Morphological and biochemical changes in lactobacillus casei grown in folate-depleted media

Abstract

Vitamin B12, or folic acid depletion in man leads to the familiar megaloblastic picture. Lactobacillus leichmannii has been investigated when grown in suboptimal concentrations of vitamin B12 and found to exhibit a condition analogous to human megaloblastosis. The investigations reported here indicate that Lactobacillus casei exhibits a similar condition when deprived of folic acid. Cultures of L. casei were grown in different concentrations of folic acid (from 0.02 ng. /ml.-2 ng. i d.) until the stationary phase was reached. Estimates of total count, viable count, dry weight, cell length, and protein, DNA and RNA content were obtained. The results showed that folic acid deprivation lead to: i. a slight fall in RNA /dry weight and protein /dry weight ratios, ii. a more than two-fold reduction in the DNA /dry weight ratio, iii. an increase in the mean cell length from 3.9μ to 11.4μ, iv. a striking reduction in the viability from 76% to 1.5%. The primary biochemical lesion caused by folic acid deficiency appears to be the same in both man and L. casei. It is suggested that a block in the synthesis of thymine causes DNA replication to be impaired. This would prevent cell division and could explain the increased size of folate-deficient cells. The analogies between folk acid deficiency in man and in L. casei suggest that a study of the bacterial system may help to clarify the biochemical basis of megaloblastosis in man.