ABSTRACT
The effect of Nannochloris sp. on the toxicity of cultures of four algae was evaluated using a Microtox 500 that measures the effect on a light-producing bacterium, Vibrio fischeri. Cultures of four algae produced a toxic effect, but in the presence of Nannochloris sp., the effect was reversed, and a stimulatory effect was observed. The effect was tested for Microcystis aeroginosa, Cyclotella menengheniana, Scenedesmus dimorphis, and Lyngbya sp. using cultures obtained from the University of Texas Culture Collection of Algae.
Subject(s)
Aliivibrio fischeri/cytology , Chlorophyta , Animals , Chlorophyta/cytology , Copepoda/cytology , Diatoms/cytology , Dinoflagellida/cytology , Microcystis/cytology , Pheromones , Photosynthesis , Scenedesmus/cytology , Toxicity TestsABSTRACT
Studies were conducted on the conditions under which the red tide organism, Karenia brevis (a.k.a., Gymnodinium breve), was treated with Nannochloris sp. The latter organism is known to produce cytolytic agents called Apparent Oceanic Naturally Occurring Cytolin (APONINs). Conventional wisdom might suggest that brevetoxins would be released upon destruction of the single-celled dinoflagellate K. brevis and that efforts to treat red tide outbreaks would lead to release of brevetoxins and enhanced toxicity toward marine species. Earlier studies described conditions by which K. brevis cells were converted to a non-motile form when cultures of K. brevis were treated with an isolate (Psi-APONIN) produced by Nannochloris sp. but when centrifuged only a small amount of the toxin was released. The present study confirms that the toxin is not released when the K. brevis is undisturbed, however, when the culture is stressed (stirred with a magnetic stirring bar for 24, 48, and 72h) toxin was released, and the toxicity could be measured using a Microtox analyzer. In the study, it was found that at as few as eighty cells of K. brevis produced a toxic effect of 20% as measured by the effect on Vibrio fischeri. Nannochloris sp. had no effect on the bacteria used in the Microtox analyzer, nor did interaction of Nannochloris sp. with K. brevis in the short term. This effect is presumed to be due to the production of Psi-APONIN and conversion of K. brevis to a non-motile or resting form.
