Astaxanthin and eicosapentaenoic acid production by S4, a new mutant strain of Nannochloropsis gaditana

Abstract

Background Astaxanthin is a ketocarotenoid with high antioxidant power used in different fields as healthcare, food/feed supplementation and as pigmenting agent in aquaculture. Primary producers of astaxanthin are some species of microalgae, unicellular photosynthetic organisms, as Haematococcus lacustris. Astaxanthin production by cultivation of Haematococcus lacustris is costly due to low biomass productivity, high risk of contamination and the requirement of downstream extraction processes, causing an extremely high price on the market. Some microalgae species are also primary producers of omega-3 fatty acids, essential nutrients for humans, being related to cardiovascular wellness, and required for visual and cognitive development. One of the main well-known producers of omega-3 fatty eicosapentaenoic acid (EPA) is the marine microalga Nannochloropsis gaditana (named also Microchloropsis gaditana): this species has been already approved by the Food and Drug Administration (FDA) for human consumption and it is characterized by a fast grow phenotype. Results Here we obtained by chemical mutagenesis a Nannochloropsis gaditana mutant strain, called S4, characterized by increased carotenoid to chlorophyll ratio. S4 strain showed improved photosynthetic activity, increased lipid productivity and increased ketocarotenoids accumulation, producing not only canthaxanthin but also astaxanthin, usually found only in traces in the WT strain. Ketocarotenoids produced in S4 strain were extractible in different organic solvents, with the highest efficiency observed upon microwaves pre-treatment followed by methanol extraction. By cultivation of S4 strain at different irradiances it was possible to produce up to 1.3 and 5.2 mgL−1 day−1 of ketocarotenoids and EPA respectively, in a single cultivation phase, even in absence of stressing conditions. Genome sequencing of S4 strain allowed to identify 199 single nucleotide polymorphisms (SNP): among the mutated genes, mutations in a carotenoid oxygenase gene and in a glutamate synthase gene could explain the different carotenoids content and the lower chlorophylls content, respectively. Conclusions By chemical mutagenesis and selection of strain with increased carotenoids to chlorophyll ratio it was possible to isolate a new Nannochloropsis gaditana strain, called S4 strain, characterized by increased lipids and ketocarotenoids accumulation. S4 strain can thus be considered as novel platform for ketocarotenoids and EPA production for different industrial applications.

Proteomic characterization of a lutein-hyperaccumulating Chlamydomonas reinhardtii mutant reveals photoprotection-related factors as targets for increasing cellular carotenoid content

“…Given the pervasive effects of the random EMS chemical mutagenesis in Mut-5, which creates an array of single nucleotide polymorphisms scattered across the genome, it may be difficult to pinpoint the genetic occurrences that confer its altered phenotype. Multiple loci are likely to have been affected by the EMS mutagenesis, as was found in previous microalgal EMS mutant generation studies [ 110 , 113 , 114 ], and determining the mutations governing the phenotype(s) of Mut-5 will require repeated genetic back-crosses, followed by phenotype segregation analyses and whole genome sequencing of daughter cells. Hence, these will be the next steps taken towards identifying the causative genetic lesion(s) contained in the genome of Mut-5.…”

“…These targets may additionally be of interest to researchers aiming to increase the production of other xanthophylls such as astaxanthin in green algae. Increasing astaxanthin levels can cause reductions in the number of LHCs and total carotenoids per cell [ 110 – 112 ]; therefore, our targets may offer a means to boost the accumulation capacity of valuable carotenoids.…”

Microalgae biofuels: illuminating the path to a sustainable future amidst challenges and opportunities

“…The use of random mutagenesis to obtain microalgal strains with the desired phenotype is widespread. Through methods, such as 60 Co γ-ray, UV exposure, and chemical mutagenesis, mutants of N. gaditana [ 246 , 247 ], N. oculate [ 248 , 249 ] and Scenedesmus sp. [ 250 , 251 ] have been successfully generated.…”

Toward the Exploitation of Sustainable Green Factory: Biotechnology Use of Nannochloropsis spp.

“…Efforts were also made to improve the astaxanthin content of Nannochloropsis. By means of chemical mutagenesis, Cecchin and coworkers isolated a new Nannochloropsis gaditana strain characterized by increased lipid and ketocarotenoid accumulation [115].…”