Authors
Davide Canini, Flavio Martini, Stefano Cazzaniga, Tea Miotti, Beatrice Pacenza, Sarah D’Adamo & Matteo Ballottari
Published
29 November 2024
Journal
Microbial Cell Factories volume 23, Article number: 322 (2024)
DOI
https://doi.org/10.1186/s12934-024-02599-4
Abstract
Background Canthaxanthin is a ketocarotenoid with high antioxidant activity, and it is primarily produced bymicroalgae, among which Nannochloropsis oceanica, a marine alga widely used for aquaculture. In the last decade,N. oceanica has become a model organism for oleaginous microalgae to develop sustainable processes to producebiomolecules of interest by exploiting its photosynthetic activity and carbon assimilation properties. N. oceanicacan accumulate lipids up to 70% of total dry weight and contains the omega-3 fatty acid eicosapentaenoic acid(EPA) required for both food and feed applications. The genome sequence, other omics data, and synthetic biologytools are available for this species, including an engineered strain called LP-tdTomato, which allows homologousrecombination to insert the heterologous genes in a highly transcribed locus in the nucleolus region. Here, N.oceanica was engineered to induce high ketocarotenoid and canthaxanthin production.
Results
We used N. oceanica LP-tdTomato strain as a background to express the key enzyme for ketocarotenoidproduction, a β-carotene ketolase (CrBKT) from Chlamydomonas reinhardtii. Through the LP-tdTomato strain, thetransgene insertion by homologous recombination in a highly transcribed genomic locus can be screened bynegative fluorescence. The overexpression of CrBKT in bkt transformants increased the content of carotenoidsand ketocarotenoids per cell, respectively, 1.5 and 10-fold, inducing an orange/red color in the bkt cell cultures.Background (LP) and bkt lines productivity were compared at different light intensities from 150 to 1200 μmol m-2s-1: at lower irradiances, the growth kinetics of bkt lines were slower compared to LP, while higher productivity wasmeasured for bkt lines at 1200 μmol m-2 s-1. Despite these results, the highest canthaxanthin and ketocarotenoidsproductivity were obtained upon cultivation at 150 μmol m-2 s-1.
Conclusions
Through targeted gene redesign and heterologous transformation, ketocarotenoids and canthaxanthincontent were significantly increased, achieving 0.3% and 0.2% dry weight. Canthaxanthin could be produced usingCO2 as the only carbon source at 1.5 mg/L titer. These bkt-engineered lines hold potential for industrial applications infish or poultry feed sectors, where canthaxanthin and ketocarotenoids are required as pigmentation agents.