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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 freezedesiccation 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 highlight 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. Darwin described the falling of fine dust particles from the sails of his vessel on many occasions while cruising in the Atlantic Ocean. He reported that the particles contained dry "infusoria" which included siliceous shells of many freshwater species and a least one marine diatom identified using microscopes available at that time 1. Although he did not attempt to grow microalgae from the dust collections, it is now well known that viable microalgae occur in the atmosphere 2-5. In a historical survey of airborne microalgae, van Overeem collected green microalgae in northern Europe using an airplane at various altitudes 3. These cells were cultivated, and nine algal isolates were identified. In the US, airborne microalgal cells were isolated in many states using car and airplane in a study conducted by Brown et al. 2. These isolates were classified into 38 and 17 genera of Chlorophyta and Chrysophyta, respectively, in addition to seven genera of cyanobacteria. More recently, airborne algae were surveyed in Hawaii, and the results of this investigation showed that these algae were dominated by cyanobacteria, followed by green algae and diatoms 6. A comprehensive review of the history of airborne microalgae studies is provided by Sharma et al. 4. Most studies on airborne microalgae have been focused on their diversity and abundance in various regions and at different altitudes, as well as the effects of these airborne cells on human health, such allergenicity and toxicity 4,7. How they resist environmental stresses in the air has rarely been discussed 8. When microalgal cells are dispersed through a long distance in the atmosphere, they encounter a few environmental stresses not common in water and on the ...

BackgroundLipids and starch are important feedstocks for bioenergy production. Genetic studies on the biosyntheses of lipids and starch in green microalgae have drawn significant attention recently. In these studies, quantifications of lipids and starch are required to clarify the causal effects. While lipids are assayed with similar procedures worldwide, starch in green microalgae has been measured using various methods with deficiencies in accuracy or high cost.ResultsA simple, accurate and low cost procedure for routine quantification of starch in green microalgae was developed. This procedure consists of quick-freezing of the cells, solvent extraction of the pigments, 134 °C autoclaving and glucoamylase double digestions of starch, followed by a glucose assay using the dinitrosalicylic acid reagent. This procedure was optimized to quantify starch in small volumes of green microalgal culture. The accuracy of starch quantification using this procedure was 102.3 ± 2.5% (mean ± SD, n = 6), as indicated by using cornstarch as internal controls. The working protocol is available at http://dx.doi.org/10.17504/protocols.io.2mhgc36.ConclusionsThis quantification approach overcomes the current problems in the starch quantification of green microalgae such as inaccuracy and high cost. This approach would provide an opportunity to compare the effects of genetic, physiological or cultivation manipulations on the productivity of starch in green microalgae elucidated in different labs, which is essential in the enhancement of lipid productivity studies in microalgae.