Amar Nath Rai

Cyanobacteria in symbiosis

Introduction. Colour Plates. 1. Cyanobacteria in Symbiosis with Diatoms S. Janson. 2. Marine Cyanobacterial Symbioses E.J. Carpenter, R.A. Foster. 3. The Nostoc-Geosiphon Endocytobiosis M. Kluge, et al. 4. Cyanolichens: An Evolutionary Overview J. Rikkinen. 5. Cyanolichens: Carbon Metabolism K. Palmqvist. 6. Cyanolichens: Nitrogen Metabolism A.N. Rai. 7. Cyanobacteria in Symbiosis with Hornworts and Liverworts D.G. Adams. 8. Associations Between Cyanobacteria and Mosses B. Solheim, M. Zielke. 9. Azolla-Anabaena Symbiosis S. Lechno-Yossef, S.A. Nierzwicki-Bauer. 10. Applied Aspects of Azolla-Anabaena Symbiosis C. van Hove, A. Lejeune. 11. Cyanobacteria in Symbiosis with Cycads J.-L. Costa, P. Lindblad. 12. Nostoc-Gunnera Symbiosis B. Bergman. 13. Ecology of Nostoc-Gunnera Symbiosis B.A. Osborne, J.I. Sprent. 14. Artificial Cyanobacterium-Plant Symbioses M.V. Gusev, et al. 14. Artificial Cyanobacterium-Plant Symbioses M.V. Gusev, et al. 15. Cyanobacterial Diversity and Specificity in Plant Symbioses U. Rasmussen, M. Nilsson. 16. Evolution of Cyanobacterial Symbioses J.A. Raven. Subject Index.

Cyanobacteria: A Precious Bio-resource in Agriculture, Ecosystem, and Environmental Sustainability

Keeping in view, the challenges concerning agro-ecosystem and environment, the recent developments in biotechnology offers a more reliable approach to address the food security for future generations and also resolve the complex environmental problems. Several unique features of cyanobacteria such as oxygenic photosynthesis, high biomass yield, growth on non-arable lands and a wide variety of water sources (contaminated and polluted waters), generation of useful by-products and bio-fuels, enhancing the soil fertility and reducing green house gas emissions, have collectively offered these bio-agents as the precious bio-resource for sustainable development. Cyanobacterial biomass is the effective bio-fertilizer source to improve soil physico-chemical characteristics such as water-holding capacity and mineral nutrient status of the degraded lands. The unique characteristics of cyanobacteria include their ubiquity presence, short generation time and capability to fix the atmospheric N2. Similar to other prokaryotic bacteria, the cyanobacteria are increasingly applied as bio-inoculants for improving soil fertility and environmental quality. Genetically engineered cyanobacteria have been devised with the novel genes for the production of a number of bio-fuels such as bio-diesel, bio-hydrogen, bio-methane, synga, and therefore, open new avenues for the generation of bio-fuels in the economically sustainable manner. This review is an effort to enlist the valuable information about the qualities of cyanobacteria and their potential role in solving the agricultural and environmental problems for the future welfare of the planet.

Nitrogenase derepresssion, its regulation and metabolic changes associated with diazotrophy in the non-heterocystous cyanobacterium Plectonema boryanum PCC 73110

Summary: The regulation of nitrogenase derepression, plus the catalytic activity and protein concentration of glutamine synthetase (GS), nitrate reductase (NR), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phycoerythrin (PE) were studied in the filamentous non-heterocystous cyanobacterium Plectonema boryanum PCC 73110. Both nitrogen limitation and microaerobic incubation were essential for the derepression of nitrogenase. Oxygen caused irreversible inactivation of nitrogenase, as well as repression of its synthesis. A temporal separation of N2 fixation and net photosynthetic O2 evolution was observed under a N2/CO2 (95:5, v/v) atmosphere. Repeated peaks of nitrogenase and growth were observed. Immunogold localization showed that in N2-fixing cultures, all cells, including those undergoing division, contained nitrogenase, and that the nitrogenase antigen was uniformly distributed throughout the cells without any preferential association with cellular structures. Rubisco was mainly located in carboxysomes of both N2-fixing and NO- 3-grown cells. Both N2-fixing and NO- 3 -grown cells showed similar levels of PE, which was associated with the thylakoid membranes. GS antigen was distributed throughout the cells and the relative amounts of this enzyme, as well as its activity, were 20% higher in N2-fixing than in NO- 3-grown cultures. NO- 3 uptake and NR systems were found to be NO- 3 inducible, with very low activities in N2-fixing cultures. The latter may be important in avoiding competition for Mo between nitrogenase and NR.

