Browsing by Subject "biodegradation"
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Item Biodegradation of Estrogenic Steroidal Hormones(2011-10-21) Kim, Sang HyunNatural and synthetic estrogens are some of the most potent hormones detected in the environment. Agriculture fields often release higher concentrations of natural estrogens to the environment, but wastewater treatment plants (WWTPs) commonly release higher concentrations of synthetic estrogens. Estrogens can disrupt endocrine functions in wildlife and humans. Less attention has been paid to the fate and occurrence of estrogens in agricultural operations than WWTPs. Their fate is influenced by major mechanisms such as sorption and biodegradation. Sorption typically accounts for less than 10 percent of estrogen removal in WWTPs. However, biodegradation is a primary method for estrogen loss at high ammonia concentration in the agricultural and municipal operation. Less attention has been paid to the biodegradation kinetics of estrogens in the field application. Therefore, this dissertation focused on the occurrence of estrogens in agricultural fields and their biodegradation by a mixed culture and a pure culture. The estrogens in turkey litter amended fields might be biodegraded to some degree by turkey litter borne bacteria. The estrogen biodegradation by a mixed culture showed different mechanisms for each estrogen. E1 and E2 were easily degraded as a carbon source of the mixed culture. E3 and EE2 were favorable for cometabolic degradation by AOB. EE2 was not readily biodegraded by the mixed culture due to a steric hindrance of enzyme expression and EE2 metabolism in the ethynylgroup of EE2. The cometabolic kinetics of individual estrogen was evaluated by using a pure culture. The cometabolism of estrogen was demonstrated by a reductant model. This model appropriately estimated the cometabolic kinetics of individual estrogens. In addition, the effect of antibiotics on the hormone degradation was investigated in Sequencing Batch Reactors (SBRs). No significant difference was detected for the removal efficiency of target compounds in the SBRs in presence or absence of antibiotics (oxytetracycline and chlortetracycline) during long sludge retention time (SRT). However, the effluent organic matter (EfOM) was less decomposed with the presence of antibiotics, especially causing less degradation of the humic-like substances in EfOM. The results indicated the flux of antibiotics to WWTPs did not affect hormone degradation, but reduced the decomposition of humic-like substance. Finally, the findings from the research provide insight into how biodegradation influences estrogen removal in agricultural fields and municipal WWTPs. The models developed in this research yielded valuable predictive values for engineered systems.Item Biodegradation of triclosan by a triclosan-degrading isolate and an ammonia-oxidizing bacterium(Texas A&M University, 2007-09-17) Zhao, FumanTriclosan is incorporated in a wide array of medical and consumer products as an antimicrobial agent or preservative. Disposal of these products transport triclosan into wastewater and later into soils and surface waters. Due to incomplete removal of triclosan in wastewater treatment plants, contamination of triclosan in the environment has raised several concerns, including: (i) an aid to the development of cross-resistance to antibiotics, (ii) the toxicity to ecological health, (iii) the formation of chlorodioxins from triclosan and its metabolites. By using 14C-labeled triclosan, 14CO2 was observed in activated sludge samples, suggesting that triclosan was biodegraded. However, little is known about the microorganisms responsible for triclosan biodegradation in activated sludge. The goal of this study is to better understand biodegradation of triclosan in activated sludge. Two specific objectives are: (i) isolating and characterizing triclosan-degrading bacteria from activated sludge, (ii) characterizing the cometabolic degradation of triclosan through an ammonia-oxidizing bacterium Nitrosomonas europaea. A triclosan-degrading strain, KCY1, was successfully isolated from the activated sludge. The strain KCY1 completely degraded triclosan in three days when OD600 was 0.4. Based on 16S rRNA analysis, the strain KCY1 has 97% similarity with Phingomonas or Phingopyxis. Negative results of oxygenase activity assays suggested that other enzymes rather than oxygenases might be responsible for the triclosan biodegradation. Experiments using N. europaea showed that triclosan could be cometabolized. In the presence of inhibitor for ammonia monooxygenase (AMO), N. europaea was unable to degrade triclosan, suggesting that AMO might be responsible for triclosan degradation. Triclosan appeared to competitively inhibit ammonia oxidation by N. europaea. Results of this study showed that triclosan might be effectively biodegraded by triclosan-degrading cultures, strain KCY1 and N. europaea.Item Biodegradation of Triclosan by Aerobic Microorganisms(2012-10-19) Lee, Do GyunTriclosan, a synthetic antimicrobial agent, is an emerging environmental contaminant. Due to incomplete removal of triclosan by wastewater treatment plants, treated wastewater is one major source of environmental triclosan. Biodegradation of triclosan has been observed in activated sludge and