Impact of the salt stress on the photosynthetic carbon flux and 13C-label distribution within floridoside and digeneaside in Solieria chordalis

Single-cell transcriptome sequencing revealing the difference in photosynthesis and carbohydrate metabolism between epidermal cells and non-epidermal cells of Gracilariopsis lemaneiformis (Rhodophyta)

The allocation of photoassimilates is considered as a key factor for determining plant productivity. The difference in photosynthesis and carbohydrate metabolism between source and sink cells provide the driven force for photoassimilates' allocation. However, photosynthesis and carbohydrate metabolism of different cells and the carbon allocation between these cells have not been elucidated in Gracilariopsis lemaneiformis. In the present study, transcriptome analysis of epidermal cells (EC) and non-epidermal cells (NEC) of G. lemaneiformis under normal light conditions was carried out. There were 3436 differentially expressed genes (DEGs) identified, and most of these DEGs were related to photosynthesis and metabolism. Based on a comprehensive analysis both at physiological and transcriptional level, the activity of photosynthesis and carbohydrate metabolism of EC and NEC were revealed. Photosynthesis activity and the synthesis activity of many low molecular weight carbohydrates (floridoside, sucrose, and others) in EC were significantly higher than those in NEC. However, the main carbon sink, floridean starch and agar, had higher levels in NEC. Moreover, the DEGs related to transportation of photoassimilates were found in this study. These results suggested that photoassimilates of EC could be transported to NEC. This study will contribute to our understanding of the source and sink relationship between the cells in G. lemaneiformis.

Cold stress tolerance of the intertidal red alga Neoporphyra haitanensis

BACKGROUND

Red algae Porphyra sensu lato grow naturally in the unfavorable intertidal environment, in which they are exposed to substantial temperature fluctuations. The strategies of Porphyra to tolerate cold stress are poorly understood.

RESULTS

Herein, investigations revealed that chilling and freezing induced alterations in the physiological properties, gene transcriptional profiles and metabolite levels in the economically important red algae species, Neoporphyra haitanensis. Control samples (kept at 20 °C) were compared to chilled thalli (10 and 4 °C) and to thalli under - 4 °C conditions. Chilling stress did not affect the health or photosynthetic efficiency of gametophytes, but freezing conditions resulted in the arrest of growth, death of some cells and a decrease in photosynthetic activity as calculated by Fv/Fm. Transcriptome sequencing analysis revealed that the photosynthetic system was down-regulated along with genes associated with carbon fixation and primary metabolic biosynthesis. Adaptive mechanisms included an increase in unsaturated fatty acids levels to improve membrane fluidity, an increase in floridoside and isofloridoside content to enhance osmotic resistance, and an elevation in levels of some resistance-associated phytohormones (abscisic acid, salicylic acid, and methyl jasmonic acid). These physiochemical alterations occurred together with the upregulation of ribosome biogenesis.

CONCLUSIONS

N. haitanensis adopts multiple protective mechanisms to maintain homeostasis of cellular physiology in tolerance to cold stress.

Trehalose and (iso)floridoside production under desiccation stress in red alga Porphyra umbilicalis and the genes involved in their synthesis

The marine red alga Porphyra umbilicalis has high tolerance toward various abiotic stresses. In this study, the contents of floridoside, isofloridoside, and trehalose were measured using gas chromatography mass spectrometry (GC-MS) in response to desiccation and rehydration treatments; these conditions are similar to the tidal cycles that P. umbilicalis experiences in its natural habitats. The GC-MS analysis showed that the concentration of floridoside and isofloridoside did not change in response to desiccation as expected of compatible solutes. Genes involved in the synthesis of (iso)floridoside and trehalose were identified from the recently completed Porphyra genome, including four putative trehalose-6-phosphate synthase (TPS) genes, two putative trehalose-6-phosphate phosphatase (TPP) genes, and one putative trehalose synthase/amylase (TreS) gene. Based on the phylogenetic, conserved domain, and gene expression analyses, it is suggested that the Pum4785 and Pum5014 genes are related to floridoside and isofloridoside synthesis, respectively, and that the Pum4637 gene is probably involved in trehalose synthesis. Our study verifies the occurrences of nanomolar concentrations trehalose in P. umbilicalis for the first time and identifies additional genes possibly encoding trehalose phosphate synthases.

