Bacteria responsible for preparation of dahi (curd)

Bacteria responsible for the preparation of dahi (curd) is Streptococcus lactis.
Curd may contain a wide variety of bacteria like Lactobacillus acidophilus, Lactococcus lactis, Lactococcus lactiscremoris etc, whereas yogurt contains Streptococcus thermophillus and Lactobacillus bulgaricus.
It is added to milk, the bacterium uses enzymes to produce energy molecules (ATP), from lactose. The byproduct of ATP energy production is lactic acid. The lactic acid produced by the bacterium curdles the milk, which then separates to form curds that are used to produce cheese.