Immobilization results in sustained calcium transport in Nostoc calcicola Bréb

The uptake pattern of Ca2+ by the cyanobacterium Nostoc calcicola Bréb in its freely suspended and immobilized form is comprised of two distinct phages; (a) rapid uptake for 1st 10 min followed by (b) slower transport at least up to 60 min. Entrapment of cyanobacterial cells in polyvinyl foam always maintained a higher Ca2+ profile over freely suspended cells. Also, the intracellular Ca2+ concentration was three times more in the former under similar experimental conditions. Whereas, illumination supported maximum Ca2+ transport in all the sets, darkness resulted in drastic reduction (90%) of Ca2+ uptake in freely suspended cells and least (15%) in polyvinyl entrapped cyanobacterial cells. Exogenously added ATP (10 microM) on the other hand, enhanced Ca2+ uptake in dark incubated freely suspended cells; ATP at the same concentration failed to bring out any significant enhancement in cation uptake in immobilized cells facing dark exposure. It was observed that these cells were still able to sustain sufficient ATP preserves to drive active transport of Ca2+ even in the dark. Furthermore, the immobilized cells exhibited remarkable Ca2+ transport rate even at the age of 20 and 50 days at which its free living counterpart took up insignificant Ca2+. These findings suggest the improved metabolic efficiency of polyvinyl foam entrapped cells over freely suspended cells in terms of Ca2+ accumulation and its possible use as a bioreactor for metal accumulation/removal in repetitive cycles without any measurable loss in cell biomass.

Isolation and partial characterization of Het- Fix- mutant strain of the diazotrophic cyanobacterium Anabaena variabilis showing chromatic adaptation

We propose a model to describe the changes taking place in biochemical processes/events to explain the development of heterocyst and nitrogenase in a diazotrophic cyanobacterium Anabaena variabilis. For this purpose, a mutant strain of A. variabilis lacking heterocyst differentiation and incapable of growth with dinitrogen as the sole source of nitrogen has been isolated after nitrosoguanidine (NTG) mutagenesis and selection by penicillin enrichment. The mutant strain (Het- Fix-) thus isolated has morphological variation and was incapable of reducing acetylene under anaerobic conditions, indicating its mutational loss of the process of nitrogen fixation. The Het- Fix- mutant strain had reduced glutamine synthetase (transferase) activity compared with its wild-type counterpart, suggesting a link between nif gene expression and the expression of gln A, the structural gene of GS. The Het- Fix- mutant strain compared with its wild-type strain also had an extremely high level of phycobiliprotein and a low level of carotenoids. Furthermore, the coiling of vegetative filaments in the Het- Fix- mutant strain, which reduced the surface area to be exposed to light, was a direct indication of the chromatic adaptation, because the mutant strain was found to be photosensitive, showing bleaching of the cells under high light intensity.

Regulation of sodium influx in the NaCl-resistant (NaCl(r)) mutant strain of the cyanobacterium Anabaena variabilis

A NaCl(r) mutant of the diazotrophic cyanobacterium Anabaena variabilis has been isolated by NTG mutagenesis and selection for NaCl resistance. The NaCl(r) strain has been characterized with respect to its mechanism of NaCl tolerance and regulation of Na(+) influx. NaCl(r) strain exhibits low Na(+) influx, accumulated high level of glycine betaine as a compatible solute, and persistent synthesis of SSPs at a higher rate than its wild-type counterpart. DCMU, an inhibitor of PS-II, inhibited Na(+) influx, suggesting that Na(+) influx is an energy-dependent process and that the energy is derived from photophosphorylation. This contention is further supported by the inhibition of Na(+) influx under dark conditions. The inhibition of Na(+) influx by KCN, DNP, NaN(3) also supports the involvement of oxidative phosphorylation in the regulation of active Na(+) influx. Thus, it appears that the synthesis of SSPs, accumulation of compatible solutes, and exhibition of low Na(+) influx in the NaCl(r) strain made this organism NaCl tolerant.

Valine 77 of heterocystous ferredoxin FdxH2 in Anabaena variabilis strain ATCC 29413 is critical for its oxygen sensitivity

Ferredoxins are small iron sulfur proteins necessary for electron donation. FdxH1 and FdxH2 are associated with two different nif gene clusters where they transfer electrons for the reduction of nitrogenase complex. FdxH1 was observed to be stable towards oxygen, whereas, FdxH2 was relatively unstable. We had identified the amino acid involved in oxygen sensitivity of ferredoxin protein using protein modeling. The exchange of valine to leucine at position 77 was critical for ferredoxin proteins in relation to its oxygen sensitivity. This exchange leads to a longer side chain, which inhibits the accessibility of oxygen to the iron sulfur cluster. Site directed mutagenesis and in vitro experiments confirms that valine indeed is involved in the oxygen sensitivity. The exchange of leucine to valine in FdxH1 makes it oxygen unstable. Thus, from the above results we can conclude that the position of leucine at position 77 is critical for oxygen sensitivity of ferredoxin and protein modeling can be used to identify specific amino acids in other oxygen-sensitive proteins.

