Anaerobic biodegradation of linear alkylbenzene sulfonate (LAS) in upflow anaerobic sludge blanket (UASB) reactors

The anaerobic biodegradation of Linear Alkylbenzene Sulfonate (LAS) was studied in Upflow Anaerobic Sludge Blanket Reactors (UASB). One reactor was fed with easily degradable substrates and commercial LAS solution during a period of 3 months (Reactor 1), meanwhile a second reactor was fed with a commercial LAS solution without co-substrate (Reactor 2) during 4 months. Both reactors were operated with an organic loading rate of 4–5 mg-LAS/l*day and a hydraulic retention time of one day.The LAS biodegradation was determined by full mass balance. LAS was analysed by HPLC in the liquid phase (influent and effluent streams of the reactors) as well as in the solid phase (granular sludge used as biomass). The results indicate a high level of removal (primary biodegradation: 64–85%). Biodegradation was higher in the absence of external co-substrates than in the presence of additional sources of carbon. This indicates that the surfactant can be partially used as carbon and energy source by anaerobic bacteria. Under the operating conditions used, inhibition of the methanogenic activity or any other negative effects on the biomass due to the presence of LAS were not observed. The methanogenic activity remained high and stable throughout the experiment.     

Sophorolipids: improvement of the selective production by Starmerella bombicola through the design of nutritional requirements

Microtiter plates were used as minireactors to study Starmerella bombicola growth and sophorolipid (SL) production. Compositional analysis of SL mixtures by liquid chromatography with electrospray ionization tandem mass spectrometry showed similar results on SLs produced using the laboratory scale (shake flask) and the microscale (24-well microtiter plates (MTP)) approach. MTP suitability on SL production was proven, being this approach, especially advantageous on SL screening. Several hydrophilic carbon sources, hydrophobic co-substrates and nitrogen sources were supplied to culture media, and their influence on SL production was evaluated. The selection of specific hydrophobic co-substrate and nitrogen sources influenced the ratio acidic/lactonic SLs. In fact, it was observed that the production of acidic C18:1 diacetylated hydroxy fatty acid SLs was favoured when culture media was supplied with avocado, argan, sweet almond and jojoba oil or when NaNO₃ was supplied instead of urea. This last case was observed after 144 h of cultivation. A new SL, lactonic C18:3 hydroxy fatty acid diacetylated SL, was detected when borage and onagra oils were used individually as co-substrates. Overall results indicated the potential of the selective production of different and new sophorolipids by Starmerella bombicola based on the selection of carbon and nitrogen sources to culture media.     

Bioremediation of PAHs-contaminated soil through composting: Influence of bioaugmentation and biostimulation on contaminant biodegradation

The degradation of several polycyclic aromatic hydrocarbons (PAHs) in soil through composting was investigated. The selected PAHs included: fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, and chrysene, with concentrations simulating a real creosote sample. The degradation of PAHs (initial concentration 1 g of total PAHs kg⁻¹ dry soil) was assessed applying bioaugmentation with the white-rot fungi Trametes versicolor and biostimulation using compost of the source-selected organic fraction of municipal solid waste (OFMSW) and rabbit food as organic co-substrates. The process performance during 30 days of incubation was evaluated through different analyses including: dynamic respiration index (DRI), cumulative oxygen consumption during 5 days (AT₅), enzymatic activity, and fungal biomass. These analyses demonstrated that the introduced T. versicolor did not significantly enhance the degradation of PAHs. However, biostimulation was able to improve the PAHs degradation: 89% of the total PAHs were degraded by the end of the composting period (30 days) compared to the only 29.5% that was achieved by the soil indigenous microorganisms without any co-substrate (control, not amended). Indeed, the results showed that stable compost from the OFMSW has a greater potential to enhance the degradation of PAHs compared to non-stable co-substrates such as rabbit food.     

