LACTOBACILLUS BULGARICUS was formally discovered in 1905 by the researcher, scientist and doctor Stamen  Grigorov.

http://www.bnr.bg/, Doctor Stamen Grigorov

Lactobacillus bulgaricus is thought to have first lived on plant life, and surviving on the energy of  plant sugars. Scientists think this is true because after recent studies on LACTOBACILLUS BULGARICUS, there are faint signs of genes which are used to break down plant sugars in it's genome. However, most of the genes have been broken down, due to mutations caused by it's new habitat; dairy.

Scientists think that Lactobacillus bulgaricus made such a drastic switch of habitats when milk became more commonly used, and that it possibly "made the jump", from plants to these dairy products when they were near. This would've gone unnoticed if it weren't for the fact that due to lactobacillus bulgaricus' fermentative metabolism,it increases the time in which milk can stay fresh. However, as you would expect, lactobacillus began to reproduce through conjugation in it's new habitat, and a new life for this bacteria was born.

Through this history of habitual changes, Lactobacillus bulgaricus also discontinued to produce amino acids, a feat which the bacterium would need to survive, living on plants. Instead, in it's new dairy habitat, it breaks down the proteins in this dairy, and absorbs the resulting amino acids. Breaking these proteins apart gives yogurt it's distinct flavor.