XHSriALGAL AXD BACTERIA-FREE CULTURES OF G. BREVIS 



489 



growtli of the "yellow bacteria" by inhibiting 

 competing bacteria. Dihydrostreptomyciii sulfate 

 (125 /ig. per ml.) initially lowers the pH of the 

 culture medium by 0.5 to 0.8 of a pH unit. This 

 change in the medium may be a factor favoring 

 the increased growth of the pigment -producing 

 bacteria. 



Cultures of an isolate from a nontreated and a 

 dihydrostreptomycin-treated unialgal culture, each 

 with an initial count of about 1 million yellow 

 bacteria per ml., had no toxic effects on F. similis. 

 Plates prepared from samples taken 23 hours after 

 the start of the experiment showed no yellpw 

 colonies. The counts of all bacteria were about 

 the same in the initial and 23-hour samples. 



A CHROMOGENIC BACTERIUM ISOLATED FROM 

 THE WEST COAST OF FLORIDA 



After Bein (1954) reported the toxic effects of 

 Flavobacterium piscicida to fish, we made a cursory 

 check for chromogenic bacteria in Florida off the 

 Fort Myers-Naples area during November 1954. 

 Gymnodinium brevis was present in the area at 

 that time although the maximum concentrations 

 were usually less than 1 million organisms per 

 liter. Small fish kills, mainly of mullet, were 

 being reported sporadically at that time. During 

 the sampling trips, however, we observed less than 

 10 dead fish. Surface samples from 15 stations 

 in this area were plated on Spencer's sea-water 

 peptone agar. Pour-plates containing 1 ml. of 

 each sample were prepared within 1 minute after 

 collection to avoid possible changes in the bacterial 

 flora. All except two of the samples from the 15 

 stations contained 0. brevis, and the counts varied 

 from 7,000 to 0.5 million per liter. 



A white, opaque colony was the most abundant 

 type in the 15 samples; some samples showed a 

 few lemon-yellow colonies. A total of two red 

 colonies were observed in the 15 plates. One of 

 these colonies was isolated from a sample taken 

 5 miles west of Wiggin's Pass on November 4, 

 1954. The G. brevis count for this sample was 

 8,000 per liter. The red-pigment-producing bac- 

 terium, which has not been identified, is a Gram- 

 negative, motile rod. 



A 24-hour pure culture of the "red bacterium" 

 was tested for toxicity to Fundulus similis as a 

 part of the studies dealing with bacteria isolated 

 from unialgal G. brens cultures. Two fish were 

 tested in each of the four containers of test material 



in which the bacterial count varied from approxi- 

 mately 0.5 to 1 million per ml. The bacterial 

 culture gave a pink tint to the test materials. .\11 

 eight fish died within 2 to 8 hours. After the last 

 fish died in each of the four containers, samples 

 were taken for bacterial counts. The red colonics 

 in the plates prepared with 0.02 to 0.03 ml. of 

 these samples were so abundant that enumeration 

 was impossible. We believe that the minimum 

 concentrations were of the order of 1 to 2 million 

 red bacteria per ml. at the time the last fish died. 

 A 6-month-old unialgal G. brenis culture (replen- 

 ished with fresh medium about three times weekly) 

 that contained 1.3 million organisms per liter 

 killed the test fish less rapidly than cultures of the 

 red bacterium. In the G. brevis culture, one fish 

 died after l)^ hours and the other one died after 

 10 to 19 hours. These death times appear rela- 

 tively long when compared with the usual death 

 times of fish subjected to other unialgal cultures. 

 These results may mean either that F. similis is 

 less sensitive to unialgal cultures than other fish 

 tested thus far, or that this culture was less toxic 

 than the others. 



FLAVOBACTERIUM PISCICIDA BEIN 



A chromogenic bacterium was isolated by 

 Reuben Lasker (Bein 1954) from a pooled water 

 sample collected after the occurrence of a fish kill 

 associated with discolored water in Whitewater 

 Bay on the southwest tip of Florida. Bein found 

 that 24-hour cultures of this bacterium, which he 

 named Flavobacterium piscicida, killed several 

 species of marine fish. He gave no quantitative 

 values concerning the concentration of bacteria 

 used other than that 500 ml. of a 24-hour culture 

 of this species grown in a 0.1 -percent peptone 

 solution in aged sea water were added to 4 gallons 

 of continuously aerated sea water. After 24 hours 

 all fish in the experimental aquariums died and 

 the water exhibited a bright orange-yellow dis- 

 coloration. 



We attempted to estimate the minimum number 

 of F. piscicida required to kill mullet {Mugil 

 cephalus), since we desired to know what concen- 

 tration of this bacterium might be required to kill 

 fish under natural conditions. Tiie Marine Lab- 

 oratory of the University of Miami provided the 

 stock from which our cultures were derived. 

 Since Bein gave no indication of the amount of 

 inoculum used to seed the medium to obtain the 



