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Iterative analysis of metabolic modulation in the cyanobacterium Aphanizomenon flos-aquae 2012 KM1/D3 upon nitric oxide synthase derived NO induction
(Elsevier B.V., 2022) Neha Gupta; Arun Kumar Mishra
Nitric oxide synthase (NOS) in mammals is recognized for its essentialities in several metabolism including blood vascular relaxation and nerves transmission etc. yet their functionalities in prokaryotes are largely unknown. Our study aimed to evaluate the putative role of nitric oxide synthase (NOS) derived nitric oxide (NO) during oxidative burst in the cyanobacterium, Aphanizomenon flos-aquae 2012/KM1/D3. Here, the accumulation of NO was dramatically reduced upon NOS inhibitor L-NG-Nitro arginine methyl ester (L-NAME) supplementation, exhibiting significant NO synthesis by NOS, whereas addition of L-arginine increase NOS derived NO in a dose dependent manner. Moreover, the reduction in the growth and metabolic activities of the cyanobacterium were evident upon L-NAME treatment that possibly pertained to decline in photopigments, PSII efficiency, loss in membrane integrity and DNA damage due to oxidative burst which culminated into cell death. Besides, the increment in carbohydrates and lipid content ensued with a decrease in protein content, indicating gluconeogenesis. Additionally, NOS inhibition disrupted the fatty acid and hydrocarbon profile, suggesting diminished membrane fluidity and cell integrity. However, higher content of flavonoids, phenolics, thiols and proline in L-NAME treated cells was also observed. Furthermore, L-arginine supplementation enhanced pigment content, photosynthetic efficiency, and reduced oxidative stress, thereby enhancing cyanobacterial growth. Further, L-arginine supplementation maintained Asc/DHAsc and GSH/GSSG ratio, conferred redox homeostasis. These results suggest that the NOS activity plays a critical role in protecting cyanobacteria from oxidative burst, maintaining their physiological balance. © 2022 Elsevier B.V.
Effects of zinc toxicity on the nitrogen-fixing cyanobacterium Anabaena sphaerica—ultastructural, physiological and biochemical analyses
(Springer Science and Business Media Deutschland GmbH, 2021) Sindhunath Chakraborty; Arun Kumar Mishra
The current study describes the mechanisms of zinc toxicity in the cyanobacterium Anabaena sphaerica after eight days treatment with 10 mg L−1 ZnCl2. The application of zinc not only showed elevated accumulation of the metal inside the cells but also exhibited devastating impacts on the cell numbers, morphology, and ultrastructure of A. sphaerica. The effects of zinc on the pigments contents, oxygen evolution rate, Fv/Fm, electron transport rate, and carbohydrate content were also evaluated in A. sphaerica. Moreover, zinc adversely affected nutrient uptake and the cellular energy budget in the test cyanobacterium which in turn hampered heterocyst development and nitrogen fixation. Alongside, the cyanobacterium experienced zinc-mediated non-competitive inhibition of glutamine synthetase activity, curtailed synthesis of amino acids and proteins. Furthermore, drastically reduced total lipid and increased unsaturated lipid contents were also the prominent characteristics of zinc stressed A. sphaerica. Most importantly, zinc stress caused severe damages to the protein, lipid, and DNA by triggering hydrogen peroxide generation and accumulation of oxidized glutathione. Therefore, excess zinc is highly toxic to the cyanobacterium A. sphaerica, and the mechanisms of its toxicity followed a cascade of events including oxidative stress mediated geopardisation of growth and ultrastructure, metabolic derangements, and macromolecular damages. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
Nitric oxide ameliorates the damaging effects of oxidative stress induced by iron deficiency in cyanobacterium Anabaena 7120
(Springer Verlag, 2016) Manish Singh Kaushik; Meenakshi Srivastava; Alka Srivastava; Anumeha Singh; Arun Kumar Mishra
In cyanobacterium Anabaena 7120, iron deficiency leads to oxidative stress with unavoidable consequences. Nitric oxide reduces pigment damage and supported the growth of Anabaena 7120 in iron-deficient conditions. Elevation in nitric oxide accumulation and reduced superoxide radical production justified the role of nitric oxide in alleviating oxidative stress in iron deficiency. Increased activities of antioxidative enzymes and higher levels of ROS scavengers (ascorbate, glutathione and thiol) in iron deficiency were also observed in the presence of nitric oxide. Nitric oxide also supported the membrane integrity of Anabaena cells and reduces protein and DNA damage caused by oxidative stress induced by iron deficiency. Results suggested that nitric oxide alleviates the damaging effects of oxidative stress induced by iron deficiency in cyanobacterium Anabaena 7120. © 2016, Springer-Verlag Berlin Heidelberg.
