated with 2 mmol/kg EDTA decreased significantly and were 23 and 54 %, respectively, lower than those of the control. The tolerant indexes of I. lactea var. chinensis under all treatments of organic acids were lower than control. The root tip anatomical structure was little affected under the treatments of 2 mmol/kg CA and 2 mmol/kg EDTA compared with control. However, the formation of photosynthesizing cells was inhibited by the treatment of 2 mmol/kg EDTA. The concentrations of chlorophyll a, chlorophyll b and total carotenoids in the leaves treated with 2 mmol/kg EDTA significantly decreased. Higher CA level and lower EDTA level could trigger the synthesis of ascorbic acid and higher level of EDTA could trigger the synthesis of glutathione. CA and EDTA could promote Pb accumulation of I. lactea var. chinensis and Pb concentration in the leaves and roots at 2 mmol/kg EDTA treatment increased significantly and reached to 160.44 and 936.08 µg/g DW, respectively, and 1.8 and 1.6 times higher than those of the control. The results indicated that I. lactea var. chinensis could be used to remediate Pb tailing and the role of EDTA in promoting Pb accumulation was better than CA did.

Physiological response of Cu and Cu mine tailing remediation of Paulownia fortunei (Seem) Hemsl.

The physiological responses and Cu accumulation of Paulownia fortunei (Seem) Hemsl. were studied under 15.7-157 µmol L(-1) Cu treatments in liquid culture for 14 days; the impacts of Cu concentration in the seedlings were evaluated under Cu mine tailing culture with acetic acid and EDTA treatment for 60 days. Results showed that the concentrations of Chl-a, Chl-b and Carotenoids significantly increased (p < 0.05) at 15.7-78.7 µmol L(-1)Cu treatment and significantly decreased at 157 µmol L(-1) treatment after 14 days of Cu exposure. The activities of superoxide dismutase (SOD) and catalase (CAT) significantly increased as Cu levels were enhanced and the activities of both SOD and CAT under 157 µmol L(-1) Cu stress were 2.9 and 1.9 times higher than that of control, respectively. The concentrations of proline and soluble sugars in the leaves of P. fortunei significantly increased as the Cu concentrations were elevated. Cu concentrations in roots, stems and leaves of P. fortunei increased significantly as Cu levels increased and reached 1911, 101 and 93 µg g(-1) dry weights (DW) at 157 µmol L(-1) Cu treatment, respectively. The seedlings of P. fortunei cultivated in Cu tailing experienced unsuccessful growth and loss of leaves in all treatments due to poor nutrition of the Cu tailing. The dry weight of P. fortunei increased under all the treatments of acetic acid after 60 days exposure. However, dry weight significantly decreased under both levels of EDTA. The Cu concentrations increased significantly in roots and decreased in leaves when each was treated with both concentrations of acetic acid. The Cu concentrations in the roots, stems and leaves increased significantly, and the concentrations of Cu in the stems and leaves under the treatment of 2 µmol L(-1) EDTA reached 189.5 and 763.1 µg g(-1) DW, respectively. The result indicated that SOD, CAT, proline and soluble sugars played an important role in coping with the oxidative stress of copper. Acetic acid could promote growth and EDTA at the experimental levels, which could also enhance Cu absorption and translocation into the stems and leaves of P. fortune. Furthermore, acetic acid and EDTA could be rationally utilized in Cu-contaminated soil.

The physiological response and sub-cellular localization of lead and cadmium in Iris pseudacorus L.

The seedling development and physiological responses of Iris pseudacorus L. to Pb and Cd and their combination were studied for 28 days liquid culture and sub-cellular localization of Pb and Cd in the root tip cells treated with 2,070 mg L(-1) Pb and 1,000 mg L(-1)Cd for 16 days sand culture was evaluated. Results showed that the dry weights (DWs) of shoots and roots of I. pseudacorus were significantly decreased at 500 mg L(-1)Pb and 25 mg L(-1)Cd + 500 mg L(-1)Pb treatments and the root DWs under all treatments were significantly decreased in comparison with that of control. The concentrations of Chla in the leaves were decreased at all treatments, while, the concentrations of Chlb and total carotenoids were not significantly decreased under 25 mg L(-1)Cd and 25 mg L(-1)Cd + 500 mg L(-1)Pb treatments. The MDA and proline concentrations and POD activities in the shoots and roots were increased under treatments of 500 mg L(-1)Pb and 25 mg L(-1)Cd + 500 mg L(-1)Pb, but POD activities in the shoots and roots and MDA concentrations in the shoots were significantly decreased at 25 mg L(-1) Cd treatment. The results of sub-cellular localization of Pb and Cd showed that numerous Pb deposits were found on the inner surface of died cell walls in the cortex treated with 2,070 mg L(-1) Pb and Cd deposits were found in the cell wall treated with 1,000 mg L(-1) Cd. Pb and Cd deposits were not found in the cytoplasm. The results indicated that POD and proline showed strong beneficial properties against Pb and Cd stress and there were some mechanisms keeping most cells with normal activities in the plant from Pb toxicity by sacrificing a few cells that accumulated a large amount Pb. Sub-cellular localizations of Pb and Cd in the root tip cells of I. pseudacorus were little difference with the localizations in other species of Iris in the previous studies.

