Possible Biological Controls on Harmful Algal Blooms

Well folks, the sunny, Popsicle-melting, happy-go-lucky days of summer are ending. Soon the chill fall mornings will be waking us while it is still dark, and the cold will slowly seep deeper into our collective consciousness until sometime around March when the ice and snow will be replaced with refreshing freezing rain. Not to discredit the enthusiastic and professional work of the summer interns, but the toughest New England weather demands only the hardiest, bitterest interns, those who have long ago shunned the bright sunshine and chosen the cold and the dark.

With that in mind, Hello! My name is Justin, and I will be a regular contributor to this this blog through the fall. Here is a picture of me from this summer, when I was hauling around barges filled with invasive water chestnuts in a little 5 HP motorboat:

there I go

Today I wanted to continue to address the issue of harmful algal blooms. As you know, we have had our fair share of HABs this summer on the Charles and you are not alone if you're wondering whether this type of event has become more common in recent years. The type of algae that produce toxic blooms tend to grow faster in warmer waters, and if climate change theory is to be believed (it is) then we must prepare ourselves to deal with more HABs in the coming years. But how?

As usual, a bunch of cool scientists have been working on this issue for quite some time already. Today there are some effective strategies for dealing with cyanobacterial blooms, such as spreading copper compounds or other algicides on the affected body of water, but these solutions have many potentially harmful side effects. The copper itself can become entrapped in sediment and is toxic to many other organisms besides cyanobacteria (Gumbo et al., 2008). Also, most algicides work by lysing the cells of cyanobacteria, that is, by dissolving their cell walls. Logically, once this happens, all of the toxins that were inside the cells are now free to cause havoc among animals living in the water. The toxins degrade over a period of a couple of weeks (Oberholster et al., 2003), time for which the body of water may have to be closed to recreation.

This is microcystin LR, one of the toxins produced by some species of cyanobacteria . It is made of seven amino acids linked together in a ring. It is a hepatotoxin, meaning that it causes damage to your liver. (From Oberholster et al., credit An and Carmichael, 1994)

So if putting chemicals on algal blooms is not a good idea, what else can we do? It has been known for a while that some species of bacteria and other microorganisms actually feed on harmful cyanobacteria and some degrade the toxins that they produce. Bacteria appear to be the most promising group of microorganisms, though some viruses also target toxic cyanobacteria. Viruses, unlike bacteria, are less likely to be able to survive low concentrations of cyanobacterial hosts and more likely to be defeated by a simple mutation in the cyanobacteria's surface proteins. It might be possible to find a species of bacteria ideal for targeting harmful cyanobacteria and release it into afflicted bodies of water. According to Sigee et al. (1999), an ideal bacterial species should:

adapt to changes in conditions (a species that ceases to multiply below 25 degrees C would be useless)
consume the prey (blue-green algae)
survive when prey is not abundant
have high prey specificity (not just eat everything that comes near it)
remain an effective predator as the prey mutates over time
be native to the local environment

The search is on for such a species. Some promising leads have turned up, such as several members of the order myxococcales. These bacteria "hunt" in groups and surround the hapless cyanobacterial cells before consuming them. These species are especially interesting because only 1 myxobacteria is needed for every 10-1 million cyanobacteria (Gumbo et al., 2008).

Of course, there is a huge difference between finding species that attack cyanobacteria in the lab and using a bacterial biological control in the field. Before use in the field, we must be sure that the predatory bacteria could not spread and become a nuisance themselves, or attack other ecologically important species. Some have suggested that an effective agent could enhanced through genetic engineering, either making it more effective at attacking cyanobacteria or less likely to attack other species. Genetic engineering, however, tends to give people the heebie-jeebies and any control program using a genetically modified organism would probably have to overcome significant public opposition. Application of a bacterial biological control must also be cost effective; one must be able to store, transport and grow the bacteria without too much effort, and it must not need extensive intervention after application.

It may be some years before we have a reliable biological control mechanism for HABs. Until then, the best way to keep the river clean is to regulate thermal pollution and the amount of excess nutrients that enter the water. Both of these factors encourage the growth of blue-green algae.

Until next time, keep it clean!




Sources:

Gumbo, R.J., Ross, G., and Cloete, E.T. Biological control of Microcystis dominated harmful algal blooms. Afr J Biotechnol. 2008. 7: 4765–4773.

P. J. Oberholster, A.-M. Botha and J. U. Grobbelaar, Microcystis aeruginosa: source of toxic microcystins in drinking water. Afr. J. Biotechnol.. 2004. 3. 159–168.

Sigee DC, Glenn R, Andrews MJ, Bellinger RD, Butlter RD, Epton HAS, Hendry RD. Biological control of cyanobacteria: principles and possibilities. Hydrobiologia. 1999. 395/396:161–172

World Health Organization. Cyanobacterial toxins: Microcystin-LR in Drinking-water. 2003.