Autotrophic and mixotrophic biomass production of the acidophilic Galdieria sulphuraria ACUF 64

Fabian Abiusi,Egbert Trompetter,Hugo Hoenink,Rene H Wijffels,Marcel Janssen

doi:10.1016/j.algal.2021.102513

Fabian Abiusi, Egbert Trompetter + Show 3 more

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https://doi.org/10.1016/j.algal.2021.102513

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Abstract

Abstract Galdieria sulphuraria is an acidophilic microalga isolated in proximity of sulfuric ponds where pH is below 3 and most organisms cannot grow. We cultivated G. sulphuraria ACUF 64 free of contamination for over 2 months in a medium containing organic carbon at pH 1.7 with continuous, high intensity, lighting. We compared biomass productivity of chemostat and repeated batch cultivations. The optimal biomass density in autotrophic and mixotrophic cultures was identified. In autotrophy biomass productivity was 28.3 g x ·m −2 ·day −1 , 1.8 to 7.7-fold higher than previously reported. Autotrophy was compared to ‘oxygen balanced’ mixotrophy where intracellular recirculation of O 2 and CO 2 take place. Aeration was not needed and 92% of the substrate carbon was converted into biomass. In mixotrophy biomass productivity was 1.8 times higher than autotrophic culture and linear growth was maintained at high biomass concentration (9.7 g x ·L −1 ). Light tolerance and high productivity in dense culture make our strain promising for mixotrophic outdoor cultivation. • Highest Galdieria sulphuraria autotrophic productivity (29 g·m −2 ·day −1 ) • Highest Galdieria sulphuraria mixotrophic productivity (51 g·m −2 ·day −1 ) • Oxygen balanced mixotrophy does not need aeration and 92% of substrate converted into biomass. • Galdieria sulphuraria can be cultivated at high light intensity. • In mixotrophy linear growth maintained at high biomass concentration (340 g x ·m −2 ).

Highlights

Microalgae are oxygenic photoautotrophic microorganisms, that use light energy to convert CO2 into organic matter and they release O2 as a by-product
The aim of our work was to assess if the strain G. sulphuraria ACUF 64 could be cultivated under ‘oxygen balanced’ mixotrophy and grow without any gas exchange in a closed photobioreactor (PBR)
The strain was cultivated at pH 1.7 and we investigated the potential of such an acidic environment to prevent bacterial contamination. We studied both autotrophic and mixotrophic cultivation of G. sulphuraria ACUF 64 at a high light in tensity to identify the cell concentration resulting in maximal biomass productivity

Summary

Introduction

Microalgae are oxygenic photoautotrophic (hereafter referred to as autotrophic) microorganisms, that use light energy to convert CO2 into organic matter and they release O2 as a by-product. Micro algal production systems can be placed on non-arable lands, and allow for fertilizer use near 100% efficiency [2] These unique qualities make microalgae a promising sustainable source of food and feed [3]. We recently created a new cultivation strategy named ‘oxygen balanced’ mixotrophy [6] In this strategy the dissolved oxygen con centration (DO) is maintained at a fixed set-point through continuous and automatic adjustment of the supply rate of a concentrated solution of the organic substrate. This strategy results in a balance between the oxygen produced by photosynthesis and oxygen consumed by respira tion while at the same time carbon dioxide is recycled within the microalgal culture. Under these conditions biomass productivity and biomass concentration was doubled and more than 90% of substrate carbon was incorporated within the biomass

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