Desert wadis are widespread in the Arabian Peninsula and play a vital role in the ecology of the region; nevertheless, these ecosystems are among the least studied. Various types of microbial mats are predominant in wadis, but information on their bacterial diversity and spatial distribution is very scarce. We investigated bacterial diversity, pigments and lipid composition of ten mats located at the down-, mid- and upstream of a desert wadi in Oman. Direct microscopy revealed the existence of different unicellular and filamentous cyanobacteria, with the dominance of the heterocystous genera Calothrix and Scytonema. The majority of MiSeq 16S rRNA sequences (44-76%) were affiliated to Cyanobacteria and Proteobacteria. While Alphaproteobacteria was the most dominant proteobacterial class (10 to 48% of total sequences), Gamma- and Deltaproteobacteria were subdominant. Cluster analysis showed that the mats’ bacterial communities at the different locations along the wadi were different and shared less than 60% of their operational taxonomic units (OTUs). Chlorophyll a and scytonemin were the most predominant pigments in all mats. Different saturated, branched and mono- and poly-unsaturated fatty acids were detected in all mats, with C16 and C18 compounds as most dominant. The detected pigments and fatty acids indicate a major role of cyanobacteria in the wadi mats and the adaptation of microorganisms therein to the harsh wadi environment. Detection of diadinoxanthin and fucoxanthin confirmed the presence of diatoms. We conclude that microbial mats are important elements in wadi ecosystems and exist in a great variety of structure and community composition.
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