Another role for which bacteria must be considered is that 

 of a detoxicating agent. Shilo and Aschner (1953) found that 

 bacteria decreased the toxicity of cultures of Prymnesium parvnin , 

 a marine and brackish water chrysomonad which is toxic to fish. 

 Similarly, bacterial activity may influence the toxicity of 

 G. brevis in the laboratory and in nature. 



STUDIES WITH BACTERIA 



Although the available evidence indicated that G. brevis causes 

 the toxicity of unialgal cultures, direct proof was lacking prior to 

 the development of bacteria- free cultures. In addition to the bacterial 

 studies previouly considered, the possibility that bacteria may cause 

 all or some of the toxic effects was investigated by testing pure 

 cultures of some of the bacteria from unialgal G. brevis cultures. 

 Furthermore, toxicity tests were conducted with pure cultures of an 

 unidentified red-pigment-producjjag bacterium isolated from Florida 

 waters and Flavobacterium piscicida Bein. Bein (1954-) suggested that 

 F. piscicida , a chromogenic bacterium, possibly was a cause of mass 

 fish mortality associated with discolored water off the west coast 

 of Florida. 



Bacteria Isolated from Unialgal Gymnodinium brevis Cultures 



Because of the preliminary nature of these studies and the 

 crudeness of the quantitative bacterial estimates, only a summary 

 will be presented- The bacteria used have not been identified; 

 presently they are being characterized morphologically and physiologically 

 by Dr. T. J. Starr. The test fish were Gulf killifish (Fundulus similis ) . 



Two test fish per container (1-liter beaker) were subjected to 

 about 500 ml of non-aerated test materials. Bacterial suspensions 

 were prepared by adding 16,5 ml of a 24-hour culture to 500 ml of 

 filtered Galveston Bay water. Control materials consisted of the 

 same ratio of sterile culture medium and bay water as well as bay 

 water alone. Crude estimates of bacterial concentrations were made 

 by preparing a pour-plate of 0.02 to 0.03 ml of a sample collected 

 shortly after the fish were added. A second sample was taken either 

 after both fish died or after 23 hours if at least one fish survived 

 this period. The colonies were too numerous to count in most of the 

 plates prepared from the second samples. Therefore, not even rough 

 estimates could be made for the bacterial concentrations. 



The most abundant colony tjrpe isolated from unialgal G. brevis 

 cultures on Spencer's peptone sea water agar and Bein's peptone agai* 

 is generally a convex white opaque colony produced by gram-negative 

 rods. This colony type may represent several different species and 

 physiological types of bacteria. Two separate isolates of the white 

 opaque colony did not give evidence of being toxic to F, similis . 

 The initial bacterial concentration was in the order of 0.5 to 1 

 million per ml. 



36 



