Uptake of Radioactive Vitamin B 12 by Various Microorganisms

Abstract

Summary

A number of microorganisms were grown in a synthetic medium in which was incorporated radioactive vit. B₁₂ tagged with Co⁶⁰. Among those studied, radioactivity was found in varying amounts in the cells of all species studied except L. arabinosus. The incorporation of the radioactivity was not related to the requirement of vit. B₁₂ for growth of the bacterial cells. It was estimated that approximately 8 molecules of the tagged vitamin united with each L. leichmannii cell. Evidence is presented to show that the radioactivity in the cell is due to vit. B₁₂ in that (1) cells grown in the presence of Co⁶⁰Cl₂ with or without addition of non-radioactive vit. B₁₂ contained no radioactivity, and (2) the microbiological activity in homogenates of distintegrated cells paralleled that calculated from radioactivity due to Co⁶⁰. Measurements of uptakes of radioactive vit. B₁₂ by two competing organisms (such as L. leichmannii and E. coli) separated by cellophane membranes readily permeable to this vitamin as well as other nutrients and metabolites demonstrate that radioactivity entered the cells of both organisms in essentially the same amounts as when each species was grown alone.