Isolation and characterisation of novel thermo- and halo-tolerant marine microalgae from the Red Sea

Carbon capture and conversion by photosynthetic microbes offers the only plausible biological route to mitigate KSA CO₂ emissions because this desert kingdom has little agriculture. We have carried out a bioprospecting survey of the Red Sea to isolate and characterise microalgal strains adapted to the local climate and highly saline waters of the Red Sea and Gulf. Microalgae were isolated from seven marine euphoric zone sample sites along a 35 km transect using a <15 μ >0.45μ filtration screen followed by culture on liquid MN media at 50 μ s-1 m-2 22°C for 14-28 days. Single colonies were obtained by serial dilution and plating on solid MNSW (seawater) media. Axenic cultures were obtained by iterative streaking on solid MNSW. A library of 89 axenic isolates was selected for high biomass accumulation, thermotolerance, halotolerance and pH tolerance to identify a set of 39 lead chlorophyta. A maximum photosynthetic sustained growth temperature of 40°C was observed over 28 days. Halotolerance ranges from 25-50 psu, with pH tolerance ranging from pH 6 to pH 11. One strain OS3S1b was particularly robust, able to tolerate pH 11, 50 psu, 40°C. Species assignment was determined by 18S small subunit rrn from 39 lead microalgae isolates. Successful reactions (consisting of 36 pairs of PCR reactions) were sequenced. Full-length amplicons were obtained for 24 strains and used to derive a phylogenetic tree. This revealed that these 24 strains form a single Red Sea specific cluster of 19 taxa somewhat related to extant unicellular Ulvophyte.