Valeriella persica sp. nov. (Chlorococcaceae, Chlorophyceae): A potential biodiesel feedstock from the hyperarid desert soil in Yazd (Iran) revealing new diagnostic criteria for green coccoids

Clear–cut delineation of the species identity of the drylands–inhabiting coccoid green algae is a challenging taxonomic work that requires an in–depth polyphasic investigation. Here, we employed an integrative polyphasic approach to characterize an interesting terrestrial green coccoid belonging to the recently proposed genus Valeriella from Iran. Despite morphological resemblances to some established taxa, this strain is distinguished by a combination of taxonomic features. Similarities and differences with morphologically allied taxa were discussed in detail, and some new diagnostic criteria for green coccoids were revealed. Our new findings threw light on the age-old problem in the taxonomy of green coccoids. The 18S rDNA phylogenetic assignment placed our strain in a well–supported lineage within the Valeriella clade (Chlorococcaceae, Chlorophyceae) with close affinity to V. minor. Therefore, here we propose Valeriella persica sp. nov. as a new species based on its phylogenetic position and key taxonomic features including cell-wall ultrastructure, life–cycle stages, reproduction strategies and ecology. We also assessed lipid content and fatty-acid profiles to evaluate suitability as potential feedstock for biofuel production. The lipid content and productivity were about 27 % and 130.5 mg L−1 day−1, respectively, at the late exponential phase. Gas chromatography (GC) coupled with flame−ionization detection (GC–FID) unraveled twenty−six species of FAs with highly significant levels of palmitic (C16:0; 24.74 %), oleic (C18:1c, ω–9; 19.02 %), linoleic (C18:2c, ω–6; 18.15 %), and α-linolenic (C18:3, ω–3; 16.28 %) acids. The biodiesel properties of V. persica are consistent with the international standards, making it a good candidate for biodiesel production on the large–scale. Overall, these ecophysiologically important compounds are well known to have major dynamic roles in regulating the fluidity and functioning of the cell and thylakoid membranes, and they, therefore, provide ecophysiological–adaptive traits to the extremely dry, desert habitat of this novel green coccoid.