Tolerance and accumulation of lead by species of Iris L.

Seedling development, accumulation and distribution of lead (Pb) in Iris lactea var. chinensis (Fisch.) Koidz. and I. tectorum Maxim. were studied using plants grown in sand culture and exposed to 0-10 mmol l(-1) concentrations of Pb supplied as Pb(NO3)(2) for 28 days. A significant reduction in dry weight (dw) of shoots and roots of I. lactea var. chinensis was observed at 6 and 10 mmol l(-1), respectively, and a significant reduction in dw of shoots and roots of I. tectorum was observed at 6 mmol l(-1). Concentration of Pb in the shoots and roots of I. lacteal var. chinensis exposed to 4 mmol l(-1) Pb reached 1,109 microg g(-1) and 2,408 microg g(-1) dw, respectively. The index of tolerance (IT) of I. lactea var. chinensis among 0-8 mmol l(-1) Pb treatments were not significantly different, while those of I. tectorum at 6 mmol l(-1) Pb were significantly decreased. The results indicated that I. lactea var. chinensis was more tolerant to Pb than I. tectorum. Sub-cellular localization of Pb in root cells was evaluated using transmission electron microscopy (TEM) and Pb deposits were found along the plasma membrane of some root tip cells of I. lactea var. chinensis treated at 10 mmol l(-1) Pb. Deposits of Pd were also observed along the surface, in the root tip cell wall and in the cytoplasm of a few malformed cells of I. tectorum exposed at 10 mmol l(-1) Pb treatment. One possible mechanism to explain these observations may be that most cells can maintain normal activities in the plant by sacrificing a small number of cells that accumulate a large amount Pb and show toxicity. Future studies should be designed to test this hypothesis.

[Effects of Zn on the growth, Cd accumulation and physiological resistance of Iris lactea var. chinensis under Cd stress].

A solution culture experiment was conducted to examine the effects of Zn (1-100 mg x L(-1)) on the growth, Cd accumulation, and antioxidant enzyme activities of Iris lactea var. chinensis under Cd stress (10 mg x L(-1)). The results showed that after the addition of Zn, the Cd content changed a little in shoots, but increased significantly in roots, with a trend of rising first and dropping then. When treated with 1 mg Zn x L(-1), the Cd content in roots was the highest, being 51.4% higher than the control. When the Zn concentration was higher than 1 mg x L(-1), the Cd content in roots decreased to some extent, but was still higher than the control. Low concentration (1-10 mg x L(-1)) Zn increased the shoot biomass and leaf chlorophyll content, but decreased the malondialdehyde (MDA) content. At 10 mg Zn x L(-1), the chlorophyll a and b contents went up to the maximum, being 5.21% and 22.27% higher than the control, respectively, while the MDA content decreased by 25.46%, indicating that low concentration Zn could alleviate Cd damage. With increasing Zn concentration, the alleviation effect of Zn on Cd damage decreased gradually. When the Zn concentration was 100 mg x L(-1), I. lactea var. chinensis was damaged most seriously, with the biomass and chlorophyll content reduced and MDA content increased significantly. Within the ranges of test Cd and Zn concentrations, the activities of superoxide dismutase (SOD) and peroxidase (POD) had an increasing trend, suggesting that SOD and POD played an important antioxidant protective role for Cd or Zn-Cd stressed I. lactea var. chinensis.

Cadmium tolerance and accumulation by two species of Iris.

Seedlings of Iris lactea var. chinensis (Fisch.) Koidz. and I. tectorum Maxim. were subjected to 0-160 mg l(-1) Cd in hydroponic system and harvested after 42 days to determine effects on root and shoot dry mass. A subset of 16-day-old seedlings was exposed to 1000 mg l(-1) Cd to characterize sub-cellular localization of Cd in root cells. The Cd contents in the shoots of I. lactea var. chinensis reached 529 microg g(-1 )dry weight (dw) at 80 mg l(-1) Cd treatment and in the shoots of I. tectorum reached 232 microg g(-1) dw at 40 mg l(-1) Cd treatment, without showing signs of visible toxicity. The Cd contents in the shoots of both two test species exceeded 100 microg g(-1), the critical value of Cd hyperaccumulator. The indices of tolerance (ITs) of I. lactea var. chinensis were higher than those of I. tectorum under 10-160 mg l(-1)Cd stress. Sub-cellular localization of Cd in root cells was evaluated using transmission electron microscopy (TEM) and Cd deposits were found in the cell walls, in the cytoplasm and on the inner surface of xylem vessels in the root tip of I. lactea var. chinensis and I. tectorum. A few cells in the root tip of I. tectorum were necrotic. The results showed that the tolerance and accumulation of Cd by I. lactea var. chinensis were higher than those of I. tectorum, suggesting that I. lactea var. chinensis has potential application in phytoremediation.