Antifungal compounds might help to stop harmful algal blooms.
Blooms of toxic algae that stain huge swathes of the oceans red could one day be controlled with a compound more usually used to treat athlete’s foot, say Japanese researchers. The team has even designed a prototype ocean-going craft to dispense the antifungal where it might be needed.
These algal blooms, nicknamed 'red tides', can cause havoc on the high seas. They cause mass deaths in economically important fisheries, harm other marine species and can even close beaches to tourists.
So researchers led by Takuji Nakashima, at the National Institute of Technology and Evaluation in Chiba, decided to investigate the effect of antifungal agents on two red-tide species, Chattonella marina and Heterocapsa circularisquama.
Some red tide phytoplankton have similar life cycles to that of the fungi that cause athlete's foot, Nakashima explains. “As antifungal imidazole compounds have been used as herbicides, we considered that antifungals might have anti-algal activity,” he adds.
Cream for the crop
The researchers tested two such compounds: bifonazole and terbinafine, both of which are used in the treatment of athlete’s foot. They applied varying concentrations of these compounds to cultures of both plankton species, and then counted the viable algal cells 24 hours later.
Both compounds have “potent algicidal activity”, the team reports in Aquaculture Research1. What's more, the effect could be reversed, in C. marina at least, by adding ergosterol, an important component of the plankton's cell membranes.
Nakashima therefore suggests that the compounds work by inhibiting the synthesis of 'sterol' compounds such as ergosterol. Donald Anderson, director of the Coastal Ocean Institute at Woods Hole Oceanographic Institution, Massachusetts, says: “In understanding red tide, this work helps to get at some of the mechanisms, membranes and cellular structures in these cells.”
Donald Anderson, director of the Coastal Ocean Institute at Woods Hole Oceanographic Institution, Massachusetts, says that he is “a staunch advocate of efforts to do something about these red tides”. But he is cautious about the compounds' ability to deal with algal blooms. “The questions I would have are: how specific is this particular control strategy? Is this in any way a targeted compound?” he says.
Nakashima admits that there are problems with using antifungals outside the lab, especially as they are quite persistent and could diffuse into the wider environment. However he has an innovative way to make sure the compounds are applied only to areas where red tides have swamped all other organisms: a prototype solar-powered machine, guided by satellite, carrying a tank of the antifungals.
“The outbreaks of red tide are monitored by satellite system,” he explains. “A release machine is controlled based on the information of satellite system. The energy of machine is replenished by solar system and the volumes of antifungal are regulated by application valves.”
Nakashima, T., Niwano, Y. & Takeshita, S. Aquaculture Res. advance online publication doi:10.1111/j.1365-2109.2008.01998.x (2008).