Xylitol production by recombinant Saccharomyces cerevisiae expressing the Pichia stipitis and Candida shehatae XYL1 genes

The xylose reductase gene (XYL1) was isolated from Pichia stipitis and Candida shehatae, cloned into YEp-based vectors under the control of ADH2 and PGK1 promoter/terminator cassettes and introduced into Saccharomyces cerevisiae Y294 by electroporation. Shake-flask fermentations were carried out with 5% xylose and 1% galactose, glucose or maltose as co-substrates. Xylose uptake was similar in both the recombinant strains when different co-substrates were used and slowed once the co-substrate was depleted. The recombinant strains converted xylose to xylitol with yields approaching the theoretical maxima. Xylitol production was most rapid when the co-substrate was still present. Approximately 50% of the xylose was not metabolized due to the depletion of the co-substrate. Received: 23 December 1999 / Received revision: 30 June 2000 / Accepted: 1 July 2000     

Biodegradation and metabolite transformation of pyrene by basidiomycetes fungal isolate Armillaria sp. F022

Armillaria sp. F022 is a white-rot fungus isolated from a tropical rain forest in Indonesia that is capable of utilizing pyrene as a source of carbon and energy. Enzymes production during the degradation process by Armillaria sp. F022 was certainly related to the increase in biomass. In the first week after incubation, the growth rate rapidly increased, but enzyme production decreased. After 7 days of incubation, rapid growth was observed, whereas, the enzymes were produced only after a good amount of biomass was generated. About 63 % of pyrene underwent biodegradation when incubated with this fungus in a liquid medium on a rotary shaker (120 rpm, 25 °C) for 30 days; during this period, pyrene was transformed to five stable metabolic products. These metabolites were extracted in ethyl acetate, isolated by column chromatography, and then identified using thin layer chromatography (TLC) and gas chromatography–mass spectrometry (GC–MS). 1-Hydroxypyrene was directly identified by GC–MS, while 4-phenanthroic acid, 1-hydroxy-2-naphthoic acid, phthalic acid, and protocatechuic acid were identified to be present in their derivatized forms (methylated forms and silylated forms). Protocatechuic acid was the end product of pyrene degradation by Armillaria sp. F022. Dynamic profiles of two key enzymes, namely laccase and 1,2-dioxygenase, were revealed during the degradation process, and the results indicated the presence of a complicated mechanism in the regulation of pyrene-degrading enzymes. In conclusion, Armillaria sp. F022 is a white-rot fungus with potential for application in the degradation of polycyclic aromatic hydrocarbons such as pyrene in the environment.     

Degradation of polycyclic aromatic hydrocarbons and long chain alkanes at 6070 °C by Thermus and Bacillus spp

Although polycyclic aromatic hydrocarbons (PAH) and alkanesare biodegradable at ambient temperature, in some cases low bioavailabilities are thereason for slow biodegradation. Considerably higher mass transfer rates and PAH solubilities and hence bioavailabilities can be obtained at higher temperatures. Mixed and pure cultures of aerobic, extreme thermophilic microorganisms (Bacillus spp., Thermus sp.) were used to degrade PAH compounds and PAH/alkane mixtures at 65 °C. The microorganismsused grew on hydrocarbons as sole carbon and energy source. Optimal growthtemperatures were in the range of 60–70 °C at pH values of 6–7. The conversion of PAH with 3–5 rings (acenaphthene, fluoranthene, pyrene, benzo[e]pyrene) was demonstrated. Efficient PAH biodegradation required a second, degradable liquid phase. Thermus brockii Hamburg metabolized up to 40 mg (l h)^-1 pyrene and 1000 mg(1 h)^-1 hexadecane at 70 °C. Specific growth rates of 0.43 h^-1 were measured for this strain with hexadecane/pyrene mixtures as the sole carbon and energy source in a 2-liter stirred bioreactor. About 0.7 g cell dry weight were formed from 1 g hydrocarbon. The experiments demonstrate the feasibility and efficiency of extreme thermophilic PAH and alkane biodegradation.     

