The first eukaryotic cells ? Acid hot-spring algae

Microalgal Carotenoids: A Review of Production, Current Markets, Regulations, and Future Direction

Microalgae produce a variety of compounds that are beneficial to human and animal health. Among these compounds are carotenoids, which are microalgal pigments with unique antioxidant and coloring properties. The objective of this review is to evaluate the potential of using microalgae as a commercial feedstock for carotenoid production. While microalgae can produce some of the highest concentrations of carotenoids (especially astaxanthin) in living organisms, there are challenges associated with the mass production of microalgae and downstream processing of carotenoids. This review discusses the synthesis of carotenoids within microalgae, their physiological role, large-scale cultivation of microalgae, up- and down-stream processing, commercial applications, natural versus synthetic carotenoids, and opportunities and challenges facing the carotenoid markets. We emphasize legal aspects and regulatory challenges associated with the commercial production of microalgae-based carotenoids for food/feed, nutraceutical and cosmetic industry in Europe, the USA, the People’s Republic of China, and Japan. This review provides tools and a broad overview of the regulatory processes of carotenoid production from microalgae and other novel feedstocks.

Lysyl oxidase-like protein secreted from an acidophilic red alga, Cyanidium caldarium

Cyanidium caldarium is a primitive acidophilic red alga which grown optimally at pH 1-3. When the alga was cultured at pH 6, which is the upper limit of acidity for its survival, most of the algal cells became large cells with four endospores which did not split into daughter cells. This suggests that the alga survives in the endospore state at pH 6 to protect against nutrient uptake deficiency due to low pH gradient across the cell membranes. The alga was also found to secrete an extracellular protein specifically at pH 6. The protein was identified to be lysyl oxidase-like protein, which had been reported to be widely distributed in the animal kingdom but not yet found in the plant kingdom. In the plant kingdom, only two primitive acidophilic algae, C. caldarium and Cyanidioschyzon merolae, possess a gene encoding this protein.

Transcriptional response of the extremophile red alga Cyanidioschyzon merolae to changes in CO2 concentrations

Cyanidioschyzon merolae (C. merolae) is an acidophilic red alga growing in a naturally low carbon dioxide (CO₂) environment. Although it uses a ribulose 1,5-bisphosphate carboxylase/oxygenase with high affinity for CO₂, the survival of C. merolae relies on functional photorespiratory metabolism. In this study, we quantified the transcriptomic response of C. merolae to changes in CO₂ conditions. We found distinct changes upon shifts between CO₂ conditions, such as a concerted up-regulation of photorespiratory genes and responses to carbon starvation. We used the transcriptome data set to explore a hypothetical CO₂ concentrating mechanism in C. merolae, based on the assumption that photorespiratory genes and possible candidate genes involved in a CO₂ concentrating mechanism are co-expressed. A putative bicarbonate transport protein and two α-carbonic anhydrases were identified, which showed enhanced transcript levels under reduced CO₂ conditions. Genes encoding enzymes of a PEPCK-type C₄ pathway were co-regulated with the photorespiratory gene cluster. We propose a model of a hypothetical low CO₂ compensation mechanism in C. merolae integrating these low CO₂-inducible components.

Photorespiratory glycolate oxidase is essential for the survival of the red alga Cyanidioschyzon merolae under ambient CO2 conditions

Photorespiration is essential for all organisms performing oxygenic photosynthesis. The evolution of photorespiratory metabolism began among cyanobacteria and led to a highly compartmented pathway in plants. A molecular understanding of photorespiration in eukaryotic algae, such as glaucophytes, rhodophytes, and chlorophytes, is essential to unravel the evolution of this pathway. However, mechanistic detail of the photorespiratory pathway in red algae is scarce. The unicellular red alga Cyanidioschyzon merolae represents a model for the red lineage. Its genome is fully sequenced, and tools for targeted gene engineering are available. To study the function and importance of photorespiration in red algae, we chose glycolate oxidase (GOX) as the target. GOX catalyses the conversion of glycolate into glyoxylate, while hydrogen peroxide is generated as a side-product. The function of the candidate GOX from C. merolae was verified by the fact that recombinant GOX preferred glycolate over L-lactate as a substrate. Yellow fluorescent protein-GOX fusion proteins showed that GOX is targeted to peroxisomes in C. merolae The GOX knockout mutant lines showed a high-carbon-requiring phenotype with decreased growth and reduced photosynthetic activity compared to the wild type under ambient air conditions. Metabolite analyses revealed glycolate and glycine accumulation in the mutant cells after a shift from high CO2 conditions to ambient air. In summary, or results demonstrate that photorespiratory metabolism is essential for red algae. The use of a peroxisomal GOX points to a high photorespiratory flux as an ancestral feature of all photosynthetic eukaryotes.

Ancient photosynthetic eukaryote biofilms in an Atacama Desert coastal cave

Caves offer a stable and protected environment from harsh and changing outside prevailing conditions. Hence, they represent an interesting habitat for studying life in extreme environments. Here, we report the presence of a member of the ancient eukaryote red algae Cyanidium group in a coastal cave of the hyperarid Atacama Desert. This microorganism was found to form a seemingly monospecific biofilm growing under extremely low photon flux levels. Our work suggests that this species, Cyanidium sp. Atacama, is a new member of a recently proposed novel monophyletic lineage of mesophilic "cave" Cyanidium sp., distinct from the remaining three other lineages which are all thermo-acidophilic. The cave described in this work may represent an evolutionary island for life in the midst of the Atacama Desert.