Isolation and characterization of the thylakoid membranes from the NaCl-resistant (NaCl(r)) mutant strain of the cyanobacterium Anabaena variabilis

NaCl-induced changes in the thylakoid membrane of wild-type Anabaena variabilis and its NaCl(r) mutant strain have been studied. Biochemical characterization of the thylakoid membrane was done by taking its absorption and fluorescence spectra at different wavelength. The thylakoid membranes of both strains were isolated by mechanical disruption of the freeze-dried and lysozyme-treated cells, followed by differential and density gradient centrifugation. The light absorption spectra of the thylakoid membrane showed three and two peaks in NaCl(r) mutant strain and its wild-type counterpart respectively at wavelengths of 400-850 nm. These peaks revealed that the thylakoid membrane contains a large amount of carotenoid and chlorophyll a. Fluorescence emission spectra of thylakoid membrane of NaCl(r) mutant and its wild-type strain at excitation wavelength of 335 nm showed two different peaks, one at 340 nm and the other at 663 nm respectively. The light absorption and fluorescence spectra of the thylakoid membrane also revealed that the membrane contained carotenoid pigment, chlorophyll (Chl) a, and a pigment with an emission peak at 335 nm. The HPLC analysis of the pigments of the thylakoid membrane indicates that the NaCl(r) mutant strain under NaCl stress contained an additional peak for the carotenoid pigment, which was lacking in its wild-type counterpart. The major peak in thylakoid membrane was that of echinenone and beta-carotene. Whereas the polypeptide composition of thylakoid membrane differed in the wild-type and its NaCl(r) mutant strain, no difference in the cell wall protein pattern was observed in both strains. The thylakoid membrane of NaCl(r) mutant strain contained two additional protein bands that were absent in its wild-type counterpart. The thylakoid membrane of the wild-type and its NaCl(r) mutant strain also showed morphological variations under NaCl stress.

Identification of amino acids responsible for the oxygen sensitivity of ferredoxins from Anabaena variabilis using site-directed mutagenesis

The filamentous cyanobacterium Anabaena variabilis (ATCC 29413) possesses two molybdenum dependent nitrogenase systems, nif1 and nif2. The nif1 system is regulated by a developmental program involving heterocyst differentiation; the nif2 system is expressed in all cells only under anaerobic conditions and the expression is controlled environmentally. The genes fdxH1 and fdxH2, encoding two [2Fe-2S] ferredoxins, are part of the these two distinct and differently regulated nif gene clusters. The sensitivity of both ferredoxins to oxygen was different; the half-life of FdxH2 in air was only approximately 1.5 h, while FdxH1 retained 80% of its nitrogenase activity after 24 h. We used site-directed mutagenesis to identify the role of individual amino acid residues responsible for oxygen sensitivity and found out that the FdxH2 double mutant I76A/V77L was much more resistant to oxygen than the wild-type ferredoxin (FdxH2) and similar to FdxH1. By modelling it was shown that the accessibility of the cavity around the iron-sulfur cluster was responsible for that.

Calcium-dependent metabolic regulations in prokaryotes indicate conserved nature of calmodulin gene

Role of free calcium and calcium binding protein calmodulin as signal molecule in cellular regulation is well established in eukaryotes. However, reports on Ca(2+)-dependent processes and their inhibition by calcium and/or calmodulin antagonists indicate towards the presence of calmodulin in prokaryotes as well. The common evolutionary origin of pro- and eukaryotes and many examples of evolutionary conservation of structure and functions support the contention of such conservation of the role of Ca2+ and calmodulin. Eukaryotic calmodulin (CaM) contains four structurally and functionally similar Ca2+ domains named I, II, III and IV. Each Ca2+ binding loop consists of 12 amino acid residues with ligands arranged spatially to satisfy the octahedral symmetry of Ca2+ binding. Plant calmodulin differ from vertebrate ones in 13 to 14 amino acid positions of which nine occur at -COOH- terminal half. Differences between protozoan and mammalian CaM also occur mostly in the same half. Isolation and characterization, although to a little extent, of CaM-like proteins from bacteria and cyanobacteria and their comparison with CaMs from diverse origin suggest high degree of conservation. Non-bulky amino acids like glycine, alanine and serine with low specific rotation are present in greater number in the primitive form of calmodulin and have been significantly reduced in highly evolved form of calmodulin, suggesting that their requirement was insignificant and were eliminated from EF hand structure during evolution. However, amino acids like glutamate/glutamine and aspartate/asparagine were highly conserved and did not show any major change in their frequency since their positions are too significant in calcium binding domain. While the number of positively charged amino acids like arginine and leucine was increased, histidine containing weakly ionized group and having a significant buffering capacity was reduced to a major extent, further suggesting that the acidic nature of calmodulin protein has been maintained during evolution. Thus it is now clear that the entire superfamily of Ca2+ binding proteins have arisen from a common genetic ancestry. Two successive tandem duplications of gene encoding a single domain containing protein of 30-40 residues gave rise to a four domain molecule from which this family was then derived.

