Investigating Microbial Biodegradation of Pyridinium Ionic Liquids

Date of Defense


Date of Graduation



Biological Sciences

First Advisor

Kathryn Docherty

Second Advisor

Blair Szymczyna

Third Advisor

Christopher Pearl


Green chemistry is an emerging discipline focused on engineering chemicals that are less damaging to humans and the environment. Ionic liquids (ILs) are classified as green chemicals due to their negligible vapor pressure components and due to their versatile physio-chemical properties, the designer-engineered field of ILs is increasing exponentially. However, negative implications of IL use are beginning to arise as studies show the toxic effects of ILs on aquatic systems due to the ILs potential to disrupt cell membranes. It is important to proactively investigate ILs to ensure they are capable of biodegradation before their use becomes widespread. This study investigates the biodegradability of the ionic liquids: 1-butyl-3-methylpyridinium bromide (bmpyrBr) and 1-octyl-3-methylpyridinium bromide and seeks to isolate a microorganism or microbial community responsible for the biodegradation of these ILs. Samples taken from two separate wastewater treatment plants located in South Bend, IN (SB) and Kalamazoo, MI (KZ) were mixed with a mineral media and bmpyrBr or ompyrBr to investigate biodegradation following a standard Organisation for Economic Cooperation and Development (OECD) protocol. A spectrophotometer was used to measure both biomass and absorbance of the ILs. Over 41 days, no decrease in the absorbance of the pyridinium ring, indicative of biodegradation, was observed until day 41 of the experiments. This indicates that these ILs would remain intact in a wastewater treatment plant and have the potential to be released into the environment following a standard treatment time period. Enrichment cultures were prepared and transferred to purify a mixed culture of microorganisms capable of biodegrading each IL. Enrichment cultures from the SB plant were capable of biodegrading bmpyrBr and cultures from the SB and KZ plants were capable of biodegrading ompyrBr. A second experiment was performed using these cultures which examined absorbance, dissolved organic carbon concentrations and microbial respiration rates were collected throughout time. Results indicate that the SB microbial enrichment culture completely biodegraded bmpyrBr within one week. However, ompyrBr was either partially biodegraded or not metabolized, possibly because concentrations in the experiment were too high and caused a toxic effect to the microbial enrichment culture. A combination of 16s rRNA gene PCR and TOPO TA cloning and sequencing will allow the microbial communities to be analyzed.


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