STIMULATION OF CELL-DIVISION AND DNA-REPLICATION IN PROTOTHECA-RICHARDSI BY PASSAGE THROUGH LARVAL AMPHIBIAN GUTS

Prototheca richardsi, an unpigmented heterotrophic alga, causes growth inhibition in amphibian larvae and has proved refractory to culture i n vitro. P. richardsi replication is dependent on regular passaging th rough tadpole digestive systems; uptake of thymidine by free-living Pr ototheca cells and incorporation into DNA are very low by comparison w ith leucine uptake and incorporation into protein, but DNA synthesis i s detectable in cells isolated from tadpole intestines. DNA replicatio n was elicited 6-8 h after ingestion in protothecans fed to tadpoles a nd subsequently re-isolated from them, providing that the tadpoles wer e fed subsequent to the ingestion. It appears that passaging through t adpole intestines provides an essential stimulus to maintaining an act ive cell division cycle in P. richardsi.