Evaluation of co-culturing a diatom and a coccolithophore using different silicate concentrations

Screening of antibiotics to obtain axenic cell cultures of a marine microalga Chrysotila roscoffensis

Due to high growth rate, outstanding abiotic stress tolerance, and rich value-added substances, Chrysotila roscoffensis, belonging to the phylum of Haptophyta, can be considered as a versatile resource for industrial exploitation of bioactive compounds. However, the application potential of C. roscoffensis has drawn attention until just recently, and the understanding related to the biological properties of this species is still scarce. For example, the sensitivities of C. roscoffensis to antibiotics, which is essential for the verification of heterotrophic capacity and the establishment of efficient genetic manipulation system is still unavailable. Aiming to provide fundamental information for future exploitation, the sensitivities of C. roscoffensis to nine types of antibiotics were tested in this study. The results demonstrated that C. roscoffensis exhibited relatively high resistances to ampicillin, kanamycin, streptomycin, gentamicin, and geneticin, while was sensitive to bleomycin, hygromycin B, paromomycin, and chloramphenicol. Using the former five types of antibiotics, a bacteria removal strategy was established tentatively. Finally, the axenicity of treated C. roscoffensis was confirmed based on a multi-strategy method including solid plate, 16S rDNA amplification, and nuclear acid staining. This report can provide valuable information for the development of optimal selection markers, which are meaningful for more extensive transgenic studies in C. roscoffensis. Moreover, our study also paves the way for the establishment of heterotrophic/mixotrophic cultivation modes of C. roscoffensis.

Upwelling and nutrient dynamics in the Arabian Gulf and sea of Oman

This study demonstrates the vertical and horizontal distribution of nutrients and the seasonal response of nutrients to upwelling in the Arabian Gulf and the Sea of Oman. Thus, monthly data on nitrate, phosphate, and silicate are obtained from the World Ocean Atlas 2018 (WOA), as well as estimates of coastal and curl driven upwelling in both regions. The results of the study indicate that the Sea of Oman's surface and deep waters contained higher concentrations of nutrients than the Arabian Gulf by 80%. In addition, both regions have exhibited a general increase in the vertical distribution of nutrients as the depth increases. Among the aforementioned nutrients, nitrate is found to be a more limiting nutrient for phytoplankton growth than phosphate as the nitrate-to-phosphate ratios (N:P) in surface waters are lower (≤ 4.6:1) than the Redfield ratio (16:1). As for the upwelling, curl-driven upwelling accounts for more than half of the total upwelling in both regions, and both play an important role in nutrient transport. Thus, nutrients are upwelled from the subsurface to the mixed layer at a rate of 50% in the Oman Sea from 140 m to 20 m during the summer and to 40 m during the winter. Similarly, the Arabian Gulf shows 50% transport for nitrates, but 32% for phosphates, from 20 m to 5-10 m. However, due to the abundance of diatoms at the surface of the Arabian Gulf, the surface silicate content is 30% higher than that of the deeper waters.

Transcriptomic mechanisms for the promotion of cyanobacterial growth against eukaryotic microalgae by a ternary antibiotic mixture

