A comparison of proline, thiol levels and GAPDH activity in cyanobacteria of different origins facing temperature-stress

Deciphering the early responses for the cross talk between primary and secondary stressor in diazotrophic cyanobacteria Anabaena sp. PCC 7120

The present study aims to unlock the cross-protection mechanism of the diazotrophic cyanobacterium Anabaena sp. PCC 7120. Heat pre-treatment elicited a beneficial response against subsequent cadmium stress as revealed by integrated morphological, physiological, biochemical, transcript, and proteomics analyses under four sets of experimental conditions: control (C), heat (HS), cadmium (Cd), and heat + cadmium (HS + Cd). Outcomes of the present study suggested a better survival strategy shown by Anabaena sp. PCC 7120 under HS + Cd compared to Cd. According to comparative proteomics, protochlorophyllide reductase, CO2 hydration protein, and NAD(P)H quinone oxidoreductase work in concert to support the light and dark reactions of photosynthesis. Furthermore, in cross protection involvement of enzymes from pentose phosphate pathway and glycolysis for fulfilling cellular energy demand; antioxidants and antioxidant enzymes in scavenging ROS, cellular detoxification, and Cd chelation, chaperons and proteases in proper protein folding and synthesis; signaling and transporters to generate cross talk and Cd efflux were found. Increased accumulation of vegetative to heterocyst connection protein (FraH) in HS + Cd compared to Cd may be envisioned to manage better nitrogen fixation.

Functional characterization of GAPDH2 through overexpression and dsRNA-mediated RNA interference in Synechocystis

Glyceraldehyde-3-phosphate dehydrogenase 2 (GAPDH2) plays a vital role in cell growth, stress responses, and various cellular processes in organisms. However, its functional characterization in cyanobacteria, particularly in Synechocystis sp. PCC 6803, remains largely unexplored, especially concerning its overexpression and RNA interference (RNAi) via double-stranded RNA (dsRNA). This study aimed to investigate the biological role of GAPDH2 in Synechocystis sp. PCC 6803 by cloning its complete coding sequence (SyGAPDH2). The SyGAPDH2 protein comprises 350 amino acids with a molecular weight of 86.480 kDa and an isoelectric point of 5.03. The sequence alignment analysis revealed two conserved domains: NADH (Nicotinamide Adenine Dinucleotide)-quinone oxidoreductase subunit NuoI and NADH-ubiquinone/plastoquinone oxidoreductase chain 6. Similarly, Phylogenetic analysis demonstrated high sequence similarity of 96 % and 94 % with Coliform (Gammaproteobacteria bacterium), respectively. We further explored the functional significance of SyGAPDH2 through overexpression using the PpsbAII+SyGAPDH2 vector and double stranded RNA (dsRNA)-mediated silencing with dsGAPDH2. Overexpression significantly enhanced cell growth, while dsRNA-mediated suppression resulted in reduced cell proliferation, with effects observed 12 h post-treatment and persisting up to 36 h. These findings emphasize the essential regulatory role of SyGAPDH2 in cellular development and stress response. This study contributes to our understanding of GAPDH2 functional importance in cyanobacteria, providing a foundation for future investigations into its subcellular localization, additional functional roles, and broader regulatory mechanisms within cyanobacterial cellular processes.

Integrated transcriptome, proteome and metabolome analyses revealed secondary metabolites and auxiliary carbohydrate metabolism augmenting drought tolerance in rice

Drought is one of the major consequences of climate change and a serious threat to rice production. Drought stress activates interactions among genes, proteins and metabolites at the molecular level. A comparative multi-omics analysis of drought-tolerant and drought-sensitive rice cultivars can decipher the molecular mechanisms involved in drought tolerance/response. Here, we characterized the global-level transcriptome, proteome, and metabolome profiles, and performed integrated analyses thereof in a drought-sensitive (IR64) and a drought-tolerant (Nagina 22) rice cultivar under control and drought-stress conditions. The transcriptional dynamics and its integration with proteome analysis revealed the role of transporters in regulation of drought stress. The proteome response illustrated the contribution of translational machinery to drought tolerance in N22. The metabolite profiling revealed that aromatic amino acids and soluble sugars contribute majorly to drought tolerance in rice. The integrated transcriptome, proteome and metabolome analysis performed using statistical and knowledge-based methods revealed the preference for auxiliary carbohydrate metabolism through glycolysis and pentose phosphate pathway contributed to drought tolerance in N22. In addition, L-phenylalanine and the genes/proteins responsible for its biosynthesis were also found to contribute to drought tolerance in N22. In conclusion, our study provided mechanistic insights into the drought response/adaptation mechanism and is expected to facilitate engineering of drought tolerance in rice.