Anthoceros-Nostoc Symbiosis: Immunoelectronmicroscopic Localization of Nitrogenase, Glutamine Synthetase, Phycoerythrin and Ribulose-1,5-bisphosphate Carboxylase/Oxygenase in the Cyanobiont and the Cultured (Free-living) Isolate Nostoc 7801

Localization of nitrogenase, glutamine synthetase (GS), phycoerythrin (PE) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) was studied with immunocytochemical techniques in the cyanobiont and the free-living cultured isolate Nostoc 7801 of Anthoceros punctatus. In both cases nitrogenase was located in heterocysts only and was uniformly distributed within the cell. GS was located both in heterocysts and vegetative cells, with a uniform cellular distribution in each cell type. Whereas heterocysts of Nostoc 7801 had about twofold higher label than vegetative cells, labelling in heterocysts and vegetative cells of the cyanobiont was similar. While the GS content of the vegetative cells of the cyanobiont and Nostoc 7801 was comparable, the apparent GS content of the cyanobiont heterocysts was 60% less than that in Nostoc 7801 heterocysts. PE and RuBisCO were located in vegetative cells only. PE was located on thylakoid membranes and RuBisCO in the cytoplasm and carboxysomes. In each case the pattern of labelling in the cyanobiont and Nostoc 7801 was similar.

The Cycas revoluta-Nostoc Symbiosis: Enzyme Activities of Nitrogen and Carbon Metabolism in the Cyanobiont

SUMMARY: A comparative study was made of enzymes involved in nitrogen and carbon metabolism in the cyanobiont directly isolated from Cycas revoluta coralloid roots, and in the cultured isolate Nostoc 7422. The symbiotic Nostoc showed high activity of glutamine synthetase and glutamate synthase, the primary ammonia-assimilating enzyme system in cyanobacteria. Ammoniaassimilating glutamate dehydrogenase (GDH) activity was undetectable, although the catabolic GDH activity was high. Both glutamate-oxaloacetic acid transaminase and malate dehydrogenase showed higher activities in the symbiotic Nostoc than in the cultured Nostoc strain. The symbiotic Nostoc did not fix CO2 in vivo although in cell-free extracts both ribulose-1,5-bisphosphate carboxylase and phosphoribulokinase activities, similar to those in the cultured strain, were present.

Absence of the glutamine-synthetase-linked methylammonium (ammonium)-transport system in the cyanobiont of Cycas-cyanobacterial symbiosis

Using the ammonium analogue 14CH3NH3+, ammonium transport was studied in the cyanobiont cells freshly isolated from the root nodules of Cycas revoluta. An L-methionine-dl-sulphoximine (MSX)-insensitive ammonium-transport system, which was dependent on membrane potential (ΔΨ), was found in the cyanobiont. However, the cyanobiont was incapable of metabolizing exogenous 14CH3NH3+or NH4+because of the absence of another ammonium-transport system responsible for the uptake of ammonium for assimilation via glutamine synthetase (EC 6.3.1.2). Such a modification seems to be the result of symbiosis because the free-living cultured isolate, Anabaena cycadeae, has been shown to possess both the ammonium-transport systems.

Isolation and characterization of a chlorate-resistant mutant (Clo-R) of the symbiotic cyanobacterium Nostoc ANTH: Heterocyst formation and N2-Fixation in the presence of nitrate, and evidence for separate nitrate and nitrite transport systems

Nostoc ANTH is a filamentous, heterocystous cyanobacterium capable of N2-fixation in the absence of combined nitrogen. A chlorate-resistant mutant (Clo-R) of Nostoc ANTH was isolated that differentiates heterocysts and fixes N2 in the presence of nitrate, but not in the presence of nitrite or ammonium. The mutant lacks nitrate uptake and thereby also lacks induction of nitrate reductase activity by nitrate. However, this mutant is able to transport and assimilate nitrite, indicating that there is a transport system for nitrite that is distinct from that for the nitrate. The lack of inhibitory effect of nitrate on N2-fixation was owing to lack of nitrate uptake and not to lack of enzymes for its assimilation (nitrate reductase and glutamine synthetase) or the lack of an ammonium transport system for retention of ammonia. The mutant has potential for use as a biofertilizer supplementing chemical nitrate fertilizer in rice fields, without N2-fixation being adversely affected.

