Mutualistic Interactions between Dinoflagellates and Pigmented Bacteria Mitigate Environmental Stress

Deciphering mechanisms of UV filter (benzophenone-3)- and high temperature-induced adverse effects in the coral Acropora tenuis, using ecotoxicogenomics

Coral reefs are at risk of bleaching due to various environmental and anthropogenic stressors such as global warming and chemical pollutants. However, there is little understanding of stressor-specific mechanisms that cause coral bleaching. Therefore, conducting accurate ecotoxicological risk assessments and deciphering modes of action of potentially deleterious ultraviolet (UV) filters (sunscreen compounds) are crucial issues. In this study, we evaluated the toxicity and bleaching effect of benzophenone-3 (BP-3), which is widely used in sunscreen products, on the reef-building coral Acropora tenuis. Furthermore, to understand differences in UV filter- and temperature-induced adverse effects, a comparative ecotoxicogenomic approach using RNA-seq was integrated into a toxicity test to clarify differences in gene expression changes induced by BP-3 and heat stress (31 °C). The lethal concentration 50 % (LC50) was calculated as 3.9 mg/L, indicating that the aquatic environmental risk on corals posed by BP-3 was low based on the risk assessment in this study. Differentially expressed genes related to oxidative stress and extracellular matrix organization were involved in coral responses to both BP-3 and heat stress, but their patterns differed. Whereas immune and heat-shock responses were activated in response to heat stress, activation of a drug metabolism pathway and several signal transduction pathways were identified in BP-3 treatment groups. Our study enhances understanding of stress responses in corals induced by UV filters and thermal stress. Using potential gene markers identified in this study for eco-epidemiological surveys of stressed corals, we urgently need to develop effective countermeasures.

Long-Read Sequencing Unlocks New Insights into the Amphidinium carterae Microbiome

Dinoflagellates are one of the largest groups of marine microalgae and exhibit diverse trophic strategies. Some dinoflagellates can produce secondary metabolites that are known to be toxic, which can lead to ecologically harmful blooms. Amphidinium carterae is one species of dinoflagellate that produces toxic compounds and is used as a model for dinoflagellate studies. The impact of the microbiome on A. carterae growth and metabolite synthesis is not yet fully understood, nor is the impact of bacterial data on sequencing and assembly. An antibiotic cocktail was previously shown to eliminate 16S amplification from the dinoflagellate culture. Even with drastically reduced bacterial numbers during antibiotic treatment, bacterial sequences were still present. In this experiment, we used novel Nanopore long-read sequencing techniques on A. carterae cultures to assemble 15 full bacterial genomes ranging from 2.9 to 6.0 Mb and found that the use of antibiotics decreased the percentage of reads mapping back to bacteria. We also identified shifts in the microbiome composition and identified a potentially deleterious bacterial species arising in the absence of the antibiotic treatment. Multiple antibiotic resistance genes were identified, as well as evidence that the bacterial population does not contribute to toxic secondary metabolite synthesis.

Multifaceted Dinoflagellates and the Marine Model Prorocentrum cordatum

BACKGROUND

Dinoflagellates are a monophyletic group within the taxon Alveolata, which comprises unicellular eukaryotes. Dinoflagellates have long been studied for their organismic and morphologic diversity as well as striking cellular features. They have a main size range of 10-100 µm, a complex "cell covering", exceptionally large genomes (∼1-250 Gbp with a mean of 50,000 protein-encoding genes) spread over a variable number of highly condensed chromosomes, and perform a closed mitosis with extranuclear spindles (dinomitosis). Photosynthetic, marine, and free-living Prorocentrum cordatum is a ubiquitously occurring, bloom-forming dinoflagellate, and an emerging model system, particularly with respect to systems biology.

SUMMARY

Focused ion beam/scanning electron microscopy (FIB/SEM) analysis of P. cordatum recently revealed (i) a flattened nucleus with unusual structural features and a total of 62 tightly packed chromosomes, (ii) a single, barrel-shaped chloroplast devoid of grana and harboring multiple starch granules, (iii) a single, highly reticular mitochondrion, and (iv) multiple phosphate and lipid storage bodies. Comprehensive proteomics of subcellular fractions suggested (i) major basic nuclear proteins to participate in chromosome condensation, (ii) composition of nuclear pores to differ from standard knowledge, (iii) photosystems I and II, chloroplast complex I, and chlorophyll a-b binding light-harvesting complex to form a large megacomplex (>1.5 MDa), and (iv) an extraordinary richness in pigment-binding proteins. Systems biology-level investigation of heat stress response demonstrated a concerted down-regulation of CO2-concentrating mechanisms, CO2-fixation, central metabolism, and monomer biosynthesis, which agrees with reduced growth yields.

KEY MESSAGES

FIB/SEM analysis revealed new insights into the remarkable subcellular architecture of P. cordatum, complemented by proteogenomic unraveling of novel nuclear structures and a photosynthetic megacomplex. These recent findings are put in the wider context of current understanding of dinoflagellates.

