Abstract:[Background] The Synechococcus is a kind of single celled cyanobacteria grown in ocean. Because of its rapid growth, it is used to purify sewage. In order to reduce the cost, the immobilized method has been adopted in production. However, what does happen in physiological and biochemical characteristics of Synechococcus after be immobilized? There is no report yet. [Objective] This paper studied the changes of physiological and biochemical characteristic and purifying sewage ability of Synechococcus after immobilization in order to provide scientific basis for promoting the application of Synechococcus. [Methods] The Synechococcus was immobilized by sodium alginate and calcium chloride. The growth rate of Synechococcus was determined by microscopic observation. The net photosynthetic efficiency of Synechococcus was detected by dissolved oxygen analyzer. The nitric oxide (NO) content was detected by fluorescence method. The content of chlorophyll and protein, the activity of nitrate reductase (NR) and Rubisco carboxylase and the index of water-quality were detected by spectrophotometer method. [Results] The maximum specific growth rate of Synechococcus was decreased by 24.30% by immobilization. The net photosynthetic rate of immobilized Synechococcus decreased from 9.10% to 29.10% in comparison with that of free Synechococcus. However, there was no significant difference in chlorophyll content between free and immobilizing Synechococcus. The activity of Rubisco carboxylase and NR were decreased by 25.70% and 40% respectively and the NO content was decreased by 32.10% by immobilization process. The removing to total nitrogen, total phosphorus, ammonia nitrogen and nitrite in Takifug rubripes culturing wastewater by Synechococcus were decreased by 30.00%, 17.70%, 20.20% and 21.20% respectively by immobilization process, but it had no effect on removing nitrate and chemical oxygen demand (COD). It is speculated that the immobilization process decreased Rubisco carboxylase activity in Synechococcus by decreasing NO content which regulating Rubisco carboxylase activity by post transcriptional modification. [Conclusion] The activity of NR was inhibited by immobilization process, which resulted in the decrease of NO content, and the latter inhibited the Rubisco activity, akey enzyme of photosynthesis, by posttranscriptional modification. The decrease of Rubisco activity led to the decrease of photosynthetic efficiency, and finally results in the decrease in growth rate and purifying sewage ability of immobilizing Synechococcus.

Abstract:[Objective] To clarify the removal of ammonium, nitrate and nitrite by a marine purple sulfur bacterium capable of growing on nitrite as sole nitrogen source. [Methods] Ammonium, nitrate and nitrite concentration in simulated wastewater were determined using the Nessler’s reagent spectrophotometry, N-(1-naphthyl)-1,2-diaminoethane dihydrochloride spectrophotometry, UV spectrophotometry, respectively. [Results] The removal of ammonium, nitrate and nitrite as well as bacterial biomass and pH increased with time, and then tended to equilibrium. Strain YL28 exhibited effective ammonium removal ability, with a maximal removal and tolerance of 9.64 mmol/L and 36.64 mmol/L, respectively. The removal rate exceeded 97.61% when the concentration of ammonium was less than 3.21 mmol/L. Compared to ammonium, the cell growth rate, biomass and pH of wastewater enhanced slowly while using nitrate and nitrite as sole nitrogen source. However, the removal of nitrate and nitrite were higher than that of ammonium. Nitrate and nitrite in wastewater could be completely removed when their concentrations were up to 13.50 mmol/L and 22.90 mmol/L, respectively. When the three inorganic nitrogen existed simultaneously in wastewater, ammonium, nitrate and nitrate could be removed by strain YL28, the removal of nitrate and nitrite was higher than that of ammonium. [Conclusion] Strain YL28 would be a promising candidate for bioremediation of polluted aquaculture wastewater, especially for nitrite-polluted marine culture wastewater.

Abstract:[Background] N2O is a powerful greenhouse gas with a 265-fold stronger warming potential than CO2. Fertilization plays an important role in affecting N2O emission from soils driven by bacterial community, and denitrification is the major source of N2O under anaerobic conditions. [Objective] To investigate N2O emission and greenhouse soil bacterial community response to the overuse of nitrogen fertilizer. [Methods] Robot system was used to monitor the denitrifying gas (N2O and N2) kinetics of soils during anaerobic incubation, and compare the difference of N2O emissions between traditional fertilization and reduced nitrogen fertilization. The soil microbial community structure was analyzed by sequencing the 16S rRNA gene V3?V4 region using Illumina MiSeq. [Results] The nitrate concentration in conventional nitrogen fertilization soil (CNS) was about two folds higher than that in reduced nitrogen fertilization soil (RNS). CNS showed higher N2O accumulation and emission rate during earlier anaerobic-incubation stage although the nitrate content was adjusted to the same level in both types of soil. Traditional fertilization significantly changed the bacterial community structure, and decreased the microbial diversity. Although Rhodanobacter was the most abundant genus both in CNS and RNS, it was enriched by traditional fertilization. However, relative abundance of denitrifying functional genes (narG, nirK, norB, nosZ) had little response to the overuse of fertilizer. [Conclusion] Traditional fertilization reshaped the bacterial community in soil. Overuse nitrogen fertilizer influenced N2O emission from soil via changing the microbial community including the microbiota related with nitrogen transformations.

