Stoichiometric flexibility regulates the co-metabolism effect during organic carbon mineralization in eutrophic lacustrine sediments

Several studies have suggested the pivotal roles of eutrophic lakes in carbon(C)cycling at regional and global scales.However,how the co-metabolism effect on lake sediment organic carbon(OC)mineralization changes in response to integrated inputs of labile OC and nutrients is poorly understood.This knowledge gap hinders our ability to predict the carbon sequestration potential in eutrophic lakes.Therefore,a 45-day microcosm experiment was conducted to examine the dominant mechanisms that underpin the co-metabolism response to the inputs of labile C and nutrients in lacustrine sediments.Results indicate that the labile C addition caused a rapid increase in the positive co-metabolism effect during the initial stage of incubation,and the co-metabolism effect was positively correlated with the C input level.The positive co-metabolism effect was consistently higher under high C input,which was 152%higher than that under low C input.The higherβ-glucosidase activity after nutrient addition,which,in turn,promoted the OC mineralization in sediments.In addition different impacts of nutrients on the co-metabolism effect under different C inputs were observed.Compared with the low nutrient treatments,the largest co-metabolism effect under high C with high nutrient treatment was observed by the end of the incubation.In the high C treatment,the intensity of the co-metabolism effect(CE)under high nitrogen treatment was 1.88 times higher than that under low nitrogen condition.However,in the low C treatment,the amount of nitrogen had limited impact on co-metabolism effect.Our study thus proved that the microorganisms obviously regulate sediment OC turnover via stoichiometric flexibility to maintain a balance between resources and microbial requirements,which is meaningful for evaluating the OC budget and lake eutrophication management in lacustrine sediments.

Degradation of Tetrachloroethene by Several Co-metabolism Substrates in Groundwater

Tetrachloroethene （PCE） is biodegraded by reductive dechlorination with co-metabolism substrates under anaerobic conditions. By inoculating sludge from an anaerobic pool, a biodegradation test of PCE is conducted in the anaerobic condition. In the test, several substrates including methanol, ethanol, formate, acetate, lactate and glucose, are conducive to the conversion from PCE to TCE and 1,1-DCE. The results show the microbe can be cultivated well under the anaerobic circumstances of mixture of sewage （sludge） and soil with the index of COD after eleven days. Degradation of PCE accords with one order reaction kinetics equation. The sequence of the reaction rate constant is Kacetate 〉Kglucose 〉 Klactate 〉 Kethanol 〉 Kformate 〉 Kmethanol, and acetate is an outstanding co-metabolism substratum whose reaction rate constant is 0.6632d^-1.

Bio-removal of mixture of benzene,toluene,ethylbenzene,and xylenes/total petroleum hydrocarbons/trichloroethylene from contaminated water

Four pure cultures were isolated from soil samples potentially contaminated with gasoline compounds either at a construction site near a gas station in Fai Chi Kei,Macao SAR or in the northern parts of China（Beijing,and Hebei and Shandong）.The effects of different concentrations of benzene,toluene,ethylbenzene,and three isomers（ortho-,meta-,and para-） of xylene（BTEX）,total petroleum hydrocarbons（TPH）,and trichloroethylene（TCE）,when they were present in mixtures,on the bio-removal effciencies of microbial isolates were investigated,together with their interactions during the bio-removal process.When the isolates were tested for the BTEX（50-350 mg/L）/TPH（2000 mg/L） mixture,BTEoX in BTEoX/TPH mixture was shown with higher bio-removal effciencies,while BTEmX in BTEmX/TPH mixture was shown with the lowest,regardless of isolates.The TPH in BTEmX/TPH mixture,on the other hand,were generally shown with higher bio-removal effciencies compared to when TPH mixed with BTEoX and BTEpX.When these BTEX mixtures（at 350 mg/L） were present with TCE（5-50 mg/L）,the stimulatory effect of TCE toward BTEoX bio-removal was observed for BTEoX/TCE mixture,while the inhibitory effect of TCE toward BTEmX for BTEmX/TCE mixture.The bio-removal effciency for TPH was shown lower in TPH（2000 mg/L）/TCE（5-50 mg/L） mixtures compared to TPH present alone,implying the inhibitory effect of TCE toward TPH bio-removal.For the mixture of BTEX（417 mg/L）,TPH（2000 mg/L） along with TCE（5- 50 mg/L）,TCE was shown co-metabolically removed more effciently at 15 mg/L,probably utilizing BTEX and/or TPH as primary substrates.

Anaerobic Biodegradation of Tetrachloroethylene with Acetic Acid as Cometabolism Substrate under Anaerobic Condition

A series of batch-type experiments with acetate acid as the primary substrate were performed using enrichment cultures developed from the anaerobic sludge to investigate the effect of acetate acid on tetrachloroethylene （PCE） biodegradation. Experimental results indicated that acetate acid was an efficient electron donor in affecting the biotransformability of PCE. Trichloroethylene （TCE） was the primary dehalogenation product, and small amounts of dichloroethylenes （DCEs） were also detected. No significant further DCEs degradation was detected. PCE degradation rate in the experiment was 36.6 times faster than background rate in natural groundwater.

Anaerobic Degradation of Tetrachloroethylene Using Different Co-substrates as Electron Donors

Objective To investigate the biodegradation of tetrachloroethylene （PCE） by acclimated anaerobic sludge using different co-substrates, i.e., glucose, acetate, and lactate as electron donors. Methods HP-6890 gas chromatograph （GC） in combination with auto-sampler was used to analyze the concentration of PCE and its intermediates, Results PCE could be degraded by reductive dechlorlnation and the degradation reaction conformed to the first-order kinetic equation. The rate constants are klaetate〉kglucose〉kacetate. The PCE degradation rate was the highest in the presence of lactate as an electron donor. Conclusion Lactate is the most suitable electron donor for PCE degradation and the electron donors supplied by co-metabolic substrates are not the limiting factors for PCE degradation,

Co-metabolic and biochar-promoted biodegradation of mixed PAHs by highly efficient microbial consortium QY1

Polycyclic aromatic hydrocarbons(PAHs), typical representatives of the persistent organic pollutants(POPs), have become ubiquitous in the environment.In this study, a novel microbial consortium QY1 that performed outstanding PAHs-degrading capacity has been enriched.The degradation characteristics of single and mixed PAHs treated with QY1 were studied, and the effect of biochar on biodegradation of mixed PAHs and the potential of biochar in PAHs-heavy metal combined pollution bioremediation were also investigated.Results showed that, in single substrate system, QY1 degraded 94.5% of 500 mg/L phenanthrene(PHE) and 17.8% of 10 mg/L pyrene(PYR) after 7 days, while in PHE-PYR mixture system, the biodegradation efficiencies of PHE(500 mg/L) and PYR(10 mg/L) reached 94.0%and 96.2%, respectively, since PHE served as co-metabolic substrate to have significantly improved PYR biodegradation.Notably, with the cooperation of biochar, the biodegradations of PHE and PYR were greatly accelerated.Further, biochar could reduce the adverse impact of heavy metals(Cd^(2+), Cu^(2+), Cr_(2)O_(7)^(2-)) on PYR biodegradation remarkably.The sequencing analysis revealed that Methylobacterium, Burkholderia and Stenotrophomonas were the dominant genera of QY1 in almost all treatments, indicating that these genera might play key roles in PAHs biodegradation.Overall, this study provided new insights into the efficient bioremediation of PAHs-contaminated site.