Browsing by Author "Amorim, Catarina Raquel Leite"
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- Microbial degradation of fluorinated compounds : studies on biodegradation mechanisms and biotreatment systemsPublication . Amorim, Catarina Raquel Leite; Castro, Paula Maria Lima; Afonso, Carlos Manuel Magalhães; Carvalho, Maria de Fátima MagalhãesFluoroorganics are an important class of chemicals compound used in a vast number of applications, including pharmaceutical, agricultural and industrial applications, leading to their disposal and accumulation in the environment. Therefore, it is important to understand and explore the biodegradation mechanisms for their removal. The work described in this thesis aimed to investigate the potential of single bacterial strains for biotransformation of fluoroorganics with different complexity as well as to explore their degradation and fate on biofilm bioreactors. In contaminated environments biodegradation can be affected by different factors. In this study, the effect of different parameters on the biodegradation of fluoroanilines (FAs) by Labrys portucalensis F11 was investigated. Strain F11 was able to degrade FAs as sole source of carbon and nitrogen nevertheless supplementation of the culture medium with nitrogen proved to be beneficial for the degradation. Strain F11 was also able to degrade FAs when cells were previously induced for haloaromatic degradation with fluorobenzene (FB). Indeed, higher removal capacity and substrate degradation rates were achieved using FB-induced cells. Co-metabolism of FAs in the presence of FB was also possible but a competitive mechanism between the substrates for the active sites of the enzymes involved in their degradation occurred. A strain capable of aerobically degrading 4-fluorocinnamic acid (4-FCA), strain S2, was isolated from a biofilm bioreactor and identified as belonging to the genus Rhodococcus. Strain S2 was able to mineralize 4-FCA as a sole carbon source but the presence of an easy degradable carbon source in the culture medium allowed a faster 4-FCA removal. However, 4-FCA concentrations higher than 1 mM led to a decrease in cell growth rate and in substrate degradation rate, indicating a toxic effect of this compound on S2 cells. A metabolic pathway for the degradation of 4-FCA by strain S2 is proposed on the basis of the identified intermediates. 4-Fluorobenzoate (4-FBA) was the major transient accumulated intermediate and for the first time trans, trans-muconate was reported as an intermediate in a biodegradation pathway. Biological degradation of 4-FCA in rotating biological contactor (RBC) was studied. After development of a stable biofilm, 35 mg L-1 of 4-FCA was intermittently fed to the bioreactor during 2 months, however only limited mineralization occurred. Therefore, the RBC was inoculated with a suspended culture of strain S2 in order to enhance the reactor performance. After bioaugmentation mineralization of 4-FCA was achieved however, a decrease in 4-FCA removal along bioreactor operation was observed. Apart from strain S2, two other 4-FCA degrading strains were isolated from the biofilm. After bioaugmentation, the degraders remained in the bioreactor by the end of the experiment but the intermittent feeding of the target compound probably led to lower cell numbers. Nevertheless, the study reinforced the need of bioaugmentation when dealing with recalcitrant compounds. Fluoroquinolones (FQs) are fluorinated antibiotics, which contamination and persistence in several environmental matrices have been well documented in the past years. Labrys portucalensis was capable to degrade the selected FQs, namely ofloxacin, norfloxacin and ciprofloxacin, when supplied individually or as a mixture, in the presence of an easy degradable carbon source. For concentrations of FQs higher than 3.5 μM an inhibitory effect on growth of the strain was observed. The removal capacity of strain F11 also decreased at high FQ concentration and stoichiometric fluoride release was not achieved. Several intermediates were identified from the degradation of each FQ and the piperazine ring and the fluorine substituent seemed to be the targets of the enzymatic attack. A granular sludge sequencing batch reactor (SBR), established with activated sludge from a wastewater treatment plant (WWTP), was operated for the treatment of an aqueous stream containing FQs. The effects of FQs on different biological processes, such as Chemical Oxygen Demand (COD), nitrogen and phosphorous removal by aerobic granular sludge were investigated. Overall, no significant alterations on COD effluent levels were registered. Nitrifiers present in the granular sludge were not affected by the presence of FQs however the activity of denitrifiers and phosphate accumulating organisms (PAO) seemed to be inhibited. Sorption and desorption of FQs onto aerobic granules occurred. During reactor operation the microbial community dynamics was monitored by plating the biofilm and by 16S DGGE. Shifts in the microbial communities due to FQs exposure were observed, however some bacteria seemed to be resistant to the selective pressure exerted by the antibiotics.