A flat white transluscent colony with an iridescent sheen, also 

 produced by gram-negative rods, is usually the second most abundant 

 colony type isolated from unialgal G. brevis cultures. An initial 

 concentration of approximately 1 million bacteria per ml of this 

 colony type gave no evidence of toxicity to F« similis , 



Chroraogenic bacteria constitute only a small portion of the 

 bacterial flora of unialgal cultures of G. brevis . However, yellow- 

 pigment-producing bacteria become abundant in cultures treated with 

 dihydrostreptomycin sulfate. They dominate in G. brevis cultures 

 treated with 500 to 1000 yg of this antibiotic per ml, and often occur 

 in nearly pure culture. This antibiotic may enhance the growth of 

 the "yellow bacteria" by inhibiting competing bacteria. Dihydro- 

 streptomycin sulfate (125 ug per ml) initially lowers the pH of 

 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 non- treated and a dihydrostreptomyc in- 

 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 yellow colonies. The counts of all bacteria were about 

 the same in the initial and 23-hour samples. 



A Chromogenic Bacterium Isolated from Water off the West Coast 



of Southern Florida 



After Bein (1954.) reported the tqxic effects of Flavobacterium 

 piscicida to fish, we made a cursory check for chromogenic bacteria 

 in Florida off the Fort %ers-Naples area during November, 1954= 

 G. brevis was present in the area at that time although the maximum 

 concentrations were usually less than 1 million 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. Four-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 G. 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 bacterium, which has not 

 been identified, is a gram-negative motile rod. 



37 



