Bioprospecting of strains of Streptococcus thermophilus from Indian fermented milk products for folate production

This study deals with the bio-prospecting of folate producing strains of Streptococcus thermophilus isolated from milk and different fermented milk products of Indian origin. From a total of 500 randomly selected colonies isolated from 209 different samples, 117 isolates were identified as S. thermophilus by classical biochemical and molecular characterization. Frequency of incidence of S. thermophilus in the different samples of milk and milk products was variable with the highest in the dahi followed by yogurt and lassi and a very low incidence in case of milk and cheese.On screening for folate using a microbiological assay with a tri-enzyme extraction, about 15% of strains was found to produce folate in the range of 40–50 μg · L−1, 35% in the range of 20–30 μg · L−1, and the remainder in the range of 4–16 μg · L−1. Comparative analysis of the random amplification of polymorphic DNA PCR fingerprint profiles was used to characterize interspecific diversity of the ten highest folate producers. The LacZ gene of two of the highest folate producing isolates were sequenced and submitted to GenBank under following accession numbers of FJ161697 and FJ161698.