Environmental metabolomics with data science for investigating ecosystem homeostasis

A natural ecosystem can be viewed as the interconnections between complex metabolic reactions and environments. Humans, a part of these ecosystems, and their activities strongly affect the environments. To account for human effects within ecosystems, understanding what benefits humans receive by facilitating the maintenance of environmental homeostasis is important. This review describes recent applications of several NMR approaches to the evaluation of environmental homeostasis by metabolic profiling and data science. The basic NMR strategy used to evaluate homeostasis using big data collection is similar to that used in human health studies. Sophisticated metabolomic approaches (metabolic profiling) are widely reported in the literature. Further challenges include the analysis of complex macromolecular structures, and of the compositions and interactions of plant biomass, soil humic substances, and aqueous particulate organic matter. To support the study of these topics, we also discuss sample preparation techniques and solid-state NMR approaches. Because NMR approaches can produce a number of data with high reproducibility and inter-institution compatibility, further analysis of such data using machine learning approaches is often worthwhile. We also describe methods for data pretreatment in solid-state NMR and for environmental feature extraction from heterogeneously-measured spectroscopic data by machine learning approaches.

Physicochemical Characterization and Biological activities of Sulfated Polysaccharides from Cultivated Solieria filiformis Rhodophyta

Crude and alkali treated carrageenan from the cultivated marine alga Solieria filiformis (Rhodophyta) were obtained, characterized and evaluated for their cytotoxic and antiprotozoal activities. Yields, molecular weights and chemical composition of carrageenans were determined. Their structures were elucidated through spectroscopic techniques including FT-IR and CP-MAS 13C NMR spectra. Crude and alkali treated carrageenan seems to be chemically similar to the iota-family carrageenan. Crude carrageenan showed antiprotozoal activity against Giardia intestinalis.

Antiviral and Cytotoxic Activities of Polysaccharides Extracted from Four Tropical Seaweed Species

Polysaccharides extracted from Rhodymenia pseudopalmata, Solieria filiformis, Hydropuntia cornea (Rhodophyta) and Sargassum fluitans (Phaeophyceae) were evaluated for its cytotoxic and antiviral activities against Herpes simplex virus (HSV-Type 1). Chemical structures were characterized by FT-IR spectroscopy and 13C-NMR analyses. Polysaccharides from Sargassum fluitans (EC50 = 42.8 μg/ml) and Solieria filiformis (EC50 = 136.0 μg/ml) showed antiviral activity against herpes simplex virus type-I in vitro at a multiplicity of infection (MOI) of 0.01 ID50/cells without cytotoxicity (1–200 μg/mL). The activity observed suggests that sulphation, molecular weight and carbohydrate nature of these polysaccharides may be involved in this activity. To better understand the antiviral activity of the polysaccharides evaluated, it seems important to study the mechanism of action involved. These polysaccharides could be studied further to evaluate their potential use as antiviral drugs.

Floridoside production by the red microalga Galdieria sulphuraria under different conditions of growth and osmotic stress

Floridoside is a compatible solute synthesized by red algae that has attracted considerable attention due to its promising antifouling and therapeutic properties. However, research on industrial applications of floridoside is hampered by limited compound availability and the development of a production process yielding high amounts of this glycoside has not been explored yet. In the present work, floridoside accumulation by the red microalgae Galdieria sulphuraria under different conditions was investigated in order to optimize the production of this glycoside in this microalgae. G. sulphuraria shows consider advantages over other red algae as potential industrial producer of floridoside due to its unicellular nature, its ability to grow heterotrophically in complete darkness and its acidophilic lifestyle. The main compatible solute accumulated by G. sulphuraria under salt stress was purified, identified as floridoside by ¹H-NMR and used as standard for quantification. Our results showed that applying the osmotic stress after the cells had grown first in medium with no salt resulted in higher floridoside yields compared to those obtained in cells growing under osmotic stress from the beginning. Among several parameters tested, the use of glycerol as carbon source for cell growth showed the most significant impact on floridoside accumulation, which reached a maximum of 56.8 mg/g dry biomass.

