Lakshmanan Uma

Nitrogen stress induced changes in the marine cyanobacterium Oscillatoria willei BDU 130511

Exclusion of combined nitrogen (NaNO3) from the growth medium caused certain changes in metabolic processes leading to cessation in growth of the non-heterocystous, non nitrogen-fixing marine cyanobacterium Oscillatoria willei BDU 130511. But antioxidative enzymes, namely superoxide dismutase and peroxidase, helped the organism to survive the nitrogen stress. Prominent effects observed during nitrogen starvation/limitation were: (i) reduction of major and accessory photosynthetic pigments, (ii) impairment of photosynthesis due to loss of one major Rubisco isoenzyme, (iii) reduced synthesis of lipids and fatty acids, (iv) modifications of protein synthesis leading to the repression of three polypeptides and synthesis of two new polypeptides, (v) enhanced glutamine synthetase and reduced nitrate reductase activities, (vi) enhanced production of hydrogen peroxide and (vii) induced appearance of four new peroxidase isoenzymes. The observed metabolic changes were reversible, and the arrested growth under prolonged nitrogen deficiency could be fully restored upon subculturing in freshly prepared ASN III medium containing nitrogen (NaNO3). The present study demonstrates the capability of a non-nitrogen-fixer to withstand nitrogen stress making it an ecologically successful organism in the marine environment. The above pleiotropic effects of nitrogen deficiency also demonstrate that nitrogen plays a crucial role in growth and metabolism of marine cyanobacteria.

Ligninolytic and antioxidative enzymes of a marine cyanobacterium Oscillatoria willei BDU 130511 during Poly R-478 decolourization

Removal of combined nitrogen and addition of Poly R-478 to the growth medium enhanced oxidative stress, and altered the activities of ligninolytic enzymes of Oscillatoria willei BDU 130511. The activities of ligninolytic and antioxidative enzymes (LiP-like, LAC, PPO, SOD, POD, CAT, and APX) were increased upon nitrogen limitation and dye supplementation. The metabolic enzymes tested (GR, GPX, EST, and MDH) showed differential expressions under varied growth conditions. Up on nitrogen limitation, O. willei BDU 130511 showed enhanced ligninolytic activity as shown by alpha-keto-gamma-methylthiolbutyric acid (KTBA) oxidation and increased H(2)O(2) production. The organism decolourized 52% of Poly R-478 due to partial degradation and adsorption of dye particles from dye-added medium after 7 days of growth. This manuscript discusses the responses of ligninolytic and antioxidative enzymes of O. willei BDU 130511 during Poly R-478 decolourization/degradation, and the organisms potential in bioremediation.

Siderophore mediated uranium sequestration by marine cyanobacterium Synechococcus elongatus BDU 130911.

Four different marine cyanobacterial morphotypes were tested for their efficacy to produce siderophores in Fe minus [Fe(-)], Fe minus Uranium dosed [Fe(-)U(+)], and Fe dosed Uranium dosed [Fe(-)U(+)] media. Of the four organisms tested, Synechococcus elongatus BDU 130911 produced the highest amount of siderophore of 58μgmg(-1) dryweight. The results clearly indicate that uranium induces siderophore production in marine cyanobacteria even in the presence of iron [Fe(-)U(+)] condition. The type of siderophore revealed by FeCl(3), Tetrazolium and Atkins tests is a hydroxamate; and thin layer chromatogram also authenticates our finding. Uranium siderophore complexation was confirmed through modified Chrome Azurol S (CAS) assay as well as based on residual uranium presence. In silico docking studies further validate siderophore complexation with uranium.

Characterization of manganese superoxide dismutase from a marine cyanobacterium Leptolyngbya valderiana BDU20041

BackgroundCyanobacteria are recognized as the primordial organisms to grace the earth with molecular oxygen ~3.5 billion years ago as a result of their oxygenic photosynthesis. This laid a selection pressure for the evolution of antioxidative defense mechanisms to alleviate the toxic effect of active oxygen species (AOS) in cyanobacteria. Superoxide dismutases (SODs) are metalloenzymes that are the first arsenal in defense mechanism against oxidative stress followed by an array of antioxidative system. Unlike other living organisms, cyanobacteria possess multiple isoforms of SOD. Hence, an attempt was made to demonstrate the oxidative stress tolerance ability of marine cyanobacterium, Leptolyngbya valderiana BDU 20041 and to PCR amplify and sequence the SOD gene, the central enzyme for alleviating stress.ResultL. valderiana BDU 20041, a filamentous, non-heterocystous marine cyanobacterium showed tolerance to the tested dye (C.I. Acid Black 1) which is evident by increased in biomass (i.e.) chlorophyll a. The other noticeable change was the total ROS production by culture dosed with dye compared to the control cultures. This prolonged incubation showed sustenance, implying that cyanobacteria maintain their antioxidant levels. The third significant feature was a two-fold increase in SOD activity of dye treated L. valderiana BDU20041 suggesting the role of SOD in alleviating oxidative stress via Asada-Halliwell pathway. Hence, the organism was PCR amplified for SOD gene resulting in an amplicon of 550 bp. The sequence analysis illustrated the presence of first three residues involved in motif; active site residues at H4, 58 and D141 along with highly conserved Mn specific residues. The isolated gene shared 63.8% homology with MnSOD of bacteria confirmed it as Mn isoform. This is the hitherto report on SOD gene from marine cyanobacterium, L. valderiana BDU20041 of Indian subcontinent.ConclusionGeneration of Reactive Oxygen Species (ROS) coupled with induction of SOD by marine cyanobacterium, L. valderiana BDU20041 was responsible for alleviating stress caused by an azo dye, C. I. Acid Black 1. The partial SOD gene has been sequenced and based on the active site, motif and metal specific residues; it has been identified as Mn metalloform.

