Abstract
Viable microalgae occur in the air. Whether they can survive the stresses such as UV, desiccation and freezing temperatures at high altitudes during long distance dispersal is rarely studied. If yes, what mechanisms confer the tolerance? Four freshwater airborne green microalgae were isolated from Dongsha Atoll in the South China Sea, classified as Scenedesmus sp. DSA1, Coelastrella sp. DSA2, Coelastrella sp. DSA3 and Desmodesmus sp. DSA6 based on their morphologies and ITS sequences. Their survival rates under UV stress were tightly correlated with their cell wall thickness. All the four airborne green microalgae survived the air-dry stress on benchtop followed by − 20 °C freeze–desiccation stress for 4 weeks, but not the two waterborne green microalgae Desmodesmus sp. F5 and Neodesmus sp. UTEX 2219-4 used as controls. Three of the four airborne microalgae survived the lyophilization treatment, excluding Desmodesmus sp. DSA6 and the two waterborne microalgae. The four airborne microalgae produced carotenoids under prolonged stress conditions, which might help detoxify the reactive oxygen species generated under environmental stresses and shield from the high-light stress in the air. Characterization of these airborne microalgae may help answer how the descendants of green algae survived on the land about 450 MYA.
Highlights
At this atoll during the winter, and may bring particles from northeastern China, Korea, Japan, or Taiwan
It is well known that viable microalgae and cyanobacteria exist in the air, even in the high altitudes that can be collected using an airplane
This study brought our understanding of microalgal dispersal one step further, which is some species have evolved to gain the potentials to survive the stresses encountered in the long distance aerial dispersal in the wind
Summary
At this atoll during the winter, and may bring particles from northeastern China, Korea, Japan, or Taiwan (see the wind map in Supplementary Figure 1). Any freshwater microalgae isolated on this tiny island would be evolved from other lands with freshwater ecosystems. Whatever brought by the wind and could still survive on this tiny island are good candidates of true airborne dispersers in nature; this is especially true for those that could only grow in freshwater. The stresses encountered by these airborne microalgae would be similar to those faced by the primitive terrestrial plants when they first left the aquatic environments. Characterization of these airborne microalgae may help answer the evolutionary questions such as how the descendants of green algae survived on the non-shaded dry land and why algae in other phyla did not. We report the isolation, characterization of the airborne freshwater microalgae from Dongsha Island and their stress tolerance to UV, desiccation and freezing temperatures, in an attempt to discover the potential mechanisms that confer the stress tolerance to airborne green microalgae
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