Algal Blooms and Microcystins: The Fouling of Lake Erie
☒ A Colorful History : Often called blue-green algae, cyanobacteria are neither restricted to blue and green hues nor are they true algae. They bring a carmine tinge to the Red Sea and make the Spirulina-eating African flamingos blush pink. When these simple bacteria appeared some 3.5 billion years ago*, they produced oxygen by photosynthesis, changing the fate of the earth forever. Then in the Precambrian era, according to the theory of endosymbiosis, they were co-opted as chloroplasts into the cells of green plants. They also form nitrogen-fixing nodules in the roots of plants and partner with fungi to colonize barren new lands as lichen. Little wonder that scientists consider them the most successful group of microbes ever. But as Shakespeare mused: Why then, can one desire too much of a good thing?
☒ Toxic Blooms: Ever opportunistic, cyanobacteria can rapidly increase in biomass to form thick green scum euphemistically known as blooms on the surface of shallow lakes. Over-fed with nutrient run-off from fertilized farmlands, sewage disposal or industrial waste, the blooms in turn feed bacteria, which then consume dissolved oxygen, killing off fish and creating dead zones. That’s not all: the blooms produce potent toxins that target the liver, brain and skin. The worst offenders are microcystins: cyclic compounds that fit snugly into the pocket of a class of enzymes known as protein phosphatases (image) and block their tumor-suppressing activity. In 1996, 76 dialysis patients at a clinic in Caruaru, Brazil, died from acute liver failure after water contaminated with microcystins was used in renal dialysis treatment. Their cyclic structure makes microcystins resistant to most water treatment processes, and boiling only concentrates the toxin. The building blocks that make up the toxin are unusual (non-protein amino acids) , and cannot be broken down by enzymes found in our cells. Recently, algal blooms in Lake Erie forced the shut-down of the entire water system in the city of Toledo, leaving half a million residents with no water. Given that this is becoming “the new normal” (http://goo.gl/dPyrtG) in many freshwater supplies around the world, what is the solution?
☒ Bioremediation: There are no short term solutions to the blooming problem! We can cut back on fertilizer use, although faster acting, more efficiently utilized phosphate formulations actually encourage algal growth. Fortunately, we can exploit the chemical warfare in the battleground of the blooms themselves. It’s thought that cyanoblooms produce these toxins to protect themselves from heat and oxidation stress. But competing bacteria like Sphingomonas secrete enzymes that can degrade microcystins. Research on natural bioremediation by culturing beneficial bacteria and studying their genetic and biochemical pathways could help nip future blooms in the bud.
Ref (image inset): http://biolinks.co.jp/pdf/MOCT.pdf
Ref ( #openaccess ): Cyanobacterial Toxin Degrading Bacteria: Who Are They? http://www.ncbi.nlm.nih.gov/pubmed/23841072
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*Edit: Corrected from 3.5 mya , thanks Martin Vogel ! It turns out that cyanobacteria are the oldest known fossils, from Archaean rocks of Western Australia. This is very cool, since the oldest rocks are only a little older: 3.8 billion years old!