Selective short chain carboxylates production by mixed culture fermentation

D. Arslan

Research output: Thesisinternal PhD, WU

Abstract

SUMMARY

Surfactants are produced and used in the formulation of many different commercial products. After use, these compounds end up in wastewater treatment plants (WWTPs) or in the environment. Although many surfactants can be degraded in aerobic conditions, anaerobic conditions are also common in Nature and in WWTPs. For achieving nutrients removal from wastewater, biological removal of nitrogen and phosphorus can be performed in a WWTP using the anaerobic-anoxic-aerobic (A2/O) concept. Using the A2/O process sequence, surfactants can be degraded anaerobically before reaching the aerobic compartment. In the anoxic compartment, facultative anaerobic bacteria can degrade surfactants by using nitrate/nitrite as electron acceptor. However, not much is known about surfactant-degrading denitrifying bacteria. In this thesis, Pseudomonas stutzeri strain SN1 and Pseudomonas nitroreducens strain SN2 were isolated from activated sludge of a WWTP with the A2/O process, using the anionic surfactant sodium dodecyl sulfate (SDS) as sole carbon and energy source. Both strains were able to completely degrade SDS coupled to nitrate reduction to dinitrogen gas (Chapter II).

In the A2/O process, the diversity of bacterial communities involved in the degradation of surfactants may differ between anoxic and oxic compartments, where two different electron acceptors are involved. Surfactants can directly affect the biological activity of microorganisms present in WWTPs and disturb the treatment efficiency. In this way, increased concentrations of surfactants may give rise to a different bacterial diversity selection in anaerobic, anoxic and oxic conditions. The degradation of the anionic surfactant sodium lauryl ether sulfate (SLES) in aerobic conditions is known, but not in denitrifying conditions. In this thesis, the bacterial diversity of enrichments cultures able to degrade different concentrations of SLES in anoxic and aerobic conditions was determined. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8 and Pseudomonas nitroreducens strain S11 were isolated from anoxic enrichments. Comamonas testosteroni strain S13 and Acinetobacter sp. S15 were isolated from aerobic enrichments (Chapter III). SLES initial degradation steps by pure bacterial cultures were previously investigated, but much is still unknown about how the cleavage of ether bonds from chemical compounds is catalyzed by bacterial enzymes. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8 and Pseudomonas nitroreducens strain S11 are able to use SLES in anoxic conditions coupled to nitrate reduction (Chapter III). SLES degradation in anoxic conditions was compared between the three strains. P. nitroreducens strain S11 was found to be the best SLES degrader in anoxic conditions and also to be an excellent aerobic SLES degrader (Chapter IV). Sulfatases and ether cleaving enzymes were probably used by P. nitroreducens strain S11 in both conditions, although differences between SLES degradation in aerobic and anoxic conditions indicated that ether cleavage and following SLES complete degradation is faster under aerobic conditions.

Although surfactants can be toxic to microorganisms, surfactant-degrading bacteria are known to be resistant to high surfactants concentration, in aerobic conditions. This was not previously investigated using surfactant-degrading denitrifying bacteria. Surfactant-resistant bacteria, with the ability to couple surfactant degradation to nitrate reduction, can be very useful for degrading the surfactants arriving to the anoxic compartments of a WWTP at high concentration.  In this thesis, high concentrations of SDS and SLES were used to investigate the effect of these on SDS/SLES-degrading bacteria (P. stutzeri strain SN1, P. nitroreducens strain SN2, P. stutzeri strain S8 and P. nitroreducens strain S11), under anoxic conditions (Chapter V). P. stutzeri strain SN1 was inhibited by increasing SDS and SLES concentrations, after degrading a certain amount of the surfactants. Overall, P. nitroreducens strains showed to be more resistant to high surfactant concentrations compared to P. stutzeri strains. Nevertheless, high concentrations of SDS and SLES did not inhibit growth and nitrate reduction ability of any of the tested Pseudomonas sp..

Protein domains represent the evolutionary conserved autonomously folding functional building blocks of the proteins. Prediction of protein domains from genomes can be used for species classification and validation of known physiological abilities. P. nitroreducens are facultative anaerobic bacteria from the P. aeruginosa group, which can degrade complex compounds. P. nitroreducens DSM 14399T shares with P. nitroreducens strain SN2 the ability for SDS degradation in anoxic conditions. For increasing the insight into P. nitroreducens DSM 14399T phylogenetic classification and physiological properties (e.g. SDS degradation) its genome was sequenced, annotated and compared to other Pseudomonas spp. genomes. This was performed by comparing functional profiles, based on protein domains presence or absence, with physiological data (Chapter VI). Functional profile comparison confirmed P. nitroreducens classification. Protein domain analysis and genes annotation validated SDS degradation by P. nitroreducens DSM 14399T. This study showed that protein domains prediction and functional profiles comparison can be used for studying and comparing different Pseudomonas species at the physiological level.

 

 

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Buisman, Cees, Promotor
  • De Wever, H., Co-promotor, External person
  • Steinbusch, Kirsten, Co-promotor
Award date21 Oct 2014
Place of PublicationWageningen
Publisher
Print ISBNs9789462571228
Publication statusPublished - 21 Oct 2014

Keywords

  • fermentation
  • carboxylic acids
  • recovery
  • waste utilization
  • technology

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