Unraveling the complexities underlying sulfur deficiency and starvation in the cyanobacterium Anabaena sp. PCC 7120
(Elsevier B.V., 2020) Surbhi Kharwar; Arun Kumar Mishra
The present study focuses to decipher the impact of long-term sulfur deficiency in the cyanobacterium Anabaena sp. PCC 7120. Cell growth parameters (cell biomass and photopigments) were analysed under varying long-term sulfur deficiency showed significant reduction in growth under sulfur limitations. The reminiscent growth of cyanobacterium in the sulfur shortage possibly pertained to minimize cell size and spherical cell shape. Additionally, lower sulfur availability exhibited negative impacts on photopigments, D1 protein (all3572) transcription and PSII efficiency in the cyanobacterium. Furthermore, depletion in protein and corresponding increase in carbohydrate and lipid contents were interpreted as reprogrammed C-allocation. Additionally, enzyme assay of ATP sulfurylase depicted increased activity in the deficient conditions. Moreover, decreased intracellular concentrations of Mg2+, Fe2+, Ca2+, Na+, and K+ at low sulfur supplementations might be a consequence of counter-ion balancing and attributed to lipid peroxidation and electrolyte leakage resulted from increased ROS. In addition, overexpression of desC followed by fatty acid unsaturation and programmed cell death markers were also noticed. Overall, the result suggest that reduced biomass in sulfur limitation is a cumulative outcome of disrupted photosynthesis, reprogrammed C-allocation, reduced electrolyte contents, and subsequent PCD in the cells of Anabaena sp. PCC 7120 reveal S deficiency exerts an adverse impact on cyanobacterial population and reduces primary productivity. © 2019 Elsevier B.V.
Differential physiological, oxidative and antioxidative responses of cyanobacterium Anabaena sphaerica to attenuate malathion pesticide toxicity
(Elsevier Ltd, 2017) Sindhunath Chakraborty; Balkrishna Tiwari; Satya Shila Singh; Alok Kumar Srivastava; Arun Kumar Mishra
Malathion, a synthetic organophosphorus pesticide, is very frequently utilized in the paddy fields to overcome crop loss caused by pest invasion. Importance and association of cyanobacteria with paddy fields creates an interesting new perspective to investigate the physiological and biochemical alterations in the paddy field cyanobacterium namely Anabaena sphaerica at different levels of malathion (5, 10, 20 and 30 µg ml−1). Malathion at 5 µg ml−1 increased the growth and exerted no adverse impact on the physiological and biochemical indices but the higher dose, 30 µg ml−1, exhibited detrimental effects on the cell growth, total pigment content, total protein content, carbohydrate content, photosynthetic efficiency and protein profile of the cyanobacterium through relentless generation of reactive oxygen species (ROS). However, enhanced level of antioxidative enzyme activity (SOD, CAT and APX) coupled with increased production of phenolics and flavonoids reflected their involvement in the ROS detoxification mechanism and in small reduction of growth at sublethal doses (10 and 20 µg ml−1). Possession of almost equal amount of total carbohydrate content and the simultaneous production of higher level of non-enzymatic antioxidants (carotenoids, phenolics and flavonoid) at sublethal doses of malathion appeared to be an additional effective detoxification system in A. sphaerica. © 2017 Elsevier Ltd
Aluminium Toxicity and Defence Mechanisms in Plants
(Nova Science Publishers, Inc., 2017) Sindhunath Chakraborty; Satya Shila Singh; Ekta Verma; Balkrishna Tiwari; Arun Kumar Mishra
In recent days, aluminium toxicity is a serious threat to agriculture all over the world. Aluminium (Al) being the most dominant metal in the Earth’s crust exhibits highly toxic effects on the plants grown in acid soils (pH below 5.0). Initially, aluminium toxicity symptoms become apparent in the apical region of the root because of its extreme sensitivity to aluminium. Cell wall rigidification, cell membrane depolarization and cytoskeletal damages are the important primary events that take place under Al stress condition. Adverse impacts of Al on these cellular components cause reduction in cell expansion, decreased nutrient uptake, organeller dysfunctioning and subsequent rapid production of reactive oxygen species (ROS).Transient generation of ROS further induces damage to the nuclear membrane and nucleic acids which ultimately lead to cell apoptosis. In the other hand, mechanisms such as release of organic acids from the root and their binding to Al extracellularly, organic acid mediated intracellular chelation and vacuolar sequestration of Al ions, synthesis of enzymatic and non-enzymatic antioxidants contribute to the Al detoxification process. Understanding the important aspects of Al phytotoxicity and mechanisms of its tolerance would be certainly beneficial to sustain agricultural productivity in acid soils by developing traits with higher resistance against aluminium. So, this article reviews the biochemistry and physiology of Al toxicity along with the various different mechanisms that are used by the plants to detoxify Al. However, emphasis has been given to the mechanisms of Al detoxification. © 2017 by Nova Science Publishers, Inc. All rights reserved.