Abstract:High concentrations of hydrogen sulfide are generated during wastewater and sludge treatment processes. Thiobacillus denitrificans is an important desulfuration engineering bacterium capable of oxidizing hydrogen sulfide and other sulfides. The current article reviews the biological characteristics of Thiobacillus denitrificans and two pathways of hydrogen sulfide oxidization. Factors, e.g. sulfide load, nitrate or nitrite concentration, oxygen content and pH value, influencing oxidation efficiency, reaction velocity, pathway and form of products are summarized. The application of Thiobacillus denitrificans in odor removal is introduced and its potential use in simultaneous control of nitrogen- and sulfur-containing odor-causing substances is also discussed.

Abstract:Toxic organic contaminants are widely released into environment, which cause adverse impact on human health and environment due to their high biotoxicant, persistence and bioaccumulation. Recently, it has achieved some research progresses on the use of nitrate as an electron acceptor for the degradation of toxic organic pollutants under anaerobic conditions. In this paper, we reviewed the recent progresses on the anaerobic degradation of some typical toxic organic contaminants (polycyclic aromatic hydrocarbons, single ring or heterocyclic organic pollutants and halogenated organics) under nitrate-reducing conditions. In addition, the next challenges, as well as the new perspectives on this field were also discussed.

Abstract:[Background] Aerobic denitrification is carried out under aerobic conditions, so that nitrification and denitrification can occur at the same time in the same reactor, which is the most competitive technology for nitrogen removal from wastewater. Mangrove wetlands are rich in microbial resources and a large number of aerobic denitrifying microorganisms are distributed. [Objective] In order to understand the denitrification mechanism of salt-tolerant microorganisms and provide a theoretical basis for the engineering practice of biological denitrification of salt-bearing wastewater, a salt-tolerant aerobic bacteria A63 was isolated from the mangrove wetland and its nitrate reduction ability was analyzed. [Methods] The species were identified by morphological characteristics and 16S rRNA gene sequencing. The nitrate reduction ability of the strain under different environmental factors was determined by single factor experiment, and its denitrification performance was optimized. [Results] It was preliminarily determined that the strain belonged to the Zobellella sp. The strain can carry out denitrification and dissimilatory nitrate reduction to ammonium (DNRA) action in the range of salinity 0%?10%, pH 5.0?10.0 and temperature 20?40 °C. The optimum growth carbon source is sodium citrate (1.2 g/L), and the optimum salinity 3.0%, the pH is 7.0?7.5, the temperature is 30?35 °C and C/N is 10. Under the optimum denitrification condition, the strain could reduce 208.8 mg/l NO3?-N to 0 in the medium within 12 hours, and only a small amount of ammonium nitrogen was produced. There was no accumulation of nitrite nitrogen, and the denitrification rate was as high as 99%. Furthermore, the strain had a significant effect on DNRA in adverse habitats such as high salinity, low C/N ratio, weak acidity and low temperature. [Conclusion] The strain A63 has a wide range of growth and remarkable nitrogen removal efficiency, so it is suitable for the treatment of mariculture wastewater. The present study lays a foundation for the development of high efficiency biological nitrogen removal process for salty wastewater in the future, and is of great significance to deepen the understanding of nitrogen transformation law and enrich the theory of biological nitrogen removal.

