“Organic” cure for harmful algal blooms?

Slightly different subject to current ones but perhaps you might find it interesting…

Over the last several decades cultural eutrophication has led to change in structure and diversity of marine benthic communities, coastal regions throughout the world have experienced an escalation in the frequency of algal blooms that are toxic or harmful. Many attempts have been made in order to tackle the problem, however high costs and in particular the use of chemical agents such as copper sulphate does not appear to be the right move as their rather extensive use resulted in an even higher contamination risk to aquatic environments and toxicity towards non-target species. Biological agents such bacteria or viruses are now considered to have potentially direct or indirect supressing effect on algae, however the relationship and mode of action of bacteria on algae has not yet been fully understood. Previously studies have already isolated certain strains of bacteria that possess algicidal properties (i.e. can regulate the growth or toxin production) and these include large groups of Cytophaga/Flavobacterium/Bacteroidetes (CFB) or to the ɣ-proteobacteria group, and to the genera Cytophaga, Saprospira, Alteromonas and Pseudoalteromonas. Similarly Su and his colleagues investigated the relationship of Alexandrium tamarense spp, a bloom forming algae that are mainly associated with paralytic shellfish poisoning and the bacteria isolated from water samples where Alexandrium sp blooms where observed.

The simplest way of explaining the methods involved was isolating and purification of A. tamerense and bacteria present in the water and inoculating it with either bacterial cells, filtrates or cell suspension of bacterial isolates which genera were confirmed through amplification of 16S rRNA genes. They investigated the proposed anti-algal properties by monitoring the growth progression of Alexandrium spp. under the presence of those bacterial isolates.

They have managed to isolate over 100 types of bacteria which 9 of them showed some algicidal properties through inhibiting the growth of algae. Bacteria mostly belonging to the ɣ-proteobacteria group have showed to have indirect effect since algicidal activity was only detected in cell free supernatants but not the bacterial cells. Therefore bacteria have probably most likely to possess some sort of chemical compound which acted indirectly on the algae; however that was just an assumption.

The initial aim of the study was to improve the understanding and explain the mode of action of bacteria on algal communities however authors apart from finding new strains of bacteria didn’t really conclude nor explained the exact interaction between those species and most of summary was based on assumptions.

To quote “our results showed high diversity of algicidal bacteria against A. tamarense” (which being fair they have done) and “providing possible choices for controlling HABs by microbial strategies” which in turn is a quite a “big” statement because authors didn’t actually find out how those bacteria attack the algae, it’s all based on more assumptions and pretty much everything is possible. Another problem of my own with this study is that it is a laboratory based study therefore everything has been done under a close control so realistically; in real conditions other strains of bacteria might also be present and perhaps protect algae against bacteria that have negative effect on them. Also environmental conditions do change and mode of action of certain bacteria can also change, especially in the time of apparent climate change.

To summarise, the paper was fairly clearly written and quite interesting however I was expecting a little bit more from their findings, few of their statements has been a little bit miss-selling but that is just my personal opinion, perhaps other readers would not agree with me.

Ref: Su J., Yang X., Zhou Y., Zheng T., (2011), Marine bacteria antagonistic to the harmful algal bloom species
Alexandrium tamarense (Dinophyceae), Biological Control, 56 (2011), 132–138