Identifcation of Electrochemically Active Bacteria and Their Potential in Water Treatment

Electrochemically active bacteria (EAB) are microorganisms capable of releasing their intracellular electrons to the extracellularly redox active materials, like electrodes. EAB can thrive under low oxygen conditions by respiring and metabolizing anaerobically, the process through which they generate electrons that could potentially be exchanged in a microbial fuel cell (MFC). Therefore, EABs have the potential to treat lake water affected by cyanobacterial Harmful Algal Blooms (cHABs), which poses a serious threat to drinking water bodies. The main source of water contamination in cHABs comes from various cyanotoxins produced by cyanobacteria. In the water contaminated from algal blooms, EAB can be employed to consume cyanobacteria through bio-catalyzed reactions and, together with other bacteria capable of breaking down cyanotoxins, used for treatment of polluted water. Therefore, this study set out to identify species of EAB present in an aquatic ecosystem, Central Park Pond (CPP) in NYC, affected by cHABs. The goal of this study was to learn the types and properties of identified EABs to tailor the MFC in treating the polluted water.

We have employed plate-based kinetic fluorescence tests to screen CCP bacteria isolated on Luria-Bertani agar plates with meat peptone as a nitrogen source. Riboflavin was used to monitor the electrochemical activity of tested bacterial cultures as oxidized Riboflavin is fluorescent, but the reduced molecule becomes non-fluorescent. The fluorescence of a sample containing EAB was expected to decrease over time as the Riboflavin was reduced by the EAB in increasing anaerobic conditions in samples covered by mineral oil and tape. To be considered an EAB candidate, the sample should display rapid drop in fluorescence within the first two hours, with fast fluorescence recovery following aeration. We have identified 76 EAB potential candidates, isolated DNA from 38, and PCR-amplified variable parts of 16s rRNA gene. All PCR fragments were gel-purified and sent out for sequencing. The sequences of rRNAs were analyzed using BLAST. 33 isolates were identified as members of the Aeromonas family, with some members known to be EAB. One sample was identified to be in the Pseudomonas family, two as Pseudomonas guineae, one in the Bacillus family, and one as Shewanella putrefaciens. The identification of Shewanella is significant as it is a known EAB, proving the efficacy of the testing method. Future research directions include experimental characterization of identified strains for their electrochemical activity.