560 Marine Microbiology 



maximal value) in batch culture. When used for continuous cul- 

 ture, the flow rate was set and time allowed for tlie adjustment 

 of a constant population density indicating a steady state. Since 

 the cell concentration was too low for measuring the turbidity, 

 cells were counted microscopically and the growth rate given as 

 division rate. To avoid errors due to varying cell size, two full 

 spiral curves as a unit cell have been counted. The size of such 

 a standard cell varied within a range of 6-8 /'. in length and 1-1.5 /'. 

 in width. When the cell count decreased below 10^/ml, counting 

 on membrane filters (7) was employed. When a steady state was 

 definitely established, the culture vessel was connected to another 

 storage bottle containing the next lower nutrient concentration. 



Corresponding experiments were conducted using natural, 

 sterile-filtered sea water as medium. The samples taken from two 

 different sources (highly contaminated water from Naples Har- 

 bour, and offshore seawater) clearly showed difterences in the 

 contents of dissolved nutrients as proved by bioassay. The 

 Spirillum was grown in batch culture and inoculated from tlie 

 exponential phase into the chemostat. When wash-out was evi- 

 dent, the dilution rate was lowered with the intention of establish- 

 ing the concentration of the unknown growth limiting factor 

 which would result in a steady state. 



RESULTS 



The growth constants measured in batch culture at 18 C. 

 were: /xm = 0.37 hr~^ and Ks = 0.06 mg asparagine-N/L. The lat- 

 ter has been graphically obtained by plotting reciprocals of four 

 determinations of m and may be subject to considerable error. 

 With the starting concentration of 28 mg asparagine-N/L in the 

 inflowing medium (Sr) at the set dilution rate (D) of 0.185 hr-^ 

 ( =/'m/2), the steady state was establislied after 6 hr. at a cell con- 

 centration of 86 X 10" /ml (yield determinations showed that both 

 nitrogens of asparagine had been used). 



The steady state was maintained for 60 hours and then the 

 culture shifted to the next lower concentration of Sk. The sub- 

 sequent decrease of the cell count is sliown in Figure 1 for the 

 four lowest concentrations of Su (2.8 - 0.14 mg asparagine-N/L). 

 Values represent means of a triplicate experiment. Re-adjustment 



