Non-heterocystous Cyanobacterium Plectonema Boryanum Research Articles

Hydrogen Generation Through Indirect Biophotolysis in Batch Cultures of the Nonheterocystous Nitrogen-Fixing Cyanobacterium Plectonema boryanum

The nitrogen-fixing nonheterocystous cyanobacterium Plectonema boryanum was used as a model organism to study hydrogen generation by indirect biophotolysis in nitrogen-limited batch cultures that were continuously illuminated and sparged with argon/CO(2) to maintain anaerobiosis. The highest hydrogen-production rate (i.e., 0.18 mL/mg day or 7.3 micromol/mg day) was observed in cultures with an initial medium nitrate concentration of 1 mM at a light intensity of 100 micromol/m(2) s. The addition of photosystem II (PSII) inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) did not reduce hydrogen-production rates relative to unchallenged controls for 50 to 150 h, and intracellular glycogen concentrations decreased significantly during the hydrogen generation period. The insensitivity of the hydrogen-production process to DCMU is indicative of the fact that hydrogen was not derived from water splitting at PSII (i.e., direct biophotolysis) but rather from electrons provided by intracellular glycogen reserves (i.e., indirect biophotolysis). It was shown that hydrogen generation could be sustained for long time periods by subjecting the cultures to alternating cycles of aerobic, nitrogen-limited growth and anaerobic hydrogen production.

Effect of UV-B and monocrotophos, singly and in combination, on photosynthetic activity and growth of non-heterocystous cyanobacterium Plectonema boryanum

The impact of artificial ultraviolet-B (UV-B 280–315 nm) irradiation and monocrotophos (an organophosphorus insecticide), singly and in combination, on survival, growth and photosynthetic activities and energy transfer within the pigments has been studied in a non-heterocystous cyanobacterium Plectonema boryanum. Survival and growth of the cyanobacterium decreased with selected dose of UV-B (30 min and 90 min) and monocrotophos (5 μg ml −1). The various doses of UV-B (30, 60, 90 and 120 min exposures) damaged the photosynthetic pigments, phycocyanin, carotenoids and chlorophyll a (Chl a); phycocyanin, however, appeared to be the main target of UV-B. This was further proved by the prominent decrease in phycocyanin absorption peak in intact cells. 14 C- fixation was found to be more sensitive to UV-B and monocrotophos, singly and in combination than photosynthetic oxygen evolution. Photosynthetic electron transport activity decreased in response to UV-B and monocrotophos individually as well as in their combined dose (UV-B + monocrotophos). This inhibition was due to a greater susceptibility of PSII than PSI. UV-B and monocrotophos either alone or in combination induced inhibition of PSII activity and its partial restoration by artificial electron donors (DPC, NH 2OH and MnCl 2) suggests that these stresses blocked the electron flow at water oxidation side. However, less restoration in combination of these stresses and 90 min UV-B exposure alone indicated that the PSII reaction centre was also affected. Suppression in emission peak (λ 650 nm) of phycocyanin revealed that both the stresses, either singly or in combination, altered the energy transfer efficiency of phycocyanin to PSII. The present findings suggest that the doses of UV-B radiation and monocrotophos singly and in combination, have adversely affected the photosynthetic activity of P. boryanum, leading to the significant decrease in survival and growth. The interactive effect of both the stresses was, however, less than additive.

Photosynthetic acclimation of the filamentous cyanobacterium, Plectonema boryanum UTEX 485, to temperature and light.

Photosynthetic acclimation to temperature and irradiance was studied in the filamentous, non-heterocystous cyanobacterium Plectonema boryanum UTEX 485. Growth rates of this cyanobacterium measured at ambient CO2 were primarily influenced by temperature with minimal effects of irradiance. Both growth temperature and irradiance affected linolenic (18:3) and linoleic acid (18:2) levels in the four major lipid classes in an independent but additive manner. In contrast, photosynthetic acclimation was not due to either growth temperature or irradiance per se, but rather, due to the interaction of these environmental factors. P. boryanum grown at low temperature and moderate irradiance mimicked cells grown at high light. Compared to cells grown at either 29 degrees C/150 micromol m(-2) s(-1) (29/150) or 15/10, P. boryanum grown at either 15/150 or 29/750 exhibited: (1) reduced cellular levels of Chl a and phycobilisomes (PBS), and concomitantly higher content of an orange-red carotenoid, myxoxanthophyll; (2) higher light saturated rates (Pmax) when expressed on a Chl a basis but lower apparent quantum yields of oxygen evolution and (3) enhanced resistance to high light stress. P. boryanum grown at 15/150 regained normal blue-green pigmentation within 16 h after a temperature shift to 29 degrees C at a constant irradiance of 150 micromol m(-2) s(-1). DBMIB and KCN but not DCMU and atrazine partially inhibited the change in myxoxanthophyll/Chl a ratio following the shift from 15 to 29 degrees C. We conclude that P. boryanum responds to either varying growth temperature or varying growth irradiance by adjusting the ability to absorb light through decreasing the cellular contents of Chl a and light-harvesting pigments and screening of excessive light by myxoxanthophyll predominantly localized in the cell wall/cell membrane to protect PSII from over-excitation. The possible role of redox sensing/signalling for photosynthetic acclimation of cyanobacteria to either temperature or irradiance is discussed.

