The Metabolism of the Amino Acids of Escherichia coli and Other Bacteria by the Rumen Ciliate Entodinium caudatum

SUMMARY Non-multiplying and growing cultures of Entodinium caudatum incubated anaerobically engulfed Escherichia coli bacteria specifically labelled with individual 14C-amino acids and incorporated the amino acids into protozoal protein without conversion to any other amino acid. The protozoal cisternae ‘pool’ and the medium contained the free amino acid and with some amino acids the N-acetyl or N-formyl derivative in addition. The constituents of the pool were probably by-products of the metabolism of the bacteria and not intermediates between bacterial and protozoal proteins. There was no extensive catabolism of the bacterial amino acids by the protozoa, although some of the bacterial leucine, isoleucine and valine was broken down to isovaleric acid, α-methylbutyric acid and isobutyric acid, respectively. The addition to the medium of the 12C-form of the 14C-amino acid present in the E. coli decreased the incorporation of 14C into the protozoa with half of the amino acids tested. The rate of loss of viability of various other bacterial species after engulfment by the protozoa was found to be independent of Gram-reaction, size or natural habitat.