Desiccation tolerance of Botryococcus braunii (Trebouxiophyceae, Chlorophyta) and extreme temperature tolerance of dehydrated cells

Microalgae: Potential for Bioeconomy in Food Systems

The efficient use of natural resources is essential for the planet’s sustainability and ensuring food security. Colombia’s large availability of water resources in combination with its climatic characteristics allows for the development of many microalgae species. The use of microalgae can potentially contribute to sustainable production in support of the agri-food sector. The nutritional composition (proteins, carbohydrates, fatty acids, vitamins, pigments, and antioxidants) of microalgae along with the ease of producing high biomass yields make them an excellent choice for human and animal nutrition and agriculture. Several species of microalgae have been studied seeking to develop food supplements for pigs, ruminants, poultry, fish, crustaceans, rabbits, and even bees. Important benefits to animal health, production, and improved bromatological and organoleptic characteristics of milk, meat, and eggs have been observed. Based on the functional properties of some microalgae species, foods and supplements have also been developed for human nutrition. Moreover, because microalgae contain essential nutrients, they can be utilized as biofertilizers by replacing chemical fertilizers, which are detrimental to the environment. In view of the above, the study of microalgae is a promising research area for the development of biotechnology and bioeconomy in Colombia.

Lethal microbial blooms delayed freshwater ecosystem recovery following the end-Permian extinction

Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers. We demonstrate that climate changes and deforestation can drive recurrent microbial blooms, inhibiting the recovery of freshwater ecosystems for hundreds of millennia. From the stratigraphic successions of the Sydney Basin, Australia, our fossil, sedimentary and geochemical data reveal bloom events following forest ecosystem collapse during the most severe mass extinction in Earth’s history, the end-Permian event (EPE; c. 252.2 Ma). Microbial communities proliferated in lowland fresh and brackish waterbodies, with algal concentrations typical of modern blooms. These initiated before any trace of post-extinction recovery vegetation but recurred episodically for >100 kyrs. During the following 3 Myrs, algae and bacteria thrived within short-lived, poorly-oxygenated, and likely toxic lakes and rivers. Comparisons to global deep-time records indicate that microbial blooms are persistent freshwater ecological stressors during warming-driven extinction events.

Harmful algal and bacterial blooms are increasingly frequent in lakes and rivers. From the Sydney Basin, Australia, this study uses fossil, sedimentary and geochemical data to reveal bloom events following forest ecosystem collapse during the end-Permian event and that blooms have consistently followed warming-related extinction events, inhibiting the recovery of freshwater ecosystems for millennia.

Australian Strains of Botryococcus braunii Examined for Potential Hydrocarbon and Carotenoid Pigment Production and the Effect of Brackish Water

The green alga Botryococcus braunii produces abundant hydrocarbons, in the form of drop-in biodiesel, which promoted interest in the species as a renewable fuel. However, despite the observation of dense populations in the wild, Botryococcus grows very slowly in culture, severely limiting its potential for development as a bioresource. Undertaking a biodiscovery program, we found new strains of Botryococcus in locations ranging from tropical to temperate Australia and from both fresh and brackish waters. As part of the ecophysiological characterisation of this new biodiversity, lipid and pigment compositions were studied for six new strains from six different locations. The strains were inoculated in either freshwater or brackish (salinity of 4)-based medium and maintained over 150 days. The growth of cultures was studied continuously, while lipid and pigment composition were analysed at final harvest on day 150. No significant differences in growth rate between fresh and brackish media were observed. Some strains were more tolerable of brackish conditions than others with a link between salinity tolerance and original location. The use of lower salinity (4 ppt) had a minimal effect on lipid composition, with only two of the six strains showing a different hydrocarbon profile in comparison to the other strains; pigment composition showed only minor variations for fresh and brackish water cultures, although the concentrations varied significantly with the freshwater cultures containing higher pigment concentrations.