Analysis and Elucidation of Phosphoenolpyruvate Carboxylase in Cyanobacteria

Phosphoenolpyruvate carboxylase (PEPC) a cytosolic enzyme of higher plants is also found in bacteria and cyanobacteria. Genetic and biochemical investigations have indicated that there are several isoforms of PEPC belonging to C3; C3/C4 and C4 groups but, the evolution of PEPC in cyanobacteria is not yet understood. The present study opens up an opportunity to understand the isoforms and functions of PEPC in cyanobacteria. The variations observed in PEPC among lower and higher orders of cyanobacteria, suggests convergent evolution of PEPC. There is a specific PEPC phosphorylation residue ‘serine’ at the N-terminus and PEPC determinant residue ‘serine’ at the C-terminal that facilitates high affinity for substrate binding. These residues were unique to higher orders of cyanobacteria, but, not in lower orders and other prokaryotes. The different PEPC forms of cyanobacteria were investigated for their kinetic properties with phosphoenolpyruvate as the substrate and the findings corroborated well with the in silico findings. In vitro enzymatic study of cyanobacteria belonging to three different orders demonstrated the role of aspartate as an allosteric effector, which inhibited PEPC by interacting with the highly conserved residues in the active site. The differences in mode of inhibition among the different order, thus, give a fair picture about the cyanobacterial PEPCs. The higher orders appear to possess the sequence coordinates and functionally conserved residues similar to isoforms of C4 type higher plants, whereas isoforms of PEPC of the lower orders did not resemble either that of C3 or C4 plants.

Biodiversity of epilithic cyanobacteria from freshwater streams of Kakoijana reserve forest, Assam, India

The biodiversity of epilithic cyanobacteria from one of the unexplored habitats of freshwater streams of Kakoijana reserve forest of Assam, India was estimated. This paper lists a total of 29 species representing 18 genera of 12 families and 4 orders as per recent system of classification. Morphological descriptions, common habitats and distribution pattern were described for each species identified that were represented systematically. Of these 29 species, 11 were unicellular, 9 non-heterocytous filamentous and 9 heterocytous filamentous forms. All the unicellular (Aphanocapsa crassa, A. muscicola, Aphanothece nidulans, A. saxicola, Chlorogloea purpurea, Chroococcus cohaerens, C. minimus, C. minor, Cyanobacterium cedrorum, Cyanocystis versicolor and Gloeocapsopsis crepidinum) and 13 (Calothrix epiphytica, C. scopulorum, Leptolyngbya boryana, L. calotrichoides, L. fragilis, L. notata, Lyngbya arboricola, Nostoc humifusum, N. oryzae, N. punctiforme, Parthasarathiella prolifica, Porphyrosiphon ceylanicus and Scytonema millei) of the remaining 18 species were recorded for the first time as freshwater epiliths. While, 5 species (Hapalosiphon welwitschii, Leptolyngbya tenuis, Oscillatoria pseudogeminata, Phormidium laetevirens, Tolypothrix fragilis) and 8 species (Aphanothece saxicola, Calothrix scopulorum Chlorogloea purpurea, Chroococcus minor, Gloeocapsopsis crepidinum, Leptolyngbya calotrichoides, L. fragilis and L. tenuis) were reported earlier as freshwater-and marine-epilithic forms respectively. All are new records for Assam except 6 species (A. nidulans, H. welwitschii, N. punctiforme, N. oryzae, O. pseudogeminata and P. ceylanicus), while 3 species (C. purpurea, L. boryana and L. calotrichoides) are new records for India. Six nitrogen fixing heterocytous forms such as, C. epiphytica, C. scopulorum, N. humifusum, N. punctiforme, N. oryzae and S. millei, were common to the neighboring paddy fields.