The role of oligoelectrolytes in microbial reductive dechlorination

• Main Author: Loo, Heup Seng.
• Other Authors: School of Civil and Environmental Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/52967
• Institution: Nanyang Technological University

Oligoelectrolytes such as 4,4ʹ-bis(4ʹ-(N,N-bis(6ʹʹ-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbenetetraiodide (DSSN+) are a class of molecules that insert spontaneously into bacterial cell membrane to facilitate extracellular electron transfer. Enhanced extracellular electron transfer in organisms can be a great asset to the environment as they can be used in applications such as bioremediation of tetrachloroethylene (PCE) polluted sites. In this project, we explored the efficiency of DSSN+ and two developmental redox mediators (RM), RM1 and RM2, on an anaerobic mixed dechlorinating culture that was acquired from a polluted site in Sydney, Australia. The results showed that RM1, RM2, DSSN+ and control setup had a dechlorination rate of 1.0283μM/h, 1.0254μM/h, 0.7139μM/h and 0.7735μM/h respectively. Based on dechlorination studies that were conducted, RM1 and RM2 showed great potential in enhancing PCE dechlorination rates with the mixed dechlorinating culture. To better understand the role of RMs behind this process, specific species which can execute extracellular electron transfer were selected for a more in depth study. Shewanella oneidensis MR-1 is one of the exoelectrogenic species that is known to facilitate Fe(III) reduction via c-type cytochrome and heme at the cell surface. Recombinant Escherichia coli strains, ccm and mtrCAB expressing heme transporter and cytochrome c genes from S.oneidensis MR-1, were also able to reduce soluble Ferric nitrilotriacetic acid (Fe(III)NTA). Thus, using RM1 and RM2 which showed enhancement of PCE dechlorination rate, we tested the ability of S.oneidensis, wild type E. coli and genetically engineered E. coli ccm and E. coli mtrCAB to dechlorinate PCE while reducing Fe(III)NTA at the same time. However, no signs of dechlorination were observed with S. oneidensis and genetically engineered E. coli strains, suggesting that this electron transfer pathway might not be suitable to channel electrons to PCE as a terminal electron acceptor. In conclusion, RM1 and RM2 have the potential of enhancing PCE dechlorination rate and given more time, more studies can be done to find out the conditions needed to optimize the compounds.