AUBURN, Ala.—A team of Auburn University College of Agriculture researchers studying the development of biofilm formed in aquaculture settings by the highly contagious fish pathogen Flavobacterium columnare has taken the first-ever microscopic image of the biofilm—a photograph fascinating enough to make the cover of the scholarly journal Applied and Environmental Microbiology.
Credit for the image, which accompanied an article in which the scientists reported their findings, goes to team member Wenlong (Colin) Cai, a graduate student in Auburn’s School of Fisheries, Aquaculture and Aquatic Sciences. Cai, fisheries professor Cova Arias and Auburn plant pathology assistant professor Leonardo De La Fuente conducted the biofilm investigation.
“We were the first to look at how different chemical parameters affect biofilm formation, with the idea of finding conditions that will prevent or limit the development of biofilm in aquaculture settings,” Arias says.
In freshwater fish species, particularly farm-raised catfish and tilapia, the bacterium F. columnare causes columnaris, a devastating disease to the aquaculture industry and the second leading bacterial disease in commercial catfish operations in the Southeast. The disease is characterized by lesions on a fish’s skin, fins and gills. As the infection and resulting necrosis worsens in the gills, the fish’s oxygen supply is cut off.
Biofilm is a layer of bacteria that forms on, coats and colonizes inert surfaces and in closed aquaculture systems is considered the source of F. columnare contagion for farmed fish. Through their project, the Auburn scientists documented the formation of and changes in biofilm under static and flow conditions and examined the effects that water temperature, pH, salinity, hardness and sugars have on the ability of the biofilm to attach to surfaces.
While F. columnare can survive in lake and pond water, it becomes less virulent over time. A key finding of the Auburn study was that F. columnare in biofilms retains its potency. The researchers found, too, that high water temperature and salinity inhibit biofilm formation, while high water hardness encourages it.
“Maintenance of hardness and salinity values within certain ranges could prevent biofilm formation by F. columnare in aquaculture systems,” Arias says.
The researchers acknowledged that the parameters of water temperature, salinity and hardness are difficult to control in commercial catfish ponds.
“But they can be maintained in hatcheries, where columnaris disease can cause more than 90 percent mortality in catfish fingerlings,” she says.
The journal article and photograph were published in the September issue of Applied and Environmental Microbiology, volume 79, number 18.