Characterization of nuclear DNA in 12 species of Chlorella (Chlorococcales, Chlorophyta) by DNA reassociation

Developing Strain-Specific Simple Sequence Repeat (SSR) Markers for Chlorella sorokiniana

Chlorella sorokiniana green microalga offers many environmentally friendly applications, including wastewater treatment, biofertilizers, animal feed, and biofuel production. Different strains of C. sorokiniana have unique properties that may suit one application but not another. There is a need to distinguish between the many available strains of C. sorokiniana to choose the one that best fits the application. Consequently, our research goal was to develop strain-specific simple sequence repeat (SSR) markers to differentiate between the different strains. Seventeen markers spanning ten out of the twelve chromosomes of the C. sorokiniana genome were developed and validated on eight different strains from culture collections and our lab, and were then analyzed by fragment analysis. The results demonstrate the potential of these polymorphic markers to detect the genetic differences between the strains of C. sorokiniana, and to serve as useful tools for the intra-species population genetic analysis and conservation genetics studies of C. sorokiniana.

Characterization of Chlorella sorokiniana, UTEX 1230

This paper characterizes the strain Chlorella sorokiniana UTEX 1230 within a laboratory setting using a 1 L bubble column. The findings show that productivity can be trebled under mixotrophic conditions (from 0.2 g·L⁻¹·d⁻¹ to 0.66 g·L⁻¹·d⁻¹) with the addition of sodium acetate. The results also indicate that both the growth rate and final yield increase with the cultivation temperature, with most parameters showing an optimum in the range of 30–35 °C. The maximum specific growth rate was found to be in the region of 0.12 h⁻¹ at a surface irradiance between 100–500 µE·m⁻²·s⁻¹. This high growth rate makes the strain particularly suited to the rapid production of biomass, suitable for either whole cell bioprocessing or bioremediation. However, the relatively low lipid productivity (9.2 mg·L⁻¹·d⁻¹) confirms previous findings which would indicate poor applicability for biodiesel production. The strain shows greater promise in wastewater treatment applications with removal rates of nitrogen and phosphorus in the region of 37 and 30 mg·L⁻¹·d⁻¹ respectively. Furthermore, the findings show that a fed-batch strategy to inorganic nutrient loading can increase the final yield by around 50% compared to a conventional batch run. This is particularly interesting as fed-batch production techniques are rarely used within microalgal cultivation, so provide an interesting avenue for further investigation. Overall, the findings show that C. sorokiniana UTEX 1230 is a robust and fast-growing microalgal strain suitable both for the laboratory and scale-up.

Phylogenetic relationship of the green alga Nanochlorum eukaryotum deduced from its chloroplast rRNA sequences

The marine green coccoidal alga Nanochlorum eukaryotum (N.e.) is of small size with an average diameter of 1.5 microns. It is characterized by primitive-appearing biochemical and morphological properties, which are considerably different from those of other green algae. Thus, it has been proposed that N.e. may be an early developed algal form. To prove this hypothesis, DNA of N.e. was isolated by a phenol extraction procedure, and the chloroplast DNA separated by preparative CsCl density-gradient centrifugation. The kinetic complexity of the nuclear and of the chloroplast DNA was evaluated by reassociation kinetics to 3 x 10(7) bp and 9 x 10(4) bp, respectively. Several chloroplast genes, including the rRNA genes, were cloned on distinct fragments. The order of the rRNA genes corresponds to the common prokaryotic pattern. The 16S rRNA gene comprises 1,548 bases and is separated from the 23S rRNA gene with its 2,920 bases by a short spacer of 460 bases, which also includes the tRNA(Ile) and tRNA(Ala) genes. The 5S rRNA gene has not been found; it must start further than 500 bases downstream from the 3'-end of the 23S rRNA gene. From the chloroplast rRNA sequences, we have deduced secondary structures of the 16S and 23S rRNAs, which are in agreement with standard models. The rRNA sequences were aligned with corresponding chloroplast sequences; phylogenetic relationships were calculated by several methods. From these calculations, we conclude that N.e. is most closely related to Chlorella vulgaris. Therefore, N.e. does not represent an early developed algal species; the primitive-appearing morphological and biochemical characteristics of N.e. must rather be explained by secondary losses.