- Three distinct clades of cultured heterocystous cyanobacteria constitute the dominant N-fixing members of biological soil crusts of the Colorado Plateau, USA. Yeager, C.M., Kornosky, J.L., Morgan, R.E., Cain, E.C., Garcia-Pichel, F., Housman, D.C., Belnap, J., Kuske, C.R. FEMS Microbiol. Ecol. (2007)