Phylogenetic and morphological diversity of cyanobacteria in soil desert crusts from the Colorado Plateau

We compared the community structures of cyanobacteria in four biological de sert crusts from Utah's Colorado Plateau developing on different substrata, We analyzed natural samples, cultures, and cyanobacterial filaments or col onies retrieved by micromanipulation from field samples using microscopy, d enaturing gradient gel electrophoresis, and sequencing of 16S rRNA genes. W hile microscopic analyses apparently underestimated the biodiversity of thi n filamentous cyanobacteria, molecular analyses failed to retrieve signals for otherwise conspicuous heterocystous cyanobacteria with thick sheaths. T he diversity found in desert crusts was underrepresented in currently avail able nucleotide sequence databases, and several novel phylogenetic clusters could be identified. Morphotypes fitting the description of Microcoleus va ginatus Gomont, dominant in most samples, corresponded to a tight phylogene tic cluster of probable cosmopolitan distribution, which was well different iated from other cyanobacteria traditionally classified within the same gen us. A new, diverse phylogenetic cluster, named "Xeronema," grouped a series of thin filamentous Phormidium-like cyanobacteria. These were also ubiquit ous in our samples and probably correspond to various botanical Phormidium and Schizothrix spp., but they are phylogenetically distant from thin filam entous cyanobacteria from other environments, Significant differences in co mmunity structure were found among sail types, indicating that soil charact eristics may select for specific cyanobacteria, Gypsum crusts were most dev iant from the rest, while sandy, silt, and shale crusts were relatively mor e similar among themselves.