Characterization of a novel marine unicellular alga, Pseudoneochloris sp. strain NKY372003 as a high carbohydrate producer

https://doi.org/10.1016/j.jbiosc.2019.12.010Get rights and content

Production of biofuels and fine chemicals from biomass-derived carbohydrates through biorefinery attracts much attention because it is recognized as an environmentally friendly process. Microalgae can serve as promising carbohydrate producers for biorefinery rather than woody and crop biomass due to high biomass productivity, high CO2 fixation, and no competition with food production. However, microalgae with high carbohydrate productivity have not been well investigated despite intensive studies of microalgal lipid production. In this study, the carbohydrate production of Pseudoneochloris sp. strain NKY372003 isolated as a high carbohydrate producer, was investigated. Cultivation conditions with various combinations of nutrient contents and photon flux density were examined to maximize the biomass and carbohydrate productivities. At the optimal condition, the biomass and carbohydrate production of this strain reached 8.11 ± 0.37 g/L and 5.5 ± 0.2 g/L, respectively. As far as we know, this is the highest carbohydrate production by microalgae among ever reported. Cell staining with Lugol's solution visualized intracellular starch granules. Because algal starch can be converted to biofuels and building blocks of fine chemicals, Pseudoneochloris sp. NKY372003 will be a promising candidate for production of fermentable carbohydrates towards biofuels and fine chemicals production.

Section snippets

Used strain

Microalgal strains were isolated from seawater obtained from sites on the coast of Yakushima island, which is one of the Osumi islands in Kagoshima prefecture, Japan. Among 292 strains isolated, strain NKY372003 was selected as the highest carbohydrate producer for further study here. This strain was maintained in IMK medium (Nihon Pharmaceutical, Osaka, Japan) dissolved in artificial seawater in Erlenmeyer flasks (50 ml) at 100 μmol photons/m2/s and 30 °C under the shaking condition.

Microscopic analysis

The

Characterization of strain NKY372003 by genotypic and morphological analyses

As a result of the screening from 292 isolates, strain NKY372003 showed fast growth and the highest carbohydrate content. Then, we examined the genotypic and morphological characteristics of this strain. Strain NKY372003 was identified based on 18S rDNA sequences (DDBJ/EMBL/GenBank accession number: LC505539), and displayed 96.95% of sequence identity with the 18S rDNA sequence of the unicellular green alga, Pseudoneochloris marina. Microscopic analysis indicated that vegetative cells of strain

Acknowledgments

This work was partially supported by JSPS KAKENHI Grant-in-Aid for Scientific Research B [grant number 17H03465].

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