Phytolectins: natural molecules with immense biotechnological potential

Lectins are structurally diverse, carbohydrate binding proteins that bind reversibly to specific mono- or oligosaccharides. Their abundance in the plant kingdom suggest that they have diverse roles to perform. They serve as recognition factor between symbiotic nitrogen fixing bacteria and host plants, as a deterrent to phytopathogens like fungi, insects, and animals, as storage protein and as an aid in sexual reproduction in Chlamydomonas, amongst others. The possible application of lectins as a factor in increasing soil fertility and as a biopesticide by genetically engineered organisms is yet to be fully explored by the biotechnologists. However, they are being used by the biomedical scientists and biochemists in blood typing and stimulation of cells for chromosome analysis and gene mapping, in cell separation, identification of complex glycoproteins and typing of bacteria. Cell targeting by lectins in cancer therapy is still in its infancy. This review gives an insight into the potential of these wonder biomolecules in agriculture, biochemistry, cell biology and medicine for the benefit of mankind.

Copper-induced changes in the urea uptake and urease activity in the cyanobacteria Anabaena doliolum and Anacystis nidulans: interaction with sulphur containing amino acids

Copper-induced changes in the urea uptake and urease activity have been investigated in the cyanobacteria Anabaena doliolum and Anacystis nidulans. Copper, at and above 5 mumol/L concentration, inhibited urea uptake and urease activity systems in both the cyanobacteria in a concentration dependent manner. However, the urea uptake and urease activity systems in A. nidulans appeared slightly more tolerant to copper than than of A. doliolum. The inhibitory effect of copper on urea uptake and urease activity was mitigated by sulphur containing amino acids (cystine and cysteine), however, methionine could not do so, indicating the involvement of sulfhydryl (-SH) groups in the assimilation of urea in cyanobacteria.

Glutamine synthetase and arginine inhibition of nitrate reductase activity in Anabaena cycadeae

Wild-type Anabaena cycadeae with normal glutamine synthetase (GS) activity utilized arginine as sole N source whereas a mutant strain lacking GS activity did not. Nitrate reductase (NR) activity, higher in the mutant strain than the wild-type strain, was inhibited by arginine though arginine-dependent NH 4 (+) generation was higher in the mutant strain than in the wild-type. This suggests that (1) NR activity is NO inf3 (sup-) -inducible and arginine-repressible; and (2) while GS activity is required for the assimilation of arginine as sole N-source, it is not required for arginine inhibition of NR activity.

Adaptive response of wild and mutant type Synechococcus cedrorum to a polychlorinated pesticide-endosulfan

The effect of endosulfan, a hexachlorinated pesticide, on growth, inorganic nitrogenous nutrient uptake (NO3-, NO2- and NH4+), change in pigmentation and glycogen content on wild type and chemically mutagenised cells of Synechococcus cedrorum was investigated. The pattern of response to pesticide stress in wild and mutant type was the same. Growth reappeared in both after a period of initial lag in presence of endosulfan. The duration of lag increased with increasing doses of pesticide. Paradoxically, however, the rate of uptake of NO3-, NO2- and NH4+, pigment and glycogen content progressively increased with increasing doses. The difference in the adaptation response between wild and mutant types was observed only in the concentration of pesticide that could be tolerated; with the mutant tolerating 2.5 fold more.

Isolation and physiological characterization of Synechococcus cedrorum 1191 strain tolerant to heavy metals and pesticides

The toxicity of heavy metals (Hg2+, Zn2+) and pesticides has been investigated by comparing the physiological properties in wild and tolerant strains of Synechococcus cedrorum 1191. The differential pattern of growth, absorption spectra of pigments and nutrient uptake was observed in tolerant strain.

Demonstration of an altered phenylalanyl-tRNA synthetase in an analogue-resistant mutant of Aspergillus nidulans

We have isolated and characterized a new class of p-fluorophenylalanine (FPA)-resistant mutant in Aspergillus nidulans using a phenA strain as the wild type, by optimizing the conditions of growth. All four spontaneous mutants selected on a medium containing FPA were found to be recessive to their wild-type alleles in heterozygous diploids. Complementation analyses and linkage data showed that they were allelic and mapped at a single locus (fpaU) in the facA-riboD interval on the right arm of linkage group V. Partial purification and characterization of Phe-tRNA synthetase from wild-type and mutant strains revealed that the mutant enzyme had a greatly reduced ability to activate the analogue. It is suggested that mutation in the fpaU gene brings about a structural alteration in Phe-tRNA synthetase.