This is a sample from a salt marsh and shows a collection of bacteria. The darkest ones are Beggiatoa
, a colourless sulphur bacterium which accumulates elemental sulphur and this makes the cells opaque or refractile. The large pink ovoid is a cell of Chromatium
a purple sulphur bacterium, the green is a cyanobacterium, Lyngbya. The curving structure at about 2 o clock is a bacterium (Nitzschia
) but illustrates that one should not assume that all prokaryotes are small.