Several clostridia are capable of causing severe diseases. For example, botulism is
caused by Clostridium botulinum, tetanus by Clostridium tetani, and gas gangrene by Clostridium perfringens. These pathogenic clostridia seem in no way unusual metabolically but are distinct in that they produce specific toxins or, in those causing gas gangrene, a group of toxins. C. perfringens and related species can also cause gastroenteritis in humans and domestic animals, and botulism outbreaks are not uncommon in birds such as ducks and a variety of other animals.
Sporosarcina
The genus Sporosarcina is unique among endospore formers because cells are cocci instead of rods. Sporosarcina consists of
strictly aerobic spherical to oval cells that divide in two or three perpendicular planes to form tetrads or packets of eight or more
cells. The major species is Sporosarcina ureae. This bacterium can be enriched from soil by plating dilutions of a pasteurized soil sample on alkaline nutrient agar supplemented with 8% urea and incubating in air. Most soil bacteria are strongly
inhibited by as little as 2% urea. However, S. ureae tolerates this, catabolizing urea to CO2
and ammonia (NH3), which dramatically raises the pH. S. ureae is remarkably alkaline-tolerant and can be grown in media up to pH 10, and this feature can be used
to an advantage in its enrichment from soil.
Heliobacteria
Heliobacteria are phototrophic gram-positive Bacteria. Heliobacteria are anoxygenic phototrophs and produce a unique pigment,
bacteriochlorophyll g. The group contains four genera: Heliobacterium, Heliophilum, Heliorestis, and Heliobacillus. All known heliobacteria produce rod-shaped or filamentous cells, but Heliophilum is morphologically unusual because its
cells form into bundles that are motile as a unit.