Growth Requirements of Symbiont‐Free and Symbiont Lambda‐Bearing Paramecium octaurelia 299 for Folic Acid and Biopterin

Abstract

ABSTRACTWe investigated the growth requirements of symbiont‐free and symbiont lambda‐bearing Paramecium octaurelia stock 299 for folic acid and biopterin in chemically defined culture medium. Symbiont‐free P. octaurelia required both folic acid and biopterin for growth. In the absence of these substances growth of symbiont‐free P. octaurelia failed after the first transfer, whereas symbiont lambda‐bearing P. octaurelia could be maintained indefinitely in serial subculture. In the absence of folic acid and biopterin, sulfanil‐amide inhibited growth of the symbiont lambda‐beating protozoa. In the presence of folic acid and biopterin, the antiobiotic selectively inhibited growth of lambda symbionts but did not affect growth of the protozoa. In both cases, inhibition by sulfanilamide was reversed by addition of p‐aminobenzoic acid to the medium. These results support our earlier finding that folic acid is required for growth of symbiont‐free P. octaurelia 299 and that growth of the lambda‐bearing strain without exogenous folate denoted synthesis of folic acid by the symbionts. In addition, it appears that the symbionts produce sufficient biopterin to meet the needs of the host protozoon for growth.