Efficient pH and dissolved CO2 conditions for indoor and outdoor cultures of green alga Parachlorella.

Efficient pH and dissolved CO2 conditions for indoor (50-450 mL scale) and outdoor (100-500 L scale) culture of a green alga BX1.5 strain that can produce useful intracellular lipids and extracellular polysaccharides were investigated for the first time in Parachlorella sp. The cultures harvested under 26 different conditions were analysed for pH, dissolved CO2 concentration, and the biomass of extracellular polysaccharides. The BX1.5 strain could thrive in a wide range of initial medium pH ranging from 3 to 11 and produced valuable lipids such as C16:0, C18:2, and C18:3 under indoor and outdoor culture conditions when supplied with 2.0% dissolved CO2. Particularly, the acidic BG11 medium effectively increased the biomass of extracellular polysaccharides during short-term outdoor cultivation. The BG11 liquid medium also led to extracellular polysaccharide production, independent of acidity and alkalinity, proportional to the increase in total sugars derived from cells supplied with high CO2 concentrations. These results suggest Parachlorella as a promising strain for indoor and outdoor cultivation to produce valuable materials.

Characteristics and function of an extracellular polysaccharide from a green alga Parachlorella.

The green alga Parachlorella sp. BX1.5 is a new strain that can significantly coproduce lipids and polysaccharides, inside and outside the cells, respectively. This study aimed to investigate the characteristics and functional properties of the extracellular polysaccharide (EPS). Ethanol-extracted EPS from the cells grown in N-starved BG11 medium was found to be a novel acidic rhamnan of straight-chain type, with a high molecular mass of > 1.75 × 106 daltons. The water-soluble EPS exhibited high viscosity as sol, even at low concentrations, with 0.5 % EPS showing almost constant viscosity at 10-40 °C. Its addition to mayonnaise resulted in improved oil-off, suggesting its possible application as a thickener or food additive. Cells with added EPS were found to exhibit resistance to environmental stress conditions, such as heat, dryness, and decompression, and ultraviolet rays. Based on these rheological and biological effects, its unique properties with respect to biorefinery have been discussed here.

Dynamic Delta-like1 expression in presomitic mesoderm cells during somite segmentation.

During somite segmentation, the expression of clock genes such as Hes7 oscillates synchronously in the presomitic mesoderm (PSM). This synchronous oscillation slows down in the anterior PSM, leading to wave-like propagating patterns from the posterior to anterior PSM. Such dynamic expression depends on Notch signaling and is critical for somite formation. However, it remains to be determined how slowing oscillations in the anterior PSM are controlled, and whether the expression of the Notch ligand Delta-like1 (Dll1) oscillates on the surface of individual PSM cells, as postulated to be responsible for synchronous oscillation. Here, by using Dll1 fluorescent reporter mice, we performed live-imaging of Dll1 expression in PSM cells and found the oscillatory expression of Dll1 protein on the cell surface regions. Furthermore, a comparison of live-imaging of Dll1 and Hes7 oscillations revealed that the delay from Dll1 peaks to Hes7 peaks increased in the anterior PSM, suggesting that the Hes7 response to Dll1 becomes slower in the anterior PSM. These results raise the possibility that Dll1 protein oscillations on the cell surface regulate synchronous Hes7 oscillations, and that the slower response of Hes7 to Dll1 leads to slower oscillations in the anterior PSM.

Coproduction of lipids and extracellular polysaccharides from the novel green alga Parachlorella sp. BX1.5 depending on cultivation conditions.

A novel strain of microalga Parachlorella sp. BX1.5 was isolated and its unique properties of producing lipids and extracellular polysaccharides (EPS) characterized. The cells could extracellularly produce a large amount of acidic EPS, when cultured in nitrogen-deficient BG110 medium (BG11-N) with 2 % CO2-air supply. The main component of intracellularly accumulated lipids was triacylglycerol (TAG), depending on the different cultivation conditions of BG11, BG11-N, BG11-P (phosphate depleted), and BG11-N-P (nitrogen and phosphate depleted). Fatty-methyl-esters (FAMEs), methyl-esterification of total lipids, consisted of abundant saturated C16 and unsaturated C18 fatty acids under the culture conditions. Cell spot assays on BG11 plates revealed the resistance of cells to pH 2-11, high temperatures of 50-70 °C, ultraviolet irradiation, and drought, under different culture conditions, thereby suggesting the biological significance of lipid and EPS accumulation. The prospects of BX1.5 as a dual producer has also been discussed for biorefineries.