Conversione del regime di crescita da eterotrofia a autotrofia allo scopo di incrementare la produzione di carotenoidi

Responsabili di progetto

Giuseppe Torzillo, Jiri Masojidek

Accordo

REPUBBLICA CECA - CAS (ex AVCR) - Czech Academy of Sciences

Bando

CNR-CAS (ex AVCR) 2016-2018

Dipartimento

Scienze del sistema terra e tecnologie per l'ambiente

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Stato del progetto

Nuovo

Proposta di ricerca

Microalgae (including cyanobacteria) represent a diverse group of phototrophic microorganisms adapted to various ecological habitats. Majority of microalgae strains grow phototrophically (with addition of inorganic carbon, e.g. carbon dioxide) obtaining their energy through the absorption of light for reduction of CO2 and the oxidation of water, with the release of oxygen and production of carbohydrates. These microorganisms are a potential source of high-value compounds such as pigments, vitamins, lipids, proteins, polysaccharides and antioxidant substances that are used for various biotechnological applications (Masojídek and Torzillo 2014). Many strains of microalgae produce high-value bioactive compounds such as carotenoids or polyunsaturated fatty acids, but phototrophic growth usually carried out in photobioreactors (PBR) is often slow due to light limitation, and difficult to scale-up. Various configurations of cultivation systems have been devised and built (for review Torzillo and Chini Zittelli, 2015). Natural carotenoid colours contain anti-oxidants which could act as health promoters apart from providing colours to food. Food colours are used to enhance the appearance of any food or beverage by imparting the desired colour which is lost during the food processing activity. Stringent regulatory frameworks, technological advancement in extraction, formulation & emulsion of colours, and demand for clean label products have brought a considerable shift in the demand from synthetic coal-tar food colours to natural colours and colouring food-stuffs
Some species of microalgae (e.g. Chlorella, Haematococcus, Scenedesmus) can also grow heterotrophically using organic substrates as sole carbon and energy sources (Doucha and Lívanský 2012, Barclay et al. 2013). Heterotrophic growth of microalgae, i.e. dark-growth in the presence of organic substrates like glucose, acetate and other organic compounds is carried out axenically in fermentors (closed vessels bubbled by air). As compared to phototrophic growth, heterotrophic cultivation has several advantages including the elimination of light limitation, higher degree of process control, and lower costs for growth and harvesting biomass because of faster growth on cheap organic substrates and higher cell densities. For example, the glucose limited fed-batch cultivation of Chlorella was developed to a large-scale production (Liu and Hu 2013).
Heterotrophic growth of microalgae eliminates the requirement for light and under such conditions cell density can be increased significantly. Some strains of Chlorella (C. vulgaris, C. zofingiensis, C. protothecoides) also exhibit high growth rate under heterotrophic conditions (i.e. in the presence of organic substrates like glucose) (e.g. Chen et al. 1997, Ip and Chen 2005). However, the content of pigments in biomass is significantly lower (2-4 times) as compared with those from phototrophic growth (Sergejevová and Masojídek 2012). Therefore, for high pigment accumulation the exposure to light of the cells, following heterotrophic growth is advisable. Although, in principle the process could be carried out with artificial light, the use of solar light is cheaper and a more sustainable process. Microalgae often respond to unfavourable conditions (irradiance intensity, nutrient limitation, temperature extremes, salinity) by modifying biomass composition towards the overproduction of various bioactive compounds (Hu 2013). Manipulation of culture conditions that directly affect biomass composition e.g. light and nutrient availability can promote their overproduction, but at the expense of biomass productivity.
Literature
Barclay et al. W, Apt K, Dong XD (2013) Commercial production of microalgae via fermentation. Handbook of Microalgal Culture: Applied Phycology and Biotechnology, (editors: A.Richmond & Q. Hu). 2nd edition, Wiley-Blackwell, , pp.134-145.
Doucha J, Lívanský K (2012) Production of high-density Chlorella culture grown in fermentors. J Appl Phycol 24:35-43
Hu Q (2013) Environmental effects on cell composition. in: Handbook of Microalgal Culture: Applied Phycology and Biotechnology, (editors: A.Richmond & Q. Hu). 2nd edition, Wiley-Blackwell, Oxford, pp 114-122
Ip PF, Chen F (2005) Production of astaxanthin by the green microalga Chlorella zofingiensis in the dark. Process Biochem 40:733-738
Liu J, Hu Q (2013) Chlorella: Industrial production of cell mass and chemicals. Handbook of Microalgal Culture: Applied Phycology and Biotechnology, (editors: A.Richmond & Q. Hu). 2nd edition, Wiley-Blackwell, , pp.329-338.
Masojídek J, Torzillo G (2014) Mass Cultivation of Freshwater Microalgae. On-line database Earth Systems and Environmental Sciences, Elsevier, 2nd edition, 13 p.
Masojidek J, Torzillo G., Kopecky J, Koblizek M, Nidiaci L, Komenda J, Lukavska, Sacchi A. (2000) Changes in chlorophyll fluorescence quenching and pigment composition in the green alga Chlorococcum sp., grown under nitrogen deficiency and salinity stress. J Applied Phycol. 12: 417-426
Sergejevová M, Masojídek J (2012) Chlorella biomass as feed supplement for freshwater fish: Sterlet, Acipenser ruthenus, Aquaculture Res 44, 157-159
Torzillo G, Goksan T, Faraloni C, Kopecky J., Masojidek J. (2003) Interplay between photochemical activities and pigment composition in an outdoor culture of Haermatococcus pluvialis during the shift from green to red stage. J, Appl Phycol. 15: 127-136
Torzillo G, Goksan T, Isik O, Gokpinar S (2005) Photon irradiance required to support optimal growth and interrelelations betwen irradiance and pigment composition in the green alga Haematococcus pluvialis. Eur J Phycol 40: 233-240
Torzillo G., Chini-Zittelli G. (2015) Tubular photobioreactors. Algal biorefineriers (Prokop et. al. eds), Springer DOI: 10.1007/978-3-319-20200-6_5

Obiettivi della ricerca

This project is aimed to testing of several Chlorophyta strains (e.g. Chlorella, Haematococcus, Scenedesmus, and Chlamydomonas) that can be converted from heterotrophic regime to fully competent phototrophic growth for production of carotenoids.
The main objective of the project is work out of a two-step cultivation procedure ¬- trophic conversion from heterotrophic to phototrophic mode. On the basis of preliminary experiments we propose to combine fast heterotrophic (or mixotrophic) growth to produce a bulk of microalgae followed by phototrophic growth regime (exposure to high irradiance) to enrich biomass in carotenoids. This process can be amplified by environmental constrains (e.g. nutrient limitation) at the final stage of phototrophic cultivation. The essential research task is the characterisation of tropic conversion process as concerns photobiochemical changes that are crucial for production process in correlation with growth and biomass composition. The heterotrophic - autotrophic regime will be compared to the full autotrophic one, i.e., both biomass accumulation and pigment accumulation will be carried out under solar light. The first approach will be mostly studied by the Czech partner who has gathered a considerable experience in fermentation process, while the genuine authotrophic process will be mainly studied by the Italian partner who has gathered a long experience in autothrophic outdoor cultivation and photobioreactor optimization.

Ultimo aggiornamento: 15/06/2025