Highly saline conditions represent a strong challenge for most microorganisms in freshwater ecosystems. Eukaryotic freshwater green algae from the Chlorophyta clade were investigated for their ability to survive in and adapt to increased salt concentration in the growth medium. Striking differences were detected between the responses of the various algae species to the elevated salt concentrations. The investigated Chlamydomonas reinhardtii cc124 and Coelastrella sp. MACC-549 algae showed a moderate resistance to increased salt concentration, while Chlorella sp. MACC-360 exhibited high salt tolerance, showed unaltered growth characteristics and photosynthetic efficiency compared to the saline-free control conditions even at 600 mM NaCl concentration. Diverse physiological responses to elevated salt concentrations were described for the tested algae including variations in their growth capacity, characteristic morphological changes, alterations in the structure and function of the photosynthetic machinery and differences in the production of reactive oxygen species. Special alterations were identified in the lipid and exopolysaccharide production patterns of the tested algal strains in response to high salinity. As a conclusion Chlorella sp. MACC-360 algae showed outstanding salt tolerance features. Together with the concomitant lipid-producing phenotype under highly saline conditions this unicellular green alga is a promising candidate for biotechnological applications.

The nuclear, chloroplast and mitochondrial genomes of a unicellular green algal species of the Coelastrella genus was sequenced, assembled and annotated. The strain was previously classified as Chlamydomonas sp. MACC-549 based on morphology and partial 18S rDNA analysis. However, the proposed multi-loci phylogenomic approach described in this paper placed this strain within the Coelastrella genus, therefore it was re-named to Coelastrella vacuolata MACC-549. The strain was selected for de novo sequencing based on its potential value in biohydrogen production as revealed in earlier studies. This is the first thorough report and characterization for green algae from the Coelastrella genus. The whole genome annotation of Coelastrella vacuolata MACC-549 (including nuclear, chloroplast and mitochondrial genomes) shed light on interesting metabolic and sexual breeding features of this algae and served as a basis to taxonomically classify this strain.

Lipid biosynthesis in microalgae can be stimulated by cultivation in low nitrogen medium. MACC-401 was isolated from the soil surface in Tres Marias (MG-Brazil). The strain shows the morphological characteristics of the Scenedesmaceae green algae. The daily biomass and lipid production of MACC-401 is remarkable, 0.36 g L⁻¹ and 110 mg L⁻¹, respectively. Exploration of the genetic background of this promising strain not only allows the utilization of this species for industrial-scale lipid production, but also provides genetic targets to select lipid-producing strains from microalgae collections. We conducted physiological experiments by cultivating MACC-401 in complete and N-limited media and performed genome sequencing as well as transcriptome analysis. The estimated nuclear genome size of MACC-401 is 99.503 Mbp and the chloroplast genome is 0.15 Mbp. The phylogenetic analysis confirmed that the MACC-401 belongs to the Scenedesmaceae family, and represents a genetically distinct accession in this family. A basic comparative transcriptome analysis resulted in the identification of N-starvation responsive genes, which could serve as markers to monitor the onset of lipid accumulation in algal cultures.