This study evaluated the responses of a mixed culture of two cyanobacterial species (Microcystis aeruginosa and Synechocystis sp.) and two eukaryotic microalgal species (Raphidocelis subcapitata and Tetradesmus obliquus) to a mixture of three frequently detected antibiotics (tetracycline, ciprofloxacin and sulfamethoxazole) at environmentally relevant exposure doses of 60-300 ng/L. Mixed antibiotics selectively stimulated (p < 0.05) the growth and photosynthetic activity as well as generated transcriptomic responses in cyanobacteria without disrupting co-existing eukaryotic microalgae. Mixed antibiotics stimulated the growth of M. aeruginosa through the regulation of genes related to ribosome, photosynthesis, redox homeostasis, quorum sensing and nutrient metabolism. The proportion of M. aeruginosa among the four phytoplankton species in the mixed-culture system was increased from 33% to 38-44% under antibiotic exposure, which promoted the dominance of M. aeruginosa. Up-regulation of carbon catabolism-related genes contributed to the increased growth of Synechocystis sp. under antibiotic exposure. Since the antibiotic-stimulated growth rate of Synechocystis sp. was still lower than that of M. aeruginosa, the proportion of Synechocystis sp. in the mixed-culture system remained stable. Synechocystis sp. was less adaptive to antibiotic exposure than M. aeruginosa, due to a lower number of up-regulated ribosomal genes and photosynthesis-related genes. Antibiotic exposure reduced the proportions of two eukaryotic microalgal species in the mixed-culture system through a selective promotion of cyanobacterial competitiveness against eukaryotic microalgae, which may facilitate the formation of cyanobacteria bloom.

Achieving superior carbon transfer efficiency and pH control using membrane carbonation with a wide range of CO2 contents for the coccolithophore Emiliania huxleyi

The economic viability of microalgal-derived products relies on rapid CO₂ transfer in a cost-effective manner. Many industrial gas streams contain concentrated CO₂ that, if converted to useful products, would lower greenhouse gas emissions and valorize the wasted CO₂. Membrane carbonation (MC) uses non-porous hollow-fiber gas-transfer membranes to deliver CO₂ without bubble formation, which makes it possible to achieve a high carbon-transfer efficiency (CTE). However, inert gasses in the industrial streams (e.g., N₂, O₂, and H₂O) can significantly lower the CO₂-delivery rate. The means to overcome the buildup of inert gases in the membrane lumen is to manage the distal end of the membranes to sweep out inert gases while not wasting significant CO₂. A MC-venting strategy was evaluated for CO₂ inputs from 5% to 100%. Abiotic tests using a restricted exit flow could achieve >95% CTE_abiotic for industrial CO₂ streams. When integrated with semi-continuous cultivation of a marine coccolithophore, Emiliania huxleyi, CO₂ delivery and venting were on-demand based on a pH set points and pH-actuated feed and venting valves. MC using the venting strategy achieved 100% CTE_biotic when delivering 100% and 50% CO₂, which was better than 50% CTE_biotic obtained from pH-controlled sparging of 100% CO₂-sparging. E. huxleyi consistently fixed ~80% of the delivered CO₂ into biomass, and the remaining ~20% to calcite coccoliths. The compact size of MC modules, stable pH control, and no shear forces from bubble agitation during the CO₂ delivery made MC an ideal match for cultivation of coccolithophores, which are sensitive to shear forces and pH fluctuations.

Anti-Inflammatory and Anticancer Effects of Microalgal Carotenoids

Acute inflammation is a key component of the immune system's response to pathogens, toxic agents, or tissue injury, involving the stimulation of defense mechanisms aimed to removing pathogenic factors and restoring tissue homeostasis. However, uncontrolled acute inflammatory response may lead to chronic inflammation, which is involved in the development of many diseases, including cancer. Nowadays, the need to find new potential therapeutic compounds has raised the worldwide scientific interest to study the marine environment. Specifically, microalgae are considered rich sources of bioactive molecules, such as carotenoids, which are natural isoprenoid pigments with important beneficial effects for health due to their biological activities. Carotenoids are essential nutrients for mammals, but they are unable to synthesize them; instead, a dietary intake of these compounds is required. Carotenoids are classified as carotenes (hydrocarbon carotenoids), such as α- and β-carotene, and xanthophylls (oxygenate derivatives) including zeaxanthin, astaxanthin, fucoxanthin, lutein, α- and β-cryptoxanthin, and canthaxanthin. This review summarizes the present up-to-date knowledge of the anti-inflammatory and anticancer activities of microalgal carotenoids both in vitro and in vivo, as well as the latest status of human studies for their potential use in prevention and treatment of inflammatory diseases and cancer.