The Genus Thiomargarita

Introduction

Thiomargarita namibiensis is by far the largest member in the group of “morphologically conspicuous sulfur bacteria” (La Riviere and Schmidt, 1992). This group harbors sulfur storing, colorless bacteria, which gain energy by the oxidation of sulfide and can be readily recognized by their very particular morphology. The spherical cells of Thiomargarita are typically 100–300 µm wide, but with some regularity, very large cells with diameters of up to 750 µm occur (Schulz et al., 1999). Therefore, Thiomargarita namibiensis is, at least in terms of volume, the largest bacterium known so far. Nevertheless, it was one of the last sulfur bacteria to be discovered (Schulz et al., 1999). This may be because this organism seems to occur only in shelf sediments off the coast of Namibia, where it inhabits a sulfidic loose sediment composed of mainly dead diatoms, which is regularly suspended (Weeks et al., 2004) by methane eruptions (Emeis et al., 2004). In contrast to their close...