The Response Of Microcoleus Vaginatus To Desiccation

Man-made cyanobacterial crusts, through inoculating cyanobacteria on to sand surface, is a new technology in desertification control. Desiccation is the most extreme stress that the inoculated cyanobacteria faced after inoculation. Desiccation not only will cause damages to inoculated cyanobacteria, but also delay the formation and development of man-made cyanobacterial crusts. The adaptation mechanism of cyanobacteria to desiccation is not only the theory foundation of this technology, but also can provide scientific guidance for the maintenance of the man-made cyanobacterial crusts. In the present study, we isolated a dominant filamentous cyanobacterium strain from natural crust in sand area and identified the strain based on morphological as well as 16 S r DNA sequence. Then we studied the adaptation mechanism of this cyanobacterium to desiccation. The main results are shown as below:1) The morphology identification results showed that the filaments were blue-green. The occurrence of this cyanobacterium in field is in bundles containing a lot of filaments, and the bundles are enclosed by a common polysaccharide shealth. However, once the isolated strain was cultured in liquid mediun, the common polysaccharide sheath disappeared. Both the results of morphology identification and phylogenetic analysis showed that the cyanobacterium was Microcoleus vaginatus.2) M. vaginatus were treated with different desiccation periods, and the results showed that, 6 days desiccation had no obvious effect on physiological and biochemical activity of M. vaginatus. Ten days desiccation caused slight damages to M. vaginatus, and MDA content increased significantly simultaneously. The photosynthetic activity of M. vaginatus treated with 6 days or 10 days desiccation could recovery to the initial status. However, prolonged desiccation(20, 24 days) caused irreversible damages, and the biomass,Yield and Fv/Fm decreased obviously, whereas MDA content continuously increased. At the same time, the respiration decreased slightly, and the carotenoid content increased. These results indicated that water supply within the first 10 day after inoculation will be beneficial for the survival rate of inoculated M. vaginatus.3) We inoculated liquid cultured M. vaginatus onto sand surface to construct the man-made M. vaginatus crusts. After one day desiccation, the secretion of EPS in M. vaginatus crusts obviously increased. All the metabolic activities were stopped in the dry crusts, and both the biomass and EPS content maintained at a relative stable level. After rehydration, the original fluorescence Fo rapidly increased. Fv/Fm gradually increased and reached a stable level according to the function: y=ax/(b+x).The photosynthetic activity increased with water content.