Axe7iic Cultivation of a Pelagic Diatom 125 



TABLE 2 

 Effect of Antibiotics on Bacteria Isolated from Diatoms 



Isolate Isolate Isolate Isolate Isolate 



No. 1 No. 2 No. 1 No. 2 No. 1 



Chaetoceros Chaetoceros Asterionella Asterionella Coscinodiscus 



+ + RM + RM + 



- + RM + - 



- + RM + RM - 



+ — — + RM 



(Difco antibiotic sensitivity disks of medium strength) 

 + inhibition — no inhibition RM^insurgence of resistant mutants 



water peptone agar and the diatom medium (added with 0.1 

 per cent gkicose) with samples of diatom cultures. 



Chaetoceros chjdimus in bacteria-free cultures seems to have 

 better pigmentation, longer chain length and a shorter generation 

 time. 



A minimum generation time of 11 hours was recorded, the 

 culture reaching a concentration above 3 X 10^ cells/ml in ten 

 to eleven days, when incubated at 19 C, under twelve hours 

 of illumination a day, at 200 foot-candles (Figure 1). Average 

 size of single cells is 14 x 20 microns. 



Growth in bacteria-free cultures continues up to thirteen to 

 fourteen days, under these experimental conditions, at which 

 time auxospores start to appear. This compared with a growth 

 period of approximately eight days for bacterized cultures, at 

 which time growth usually declines, as shown in Figure 1. 



The medium is now being dissected and more detailed 

 studies of the association between diatoms and bacteria are 

 planned, since very little is known of the interaction between 

 these microorganisms in the sea. 



Diatom bloom, termination of growth and succession of forms 

 in the natural environment, may be phenomena in which bacteria 

 play an important role. 



