Identification of suitable Botryococcus braunii strains for non-destructive in situ hydrocarbon extraction

Abstract

The process of milking microalgae is a promising approach to reduce the downstream costs for the production of valuable substances from microalgae by avoiding the steps of harvest, dewatering, and cell disruption of the common process chain (cultivation, harvesting, dewatering, cell disruption, extraction, purification). The green microalga Botryococcus braunii is particularly suited for this process due to its ability to produce large amounts of long-chain hydrocarbons accumulating in an extracellular matrix. The extracellular location of hydrocarbons is an enormous advantage in comparison with other microalgae that accumulate lipids in intracellular lipid bodies. At present, only a few B. braunii strains (UTEX 572, CCAP 807/2, SAG 807/1, FACHB 357, Bot22, and SCCAP 1761) have been examined for the process of long-term repetitive milking. In order to identify promising candidates for the milking process, twelve different B. braunii strains (SAG 30.81, SAG 807/1, UTEX 572, UTEX 2441, CCAP 807/2, ACOI 58, ACOI 1257, SCCAP K-1489, var. Showa, Bot22, SCCAP K-1761, and CCALA 779) were investigated in terms of growth, lipid accumulation, nutrient uptake, solvent compatibility, and extracellular hydrocarbon extractability. Based on these results, a ranking was defined in view of eligibility for non-destructive hydrocarbon extraction. Results indicate a particular potential for hydrocarbon milking for two of those twelve B. braunii strains. The strain Showa (71 out of 75 ranking points), which has not yet been examined for long-term repetitive milking, and the strain Bot22 (64 out of 75 ranking points) seem to be the most suitable strains for the milking process. They both possess good extractant compatibility including hydrocarbon extractability as well as high biomass and lipid productivity.

Metabolic response of Botryococcus braunii to high bicarbonate dosages and other conditions: analysis of photosynthetic performance, productivity, and lipidomic profile

“…Moreover, the fact that the increased lipid productivity remained constant between D6 and D12 might result convenient from a process design perspective, since it would facilitate the operation of a continuous process for lipidrich biomass production and its subsequent transformation, rather than designing a two-stage system consisting of a cell growth phase, followed by a nutritional stress and lipid accumulation stage (Biller et al 2015). Furthermore, it might help to improve systems such as the in situ milking proposed by some researchers (Hejazi and Wijffels 2004;Kleinert and Griehl 2020), where the basic concept relies on the continuous solvent-based lipid extraction, omitting the cellular disruption step.…”

“…Even though the unique chemical characteristics of B. braunii biomass makes it suitable for future energetic exploitation, the use of this strain as a realistic alternative for bioenergy production is hampered by its slow growth and low productivity (Kleinert and Griehl 2020). Consequently, a number of studies have addressed the partial elucidation of the pathways of lipid metabolism with two main purposes: (i) identifying metabolic targets that could potentially be tuned for reaching higher lipid yields (Wolf et al 1985;Metzger et al 1986;Niehaus et al 2011;Molnár et al 2012); and (ii) identifying key enzymatic steps in order to engineer fast-growing organisms (Niehaus et al 2012;Bell et al 2014;Muzika et al 2015;Zhuang and Chappell 2015;Thapa et al 2016).…”

In situ extraction (milking) of the two promising Botryococcus braunii strains Showa and Bot22 under optimized extraction time

“…The in situ extraction or "milking" of microalgae offers a promising approach to reduce the downstream costs of producing low-value products such as lipids from microalgae (Hejazi and Wijffels 2004;Borowitzka and Moheimani 2013;Griehl et al 2015;Chaudry et al 2018;Jackson et al 2020;Kleinert and Griehl 2021). In the in situ extraction process, the microalgae culture suspension is extracted directly during the cultivation, eliminating the cost and energy intensive steps of harvesting, dewatering, and cell disruption, which account for 50 to 80% of the total costs of the classical process chain (Acién et al 2012;Khoo et al 2020).…”

“…Due to these strain-specific properties, most research focusing on non-destructive in situ extraction during cultivation is conducted using B. braunii and only a few other microalgae have been investigated with regard to in situ extraction (Kleinert and Griehl 2021). Currently, two process methods are used for the in situ extraction of B. braunii.…”

“…Currently, only a handful of strains among the B. braunii have been investigated for repeated non-destructive in situ extraction with variations in setups for the extraction process, solvents, extraction times, and extraction cycles (Kleinert and Griehl 2021). These variations in experimental setups and methods make it difficult to compare the respective studies and prevent the derivation of characteristic strain-specific parameters such as optimal extraction time for establishing an in situ extraction process.…”