the environment, suggesting that it is possible to develop a cost-effective biotreatment strategy for triclosan removal from wastewater. However, current knowledge on triclosan biodegradation is scarce and limited. To bridge this knowledge gap, this dissertation characterized cultivable triclosan-degrading microorganisms, identified uncultivable triclosan-utilizing bacteria, and elucidated triclosan biodegradation pathways. Furthermore, two treatment strategies were examined to enhance triclosan biodegradation in nitrifying activated sludge (NAS). A wastewater bacterial isolate, Sphingopyxis strain KCY1 (hereafter referred as strain KCY1), can completely degrade triclosan with a stoichiometric release of chloride. This strain can retain its degradation ability toward triclosan when after grown in complex nutrient medium containing triclosan as low as 5 micrograms/L. Based on five identified metabolites, a meta-cleavage pathway was proposed for triclosan biodegradation by strain KCY1. By using [13C12]-triclosan stable isotope probing, eleven uncultured triclosan-utilizing bacteria in a triclosan-degrading microbial consortium were identified. These clones are distributed among alpha-, beta-, or gamma-Proteobacteria, suggesting that triclosan-utilizing bacteria are phylogenetically diverse. None of these clone sequences were similar to known triclosan degraders. Growth substrates affected the triclosan degradation potential of four selected oxygenase-expressing bacteria. Biphenyl-grown Burkholderia xenovorans LB400 and propane-grown Rhodococcus ruber ENV425 cannot degrade triclosan. On the other hand, propane- and 2-propanol-grown Mycobacterium vaccae JOB5 can degrade triclosan completely. Due to product toxicity, finite transformation capacities for triclosan were observed for Rhodococcus jostii RHA1 grown on biphenyl, propane, and LB medium with dicyclopropylketone (alkane monooxygenase inducer). Four chlorinated metabolites were detected during triclosan degradation by biphenyl-grown RHA1 and a meta-cleavage pathway was proposed. Complete triclosan (5 mg/L) degradation was observed within 96 hrs in NAS receiving ammonia amendment (0 to 75 mg/L of NH4-N). The fastest triclosan degradation was observed in the NAS exhibiting the highest amount of ammonia. When ammonia oxidation was active in NAS, the amendment of strain KCY1 did not further enhance triclosan removal. Overall, the results suggested that triclosan biodegradation can be enhanced by increasing the activity of ammonia oxidation in NAS.Item Bioremediation of the organophosphate methyl parathion using genetically engineered and native organisms(Texas A&M University, 2005-11-01) Diaz Casas, Adriana Z.Toxic waste disposal problems have become enormous due to the proliferation of xenobiotic compounds for use in agricultural, industrial and numerous other applications. Organophosphate (OP) pesticides are commonly used in agriculture and their toxicity is associated with inhibition of cholinesterase in the exposed organism. Some OPs have been shown to produce OP-induced delayed neuropathy (OPIDN). The overall goal of the work described in this thesis was to develop bacterial consortia to remediate hazardous substances at significantly higher rates than found with natural systems. Specifically, degradation of methyl parathion (MP) by hydrolysis with a genetically engineered Escherichia coli was investigated along with degradation of one of the resulting products, p-nitrophenol (PNP), by Sphingobium chlorophenolicum ATCC 53874. Simultaneous degradation of both MP and PNP was investigated using a consortium of a genetically engineered Escherichia coli and a native S. chlorophenolicum. Concentrations of MP and PNP were measured by high performance liquid chromatography (HPLC). Non-growing freely suspended recombinant OPH+ E. coli cells efficiently degraded MP without addition of nutrients for growth. Maximum reactor productivity was found with a biomass concentration of 25 g/L. Substrate inhibition did not occur up to 3 g MP/L. The simple Michaelis-Menten kinetic model for enzymatic reactions provided a good fit of the degradation data with Vm=11.45 ??mol/min??g-biomass and Km=2.73 g/L. B. cepacia failed to degrade PNP under the experimental conditions evaluated, so further studies were not conducted. Growing cultures of S. chlorophenolicum degraded PNP at concentrations up to 0.1 g/L without a lag phase in mineral salts glutamate medium. Parameters such as initial pH, growth medium and growth stage for addition of PNP were important degradation factors. The bacterium exhibited substantial growth in the degradation process. Hydroquinone (HQ) or nitrocatechol (NC) were not identified as products of PNP degradation. The recombinant OPH+ E. coli and S. chlorophenolicum consortium failed to degrade PNP when starting with higher concentrations of MP. The presence of organic solvent in the bacterial consortium degradation medium negatively affected the degradation of PNP. The genetically engineered organism efficiently degraded high concentrations of MP, but the resulting high concentration of intermediate product (PNP) inhibited growth of the native type organism. Biodegradation by consortia of genetically engineered non-growing and native-type organisms generally will be limited by the growing native-type organism.