Dharmar Prabaharan

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.

Oxygen-free hydrogen production by the marine cyanobacterium Phormidium valderianum BDU 20041

Abstract To circumvent the co-production of oxygen during hydrogen photoproduction, certain physico-chemical conditions were manipulated. Then, under white light (intensity 5.5 μmol photon m−2 s−1, 18 h dark/6 h light cycle); temperature 27°C; pH 7.5; salinity 25 g l−1, the marine, filamentous, non-heterocystous cyanobacterium Phormidium valderianum BDU 20041 was found to produce a maximum of 0.2 μmol hydrogen h−1 mg−1 dry wt in the gas phase without oxygen co-production; this was on a par with the maximum yield reports in the literature. To compensate for possible reduction in CO2 fixation under these conditions, when 10 m m of different carbohydrates were used, those other than galactose, lactose and trehalose were found to be favourable. For continuous production of hydrogen when amino acids were added as a nitrogen source, isoleucine was found to be the least inhibitory. The organism was found to be essentially a dark hydrogen producer.

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.

Lipid membrane modulation and pigmentation: A cryoprotection mechanism in Arctic pigmented bacteria

The present study aims to address the effect of gradual change in temperature (15–4 °C) followed by freeze–thaw on pigmented bacterial strains – Leeuwenhoekiella aequorea, Pseudomonas pelagia, Halomonas boliviensis, Rhodococcus yunnanensis, and Algoriphagus ratkwoskyi, isolated from Kongsfjorden (an Arctic fjord) to understand their survival in present climate change scenario. The total cell count and retrievability of the isolates were not affected despite the variation in temperature. In all the isolates, the saturated fatty acids, particularly stearic and palmitic acid were predominant at higher temperature, while at 4 °C, the unsaturated fatty acids, primarily cis‐10‐pentadecenoic, palmitoleic, and oleic acid, were major constituents, confirming homeoviscous adaptation. Even after freeze–thaw, the unsaturated fatty acid composition was retained in all the isolates except A. ratkwoskyi. The increase in unsaturated fatty acids was at the expense of their saturated analogs, probably by desaturase activity. The major pigment in the isolates resembled Zeaxanthin, whose concentration was found to be 26–65% higher after freeze–thaw, suggesting its vital role as a cryoprotective agent in regulating membrane fluidity. Such experimental simulations related to freeze–thaw in polar bacterial isolates are helpful in understanding the physiological plasticity adaptations, which could be critical for survival in harsh and rapidly changing polar environments.