Purple bacteria or purple photosynthetic bacteria are pigmented by bacteriochlorophyll and carotenoids, giving them a colourful range of purples, pinks and oranges. They photosynthesize without producing oxygen as a by-product. This type of bacteria are proteobacteria which are phototrophic (produce their own food via photosynthesis).
One type, purple sulphur bacteria, deposit elemental sulphur –brimstone – instead. Others oxidise iron to form rusty banded iron formations.