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Dehalococcoides spp. in river sediments: Insights in functional diversity and dechlorination activity

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  1. Tez No: 400482
  2. Yazar: NESLİHAN TAŞ
  3. Danışmanlar: DR. HAUKE SMIDT, PROF. DR. W. M. DE VOS HOOGLERAAR
  4. Tez Türü: Doktora
  5. Konular: Çevre Mühendisliği, Environmental Engineering
  6. Anahtar Kelimeler: Dehalococcoides spp, reductive dechlorination, hexachlorobenzene (HCB), biogeography, river sediment
  7. Yıl: 2009
  8. Dil: İngilizce
  9. Üniversite: Wageningen Universiteit
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 206

Özet

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Özet (Çeviri)

Chlorinated pollutants are toxic and persistent organic compounds that, if left untreated, remain in the environment for decades. Even though their production and usage prohibited, they can still be detected in various environments. The discovery of microorganisms, which can transform chlorinated organics to non- or less toxic compounds, triggered the scientific community to undertake continued efforts towards understanding the functioning of these microorganisms in the environment, because they offer a great potential for cleansing of polluted environments. This thesis aimed to describe the diversity and functioning of a unique group of anaerobic bacteria, Dehalococcoides spp., which are specialized in and dedicated to the degradation of chlorinated compounds. Chlorinated compounds are used by Dehalococcoides spp. as terminal electron acceptors in an anaerobic respiration process, called halorespiration, resulting in the reductive transformation of the compound. This research explicitly focused on detection of diversity and activity of Dehalococcoides spp. in sediments and flood plain soils of several European river basins, which were shown to be sinks of many chlorinated organic pollutants, including hexachlorobenzene (HCB). By using state-of-the-art biomolecular techniques, integrated with controlled microcosm experiments and multivariate statistical analysis, environmental factors affecting reductive dechlorination by Dehalococcoides spp. were identified. Furthermore, correlations between environmental conditions and Dehalococcoides spp. activity and composition in the selected river basins were established. Seasonal variation, as well as spatial and temporal fluctuations in total organic carbon and/or nitrogen content and HCB contamination, were demonstrated to affect not only the abundance of Dehalococcoides spp. but also the composition of active populations and the diversity of genes involved in reductive dechlorination. HCB was transformed to less chlorinated compounds in the majority of sediment- and soil samples. Dehalococcoides spp., which were responsible for HCB transformation, were found to adapt to changes in environmental conditions, such as temperature and salinity, in a relatively fast manner unless the changes were extreme (for example, temperatures lower than 15°C, or high sea salt concentrations of 0.5M). Moreover, endogenous microorganisms present in European rivers? sediment demonstrated to possess a great potential to tackle several chlorinated compounds, such as chlorinated ethenes and HCB, simultaneously. Even with today?s enhanced biomolecular techniques, it is difficult to understand the full extent of the dechlorination process since it is a part of a complex web of metabolic and regulatory interactions. Thus, it is proposed to study reductive dechlorination and the function of Dehalococcoides spp. in larger communities and within the environments where they belong. Along with the elucidation of functional properties of such communities, the true role and importance of Dehalococcoides spp. in the environment can be assessed.

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