Abstract
Microalgae are an ubiquitous and powerful driver of geochemical cycles which have formed Earth’s biosphere since early in the evolution. Lately, microalgal research has been strongly stimulated by economic potential expected in biofuels, wastewater treatment, and high-value products. Similar to bacteria and other microorganisms, most work so far has been performed on the level of suspensions which typically contain millions of algal cells per millilitre. The thus obtained macroscopic parameters average cells, which may be in various phases of their cell cycle or even, in the case of microbial consortia, cells of different species. This averaging may obscure essential features which may be needed for the correct understanding and interpretation of investigated processes. In contrast to these conventional macroscopic cultivation and measuring tools, microfluidic single-cell cultivation systems represent an excellent alternative to study individual cells or a small number of mutually interacting cells in a well-defined environment. A novel microfluidic photobioreactor was developed and successfully tested by the photoautotrophic cultivation of Chlorella sorokiniana. The reported microbioreactor facilitates automated long-term cultivation of algae with controlled temperature and with an illumination adjustable over a wide range of photon flux densities. Chemical composition of the medium in the microbioreactor can be stabilised or modulated rapidly to study the response of individual cells. Furthermore, the algae are cultivated in one focal plane and separate chambers, enabling single-cell level investigation of over 100 microcolonies in parallel. The developed platform can be used for systematic growth studies, medium screening, species interaction studies, and the thorough investigation of light-dependent growth kinetics.
Highlights
Microalgae are a diverse group of photosynthetic organisms, including eukaryotic algae and prokaryotic cyanobacteria, which has formed our oxygen-containing atmosphere and remains responsible for a major fraction of carbon cycling which stabilises the Earth’s climate [1]
Microalgae are typically grown for biotechnological use in large-scale open cultivation systems [9] or in closed photobioreactors, [10] which often integrate monitoring of incident irradiance and real-time measurements of suspension parameters, e.g., optical density, pH, and temperature [11]
The culture is often further characterised by taking suspension aliquots and measuring in these samples, for example, chemical composition, dry weight and pigment content. These are mean parameters which typically represent several millilitres of the suspension with millions of algal cells contributing to the average
Summary
Microalgae are a diverse group of photosynthetic organisms, including eukaryotic algae and prokaryotic cyanobacteria, which has formed our oxygen-containing atmosphere and remains responsible for a major fraction of carbon cycling which stabilises the Earth’s climate [1]. Microalgae are typically grown for biotechnological use in large-scale open cultivation systems [9] or in closed photobioreactors, [10] which often integrate monitoring of incident irradiance and real-time measurements of suspension parameters, e.g., optical density, pH, and temperature [11]. More key data, such as chlorophyll fluorescence or dissolved O2/CO2, are measured in real time in laboratory photobioreactors [12]. These are mean parameters which typically represent several millilitres of the suspension with millions of algal cells contributing to the average
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