The oleaginous microalgae species Chlorococcum sphacosum GD is a promising feedstock for biodiesel production from soil. However, its metabolic mechanism of lipid production remains unclear. In this study, the lipid accumulation and metabolism mechanisms of Chlorococcum sphacosum GD were analyzed under salt stress based on transcriptome sequencing. The biomass and lipid content of the alga strain were determined under different NaCl concentrations, and total RNA from fresh cells were isolated and sequenced by HiSeq 2000 high throughput sequencing technology. As the salt concentration increased in culture medium, the algal lipid content increased but the biomass decreased. Following transcriptome sequencing by assembly and splicing, 24,128 unigenes were annotated, with read lengths mostly distributed in the 200–300 bp interval. Statistically significant differentially expressed unigenes were observed in different experimental groups, with 2051 up-regulated genes and 1835 down-regulated genes. The lipid metabolism pathway analysis showed that, under salt stress, gene-related fatty acid biosynthesis (ACCase, KASII, KAR, HAD, FATA) was significantly up-regulated, but some gene-related fatty acid degradation was significantly down-regulated. The comprehensive results showed that salt concentration can affect the lipid accumulation and metabolism of C. sphacosum GD, and the lipid accumulation is closely related to the fatty acid synthesis pathway.

No abstract

A new freshwater algal species of Fritschiella aquatilis was found in a freshwater aquarium in China (Shanxi Province), floating on the surface or sinking at the bottom of the water. This new species is characterized by bright-green, globular thallus with hairy morphology, which composed numerous small single celled filamentous branches. Most characteristics are in agreement with description of Fritschiella. But the new species differs from other members in this genus by the particularly aquatic habitat and macroscopic thalli morphology (the only reported Fritschiella tuberosa Iyengar species is terrestrial). Concatenated sequences from 28S rDNA, 18S rDNA, rbcL gene phylogenetic analysis of F. aquatilis to discuss taxonomic status. All phylogenetic trees have yielded a Fritschiella clade included the sequence, and F. aquatilis formed an independent branch evidently distinguished from other species. Comparing with F. tuberosa, the internal transcribed spacer (ITS) secondary structure of the new species has some compensatory base changes (CBCs) and hemi-CBCs, especially at the Helix1 and Helix 2 end. Thus, the results of morphological and molecular characteristics support F. aquatilis to be recognized as a new species. This new alga brings the total number of recognized Fritschiella species, and the habitats circumscription of the genus Fritschiella expanded to include terrestrial and aquatic.

A new freshwater alga species of Ulvella shanxiensis, is found in the circulating neutral water spring in China (Shanxi Province), growing epilithic and epiphytic on other substrates. This new species is characterized by olive-green, disc-shaped hollow thallus with irregularly vesicular morphology, which composed of 2–3 layers cells. Most characteristics were in agreement with Ulvella, but distinguished from the other freshwater members by thalli dimensions and cell diameter. In addition to describing the morphological structures of U. shanxiensis in detail, phylogenetic analysis based on sequences of the rbcL and 18S rDNA gene placed the algae in single clade with two samples, and demonstrated the separation between U. shanxiensis and other Ulvella species with a considerable sequence distance. Comparing with U. bullata, the internal transcribed spacer secondary structure of the new species has some compensatory base changes in 1 Helix and hemi-CBCs in 2–3 Helix, differed in several ways from that of other Ulvella algae. Consequently, these results of morphological observation and phylogenetic analysis suggest this alga as a new species, and bring a new record in the total number of recognized freshwater Ulvella species in China.

No abstract