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

Abstract

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.

Effect of Enzymatic Beech Fagus Sylvatica Wood Hydrolysate on Chlorella Biomass, Fatty Acid and Pigment Production

“…In the literature, high microalgal cell densities can be achieved during heterotrophic cultivation in scaled-up bioreactors [28]. Hence, application of this wood hydrolysate to microalgae cultivation in the dark could be interesting in terms of industrial production in large-volume closed tanks [25].…”

The medium for intensive culture of the diatom Cylindrotheca closterium (Ehrenb.) Reimann et Lewin (Bacillariophyta)

“…Обычно для создания подобных сред применяют метод, предложенный в литературе (Ketchum, 1954;Tamiya, 1957;Кузнецов, Семененко, 1966). При этом, чтобы получить сбалансированную по биогенным элементам питательную среду, следует учитывать стехиометрические соотношения химических элементов, входящих в состав культивируемого вида (Bumbak et al, 2011). В зависимости от стадии роста биохимический состав клеток может меняться, что приводит к изменению стехиометрических соотношений биогенных элементов, поэтому в культуре микроводорослей часто наблюдается избыточное потребление некоторых биогенных элементов (Левич и др., 1986; Тренкеншу, Лелеков, 2005; Тренкеншу, 2005).…”

Induction of D-xylose uptake and expression of NAD(P)H-linked xylose reductase and NADP¿+¿-linked xylitol dehydrogenase in the oleaginous microalga Chlorella sorokiniana

“…D-glucose (mainly from cellulose) and D-xylose (from hemicellulose) are two major carbohydrates in the lignocellulosic hydrolysates. D-glucose has been proven as a suitable carbon source for the growth of many microalgae, such as Crypthecodinium cohnii, Schizochytrium sp., Nitzschia laevis, Euglena gracilis, Galdieria sulphuraria and Chlorella species [10]. Li et al [11] successfully demonstrated that the microalga Chlorella pyrenoidosa could be cultured for lipid production on rice straw hydrolysates primarily containing D-glucose.…”