Disentangling the role of extracellular polysaccharides in desiccation tolerance in lichen-forming microalgae. First evidence of sulfated polysaccharides and ancient sulfotransferase genes

Trebouxia sp. TR9 and Coccomyxa simplex are desiccation-tolerant microalgae with flexible cell walls, which undergo species-specific remodelling during dehydration-rehydration (D/R) due to their distinct ultrastructure and biochemical composition. Here, we tested the hypothesis that extracellular polysaccharides excreted by each microalga could be quantitatively and/or qualitatively modified by D/R. Extracellular polysaccharides were analysed by size exclusion and anion exchange chromatography, specific stains after gel electrophoresis and gas chromatography/mass spectrometry of trimethylsilyl derivatives (to determine their monosaccharide composition). The structure of a TR9-sulfated polymer was deduced from nuclear magnetic resonance (NMR) analyses. In addition, sugar-sulfotransferase encoding genes were identified in both microalgae, and their expression was measured by RT-qPCR. D/R did not alter the polydispersed profile of extracellular polysaccharides in either microalga but did induce quantitative changes in several peaks. Furthermore, medium-low-sized uronic acid-containing polysaccharides were almost completely substituted by higher molecular mass carbohydrates after D/R. Sulfated polysaccharide(s) were detected, for the first time, in the extracellular polymeric substances of both microalgae, but only increased significantly in TR9 after cyclic D/R, which induced a sugar-sulfotransferase gene and accumulated sulfated ß-D-galactofuranan(s). Biochemical remodelling of extracellular polysaccharides in aeroterrestrial desiccation-tolerant microalgae is species-specific and seems to play a role in the response to changes in environmental water availability.

Resilience to Freezing in the Vegetative Cells of the Microalga Lobosphaera incisa (Trebouxiophyceae, Chlorophyta)

The chlorophyte microalga Lobosphaera incisa was isolated from the snowy slopes of Mt. Tateyama in Japan. This microalga stores exceptionally high amounts of the omega-6 LC-PUFA arachidonic acid in triacylglycerols, and therefore represents a potent photosynthetic source for this essential LC-PUFA. Assuming that freezing tolerance may play a role in adaptation of L. incisa to specific ecological niches, we examined the capability of L. incisa to tolerate extreme sub-zero temperatures. We report here, that the vegetative cells of L. incisa survived freezing at -20°C and -80°C (over 1 month), without cryoprotective agents or prior treatments. Cells successfully recovered upon thawing and proliferated under optimal growth conditions (25°C). However, cells frozen at -80°C showed better recovery and lower cellular ROS generation upon thawing, compared to those preserved at -20°C. Photosynthetic yield of PSII, estimated by F_v /F_m , temporarily decreased at day 1 post freezing and resumed to the original level at day 3. Interestingly, the thawed algal cultures produced a higher level of chlorophylls, exceeding the control culture. The polar metabolome of the vegetative cells comprised a range of compatible solutes, dominated by glutamate, sucrose, and proline. We posit that the presence of endogenous cryoprotectants, a rigid multilayer cell wall, the high LC-PUFA content in membrane lipids, and putative cold-responsive proteins may contribute to the retention of functionality upon recovery from the frozen state, and therefore for the survival under cryospheric conditions. From the applied perspective, this beneficial property holds promise for the cryopreservation of starter cultures for research and commercial purposes.

PtDRG1, a Desiccation Response Gene from Pyropia tenera (Rhodophyta), Exhibits Chaperone Function and Enhances Abiotic Stress Tolerance

Pyropia are commercially valuable marine red algae that grow in the intertidal zone. They are extremely tolerant to desiccation stress. We have previously identified and reported desiccation response genes (DRGs) based on transcriptome analysis of P. tenera. Among them, PtDRG1 encodes a polypeptide of 22.6 kDa that is located in the chloroplast. PtDRG1 does not share sequence homology with any known gene deposited in public database. Transcription of PtDRG1 gene was upregulated by osmotic stress induced by mannitol or H₂O₂ as well as desiccation stress, but not by heat. When PtDRG1 was overexpressed in Escherichia coli or Chlamydomonas, transformed cells grew much better than control cells under high temperature as well as osmotic stress induced by mannitol and NaCl. In addition, PtDRG1 significantly reduced thermal aggregation of substrate protein under heat stress condition. These results demonstrate that PtDRG1 has a chaperone function and plays a role in tolerance mechanism for abiotic stress. This study shows that red algae have unknown stress proteins such as PtDRG1 that contributes to stress tolerance.