GROWTH OF LEUCONOSTOC CITROVORUM IN SKIMMILK FORTIFIED WITH COBALT, MANGANESE, AND IRON COMPOUNDS1

Abstract

Cobalt chloride, manganous chloride, ferric citrate, and ferrous sulfate were tested for their effects on growth of and chain formation by four strains of Leuconostoc citrovorum. Chemicals were added to sterile skimmilk before inoculation with test cultures. Numbers of L. citrovorum were determined with plate count procedures at periodic intervals during 30 hr of incubation at 22 or 30 C. Smears made concurrently were stained and examined microscopically to determine numbers of cells in chains. Cobalt chloride at a concentration of 0.1% completely inhibited growth of all strains of L. citrovorum, whereas 0.01% retarded growth of three strains, and 0.001% was essentially without effect. Chains of L. citrovorum strains exposed to 0.1% cobalt chloride remained fairly constant in length throughout the incubation, probably because the organism failed to grow. Lower concentrations of cobalt chloride had no marked effects on chain length of L. citrovorum. Manganous chloride (0.00001–0.001%), ferric citrate (0.001–0.1%), and ferrous sulfate (0.001–0.1%) were essentially without effect on growth of most L. citrovorum strains at 22 or 30 C. One strain produced markedly longer chains in the presence of manganous chloride, whereas others behaved similarly but less dramatically. Ferric citrate at the higher concentrations caused somewhat longer chains to be formed when L. citrovorum grew at either 22 or 30 C. The organism also tended to form longer chains when skimmilk contained 0.01 or 0.1% ferrous sulfate. This chemical also markedly reduced the generation time of L. citrovorum when incubation was at 22 C.