NOS-derived NO mediated physiological and biochemical responses of heterocytous cyanobacterium Aphanizomenon flos-aquae 2012/KM1/D3 against H2O2-induced oxidative stress
(Elsevier B.V., 2024) Neha Gupta; Samujjal Bhattacharjee; Arun Kumar Mishra
The essential role of nitric oxide synthase (NOS)-derived nitric oxide (NO) in the survival, proliferation, and cell differentiation of mammals is well known. However, the characterization and functionality of NOS in photosynthetic prokaryotes, including cyanobacteria, remained elusive. This study demonstrated compelling evidences unveiling the functionality of NOS-derived NO in cyanobacterium Aphanizomenon flos-aquae 2012/KM1/D3 during its progression from the exponential growth phase to stationary under H2O2-induced oxidative incursions. The pivotal role of NOS in Aphanizomenon flos-aquae was elucidated by analyzing the morpho-physiological and biochemical perturbations upon H2O2 exposure in both NOS elicited and inhibited conditions. Results highlighted that in the NOS-inhibited condition, H2O2 treatment significantly diminished the growth and metabolic activities of the cyanobacterium, likely due to compromised membrane integrity and DNA damage from oxidative stress, ultimately resulting in cell death. Conversely, NOS elicitation bestows increased tolerance against oxidative bursts by maintaining ATP/ADP, Asc/DHAsc and GSH/GSSG ratios — essential markers of redox homeostasis — ultimately fostering redox balance and energy status. Additionally, NOS-derived NO transiently suppresses NADPH oxidases, responsible for regenerating damaging superoxide radicals and directly endorses catalase activity. Besides, our findings forecasted coordinated action between GSNOR and NOS in dynamically regulating NO flux. Further, we have demonstrated the generation of S-nitrosothiols (SNO) by NOS-derived NO, providing an additional line of defense against oxidative damage. This protective impact of NO against H2O2-induced stress on cyanobacterial growth was not evident in cells pre-treated with L-NAME. This suggests that NOS inhibition renders the cells more susceptible to deleterious accumulation of ROS, as evidenced by distinctive cytoplasmic alterations, membrane impairment, compromised antioxidative system, and exacerbated oxidative DNA fragmentation. These findings underscore the significance of NOS-derived NO in safeguarding genomic stability and cellular integrity, presenting potential avenues for understanding and manipulating cellular responses to oxidative stress in cyanobacteria. © 2024 Elsevier B.V.
