Biodegradation Of Microcystins In Lake Erie Source Waters And Filters From Drinking-Water Plants

Science Center Objects

Harmful cyanobacterial “algal” blooms (cyanoHABs) and associated toxins, such as microcystin, are a major global water-quality issue.  In Lake Erie, researchers and local health officials have identified the presence of cyanobacterial blooms during the summer and early fall seasons. This is especially pronounced in the Lake Erie Western Basin, where the City of Toledo was forced to issue a do-not-drink water advisory for 400,000 residents during August 2-4, 2014. Levels of microcystin that exceeded the World Health Organization recommended drinking-water standard of 1 microgram per liter were responsible for the Toledo advisory.

Reducing sources and causes of cyanoHABs are long-term goals for water-resource managers worldwide.  Strategies are needed to monitor for and predict cyanoHAB occurrence and toxins, and to treat water to reduce or eliminate toxins.  Treatment methods for reducing microcystins in drinking water, such as adsorption on activated carbon and chlorination, are effective techniques; however, they are costly, and some treatments may result in toxic by-products. 

Biodegradation of microcystins is a promising, environmentally friendly, and cost-effective treatment technique (Gagala and Mankiewicz-Boczek, 2012). Bacteria with the ability to biodegrade microcystins have been isolated in an Australian river (Jones and others, 1994), a reservoir in Japan (Takenaka and Watanabe, 1997), and other locations in Europe, Australia, and Asia.  In the U.S., microcystin-degrading bacteria were isolated from a water sample collected from Lake Erie (Mou and others, 2013) and from the biofilm of an active anthracite biofilter from a Los Angeles drinking-water plant (Eleuterio and Batista, 2010). In a laboratory study, Ho and others (2006) showed that microcystins were biodegraded through a sand filter under conditions similar to those of a rapid sand filter. Ho and others included molecular tests for a known microcystin-degrading gene (mlr).

Researchers have reported that efficient biodegradation of microcystins in processes such as sand filtration appears to be site specific (Ho and others, 2012). Studies are needed, therefore, to gain knowledge of the potential for biodegradation of cyanobacterial toxins by indigenous bacteria in a variety of waters (Gagala and Mankiewicz-Boczek, 2012). These studies may lead to economically feasible and effective treatments for toxins caused by cyanoHABs.

Biodegradation of microcystins in Lake Erie source waters and filters from drinking-water plants

Biodegradation of microcystins in Lake Erie source waters and filters from drinking-water plants
(Public domain.)


Goal and objectives

The overall goal is to identify the presence of microcystin-degrading bacteria in Lake Erie waters and filters of drinking-water plants that may lead to biodegradation as a future control strategy. Specific objectives are the following:

  1. Determine whether naturally occurring microcystin-degrading bacteria can be isolated from source waters and anthracite/sand filters in drinking-water plants in the Lake Erie Western Basin
  2. Identify potential biodegrading isolates
  3. Compare rates of biodegradation for naturally-occurring degraders to a known degrader.


Source-water and anthracite/sand filter samples (Aug, 2015‒July, 2016)

Source-water samples were collected from drinking-water plants in the Western Basin and watershed and used in 300-mL microcosms with nutrients and microcystin amendments: (A) unfiltered with microcystin, (B) 5-μm filter with microcystin, (3) 0.2-μm filter with microcystin (abiotic control), and (D) unfiltered with no microcystin (background control).   Microcosms were incubated at 25°C in a water-bath shaker for 14 days, with aliquots removed at time 0 (T0) and at 1, 2, 4, 8, and 14 days.  Biodegradation occurred in many of the samples.

  • Microcystin concentrations were measured by use of enzyme-linked immunosorbent assay (ELISA) (ADDA kits, Abraxis LLC, Warminster, Pa.)

Identification of isolates (Aug, 2016 – March, 2017)

From the microcosms, 107 isolates were plated on minimal medium with microcystin as the sole carbon source to isolate and identify biodegrading bacteria.  None possessed the mlrA gene. The following tests of isolates are in progress:

  • Qualitative assessment of biodegradation potential by use of BioLog plates—growth in a 96-well plate containing minimal media with microcystin as the only carbon source
  • Identify genus and species of potential microcystin biodegraders through sequencing
  • Qualitative assessment of biofilm formation

Biodegradation rates of selected isolates (Nov-Dec, 2017)

  • Select two isolates identified as microcystin biodegraders and compare rates of biodegradation to that of a known biodegrader.

Eleuterio, L., and Batisa, J.R., 2010, Biodegradation studies and sequencing of microcystin-LR degrading bacteria isolated from a drinking water biofilter and a fresh water lake: Toxicon, v. 55, p. 1434–1442.

Gagala, H., and Mankiewicz-Boczek, J., 2012, The natural degradation of microcystins (cyanobacterial hepatotoxins) in fresh water—The future of model treatment systems and water quality improvement: Polish Journal of Environmental Studies, v. 21, no. 5, p. 1125–1139.

Ho, L., Meyn, T., Keegan, A., Hoefel, D., Brookes, J., Saint, C.P., and Newcombe, G., 2006, Bacterial degradation of microcystin toxins within a biologically active sand filter: Water Research, v. 40, p. 768–774.

Ho, L., Sawade, E., and Newcombe, G., 2012, Biological treatment options for cyanobacteria metabolite removal—A review: Water Research, v. 46, p. 1536–1548.

Hoefel, D., Adriansen, C., Bouyssou, M., Sant, C.P., Newcombe, G., and Ho, L. 2009, Development of an mlrA gene-directed TaqMan PCR assay for quantitative assessment of microcystin-degrading bacteria within water treatment plant sand filter biofilms: Applied and Environmental Microbiology, v. 75, p. 5167–5169.

Jones, G.J., Bourne, D.G., Blakeley, R.L., and Doelle, H., 1994, Degradation of the cyanobacterial hepatotoxin microcystin by aquatic bacteria: Natural Toxins, v. 2, no. 4, p. 228–235.

Mou, X., and Lu, X., Jaconb, J., Sun, S., and Heath, R., 2013. Metagenomic identification of bacterioplankton taxa and pathways involved in microcystin degradation in Lake Erie: PLoS ONE, v. 8, no., 4, e61890.

Ohio Environmental Protection Agency, 2015, State of Ohio—harmful algal bloom response strategy for recreational waters, accessed August 2015 at

Takenaka, S., and Watanabe, M., 1997. Microcystin LR degradation by Pseudmonas aeruginosa alkaline protease: Chemosphere, v. 34, no. 4, p. 749–757.