Abstract:[Background] Unlike general acetogenic bacteria which usually reduce two molecules of CO2 into one molecule of acetyl-CoA via Wood-Ljungdahl pathway, the formate dehydrogenase-lacking acetogen Clostridium bovifaecis reduces one molecule of formate and one molecule of CO2 into acetyl-CoA and conducts acetogenic utilization of glucose only in the presence of formate. Nitrate is the preferred electron acceptor for acetogens which vary in their ability to utilize this alternative electron acceptor. However, the effect of nitrate on the carbon fixation by formate dehydrogenase-lacking Wood-Ljungdahl pathway remains unclear. [Objective] To investigate the effect of nitrate on the carbon fixation by formate-dependent acetogenesis in C. bovifaecis. [Methods] We measured the growth, substrate consumption, and product yield of C. bovifaecis cultured in the medium containing 10 mmol/L or 30 mmol/L nitrate and using glucose + formate + CO2 as substrates. The medium without nitrate was taken as the control. [Results] The main product was ethanol with the concentrations of 5.80 mmol/L and 1.66 mmol/L, respectively, in the media with 10 mmol/L and 30 mmol/L nitrate, which were significantly lower than that (7.13 mmol/L) of the control. In addition, the glucose consumption significantly decreased in the presence of nitrate. Formate consumption decreased with the increase in nitrate concentration and became zero at the nitrate concentration of 30 mmol/L. [Conclusion] Nitrate of 30 mmol/L inhibited carbon fixation by formate-dependent acetogenesis, and that of 10 mmol/L decreased the glycolysis in C. bovifaecis.

Abstract:[Background] Heterotrophic nitrifying-aerobic denitrifying microorganisms have received more and more attention, because they achieve the vision of simultaneous nitrification and denitrification in one system. The nitrogen removal pathway is different along with different bacteria. While the nitrogen metabolic pathway of bacteria is direct correlation with the type and activity of nitrogen elimination enzyme. So find out the nitrogen removal pathway of Pseudomonas alcaliphila AD-28 will provide technical support in application. [Objective] In order to reveal the nitrogen removal mechanism, the nitrogen removal characteristic and key enzymes for nitrogen degradation of Pseudomonas alcaliphila AD-28 were studied. [Methods] The nitrogen removal characteristic of strain AD-28 was investigated when sodium citrate was used as carbon source, ammonium sulfate, sodium nitrite and potassium nitrate were used as nitrogen sources. At the same time, the activities of key enzymes-ammonia monooxygenase (AMO), hydroxylamine oxidoreductase (HAO), nitrite reductase (NIR) and nitrate reductase (NAR) were measured. [Results] After 24 h treatment by strain AD-28, bacteria density (OD600) reached 1.971, the degradation rates of NH4+-N, NO3?-N, NO2?-N and total nitrogen (TN) were all exceeded 96% when the initial concentrations were 18.85, 26.13, 19.47, 66.11 mg/L, respectively. The corresponding specific activities of AMO, HAO, NIR and NAR were 0.028, 0.003, 0.011, 0.027 U/mg, respectively. [Conclusion] The results suggest that AD-28 is a simultaneous heterotrophic nitrification-aerobic denitrification strain. The nitrogen removal pathway of the stain was deduced as following. NH4+-N was oxidized to NH2OH by AMO, then NH2OH oxidized to NO2?-N by HAO, NO2?-N and NO3?-N removed from the medium by NIR and NAR.

Abstract:[Objective] To study the effect of Cr(Ⅵ) reduction ability of Serratia sp. S2 under ammonia nitrogen (AN) and nitrate nitrogen (NN) with different concentration. [Methods] Simulated the nitrogen pollution of common environment in the laboratory and added different doses of AN or/and NN to the cultivation system in order to evaluate the effect of different types and concentrations of nitrogen, S2 was cultured in the premise of the Cr(Ⅵ) containing culture. Shake culture at constant 37 °C and measure A600, removal rate of Cr(Ⅵ), amount of AN and NN at a regular intervals. [Results] The growth inhibition of Cr(Ⅵ) to S2 was remittenced under the low and middle AN groups. The decline of S2 was accelerated under the high AN and NN groups. The removal rate of Cr(Ⅵ) and amount of AN among experience and control groups according to the independent effect of AN had no significant relationship. The removal rate of Cr(Ⅵ) of low concentration groups had a significant reduction of more than 10.0% and a increase of 7.1% in high concentration groups according to the independent effect of NN. S2 had the ability to reduce 200 mg/L NN to the level of control groups within 4 h. While AN and NN effect at the same time, AN played a leading role in low concentration groups and NN in high groups during the course of Cr(Ⅵ) reduction. [Conclusion] The presence of AN had no significant effect to the Cr(Ⅵ)-removal ability. Different concentrations of NN had different effect to Cr(Ⅵ)-removal ability. High concentration groups had an advantage effect. S2 had a significant ability of reducing NN.

Abstract:An aerobic denitrifying bacterial strain CY1 was isolated from soil. The denitrifying experiment results showed that under anaerobic or aerobic conditions the reduction efficiency within 30 hours was up to 99.98% (anaerobic) and 60.16% (anaerobic) respectively with initial NO3-N concentration of 137.25 mg/L. According to its morphologica, physiological and biochemical characters, as well as 16S rDNA sequence homology comparison, strain CY1 was identified as a member of Paracoccus pantotrophus.