General Information: Heliobacterium modesticaldum strain Ice1, the type strain of this species, was isolated from Icelandic hot spring volcanic soils. It grows optimally above 50 degrees Celsius, grows best photoheterotrophically, but can grow in the dark chemotrophically on pyruvate. Phototrophic thermophile. This organism is an anoxygenic phototroph isolated from hot spring microbial mats and volcanic soil. Cell wall structure, the ability to form endospores, and 16S ribosomal RNA analysis place Heliobacterium modesticaldum in a family of phototrophic bacteria related to the Clostridia. Heliobacterium modesticaldum is able to fix nitrogen and may contribute significantly to the nitrogen availability in microbial mats.