Desert stream phototrophic mats: a promising source for biofuel production

Desert streams occur in abundance in the mountain regions of the Arabian Peninsula, where massive areas are covered by phototrophic microbial mats. In this study, 11 different phototrophic microbial mats were screened for their carbohydrate and lipid contents and their ability to produce methane, and mats with potential were further used for biofuel production. A maximum bioethanol yield of 0.76 ± 0.1 g/L was obtained by enzymatic saccharification of one mat, which was dominated by the alga Spirogyra, followed by fermentation of the produced sugars using the native Clostridium strain AK-1. A lipid content of 9–18 wt% was measured from the microbial mats. An increase of 4% and 9% was observed, when the mat with the highest lipid content was incubated under 3% salinity and nitrogen deprivation conditions, respectively. Anaerobic digestion of one selected cyanobacterial mat for biomethane production yielded a maximum of 95 mL CH₄/g VS (volatile solids) after 49 days. MiSeq analysis revealed that the microbial community of this mat was 99.5% dominated by archaea, mainly belonging to the genera Methanoculleus (56.7%), Methanobacterium (27%) and Methanosarcina (7.6%). Our results demonstrate the potential of using microbial mats from desert streams to produce bioethanol, biodiesel and biomethane.