Heterosides--compatible solutes occurring in prokaryotic and eukaryotic phototrophs

The acclimation to osmotic and/or salt stress conditions induces an integrated response at different cellular levels. One acclimation strategy relies on the massive accumulation of low molecular mass compounds, so-called compatible solutes, to balance osmotic gradients and to directly protect critical macromolecules. Heterosides are compounds composed of a sugar and a polyol moiety that represent one chemical class of compatible solutes with interesting features. Well-investigated examples are glucosylglycerol, which is found in many cyanobacteria, and galactosylglycerols (floridoside and isofloridoside), which are accumulated by eukaryotic algae under salt stress conditions. Here, we review knowledge on physiology, biochemistry and genetics of heteroside accumulation in pro- and eukaryotic photoautotrophic organisms.

HRMAS NMR Analysis of Algae and Identification of Molecules of Interest via Conventional 1D and 2D NMR: Sample Preparation and Optimization of Experimental Conditions

Nuclear magnetic resonance (NMR) has become an astounding tool for molecular characterization. Thanks to the development of probes and the increase of magnetic field, NMR has entered the field of biology and facilitated the identification of natural compounds. Indeed, this nondestructive NMR tool makes possible the complete characterization of less and less quantities of material via 1D and 2D sequences on many nuclei (e.g., (1)H, (13)C, (31)P, (15)N). More recently, the development of high-resolution magic-angle spinning (HRMAS) probes have permitted direct analysis of living tissue (e.g., a piece of algae) without prior extraction providing information on both the total content and the ratio of different molecules within the sample; thus HRMAS facilitates a wide range of analyses, such as species differentiation or studies of metabolomics according to various environmental or experimental conditions. This chapter describes the specific sample preparation, based on an algal sample or extract, required for all NMR analyses in order to optimize the NMR response and obtain the most valuable information.

Mannosylglycerate: structural analysis of biosynthesis and evolutionary history

Halophilic and halotolerant microorganisms adapted to thrive in hot environments accumulate compatible solutes that usually have a negative charge either associated with a carboxylic group or a phosphodiester unit. Mannosylglycerate (MG) has been detected in several members of (hyper)thermophilic bacteria and archaea, in which it responds primarily to osmotic stress. The outstanding ability of MG to stabilize protein structure in vitro as well as in vivo has been convincingly demonstrated. These findings led to an increasingly supported link between MG and microbial adaptation to high temperature. However, the accumulation of MG in many red algae has been known for a long time, and the peculiar distribution of MG in such distant lineages was intriguing. Knowledge on the biosynthetic machinery together with the rapid expansion of genome databases allowed for structural and phylogenetic analyses and provided insight into the distribution of MG. The two pathways for MG synthesis have distinct evolutionary histories and physiological roles: in red algae MG is synthesised exclusively via the single-step pathway and most probably is unrelated with stress protection. In contrast, the two-step pathway is strongly associated with osmoadaptation in (hyper)thermophilic prokaryotes. The phylogenetic analysis of the two-step pathway also reveals a second cluster composed of fungi and mesophilic bacteria, but MG has not been demonstrated in members of this cluster; we propose that the synthase is part of a more complex pathway directed at the synthesis of yet unknown molecules containing the mannosyl-glyceryl unit.

Mass spectrometry-based metabolomics to elucidate functions in marine organisms and ecosystems

Marine systems are very diverse and recognized as being sources of a wide range of biomolecules. This review provides an overview of metabolite profiling based on mass spectrometry (MS) approaches in marine organisms and their environments, focusing on recent advances in the field. We also point out some of the technical challenges that need to be overcome in order to increase applications of metabolomics in marine systems, including extraction of chemical compounds from different matrices and data management. Metabolites being important links between genotype and phenotype, we describe added value provided by integration of data from metabolite profiling with other layers of omics, as well as their importance for the development of systems biology approaches in marine systems to study several biological processes, and to analyze interactions between organisms within communities. The growing importance of MS-based metabolomics in chemical ecology studies in marine ecosystems is also illustrated.