N-Hydroxyguanidines oxidation by a N3S copper-complex mimicking the reactivity of Dopamine β-Hydroxylase

N-Aryl-N′-hydroxyguanidines are compounds that display interesting pharmacological properties but their chemical reactivity remains poorly investigated. Some of these compounds are substrates for the heme-containing enzymes nitric-oxide synthases (NOS) and act as reducing co-substrates for the copper-containing enzyme Dopamine β-Hydroxylase (DBH) [P. Slama, J.L. Boucher, M. Réglier, Biochem. Biophys. Res. Commun. 316 (2004) 1081-1087]. DBH catalyses the hydroxylation of the important neurotransmitter dopamine into norepinephrine in the presence of both molecular oxygen and a reducing co-substrate. Although many molecules have been used as co-substrates for DBH, their interaction at the active site of DBH and their role in mechanism are not clearly characterized. In the present paper, we have used a water-soluble copper-N₃S complex that mimics the Cu_B site of DBH, and aromatic N-hydroxyguanidines as reducers to address this question. N-Aryl-N′-hydroxyguanidines readily reduced copper(II) to Cu(I) and were oxidized into a nitrosoamidine as previously observed in reactions performed with purified DBH. These data describe for the first time the reactivity of N-aryl-N′-hydroxyguanidines with a water-soluble copper(II) complex and help to understand the interaction of co-substrates with copper at the active site of DBH.     

Biodegradation of high molecular weight lignin under sulfate reducing conditions: lignin degradability and degradation by-products

This study is designed to investigate the biodegradation of high molecular weight (HMW) lignin under sulfate reducing conditions. With a continuously mesophilic operated reactor in the presence of co-substrates of cellulose, the changes in HMW lignin concentration and chemical structure were analyzed. The acid precipitable polymeric lignin (APPL) and lignin monomers, which are known as degradation by-products, were isolated and detected. The results showed that HMW lignin decreased and showed a maximum degradation capacity of 3.49 mg/l/day. APPL was confirmed as a polymeric degradation by-product and was accumulated in accordance with HMW lignin reduction. We also observed non-linear accumulation of aromatic lignin monomers such as hydrocinnamic acid. Through our experimental results, it was determined that HMW lignin, when provided with a co-substrate of cellulose, is biodegraded through production of APPL and aromatic monomers under anaerobic sulfate reducing conditions with a co-substrate of cellulose.     

Identification and biodegradation efficiency of a newly isolated 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) aerobic degrading bacterial strain

Polybrominated diphenyl ethers (PBDEs) are bioaccumulative, toxic and persistent, globally distributed organic chemicals in environment. However, very little is known for their aerobic biodegradation. In this research, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was selected as a model congener of PBDEs to study its aerobic biodegradation. A new BDE-47 degrading strain BFR01 identified as Pseudomonas stutzeri was isolated from polluted soil in a former brominated flame retardant production corporation. Stain BFR01 could utilize BDE-47 as a sole source of carbon and energy, and transformed 97.94% of BDE-47 in two weeks; the biodegradation of BDE-47 fitted well with the first-order kinetics, with the first-order kinetics constant of 0.32 d⁻¹. The biodegradation efficiency of stain BFR01 was higher than other reported PBDEs aerobic degrading bacteria. The biodegradation efficiency achieved maximum at pH 7.0 and 40 °C. The presence of additional carbon sources could enhance the biodegradation efficiency of BDE-47 by 1–6%. Furthermore, no lower brominated diphenyl ethers or biphenyl were detected, suggesting that the pathway of BDE-47 biodegradation by strain BFR01 might not be debromination with lower brominated diphenyl ethers as products. This is the first report of aerobic degradation of BDE-47 by P. stutzeri.     

Characterization of acetyl-CoA: Ecdysone 3-acetyltransferase in Schistocerca gregaria larvae

