Figure 11.

Conceptual model of iron oxide mat development (four stages) in high-temperature, acidic geothermal springs of Yellowstone National Park. Stage I is defined by the primary colonization of lithoautotrophic populations of Hydrogenobaculum spp. and Metallosphaera yellowstonensis. Stage II is represented by visible iron oxide accretion, encrustation of Hydrogenobaculum spp. by Fe(III)-oxides, and initial formation of microterracettes. Heterotrophic archaea begin colonizing in Stage III and gradients in O₂ are apparent. As iron oxide depth increases to form “mature” 0.5–2 cm thick mats (Stage IV) the microbial community undergoes succession toward organoheterotrophic archaea, where steep gradients in oxygen, and macroscale ridges and pools are observed.