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Lipid-rich microalgae are a potential source for the bio-oil production. We isolated a novel oleaginous Thraustochytrid microalga from seawater, Schizochytrium sp. ABC101, and tested the effect of different growth conditions on its production of lipids. Batch fermentation experiments indicated that depletion of nitrogen led to lipid accumulation, and lipid accumulation led to increased cell size and decreased cell wall thickness. Based on these results, we tested three types of fed-batch fermentations (carbon and no nitrogen feeding, carbon and limited nitrogen feeding, carbon and sufficient nitrogen feeding) to examine the effect of adjusting the nitrogen supply on lipid accumulation. The limited nitrogen feeding provided the most efficient lipid production, with maxima after 60 h (dry cell weight [DCW]: 64.7 g/L, lipids: 25.4 g/L, docosahexaenoic acid [DHA]: 11.0 g/L). Use of corn steep liquor (CSL) as the sole nitrogen source also led to excellent performance, with maxima at 84 h (DCW: 86.0 g/L, lipids: 37.2 g/L, DHA: 16.7 g/L). In addition, use of CSL rather than yeast extract reduced the lipid production cost by 50%. Our results suggest that regulation of the nitrogen source improves the efficiency of microalgal lipid production and use of a low-cost nitrogen source reduces production costs.

The translucent white-coloured, Gram-stain-negative, aerobic, non-motile, fusiform-shaped bacterium (designated strain SY72T) was isolated from waste-activated sludge. Optimal growth occurred at 30–37 °C and pH 6.0–7.0. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that the novel isolate belonged to the family Rhodobacteraceae of the class Alphaproteobacteria . Strain SY72T is closely related to Tabrizicola aquatica KCTC 23724T (97.8 % 16S rRNA gene sequence similarity) and Pseudorhodobacter aquaticus DC2N1-10T (96.4 %), respectively. DNA–DNA relatedness between strain SY72T and the closest phylogenetically related strain, Tabrizicola aquatica KCTC 23724T, was 18.0±0.7 %. In strain SY72T, the predominant respiratory quinone was ubiquinone Q-10, and the cellular fatty acids consisted mainly of C18 : 1ω7c and C18 : 1ω7c-11 methyl. The major polar lipids were phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol and phosphatidylethanolamine. Photoautotrophic and photoheterotrophic growth did not occur in strain SY72T. Furthermore, strain SY72T did not produce photosynthetic pigments or contain the photosynthetic genes pufL and pufM, by which it differed from the phototrophic species of the family Rhodobacteraceae . On the basis of distinct phenotypic and phylogenetic properties, strain SY72T represents a novel species of the genus Tabrizicola , for which the name Tabrizicola fusiformis sp. nov. is proposed. The type strain is SY72T (=KCTC 62105T=NBRC 113021T).

We isolated and characterized an oleaginous Thraustochytrid microalga. Based on 18 s rRNA sequencing, we classified this strain as Schizochytrium sp. SH103. Growth of these cells in a 5 L fermentor with a microbubble-type sparger (MTS) efficiently increased the oxygen transfer coefficient (OTC), while inducing only low external stress. For fermentation under conditions of low agitation (100 rpm) and aeration (3 L/min), the OTC was 8.6-fold higher using a MTS than a general type sparger (GTS). Under these same conditions, dry cell weight (DCW) productivity (0.54 vs. 1.26 g/L·h) and total lipid productivity (0.29 vs. 0.61 g/L·h) were each about 2.2-fold higher using a MTS than a GTS. Under conditions that optimized the OTC in a MTS fermentor (876 h−1), DCW productivity, total lipid productivity and DHA productivity were each 1.3-fold greater than non-optimized condition. Fed-batch fermentation experiments indicated the maximal DCW was 100.6 g/L at 48 h, maximal DCW productivity was 2.1 g/L·h, maximal lipid content was 48.6 g/L at 48 h, and lipid productivity was 1.0 g/L·h. Additionally, the results of experiments using a 50 L MTS fermentor (96.0 g/L DCW and 44.3 g/L total lipids at 48 h) were similar to those using the 5 L fermentor. Our results suggest that use of a MTS may help to achieve the efficient fermentation of heterotrophic microalgae for high cell densities.