Characterization of the acetyltransferase (acetyl-CoA: ecdysone 3-acetyltransferase) which catalyzes the conversion of ecdysone into ecdysone 3-acetate was carried out in gastric caecae of day 7 last instar larvae of Schistocerca gregaria. This enzyme is one of the enzymic systems involved in the inactivation of ecdysteroids. The acetyltransferase exhibited a microsomal subcellular localization, an apparent K_m for ecdysone of 71 μM, a maximal specific activity of 7.2 nmol/min/mg of protein and was inhibited competitively in the presence of 20-hydroxyecdysone with K_i = 68.8 μM. The enzyme required acetyl-CoA as co-substrate for its activity, the apparent K_m for acetyl-CoA being 47.2 μM. Acetic acid could not replace acetyl-CoA as the co-substrate, indicating that the enzyme is an acetyl-CoA: ecdysone acetyltransferase and not a hydrolase. Similarly, esterification of ecdysone was not observed when long-chain fatty acyl-CoA derivatives were substituted as co-substrates. The reaction was linear for 20 min and with protein concentration up to 0.8 mg/ml.The formation of 20-hydroxyecdysone 3-acetate has been demonstrated in the same microsomal fraction and required also acetyl-CoA as co-substrate. The apparent K_m of the acetyltransferase for 20-hydroxyecdysone was 53.5 μM, revealing that the enzyme had a somewhat stronger affinity for 20-hydroxyecdysone than for ecdysone.     

Degradation pathway, toxicity and kinetics of 2,4,6-trichlorophenol with different co-substrate by aerobic granules in SBR

The present study deals with cultivation of 2,4,6-trichlorophenol (TCP) degrading aerobic granules in two SBR systems based on glucose and acetate as co-substrate. Biodegradation of TCP containing wastewater starting from 10 to 360 mg L⁻¹ with more than 90% efficiency was achieved. Sludge volume index decreases as the operation proceeds to stabilize at 35 and 30 mL g⁻¹ while MLVSS increases from 4 to 6.5 and 6.2 g L⁻¹ for R1 (with glucose as co-substrate) and R2 (with sodium acetate as co-substrate), respectively. FTIR, GC and GC/MS spectral studies shows that the biodegradation occurred via chlorocatechol pathway and the cleavage may be at ortho-position. Haldane model for inhibitory substrate was applied to the system and it was observed that glucose fed granules have a high specific degradation rate and efficiency than acetate fed granules. Genotoxicity studies shows that effluent coming from SBRs was non-toxic.     

Engineering Escherichia coli for methanol-dependent growth on glucose for metabolite production

Synthetic methylotrophy aims to engineer methane and methanol utilization pathways in platform hosts like Escherichia coli for industrial bioprocessing of natural gas and biogas. While recent attempts to engineer synthetic methanol auxotrophs have proved successful, these studies focused on scarce and expensive co-substrates. Here, we engineered E. coli for methanol-dependent growth on glucose, an abundant and inexpensive co-substrate, via deletion of glucose 6-phosphate isomerase (pgi), phosphogluconate dehydratase (edd), and ribose 5-phosphate isomerases (rpiAB). Since the parental strain did not exhibit methanol-dependent growth on glucose in minimal medium, we first achieved methanol-dependent growth via amino acid supplementation and used this medium to evolve the strain for methanol-dependent growth in glucose minimal medium. The evolved strain exhibited a maximum growth rate of 0.15 h⁻¹ in glucose minimal medium with methanol, which is comparable to that of other synthetic methanol auxotrophs. Whole genome sequencing and ¹³C-metabolic flux analysis revealed the causative mutations in the evolved strain. A mutation in the phosphotransferase system enzyme I gene (ptsI) resulted in a reduced glucose uptake rate to maintain a one-to-one molar ratio of substrate utilization. Deletion of the e14 prophage DNA region resulted in two non-synonymous mutations in the isocitrate dehydrogenase (icd) gene, which reduced TCA cycle carbon flux to maintain the internal redox state. In high cell density glucose fed-batch fermentation, methanol-dependent acetone production resulted in 22% average carbon labeling of acetone from ¹³C-methanol, which far surpasses that of the previous best (2.4%) found with methylotrophic E. coli Δpgi. This study addresses the need to identify appropriate co-substrates for engineering synthetic methanol auxotrophs and provides a basis for the next steps toward industrial one-carbon bioprocessing.     

