Isolation and characterisation of a highly halotolerant, thermotolerant Geitlerinema sp. CT7802 from the Gulf of Arabia

As part of a wider survey of extreme habitats in Saudi Arabia seeking cyanobacteria with potential for industrial applications, we isolated a filamentous cyanobacterial strain CT7802 from an industrial brine outfall site in the Eastern Province of Saudi Arabia. Following generation of axenic culture, microscopic studies revealed that cells form flexous trichomes, unconstricted at the cross-walls, trichome ends not attenuated, terminal cells are rounded with calyptra present, sheath thin, trichomes are blue-green. Microscopic filaments extend and eventually coalesce to form macroscopic filaments that form extensive mats. Halotolerance tests revealed that CT7802 was able to grow in Red Sea water (40 p.s.u) as well as brine (>60 p.s.u.). Thermotolerance tests identified an optimum growth temperature of 38°C but cells remained viable at a sustained temperature of 40°C. To investigate media preference in more detail, CT7802 growth was measured in seven defined, Red Sea water-based media (MN, BG-11sw, ASN III, WALNE, F/2, CHU10, A&A against a Red Sea Water (RSW) control at 38°C, 50 μmol quanta s^-1 m^-2 (12 hours light/dark cycle). Culture growth was followed spectrophotometrically measuring OD₆₀₀ nm, as well as by dry cell weight for 27 days. This experiment revealed that CT802 grew optimally on Walne medium that contains elevated levels of iron, boron and manganese. Full-length 16S SSU speciation analysis assigned CT7802 to the oscillatorial genus Geitlerinema. This genus, we note, contains other isolates from marine or hypersaline environments. Although CT7802 is phenotypically and genotypically consistent with the major Geitlerinema taxon, it may be a new sub-generic clade.