Isolation and characterization of a Mastigocladus species capable of growth, N(2)-fixation and N-assimilation at elevated temperature.

A Mastigocladus species was isolated from the hot spring of Jakrem (Meghalaya) India. Uptake and utilization of nitrate, nitrite, ammonium and amino acids (glutamine, asparagine, arginine, alanine) were studied in this cyanobacterium grown at different temperatures (25°C, 45°C). There was 2–3 fold increase in the heterocyst formation and nitrogenase activity in N-free medium at higher temperature (45°C). Growth and uptake and assimilation of various nitrogen sources were also 2–3 fold higher at 45°C indicating that it is a thermophile. The extent of induction and repression of nitrate uptake by NO3− and NH4+, respectively, differed from that of nitrite. It appeared that Mastigocladus had two independent nitrate/nitrite transport systems. Nitrate reductase and nitrite reductase activitiy was not NO3−-inducible and ammonium or amino acids caused only partial repression. Presence of various amino acids in the media partially repressed glutamine synthetase activity. Ammonium (methylammonium) and amino acid uptake showed a biphasic pattern, was energy-dependent and the induction of uptake required de novo protein synthesis. Ammonium transport was substrate (NH4+)-repressible, while the amino acid uptake was substrate inducible. When grown at 25°C, the cyanobacterium formed maximum akinetes that remained viable upto 5 years under dry conditions.

N 2 -Fixing Cyanobacterial Systems as Biofertilizer

Soil and water surfaces, as well as plant surfaces and tissues are the known locations that harbor free-living phototrophic N2-fixing cyanobacteria. These organisms are known to contribute substantial amounts of fixed nitrogen (20–30 kg N ha−1annually). In continents where rice is the prime crop for majority of the population (amounting to over 40 % of world’s population), these organisms assume great importance. Two third of the total of 180 million tons of fixed nitrogen that gets added to the earth’s surface globally, comes from biological activities mainly contributed by these and other microbes. Rice field ecosystems are ideal for cyanobacterial growth as they provide optimum growth conditions. Azolla-Anabaena symbiotic association, another cyanobacterial system has been exploited as a biofertilizer in many Asian countries. This symbiosis is very important agronomically because its contribution has been estimated to be ~600 kg N ha−1. With the adverse consequences of chemical agriculture, focus on nitrogen enrichment has shifted again to biological nitrogen fixation, especially towards both free-living and symbiotic cyanobacteria. During past few decades, research studies have yielded a large quantity of information on cyanobacterial nitrogen fixation from isolation, molecular understanding and manipulations to large-scale production for agriculture. Substantial research studies have also been devoted towards creating and understanding the artificial associations of cyanobacteria with crop plants. In this chapter, various N2-fixing cyanobacterial systems in light of their use as biofertilizers are reviewed.

A Common Transport System for Methionine, l -methionine- dl -Sulfoximine (MSX), and Phosphinothricin (PPT) in the Diazotrophic Cyanobacterium Nostoc muscorum

We present evidence, for the first time, of the occurrence of a transport system common for amino acid methionine, and methionine/glutamate analogues l-methionine-dl-sulfoximine (MSX) and phosphinothricin (PPT) in cyanobacterium Nostoc muscorum. Methionine, which is toxic to cyanobacterium, enhanced its nitrogenase activity at lower concentrations. The cyanobacterium showed a biphasic pattern of methionine uptake activity that was competitively inhibited by the amino acids alanine, isoleucine, leucine, phenylalanine, proline, valine, glutamine, and asparagine. The methionine/glutamate analogue-resistant N. muscorum strains (MSX-R and PPT-R strains) also showed methionine-resistant phenotype accompanied by a drastic decrease in 35S methionine uptake activity. Treatment of protein extracts from these mutant strains with MSX and PPT reduced biosynthetic glutamine synthetase (GS) activity only in vitro and not in vivo. This finding implicated that MSX- and PPT-R phenotypes may have arisen due to a defect in their MSX and PPT transport activity. The simultaneous decrease in methionine uptake activity and in vitro sensitivity toward MSX and PPT of GS protein in MSX- and PPT-R strains indicated that methionine, MSX, and PPT have a common transport system that is shared by other amino acids as well in N. muscorum. Such information can become useful for isolation of methionine-producing cyanobacterial strains.