we report here a quantitative study demonstrating that a low , otherwise sub-supportive , concentration ( approximately 0.020-0.050 micrograms ml-1 ) of an essential phytosterol ( stigmasterol ) is adequate for growth of this ciliate , provided that a second , relatively non-specific sterol is available at a higher concentration ( 1.0 micrograms ml-1 ) to allow for membrane biosynthesis .
C0031866
phytosterol
C0038323
sterol