Simultaneous Biodegradation of Polyaromatic Hydrocarbons by a <Emphasis Type="Italic">Stenotrophomonas</Emphasis> sp: Characterization of <Emphasis Type="Italic">nid</Emphasis> Genes and Effect of Surfactants on Degradation

A polyaromatic hydrocarbon degrading bacterium was isolated from a petroleum contaminated site and designated as Stenotrophomonas sp. strain IITR87. It was found to utilize pyrene, phenanthrene and benzo(a)pyrene as sole carbon source, but not anthracene, chrysene and fluoranthene. Gas chromatography and mass spectroscopy analysis resulted in identification of pyrene metabolites namely monohydroxypyrene, 4-oxa-pyrene-5-one, dimethoxypyrene and monohydroxyphenanthrene. Southern hybridization using naphthalene dioxygenase gene (nidA) as probe against the DNA of strain IITR87 revealed the presence of nidA gene. PCR analysis suggests dispersed occurrence of nid genes in the genome instead of a cluster as reported in a PAH-degrading Mycobacterium vanbaalenii PYR-1. The nid genes in strain IITR87, dioxygenase large subunit (nidA), naphthalene dioxygenase small subunit (nidB) and aldehyde dehydrogenase gene (nidD) showed more than 97 % identity to the reported nid genes from Mycobacterium vanbaalenii PYR-1. Most significantly, the biodegradation of PAHs was enhanced 25–60 % in the presence of surfactants rhamnolipid and Triton X-100 due to increased solubilization and bioavailability. These results could be useful for the improved biodegradation of high-molecular-weight PAHs in contaminated habitats.     

Degradation and Mineralization of High-Molecular-Weight Polycyclic Aromatic Hydrocarbons by Defined Fungal-Bacterial Cocultures

This study investigated the biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) in liquid media and soil by bacteria (Stenotrophomonas maltophilia VUN 10,010 and bacterial consortium VUN 10,009) and a fungus (Penicillium janthinellum VUO 10,201) that were isolated from separate creosote- and manufactured-gas plant-contaminated soils. The bacteria could use pyrene as their sole carbon and energy source in a basal salts medium (BSM) and mineralized significant amounts of benzo[a]pyrene cometabolically when pyrene was also present in BSM. P. janthinellum VUO 10,201 could not utilize any high-molecular-weight PAH as sole carbon and energy source but could partially degrade these if cultured in a nutrient broth. Although small amounts of chrysene, benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene were degraded by axenic cultures of these isolates in BSM containing a single PAH, such conditions did not support significant microbial growth or PAH mineralization. However, significant degradation of, and microbial growth on, pyrene, chrysene, benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene, each as a single PAH in BSM, occurred when P. janthinellum VUO 10,201 and either bacterial consortium VUN 10,009 or S. maltophilia VUN 10,010 were combined in the one culture, i.e., fungal-bacterial cocultures: 25% of the benzo[a]pyrene was mineralized to CO₂ by these cocultures over 49 days, accompanied by transient accumulation and disappearance of intermediates detected by high-pressure liquid chromatography. Inoculation of fungal-bacterial cocultures into PAH-contaminated soil resulted in significantly improved degradation of high-molecular-weight PAHs, benzo[a]pyrene mineralization (53% of added [¹⁴C]benzo[a]pyrene was recovered as ¹⁴CO₂ in 100 days), and reduction in the mutagenicity of organic soil extracts, compared with the indigenous microbes and soil amended with only axenic inocula.     

How UV photolysis accelerates the biodegradation and mineralization of sulfadiazine (SD)

Sulfadiazine (SD), one of broad-spectrum antibiotics, exhibits limited biodegradation in wastewater treatment due to its chemical structure, which requires initial mono-oxygenation reactions to initiate its biodegradation. Intimately coupling UV photolysis with biodegradation, realized with the internal loop photobiodegradation reactor, accelerated SD biodegradation and mineralization by 35 and 71 %, respectively. The main organic products from photolysis were 2-aminopyrimidine (2-AP), p-aminobenzenesulfonic acid (ABS), and aniline (An), and an SD-photolysis pathway could be identified using C, N, and S balances. Adding An or ABS (but not 2-AP) into the SD solution during biodegradation experiments (no UV photolysis) gave SD removal and mineralization rates similar to intimately coupled photolysis and biodegradation. An SD biodegradation pathway, based on a diverse set of the experimental results, explains how the mineralization of ABS and An (but not 2-AP) provided internal electron carriers that accelerated the initial mono-oxygenation reactions of SD biodegradation. Thus, multiple lines of evidence support that the mechanism by which intimately coupled photolysis and biodegradation accelerated SD removal and mineralization was through producing co-substrates whose oxidation produced electron equivalents that stimulated the initial mono-oxygenation reactions for SD biodegradation.     

