Cold Adaptation Mechanisms of a Snow Alga Chlamydomonas nivalis During Temperature Fluctuations

Abstract

Cold environments, such as glaciers and alpine regions, constitute unique habitats for organisms living on Earth. In these harsh ecosystems, snow algae survive, florish, and even become primary producers for microbial communities. How the snow algae maintain physiological activity during violent ambient temperature changes remains unsolved. To explore the cold adaptation mechanisms of the unicellular snow alga Chlamydomonas nivalis, we compared its physiological responses to a model organism from the same genus, Chlamydomonas reinhardtii. When both cell types were exposed to a shift from 22°C to 4°C, C. nivalis exhibited an apparent advantage in cold tolerance over C. reinhardtii, as C. nivalis had both a higher growth rate and photosynthetic efficiency. To determine the cold tolerance mechanisms of C. nivalis, RNA sequencing was used to compare transcriptomes of both species after 1 h of cold treatment, mimicking temperature fluctuations in the polar region. Differential expression analysis showed that C. nivalis had fewer transcriptomic changes and was more stable during rapid temperature decrease relative to C. reinhardtii, especially for the expression of photosynthesis related genes. Additionally, we found that transcription in C. nivalis was precisely regulated by the cold response network, consisting of at least 12 transcription factors and 3 RNA-binding proteins. Moreover, genes participating in nitrogen metabolism, the pentose phosphate pathway, and polysaccharide biosynthesis were upregulated, indicating that increasing resource assimilation and remodeling of metabolisms were critical for cold adaptation in C. nivalis. Furthermore, we identified horizontally transferred genes differentially expressed in C. nivalis, which are critical for cold adaptation in other psychrophiles. Our results reveal that C. nivalis adapts rapid temperature decrease by efficiently regulating transcription of specific genes to optimize resource assimilation and metabolic pathways, providing critical insights into how snow algae survive and propagate in cold environments.

CsubMADS1, a lag phase transcription factor, controls development of polar eukaryotic microalga Coccomyxa subellipsoidea C‐169

“…Since C‐169 is a polar microalga, mucilage production may be an essential mechanism to survive harsh winters experienced in Antarctica (Holm‐Hansen, 1964; Morgan‐Kiss et al ., 2006). An earlier study using the snow alga C. nivalis showed that 12 TFs that belong to a cold response network precisely regulate transcription in response to cold stress (Peng et al ., 2020). At low temperatures, C‐169 strongly increases the expression of lipid biosynthesis genes to preserve membrane fluidity and produces antifreeze proteins to protect the cytoplasm (Blanc et al ., 2012).…”

“…The availability of its genome, the adaptation to extreme climatic conditions, the organism being free‐living, and the flexibility to culture it under laboratory conditions makes it possible for us to study the molecular basis of its development (Blanc et al ., 2012). A recent report based on transcriptome studies of the snow algae Chlamydomonas nivalis describes the key role of TFs in their efficient cold adaptation (Peng et al ., 2020). In streptophytes, the MIKC type MADS TFs have I, K, and C domains, with each domain having a specific role in the function of the TF.…”

Pilot-Scale Cultivation of the Snow Alga Chloromonas typhlos in a Photobioreactor

“…Productivities and growth rates for the Chloromonas species were lower than the literature values: over the nine batches average volumetric and areal productivities of 0.043 ± 0.021 g L −1 d −1 and 1.072 ± 0.514 g m −2 d −1 , respectively, were obtained, while growth rates varied between 0.020 and 0.105 d −1 . However, a comparison is difficult to obtain due to insufficient information or the different cultivation techniques used ( Teoh et al, 2013 ; Idrissi Abdelkhalek et al, 2016 ; Hulatt et al, 2017 ; Onuma et al, 2018 ; Morales-Sánchez et al, 2020 ; Peng et al, 2021 ). Compared to commercially cultivated algae, the production and growth rate is lower and needs to be improved to be competitive ( de Vree et al, 2015 ; Barka and Blecker, 2016 ; Benedetti et al, 2018 ; Darvehei et al, 2018 ; Metsoviti et al, 2019 ).…”

“…Like many cold adapted algae, C. typhlos is a potential source of lipids and carotenoids produced at lower temperatures and high light intensities as a mechanism to protect the cells ( Gorton et al, 2007 ; Remias et al, 2010 ; Liu and Nakamura, 2019 ; Hoham and Remias, 2020 ; Shi et al, 2020 ; Peng et al, 2021 ). If C. typhlos can produce sufficient biomass and valuable products such as astaxanthin at a low temperature with high light intensities, it can be a sustainable approach to cultivate microalgae during colder periods without excessive heating.…”

“…Potentially, C. typhlos is able to activate and upregulate its photosynthetic system very fast, leading to a substantial increase in absorption of light while reducing the scattered light and causing a rapid and substantial drop in turbidity ( Thorne and Nannestad, 1959 ; Kourti, 2000 ; Gregory, 2009 ). For extremophiles, a fast activation or deactivation of their metabolism can be crucial to cope with harsh conditions ( Harel et al, 2004 ; Peng et al, 2021 ).…”