Query: NC_010337:2793667 Heliobacterium modesticaldum Ice1, complete genome Lineage: Heliobacterium modesticaldum; Heliobacterium; Heliobacteriaceae; Clostridiales; Firmicutes; Bacteria 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.
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General Information: This strain carries the anthrax toxin plasmid pXO1 but not the capsule plasmid pXO2 and is therefore avirulent but toxigenic. It is the counterpart to the Pasteur strain that carries pXO2 but not pXO1. This strain is often used for vaccine development. Under starvation conditions this group of bacteria initiate a pathway that leads to endospore formation, a process that is thoroughly studied and is a model system for prokaryotic development and differentiation. Spores are highly resistant to heat, cold, dessication, radiation, and disinfectants, and enable the organism to persist in otherwise inhospitable environments. Under more inviting conditions the spores germinate to produce vegetative cells. This organism was the first to be shown to cause disease by Dr. Louis Pasteur (the organism, isolated from sick animals, was grown in the laboratory and then used to infect healthy animals and make them sick). This organism was also the first for which an attenuated strain was developed as a vaccine. Herbivorous animals become infected with the organism when they ingest spores from the soil whereas humans become infected when they come into contact with a contaminated animal. PA/LF and PA/EF complexes are internalized by host cells where the LF (metalloprotease) and EF (calmodulin-dependent adenylate cyclase) components act. At high levels LF induces cell death and release of the bacterium while EF increases host susceptibility to infection and promotes fluid accumulation in the cells.