Characterization of the bottom sediments contaminated with polychlorinated biphenyls: Evaluation of ecotoxicity and biodegradability

At the locality of the former producer of PCBs Chemko Strá?ske in East Slovakia, a large amount of PCBs (the commercial mixture DELOR 103, an equivalent of AROCLOR 1242) is still persisting in sediments and negatively influences health of the population. The objective of this work was to provide a study of ecotoxicity and genotoxicity of PCBs in contaminated sediments. Toxicity of the PCB-contaminated sediments sampled from Zemplínska ?írava and Strá?sky canal (surroundings of the former producer of PCBs) was determined applying a standard aquatic plant toxicity test using Lemna minor. The endpoints for the test were frond numbers and frond areas. The sediment sampled from Zemplínska ?írava was more toxic to L. minor than the one sampled from Strá?sky canal. The results on genotoxicity showed that both sediments were not mutagenic toward the standard strains of the Ames test, Salmonella typhimurium TA98 and TA100. This work deals also with biodegradation of PCBs in two samples of the above mentioned contaminated sediments: a) in the natural sediments by autochthonous microbial consortium and b) in the bioaugmented sediments inoculated by allochthonous bacterial strains, two bacterial isolates from long-term PCB-contaminated soil Pseudomonas stutzeri and Alcaligenes xylosoxidans. Both approaches were applied under the biostimulation conditions, with addition of glucose or biphenyl as co-substrates, as well. The highest PCB degradation was observed in the bioaugmented sediment inoculated with bacterial strain P. stutzeri. Addition of biphenyl, as the co-substrate and the inducer, positively affected degradation of PCBs. The bphA1 gene, encoding enzyme biphenyldioxygenase, responsible for the start of PCB degradation, was identified in genome of P. stutzeri, a potential PCB-degrader isolated from long-term PCB-contaminated soil, but not in genome of A. xylosoxidans.     

Decolorization of Textile Reactive Dyes by Bacterial Monoculture and Consortium Screened from Textile Dyeing Effluent

Dyeing effluents have become a vital source of water pollution. Due to the xenobiotic properties and toxicity to all life forms including humans, removal of undesirable color and associated toxicity is crucial. In this study, five dye decolorizing bacteria were isolated from dyeing effluent using selective enrichment culture in Bushnell-Haas (BH) medium amended with co-substrate (i.e. glucose, yeast extract) and 100?mg?L^?1 of each commercially available reactive dyes viz. Novacron Orange FN-R, Novacron Brilliant Blue FN-R, Novacron Super Black G, Bezema Yellow S8-G and Bezema Red S2-B. The isolated bacteria were identified and assigned as Neisseria sp., Vibrio sp., Bacillus sp., Bacillus sp. and Aeromonas sp. based on their phenotypic (cultural, morphological, physiological and biochemical characteristic) observation. The dye decolorization efficiency was estimated spectrophotometrically up to 6?days of static incubation at 37?°C and observed that all of the isolates were unable to induce decolorization in absence of co-substrate. In case of monoculture, decolorization percentage varies from no visible decolorization (Bezema Red S2-B by Ek-5) to highest 90% decolorization (Novacron Brilliant Blue FN-R by Ek-13) whereas the decolorization percentage of bacterial consortium varies from 65% (Bezema Yellow S8-G) to 90% (Novacron Brilliant Blue FN-R and Novacron Super Black G). The study outlines the co-substrates mediated decolorization process where bacterial consortium proved as efficient dye decolorizer than that of the monocultures. This finding confers possibility of using novel microbial consortium for biological treatment of disreputable dyeing effluents.     

