A New Remote Sensing-Based System for the Monitoring and Analysis of Growth and Gas Exchange Rates of Photosynthetic Microorganisms Under Simulated Non-Terrestrial Conditions.

Mariano Battistuzzi,Luca Poletto,Lorenzo Cocola,Riccardo Claudi,Nicoletta La Rocca,Tomas Morosinotto,Eleonora Alei,M Sergio Erculiani,Bernardo Salasnich

doi:10.3389/fpls.2020.00182

Abstract

Oxygenic photosynthetic microorganisms are a focal point of research in the context of human space exploration. As part of the bioregenerative life-support systems, they could have a key role in the production of breathable O2, edible biomasses and in the regeneration of CO2 rich-atmospheres and wastewaters produced by astronauts. The test of the organism’s response to simulated physico-chemical parameters of planetary bodies could also provide important information about their habitability potential. It is believed that the success of future planetary and space missions will require innovative technologies, developed on the base of preliminary experiments in custom-made laboratory facilities. In this context, simulation chambers will play a pivotal role by allowing the growth of the microorganisms under controlled conditions and the evaluation in real-time of their biomass productivity and impact on atmosphere composition. We here present a system capable of addressing these requirements with high replicability and low costs. The setup is composed by three main parts: 1) a Star Light Simulator, able to generate different light intensities and spectra, including those of non-solar stars; 2) an Atmosphere Simulator Chamber where cultures of photosynthetic microorganisms can be exposed to different gas compositions; 3) a reflectivity detection system to measure from remote the Normalized Difference Vegetation Indexes (NDVI). Such a setup allows us to monitor photosynthetic microorganism’s growth and gas exchange performances under selected conditions of light quality and intensity, temperature, pressure, and atmospheres simulating non-terrestrial environments. All parameters are detected by remote sensing techniques, thus without interfering with the experiments and altering the environmental conditions set. We validated the setup by growing cyanobacteria liquid cultures under different light intensities of solar illumination, collecting data on their growth rate, photosynthetic activity, and gas exchange capacity. We utilized the reflectivity detection system to measure the reflection spectra of the growing cultures, obtaining their relative NDVI that was shown to correlate with optical density, chlorophyll content, and dry weight, demonstrating the potential application of this index as a proxy of growth.

Highlights

Oxygenic photosynthetic microorganisms such as cyanobacteria and eukaryotic algae have been fundamental for life evolution on our planet by creating an oxygen-rich atmosphere
The periodic registration of the reflectivity spectra of the growing culture necessary for the determination of its NDVI was achieved by mounting on top of the upper window of the atmosphere simulator chamber (ASC) the custom-made baffling system, embedding the optical fiber probe connected to the spectrometer (Figure 1B)
If cultures are more concentrated, cell pigments absorb all light energy available and cell duplication does not result in any increased activity since this is already maximal for those conditions

Summary

Introduction

Oxygenic photosynthetic microorganisms such as cyanobacteria and eukaryotic algae have been fundamental for life evolution on our planet by creating an oxygen-rich atmosphere. Only seven facilities have been realized worldwide, capable of integrating full-scale life support system tests [reviewed by (Escobar and Nabity, 2017)] They generally consist of human/microbial/plant associations where microorganism strains are selected from wild type or engineered species to obtain reliable culturing and high rate processes. The impact of their photosynthetic gas exchange on simulated atmospheres could provide a database of atmospheric biosignatures to be compared with future astronomical observations, such as those based on spectrometers mounted on large ground telescopes, like HIRES at the European extremely large telescope (E-ELT) (Marconi et al, 2016), or on the generation satellites [JWST, ARIEL, (Stevenson et al, 2016; Pascale et al, 2018)], designed to characterize exoplanet’s atmospheres In this context, cyanobacteria are considered the most promising organisms to be tested due to the capability of several species to thrive even in extreme environments of the Earth, such as hot and cold deserts and polar ices, often considered as analogs for extraterrestrial planets.

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