Analyzing dose dependency of antioxidant defense system in the cyanobacterium Nostoc muscorum Meg 1 chronically exposed to Cd2

The aim of the present study was to analyze the dose dependency of oxidant-antioxidant homeostasis in Cd²⁺ exposed Nostoc muscorum Meg 1 cells. Quantification of percent DNA loss, protein oxidation and lipid peroxidation was carried out to assess Cd²⁺ induced ROS mediated damages to the organism. The countermeasures adopted by the cyanobacterium were also evaluated by computing various components of both enzymatic and non-enzymatic antioxidants. Exposure to different Cd²⁺ (0.1, 0.2, 0.3, 0.5, 1, 1.5, 2, 2.5, 3 ppm) doses showed substantial increase in ROS content in the ranges of 20-181% and 116-323% at the end of first and seventh day. The DNA damage, protein oxidation and lipid peroxidation were increased by 11-62%, 7-143% and 13-183% with increasing Cd²⁺ concentrations at the end of seven days. TEM images clearly showed damages to the cell wall, cell membrane and thylakoid organization at higher Cd²⁺ (0.5-3 ppm) concentrations. Cd²⁺ exposure up to 0.5 ppm registered increase in contents of antioxidative enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR)) and in non-enzymatic antioxidants (glutathione, total thiol, phytochelatin and proline) indicating stimulation of ROS mitigating machinery. However, toxicity of Cd²⁺ was evident as at higher concentrations the cellular morphology and ultra-structures were negatively affected and the capacities of the cells to generate various antioxidant measures were highly compromised. The organism registered 96-98% sorption ability from a solution supplemented with 0.3 ppm Cd²⁺ and thus show realistic potential as Cd²⁺ bioremediator in wastewater treatment.

Role of Ca2+ as protectant under heat stress by regulation of photosynthesis and membrane saturation in Anabaena PCC 7120

The present study was aimed at understanding the effects of heat stress on selected physiological and biochemical parameters of a model cyanobacterium, Anabaena PCC 7120 in addition to amelioration strategy using exogenous Ca²⁺. A comparison of the cells exposed to heat stress (0-24 h) in the presence or absence of Ca²⁺ clearly showed reduction in colony-forming ability and increase in reactive oxygen species (ROS) leading to loss in the viability of cells of Ca²⁺-deficient cultures. There was higher level of saturation in membrane lipids of the cells supplemented with Ca²⁺ along with higher accumulation of proline. Similarly, higher quantum yield (7.8-fold) in Ca²⁺-supplemented cultures indicated role of Ca²⁺ in regulation of photosynthesis. Relative electron transport rate (rETR) decreased in both the sets with the difference in the rate of decrease (slow) in Ca²⁺-supplemented cultures. The Ca²⁺-supplemented sets also maintained high levels of open reaction centers of PS II in comparison to Ca²⁺-deprived cells. Increase in transcripts of both subunits ((rbcL and rbcS) of RubisCO from Ca²⁺-supplemented Anabaena cultures pointed out the role of Ca²⁺ in sustenance of photosynthesis of cells via CO₂ fixation, thus, playing an important role in maintaining metabolic status of the heat-stressed cyanobacterium.

Effects of nitrogen and phosphorus on anatoxin-a, homoanatoxin-a, dihydroanatoxin-a and dihydrohomoanatoxin-a production by Phormidium autumnale

Anatoxins are powerful neuromuscular blocking agents produced by some cyanobacteria. Consumption of anatoxin-producing cyanobacterial mats or the water containing them has been linked to numerous animal poisonings and fatalities worldwide. Despite this health risk, there is a poor understanding of the environmental factors regulating anatoxin production. Non-axenic Phormidium autumnale strain CAWBG557 produces anatoxin-a (ATX), homoanatoxin-a (HTX) and their dihydrogen-derivatives dihydroanatoxin-a (dhATX) and dihydrohomoanatoxin-a (dhHTX). The effects of varying nitrogen and phosphorus concentrations on the production of these four variants were examined in batch monocultures. The anatoxin quota (anatoxin per cell) of all four variants increased up to four fold in the initial growth phase (days 0-9) coinciding with the spread of filaments across the culture vessel during substrate attachment. Dihydroanatoxin-a and dhHTX, accounted for over 60% of the total anatoxin quota in each nitrogen and phosphorus treatment. This suggests they are being internally synthesised and not just derived following cell lysis and environmental degradation. The four anatoxin variants differed in their response to varying nitrogen and phosphorus concentrations. Notably, dhATX quota significantly decreased (P ≤ 0.03) when nitrogen and phosphorus concentrations were elevated (nitrogen = 21 mg L(-1); phosphorus = 3 mg L(-1)), while HTX quota increased when the phosphorus concentrations were reduced (ca. < 0.08 mg L(-1)). This is of concern as HTX has a high toxicity and anatoxin producing P. autumnale blooms in New Zealand usually occur in rivers with low water column dissolved reactive phosphorus.

A New Cytotoxic Phenolic Derivative from the Roots of Antidesma Acidum

A new phenolic derivative, acidumonate (1), together with a synthetically known compound, 4-(( E)-3,3-dimethylpenta-1,4-dienyl)-phenol (2), and sixteen known natural products, antidesmol (3), mellein (4), sitosterol (5), stigmasterol (6), 5-cholesten-3 β-ol (7), 4-cholesten-3-one (8), 3-(1,1-dimethylallyl)-scopoletin (9), (-)- 5,7-dihydroxy-2-eicosyl-chromone (10), 2,5-dimethoxy-1,4-benzoquinone (11), barbatumol A (12), N-trans-feruloyltyramine (13), syringic aldehyde (14), p-hydroxybenzoic acid (15), taxifolin (16), (+)-catechin (17) and gallocatechin (18), were isolated from the roots of Antidesma acidum. The structural assignment of the new compound was based on spectroscopic methods. All isolated compounds were evaluated for their cytotoxicity (KB and HeLa cells). Compound 1 showed good cytotoxicity against both cell lines (with IC50 values of 2.60 and 3.80 μg/mL, respectively).