Lactobacillus elbrueckii subspecies bulgaricus (also known as Lactobacillus bulgaricus) is one of several bacteria used for the production of yogurt. First identified in 1905 by the Bulgarian doctor Stamen Grigorov, it is named after Bulgaria. Morphologically, it is a Gram-positive rod that may appear long and filamentous. It is also non-motile, and it does not form spores. It has complex nutritional requirements, including the inability to ferment any sugar except for lactose. This bacterium is also regarded as aciduric or acidphilic, due to the fact that it requires a relatively low pH (around 5.4-4.6) in order to grow effectively.