Microbes to the rescue the war against harmful algal blooms.

This paper discusses the dangers associated with harmful algal blooms (HABs) and the use of biological control as the most promising method to control and prevent these blooms. Harmful algal blooms are commonly found in eutrophic water bodies. Understanding these blooms and developing techniques used to control them is vital as they pose a serious health risks to all forms of life. They reduce water quality, they have serious negative effects on lake ecology and current methods of control are inefficient in terms of time and money. As pollution to our water sources is increasing we will see more and more harmful algal blooms worldwide the problems are becoming more relevant and so development of new methods of control is becoming vital.

We already use a number of different methods to control blooms however they generally have adverse effects on ecology, are costly and time consuming. The use of algicides such as harmful chemicals like copper are used to induce cell lysis releasing toxic chemical into the surrounding waters. The toxins do eventually degrade however long waiting periods are necessary. Microsystins are susceptible to breakdown by aquatic bacteria. These microbes are found naturally in rivers and reservoirs. Although these bacteria are indigenous to the lakes; blooms still occur. This is because the concentration of predatory bacteria is often not sufficient enough to cause lysis when there are enough hosts, and then lysis will occur.
Criteria for a good biological control agent are: high tolerance to a variation on conditions, ability to survive low prey densities, should be indigenous to limit environmental impact (not genetically modified). There is a fear that bacteria might switch hosts and have serious impact on other important crops or organisms. Viral pathogens would be ideal as biocontrol agents as they are target selective and specific for nuisance cyanobacteria. Despite this bacterial agents are considered more promising as they can survive on alternate food sources during non-bloom periods. This would mean they would be more likely to survive for extended periods of time and so would be needed to be reapplied less often.
Many trials have been carried out with success, Bourne et al. (1996) isolated a bacterium which is thought to be able to remove 90% of toxins in 2 to 10 days also Nakamura et al in 2003 immobilised Bacilus cereus. Placed in floating biodegradable plastic carriers they used them to control microcystis blooms successful eliminating 99% of the bloom in 4 days. The bacteria utilised the starch as a nutrient source and the floating carrier enabled immobilized bacteria to be directed to floating cyanobacteria blooms.
More research is needed in this field as the mechanisms involved in cyanobacterial lysis are poorly understood. Studies on application of biocontrol agents are rather limited. Most studies have been limited to lysis of laboratory cultured bacteria. Much more testing is need before further tests can be carried out on our freshwater systems. We need to learn more about anti algal activity and the effects of bacteria on other organisms
This is an extremely interesting area of research which is going to become more important as blooms become more common. The risks of control through predatory bacteria needs to be better understood however it appears to be an encouraging step forward in the management of toxins.


A review of: R. Jabulani Gumbo et al. Biological control of Mircocystis dominated harmful algal blooms African Journal of Biotechnology Vol. 7 (25), pp. 4765-4773, 29 December, 2008