Best practices in heterotrophic high-cell-density microalgal processes: achievements, potential and possible limitations

Microalgae of numerous heterotrophic genera (obligate or facultative) exhibit considerable metabolic versatility and flexibility but are currently underexploited in the biotechnological manufacturing of known plant-derived compounds, novel high-value biomolecules or enriched biomass. Highly efficient production of microalgal biomass without the need for light is now feasible in inexpensive, well-defined mineral medium, typically supplemented with glucose. Cell densities of more than 100 g l−1 cell dry weight have been achieved with Chlorella, Crypthecodinium and Galdieria species while controlling the addition of organic sources of carbon and energy in fedbatch mode. The ability of microalgae to adapt their metabolism to varying culture conditions provides opportunities to modify, control and thereby maximise the formation of targeted compounds with non-recombinant microalgae. This review outlines the critical aspects of cultivation technology and current best practices in the heterotrophic high-cell-density cultivation of microalgae. The primary topics include (1) the characteristics of microalgae that make them suitable for heterotrophic cultivation, (2) the appropriate chemical composition of mineral growth media, (3) the different strategies for fedbatch cultivations and (4) the principles behind the customisation of biomass composition. The review confirms that, although fundamental knowledge is now available, the development of efficient, economically feasible large-scale bioprocesses remains an obstacle to the commercialisation of this promising technology

Micro-algae come of age as a platform for recombinant protein production

A complete set of genetic tools is still being developed for the micro-alga Chlamydomonas reinhardtii. Yet even with this incomplete set, this photosynthetic single-celled plant has demonstrated significant promise as a platform for recombinant protein expression. In recent years, techniques have been developed that allow for robust expression of genes from both the nuclear and plastid genome. With these advances, many research groups have examined the pliability of this and other micro-algae as biological machines capable of producing recombinant peptides and proteins. This review describes recent successes in recombinant protein production in Chlamydomonas, including production of complex mammalian therapeutic proteins and monoclonal antibodies at levels sufficient for production at economic parity with existing production platforms. These advances have also shed light on the details of algal protein production at the molecular level, and provide insight into the next steps for optimizing micro-algae as a useful platform for the production of therapeutic and industrially relevant recombinant proteins

Docosahexaenoic acid production by the marine algae Crypthecodinium cohnii

This thesis focuses on the production of docosahexaenoic acid (DHA; 22:6), an w-3 polyunsaturated fatty acid with applications in foods and pharmaceuticals, by Crypthecodinium cohnii. This chloroplastless heterotrophic marine microalga has been studied since the end of the nineteenth century and has been identified as a good producer of DHA. C. cohnii can accumulate lipid to over 20% of its biomass dry weight, with a high content of DHA (over 30% of the total lipid). Other polyunsaturated fatty acids represent less than 1% of the C. cohnii-derived oil. The aim of the research described in this thesis was to identify relevant process parameters for the large-scale production of docosahexaenoic acid (DHA) with C. cohnii. Several cultivation protocols for C. cohnii were developed, analysed and optimised with respect to the production of biomass, lipid and DHA and solutions were sought for newly identified bottlenecks for industrial DHA production.Applied Science

Biotechnological production and applications of the omega-3 polyunsaturated fatty acid docosahexaenoic acid

Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid composed of 22 carbon atoms and six double bonds. Because the first double bond, as counted from the methyl terminus, is at position three, DHA belongs to the so-called omega-3 group. In recent years, DHA has attracted much attention because of its beneficial effect on human health. At present, fish oil is the major source of DHA, but alternatively it may be produced by use of microorganisms. Marine microorganisms may contain large quantities of DHA and are considered a potential source of this important fatty acid. Some of these organisms can be grown heterotrophically on organic substrates without light. These processes can be well controlled and DHA with constant quality can be produced all year round. This paper reviews recent advances in the biotechnological production of DHA by marine microorganisms

Fed-batch cultivation of the docosahexaenoic-acid-producing marine alga Crypthecodinium cohnii on ethanol

The heterotrophic marine microalga Crypthecodinium cohnii produces docosahexaenoic acid (DHA), a polyunsaturated fatty acid with food and pharmaceutical applications. So far, DHA production has been studied with glucose and acetic acid as carbon sources. This study investigates the potential of ethanol as an alternative carbon source for DHA production by C. cohnii. In shake-flask cultures, the alga was able to grow on ethanol. The specific growth rate was optimal with 5 g l-1 ethanol and growth did not occur at 0 g l-1 and above 15 g l-1. By contrast, in fed-batch cultivations with a controlled feed of pure ethanol, cumulative ethanol addition could be much higher than 15 g l-1, thus enabling a high final cell density and DHA production. In a representative fed-batch cultivation of C. cohnii with pure ethanol as feed, 83 g dry biomass l-1, 35 g total lipid l-1 and 11.7 g DHA l-1 were produced in 220 h. The overall volumetric productivity of DHA was 53 mg l-1 h-1, which is the highest value reported so far for this alga

A process for production of polyunsaturated fatty acids by marine microorganisms

The present invention relates to a new process of producing polyunsaturated fatty acids by culturing marine microorganisms on a monoalcohol. The new process is particularly suitable for producing docosahexaenoic acid by dinoflagellates (Crypthecodinium cohnii). The process can be performed as a batch, fed-batch, or continuous proces

Biotechnological production and applications of the omega-3 polyunsaturated fatty acid docosahexaenoic acid

Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid composed of 22 carbon atoms and six double bonds. Because the first double bond, as counted from the methyl terminus, is at position three, DHA belongs to the so-called omega-3 group. In recent years, DHA has attracted much attention because of its beneficial effect on human health. At present, fish oil is the major source of DHA, but alternatively it may be produced by use of microorganisms. Marine microorganisms may contain large quantities of DHA and are considered a potential source of this important fatty acid. Some of these organisms can be grown heterotrophically on organic substrates without light. These processes can be well controlled and DHA with constant quality can be produced all year round. This paper reviews recent advances in the biotechnological production of DHA by marine microorganisms