Microalgae-bacteria nexus for environmental remediation and renewable energy resources: Advances, mechanisms and biotechnological applications

Microalgae and bacteria, known for their resilience, rapid growth, and proximate ecological partnerships, play fundamental roles in environmental and biotechnological advancements. This comprehensive review explores the synergistic interactions between microalgae and bacteria as an innovative approach to address some of the most pressing environmental issues and the demands of clean and renewable freshwater and energy sources. Studies indicated that microalgae-bacteria consortia can considerably enhance the output of biotechnological applications; for instance, various reports showed during wastewater treatment the COD removal efficiency increased by 40%-90.5 % due to microalgae-bacteria consortia, suggesting its great potential amenability in biotechnology. This review critically synthesizes research works on the microalgae and bacteria nexus applied in the advancements of renewable energy generation, with a special focus on biohydrogen, reclamation of wastewater and desalination processes. The mechanisms of underlying interactions, the environmental factors influencing consortia performance, and the challenges and benefits of employing these bio-complexes over traditional methods are also discussed in detail. This paper also evaluates the biotechnological applications of these microorganism consortia for the augmentation of biomass production and the synthesis of valuable biochemicals. Furthermore, the review sheds light on the integration of microalgae-bacteria systems in microbial fuel cells for concurrent energy production, waste treatment, and resource recovery. This review postulates microalgae-bacteria consortia as a sustainable and efficient solution for clean water and energy, providing insights into future research directions and the potential for industrial-scale applications.

Functional analyses of bacterial genomes found in Symbiodiniaceae genome assemblies

Bacterial-algal interactions strongly influence marine ecosystems. Bacterial communities in cultured dinoflagellates of the family Symbiodiniaceae have been characterized by metagenomics. However, little is known about whole-genome analysis of marine bacteria associated with these dinoflagellates. We performed in silico analysis of four bacterial genomes from cultures of four dinoflagellates of the genera Symbiodinium, Breviolum, Cladocopium and Durusdinium. Comparative analysis showed that the former three contain the alphaproteobacterial family Parvibaculaceae and that the Durusdinium culture includes the family Sphingomonadaceae. There were no large genomic reductions in the alphaproteobacteria with genome sizes of 2.9-3.9 Mb, implying they are not obligate intracellular bacteria. Genomic annotations of three Parvibaculaceae detected the gene for diacetylchitobiose deacetylase (Dac), which may be involved in the degradation of dinoflagellate cell surfaces. They also had metabolic genes for dissimilatory nitrate reduction to ammonium (DNRA) in the nitrogen (N) cycle and cobalamin (vitamin B12 ) biosynthetic genes in the salvage pathway. Those three characters were not found in the Sphingomonadaceae genome. Predicted biosynthetic gene clusters for secondary metabolites indicated that the Parvibaculaceae likely produce the same secondary metabolites. Our study suggests that the Parvibaculaceae is a major resident of Symbiodiniaceae cultures with antibiotics.

Environmental Concentrations of Herbicide Prometryn Render Stress-Tolerant Corals Susceptible to Ocean Warming

Global warming has caused the degradation of coral reefs around the world. While stress-tolerant corals have demonstrated the ability to acclimatize to ocean warming, it remains unclear whether they can sustain their thermal resilience when superimposed with other coastal environmental stressors. We report the combined impacts of a photosystem II (PSII) herbicide, prometryn, and ocean warming on the stress-tolerant coral Galaxea fascicularis through physiological and omics analyses. The results demonstrate that the heat-stress-induced inhibition of photosynthetic efficiency in G. fascicularis is exacerbated in the presence of prometryn. Transcriptomics and metabolomics analyses indicate that the prometryn exposure may overwhelm the photosystem repair mechanism in stress-tolerant corals, thereby compromising their capacity for thermal acclimation. Moreover, prometryn might amplify the adverse effects of heat stress on key energy and nutrient metabolism pathways and induce a stronger response to oxidative stress in stress-tolerant corals. The findings indicate that the presence of prometryn at environmentally relevant concentrations would render corals more susceptible to heat stress and exacerbate the breakdown of coral Symbiodiniaceae symbiosis. The present study provides valuable insights into the necessity of prioritizing PSII herbicide pollution reduction in coral reef protection efforts while mitigating the effects of climate change.

Astaxanthin: Past, Present, and Future

Astaxanthin (AX), a lipid-soluble pigment belonging to the xanthophyll carotenoids family, has recently garnered significant attention due to its unique physical properties, biochemical attributes, and physiological effects. Originally recognized primarily for its role in imparting the characteristic red-pink color to various organisms, AX is currently experiencing a surge in interest and research. The growing body of literature in this field predominantly focuses on AXs distinctive bioactivities and properties. However, the potential of algae-derived AX as a solution to various global environmental and societal challenges that threaten life on our planet has not received extensive attention. Furthermore, the historical context and the role of AX in nature, as well as its significance in diverse cultures and traditional health practices, have not been comprehensively explored in previous works. This review article embarks on a comprehensive journey through the history leading up to the present, offering insights into the discovery of AX, its chemical and physical attributes, distribution in organisms, and biosynthesis. Additionally, it delves into the intricate realm of health benefits, biofunctional characteristics, and the current market status of AX. By encompassing these multifaceted aspects, this review aims to provide readers with a more profound understanding and a robust foundation for future scientific endeavors directed at addressing societal needs for sustainable nutritional and medicinal solutions. An updated summary of AXs health benefits, its present market status, and potential future applications are also included for a well-rounded perspective.