Iron requirement of Lactobacillus spp. in completely chemically defined growth media

A completely chemically-defined growth medium, containing guanine, thymine, cytidine, 2'-deoxyadenosine and 2'-deoxyuridine as DNA precursors, was dev eloped for Lactobacillus johnsonii, on the basis of statistically designed techniques suitable for other lactobacilli. Particular focus was given to t he nucleotide composition of different defined media, and to the specific n ucleotide requirements of Lact. johnsonii. Most of the lactobacilli tested grew in a medium containing five free bases, four ribonucleosides or five d eoxyribonucleosides. Adenine and guanine were replaceable by inosine. The r equirement for thymine and cytosine was satisfied with uracil. The presence of inosine and uracil was identified as being essential for the growth of different Lactobacillus species, displaying their inability to synthesize p urines and pyrimidines de novo. Defined recipes with different nucleotide c omposition were used to investigate iron requirements of lactobacilli. Only marginal differences in growth were observed in iron-depleted media supple mented with five free bases, four ribonucleosides or five deoxyribonucleosi des; iron depletion had a greater effect on growth when inosine and uracil were supplied as the only nucleotide sources. The results suggest that iron plays a role in the pyrimidine and purine metabolism of lactobacilli. Lact obacillus spp., particularly Lact. johnsonii, require iron under particular environmental conditions with limited or specific nucleotide sources.