Abstract Recovery of Photosynthesis in Biological Soil Crusts Using MALDI-TOF and Metagenomics Analysis Amal Salim Mabrook Al-Habsi Cyanobacteria are dominant in biological soil crusts and they have long been the focus of scientific research because of their ecological value. Biological soil crusts are characterized by their fast restoration of photosynthesis upon onset of rehydration. We investigated the recovery process of photosynthetic activity in biological soil crusts from Oman using MALDI-TOF fluorescence measurements of 13C labeled chlorophyll (Chll a molecules at different time intervals after addition of water. Our results showed that recovery can be divided into two phases.) The initial phase was fast and was characterized chlorophyll a was not "Clabeled, indicating that this molecule or its precursors were preserved intact under dry conditions. The second phase was slower and was marked by a de novo synthesis of chlorophyll a, as indicated by the incorporation of 13 C labeled. The de novo synthesis of chlorophyll a is most likely related to the growth of cyanobacteria in the crusts In conclusion, the crust ability for rapid recovery upon rehydration is related to quick structural reorganization of chlorophyll a, and fast restoration of its activity without de novo synthesis at the first 24 h. Metagenomics is a new field of research that has developed over the past decade to study the genomes of non-cultured microbes with the ambition to better understand the role of microorganisms in biogeochemical cycles and to look for biotechnologically relevant enzymes and biomolecules (Schmeisser et al., 2007). In this study, metagenomics analysis was performed on Omani desert crusts to identity. microbial communities and their functions in this ecosystem This study gains its relevance from the fact that this is the first study of its kind in Oman and since very little is known about the diversity and function of microbial communities in the relatively widespread crusts in Oman (Abed et al., 2010). Different genes coding for pathways in biogeochemical processes were found to match with the metagenomics data available in public databases. Out of 806,600 reads generated from sequencing of a total of 347,844,129 bp and total of 109 annotated genes, almost one third of the genes were affiliated to their counterparts in the oxidative phosphorylation pathways. Photosynthesis related genes constituted approximately a quarter of the total number of genes. All genes. found in the metagenomics data play an important role in the photosynthesis process. However, more work is needed to secure other functional genes relevant to other organisms, and this is not done because it is beyond the scope of this study