Role of manganese in protection against oxidative stress under iron starvation in cyanobacterium Anabaena 7120
(Wiley-VCH Verlag, 2015) Manish Singh Kaushik; Meenakshi Srivastava; Ekta Verma; Arun Kumar Mishra
The cyanobacterium Anabaena sp. PCC 7120 was grown in presence and absence of iron to decipher the role of manganese in protection against the oxidative stress under iron starvation and growth, manganese uptake kinetics, antioxidative enzymes, lipid peroxidation, electrolyte leakage, thiol content, total peroxide, proline and NADH content was investigated. Manganese supported the growth of cyanobacterium Anabaena 7120 under iron deprived conditions where maximum uptake rate of manganese was observed with lower Km and higher Vmax values. Antioxidative enzymes were also found to be elevated in iron-starved conditions. Estimation of lipid peroxidation and electrolyte leakage depicted the role of manganese in stabilizing the integrity of the membrane which was considered as the prime target of oxygen free radicals in oxidative stress. The levels of total peroxide, thiol, proline and NADH content, which are the representative of oxidative stress response in Anabaena 7120, were also showed increasing trends in iron starvation. Hence, the results discerned, clearly suggested the role of manganese in protection against the oxidative stress in cyanobacterium Anabaena 7120 under iron starvation either due to its antioxidative properties or involvement as cofactor in a number of antioxidative enzymes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Deciphering salinity tolerance in the cyanobacterium Anabaena sphaerica: an evaluation of physiological and biochemical adjustments
(Institute for Ionics, 2022) Surbhi Kharwar; Samujjal Bhattacharjee; Arun Kumar Mishra
Besides being a determinant of species distribution around the globe, salinity over the threshold limit imparts detrimental effects on life forms. The present study deciphered the tolerance of heterocytous cyanobacterium Anabaena sphaerica to 77.5, 100, and 200 mM NaCl by analyzing physiological and biochemical adjustments within the cells. Exposing the cyanobacterium to high NaCl reduces growth dynamics, photosynthesis, and membrane stability. Intracellular Na+ accumulation not only induces ionic imbalances by increasing Na+/Mg2+ and Na+/K+ ratios, but also causes oxidative burst in the cell. Moreover increased glutathione, proline, and sucrose contents along with higher enzymatic antioxidants such as superoxide dismutase and catalase, delineated cyanobacterial resilience against both osmotic and oxidative stresses. Additionally, Fourier-transform infrared (FTIR) spectroscopy exhibited carbohydrate accumulation in the stressed cells as a function of reprogrammed carbon allocation, which might also occur as an adaptive measure. However, escalation in the activities of nitrate reductase and nitrite reductase at 77.5 and 100 mM NaCl depicted an increase in nitrate assimilation, indicating the ability of cyanobacterium to withstand at least 100 mM NaCl in the surrounding. Hence, A. sphaerica displays significant tolerance to salinity and, thus, can play a crucial role in ameliorating salinity from salt-affected paddy fields. © 2022, The Author(s) under exclusive licence to Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.
Nitrogen starvation–induced oxidative stress relieves PII-mediated inhibition of acetyl-CoA carboxylase (ACCase) activity and signals enhanced lipid synthesis in Synechococcus PCC 7942
(Springer Science and Business Media B.V., 2021) Ekta Verma; Sindhunath Chakraborty; Surbhi Kharwar; Balkrishna Tiwari; Satya Shila Singh; Arun Kumar Mishra
The present study shows the existence of PII-acetyl-CoA carboxylase interaction in the cyanobacterium Synechococcus sp. PCC 7942 and the possible adverse impact of nitrogen starvation on this interaction. The in silico and in vitro analysis of PII-acetyl-CoA carboxylase interaction revealed that the biotin carboxyl carrier protein subunit of acetyl-CoA carboxylase enzyme actually interacts with the T-loop of PII protein. However, exposure of the cyanobacterium to nitrogen-starved condition showed a higher expression and activity of acetyl-CoA carboxylase at the intracellular level which denoted the impairment of PII-acetyl-CoA carboxylase interaction. A similar stimulatory effect of nitrogen starvation has also been noticed in the PII mutant of Synechococcus PCC 7942. Further, the physiological study reflected that nitrogen starvation–caused reactive oxygen species generation in the wild-type and PII mutant strains and lipid was increased in both strains of Synechococcus sp. PCC 7942. Proteomic analysis showed the upregulation of glycogen synthase, biotin carboxylase, and antioxidative enzymes and the deregulation of proteins involved in photosynthesis, energy metabolism, and protein synthesis. Interestingly, enhanced accumulation of transcripts of few tricarboxylic acid cycle genes was also noticed in the wild type. Although oxidative stress and lipid production were enhanced in both the test strains under nitrogen starvation, the impacts were more prominent in the mutant strain. Our results suggest that the nitrogen starvation–induced oxidative stress possibly relieved the PII-mediated inhibition of acetyl-CoA carboxylase and led to increased lipid synthesis in Synechococcus PCC 7942. © 2020, Springer Nature B.V.

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