Microalgae are a valuable natural resource for a variety of value-added products. The growth of microalgae is determined by the impact of many factors, but, from the point of view of the implementation of autotrophic growth, light is of primary importance. This work presents an overview of the influence of light conditions on the growth of microalgae, the content of lipids, carotenoids, and the composition of fatty acids in their biomass, taking into account parameters such as the intensity, duration of lighting, and use of rays of different spectral composition. The optimal light intensity for the growth of microalgae lies in the following range: 26−400 µmol photons m−2 s−1. An increase in light intensity leads to an activation of lipid synthesis. For maximum lipid productivity, various microalgae species and strains need lighting of different intensities: from 60 to 700 µmol photons m−2 s−1. Strong light preferentially increases the triacylglyceride content. The intensity of lighting has a regulating effect on the synthesis of fatty acids, carotenoids, including β-carotene, lutein and astaxanthin. In intense lighting conditions, saturated fatty acids usually accumulate, as well as monounsaturated ones, and the number of polyunsaturated fatty acids decreases. Red as well as blue LED lighting improves the biomass productivity of microalgae of various taxonomic groups. Changing the duration of the photoperiod, the use of pulsed light can stimulate microalgae growth, the production of lipids, and carotenoids. The simultaneous use of light and other stresses contributes to a stronger effect on the productivity of algae.

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A novel freshwater strain of Coelastrella multistriata MZ–Ch23 was discovered in Tula region, Russia. The identification is based on morphological features, phylogenetic analysis of SSU rDNA gene and ITS1–5.8S rDNA–ITS2 region and predicted secondary structure of the ITS2. Phylogenetic analysis places the novel strain in the “core” Coelastrella clade within the Chlorophyceae. This is the first record of Coelastrella multistriata in the algal flora of Russia. Cultivation experiments were carried out to evaluate growth dynamics of the newly identified strain and the impact of nitrogen and/or phosphorus depletion on the fatty acid profiles and lipid productivity. On the fully supplemented Bold’s basal medium and under phosphorus-depleted conditions as well, the fatty acid profiles were dominated by α-linolenic acid (29.4–38.1% of total fatty acids). Depletion of either nitrogen or both nitrogen and phosphorus was associated with increased content of oleic acid (32.9–33.7%) and linoleic acid (11.9%). Prolongation of the growth to two months (instead of 25 days) resulted in increased content and diversity of very long-chain fatty acids including saturated species. The total very long-chain fatty acid content of 9.99% achieved in these experiments was 1.9–12.3-fold higher than in stress experiments. The highest variation was observed for oleic acid (3.4–33.7%). The novel strain showed the ability to accumulate lipids in amounts up to 639.8 mg L−1 under nitrogen and phosphorus starvation, which exceeds the previously obtained values for most Coelastrella strains. Thus, the newly identified MZ–Ch23 strain can be considered as a potential producer of omega-3 fatty acids on fully supplemented Bold’s basal medium or as a source of biomass with high content of saturated and monounsaturated fatty acids after nitrogen and phosphorus starvation.

A novel freshwater strain of Coccomyxa elongata (MZ–Ch64) was isolated from the Zaporizhia region, Ukraine. The identification was based on the phylogenetic analysis of SSU rDNA gene and ITS1–5.8S rDNA–ITS2 region and predicted secondary structure of the ITS2. Phylogenetic analysis placed this strain in the Coccomyxa group, within the class Trebouxiophyceae. The novel strain MZ–Ch64 formed a strongly supported lineage closest with C. elongata. The MZ–Ch64 strain differed from the morphological description of the species by the size of vegetative cells and absence of small mucilaginous caps at one end of the cell. A number of experiments with different concentrations of phosphate and nitrate were conducted to evaluate changes in the resulting fatty acid profiles and biomass productivity. The fatty acid profile and total fatty acids varied significantly under different nutrient deficiencies. The dominant fatty acid during cultivation on standard BBM medium, as well as in phosphorus‐depleted conditions, was oleic acid (to 48.0%–54.6% of total fatty acids). Absence of nitrogen alone, and absence of both nitrogen and phosphorus, led to an increase of palmitic acid (to 24.7%–25.6%), cis‐7‐hexadecenoic acid (to 14.8%) and α‐linolenic acid (to 9.1%–10.1%) in comparison with the control sample. The greatest variation was found for oleic acid (31.9%–54.6%). Thus, this strain can be considered as a potential producer of oleic acid or cis‐7‐hexadecenoic and α‐linolenic acids for biotechnological applications.

The new species Nephrochlamys yushanlensis sp. nov. is described from a freshwater plankton sample. A comparison of morphology, 18S rDNA gene and ITS2 sequences, and fatty acid profiles showed that the novel strain represents a new lineage within the genus Nephrochlamys. For the first time with a member of the Selenastraceae, experiments with phosphate and nitrate deprivation were conducted to evaluate changes in biomass, lipid and triacylglycerol (TAGs) accumulation, and composition of fatty acids. Biomass dry weight under simultaneous nitrogen and phosphorus depletion was 1.73 g · L−1, which is significantly lower than the 2.41 g · L−1 observed in the control. All conditions of nutrient restriction significantly increased the lipid content in comparison with the control. The largest increase in the total lipid content, reaching 58.64% DW per cell at the end of cultivation, occurred with nitrogen deficiency. Significant increases in TAGs content (to 23.69% and 21.74%, respectively) occurred in phosphorus‐ and nitrogen‐depleted conditions in comparison to the control (16.90%). Oleic (49.8–64.1%), palmitic (21.1–22.7%), and linoleic (8.6–10.3%) acids were the dominant fatty acids when cultured on standard BBM medium, as well as with the shortage of nutrients. Phosphorus deprivation as well as absence of both nitrogen and phosphorus led to the appearance of FAMEs α‐linolenic (1.5–4.1%) and stearidonic (1.0–1.8%) acids. In general, FAME profiles revealed that the relative percentage of saturated and monounsaturated fatty acids increased (88.9% of total fatty acids) in nitrogen‐depletion conditions, suggesting this strain may be suitable for biodiesel production.

Until now, the reported diversity of representatives from the genus Hantzschia inhabiting soils from different parts of Eurasia was limited to the few species H. amphioxys, H. elongata and H. vivax and some of their infraspecific taxa. We have studied the morphology, ultrastructure and phylogeny of 25 soil diatom strains, which according to published description would be assigned to “H. amphioxys sensu lato” using 18S rDNA, 28S rDNA and rbcL. We show that strains are made up of seven different species of Hantzschia, including five new for science. Five strains were identified as H. abundans. This species has a slight curvature of the raphe near its external proximal ends. Four of the examined strains were represented by different populations of H. amphioxys and their morphological characteristics fully correspond with its isolectotype and epitype. The main specific features of this species include 21–25 striae in 10 μm, 6–11 fibulae in 10 μm, 40–50 areolae in 10 μm and internal proximal raphe endings bent in opposite directions. H. attractiva sp. nov., H. belgica sp. nov., H. parva sp. nov., H. pseudomongolica sp. nov. and H. stepposa sp. nov. were described based on differences in the shape of the valves, significant differences in dimensions, a lower number of striae and areolae in 10 μm and the degree and direction of deflection of the internal central raphe endings. Based on the study of the morphological variability and phylogeny of soil Hantzschia-species from different geographical locations we conclude that while some species such as H. amphioxys are truly cosmopolitan in their distributions, some sympatric populations of pseudocryptic taxa exist in the Holarctic.

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