Phylogenetic and Morphological Diversity of Cyanobacteria in Soil Desert Crusts from the Colorado Plateau

We compared the community structures of cyanobacteria in four biological desert crusts from Utah's Colorado Plateau developing on different substrata. We analyzed natural samples, cultures, and cyanobacterial filaments or colonies retrieved by micromanipulation from field samples using microscopy, denaturing gradient gel electrophoresis, and sequencing of 16S rRNA genes. While microscopic analyses apparently underestimated the biodiversity of thin filamentous cyanobacteria, molecular analyses failed to retrieve signals for otherwise conspicuous heterocystous cyanobacteria with thick sheaths. The diversity found in desert crusts was under-represented in currently available nucleotide sequence databases, and several novel phylogenetic clusters could be identified. Morphotypes fitting the description of Microcoleus vaginatus Gomont, dominant in most samples, corresponded to a tight phylogenetic cluster of probable cosmopolitan distribution, which was well differentiated from other cyanobacteria traditionally classified within the same genus. A new, diverse phylogenetic cluster, named "Xeronema," grouped a series of thin filamentous Phormidium-like cyanobacteria. These were also ubiquitous in our samples and probably correspond to various botanical Phormidium and Schizothrix spp., but they are phylogenetically distant from thin filamentous cyanobacteria from other environments. Significant differences in community structure were found among soil types, indicating that soil characteristics may select for specific cyanobacteria. Gypsum crusts were most deviant from the rest, while sandy, silt, and shale crusts were relatively more similar among themselves.