Evaluating and modeling biogas production from municipal fat, oil, and grease and synthetic kitchen waste in anaerobic co-digestions

The feasibility of using synthetic kitchen waste (KW) and fat, oil, and grease (FOG) as co-substrates in the anaerobic digestion of waste activated sludge (WAS) was investigated using two series of biochemical methane potential (BMP) tests. Ranges of ideal substrate to inoculum (S/I) ratio were determined for the FOG (0.25-0.75) and KW (0.80-1.26) as single substrates in the first experiment. The second experiment, which estimated the methane production performances of FOG and KW as co-substrates for WAS co-digestion, was conducted based on the optimal parameters selected from the results of the first experiment. Results indicated that co-digestions with FOG and KW enhanced methane production from 117±2.02 mL/gTVS (with only WAS) to 418±13.7 mL/gTVS and 324±4.11 mL/gTVS, respectively. FOG exhibited more biogas production than KW as co-substrate. Non-linear regression results showed that co-substrate addition shortened the lag phases of organic biodegradation from 81.8 (with only WAS) to 28.3 h with FOG and 3.90 h with KW.     

Microbial Degradation of Acetamiprid by Ochrobactrum sp. D-12 Isolated from Contaminated Soil

Neonicotinoid insecticides are one of the most important commercial insecticides used worldwide. The potential toxicity of the residues present in environment to humans has received considerable attention. In this study, a novel Ochrobactrum sp. strain D-12 capable of using acetamiprid as the sole carbon source as well as energy, nitrogen source for growth was isolated and identified from polluted agricultural soil. Strain D-12 was able to completely degrade acetamiprid with initial concentrations of 0–3000 mg·L⁻¹ within 48 h. Haldane inhibition model was used to fit the special degradation rate at different initial concentrations, and the parameters q _max, K _s and K _i were determined to be 0.6394 (6 h)⁻¹, 50.96 mg·L⁻¹ and 1879 mg·L⁻¹, respectively. The strain was found highly effective in degrading acetamiprid over a wide range of temperatures (25–35°C) and pH (6–8). The effects of co-substrates on the degradation efficiency of acetamiprid were investigated. The results indicated that exogenously supplied glucose and ammonium chloride could slightly enhance the biodegradation efficiency, but even more addition of glucose or ammonium chloride delayed the biodegradation. In addition, one metabolic intermediate identified as N-methyl-(6-chloro-3-pyridyl)methylamine formed during the degradation of acetamiprid mediated by strain D-12 was captured by LC-MS, allowing a degradation pathway for acetamiprid to be proposed. This study suggests the bacterium could be a promising candidate for remediation of environments affected by acetamiprid.     

Biodegrading of pyrene by a newly isolated Pseudomonas putida PL2

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic compounds derived from natural sources and anthropogenic processes, which have been recommended as priority pollutants. Degradation of PAHs in the environment is becoming more necessary and urgent. In the current study, strain PL2, which is capable of growing aerobically on pyrene (PYR) as the sole carbon source, was isolated from hydrocarbons-contaminated soil and then identified as Pseudomonas putida by morphological and physiological characteristics as well as 16S rDNA sequence. The strain PL2 was able to degrade 50.0% of the pyrene at 28°C within 6 days in the presence of 50 mg/L pyrene, while the strain PL2 degraded 50.0% of the pyrene within 2 days when a solution of 50 mg/L pyrene and 50 mg/L phenanthrene was used. In addition, phenanthrene was shown to increase the biodegradation efficiency of pyrene by the strain PL2. The order of degradation by the strain PL2 was pH 6.0 > pH 7.0 > pH 5.0 > pH 8.0. The degradation rate of PYR in the soil by the strain PL2 reached 70.0% at the 10^th day. The dynamics of PYR degradation in soil by PL2 was fit to the first order model and the strain PL2 was shown to efficiently degrade PYR in soil. The current study showed that P. putida PL2 was a novel bacterium that could degrade pyrene and holds great promise for use in PAHs bioremediation in soil.