Differential expression of photosynthesis and nitrogen fixation genes in the cyanobacterium Plectonema boryanum.

The filamentous non-heterocystous cyanobacterium Plectonema boryanum fixes dinitrogen at a high rate during microaerobic growth in continuous illumination by temporal separation of oxygen-evolving photosynthesis and oxygen-sensitive dinitrogen fixation. The onset of nitrogen fixation is preceded by a depression in photosynthesis that establishes a sufficiently low level of dissolved oxygen in the growth medium. A several-fold reduction in the level of transcripts coding for phycocyanin (cpcBA) and the chlorophyll a binding protein of photosystem II (psbC) and psbA accompanied the depression in photosynthetic oxygen evolution. Unlike most of the other organisms examined to date, in P. boryanum, psbC and psbD do not appear to be co-transcribed. The psbC transcripts were down-regulated several fold, while the psbD transcript declined marginally during the nitrogen fixation phase. A decrease in dissolved oxygen and a dramatic increase in the level of nifH transcripts and the enzyme activity of nitrogenase were characteristic of the nitrogen fixation phase. The level of transcript for glnA, which encodes glutamine synthetase, was not altered. Reciprocal regulation of gene expression was well orchestrated with the alternating cycles of photosynthesis and nitrogen fixation in P. boryanum.

Enhanced hydrogen photoproduction by non-heterocystous cyanobacterium Plectonema boryanum

Nitrogenase activity was derepressed in Plectonema boryanum following 18–24 h of microaerobic incubation. The cyanobacterium evolved hydrogen at a slow rate. Addition of reducing substances (sulfide, sulfite or dithionite) to the diazotrophic cultures resulted in an increase in nitrogenase activity or photoproduction of hydrogen. The reducing substances also restored phycocyanin degradation.

Characteristics and Regulation of the Ammonium Transport System in Filamentous Nonheterocystous Cyanobacterium Plectonema boryanum

Summary Ammonium transport in Pectonema boryanum , a filamentous noneterocystous cyanoacterium was investigated in cells exposed to N-sufficient (medium with nitrate) or N-stress (medium without nitrate) conditions. T N-sufficient cells exhibited a single transport system (K m = 20 μM; V max = 258 mmol kg -1 protein min -1 ) and a 40-fold concentration gradient was formed following 10 min of transport. The transport was maximally operative at pH 7.0 and 33°C. The transport was not inhibited by methylamine (K m = 33.3 μM; V max =50 mmol kg -1 protein min -1 ). Following transfer o N-sufficient cells to N-stress conditions, the intracellular ammonium pool declined from 0. 38 to 0. 16 mM during the initial value during the first 6 h, but resumed to the initial value during the next 48 h. The N-stressed cells exhibited two ammonium transport systems with 〈high〉 and ⎒low affinity〉 respectively. The kinetics of the former system was similar to the N-sufficient cells, while the latter system had altered kinetics (K m = 50 μM; V max = 650 mmol kg -1 protein min -1 ). The results suggest that P. boryanum possesses multiple transport systems, and that their expression is regulated, depending upon the presence or absence of nitrate in the growth medium.

Hydrogen photoproduction by filamentous non-heterocystous cyanobacterium Plectonema boryanum and simultaneous release of ammonia

Abstract Plectonema boryanum (filamentous, non-heterocystous cyanobacterium) photoproduced H 2 when cells grown aerobically in nitrate were transferred to microaerobic or anaerobic conditions without nitrate. It was observed that H 2 photoproducing cells simultaneously excreted ammonium in the medium, which was possibly due to phycocyanin degradation [decrease in chlorophyll a (Chl a ):phycocyanin ratio in comparison to aerobic nitrate-grown cells]. Although nitrogenase (measured as H 2 evolution) was induced in Ar:CO 2 (96:4 v/v), inclusion of N 2 in the gas phase (Ar:CO 2 :N 2 , 72:4:24 v/v) resulted in a 2-fold increase in H 2 evolution. Addition of l -methionine DL-sulphoximine (MSX, glutamine-synthetase inhibitor), besides stimulating ammonium excretion in the medium, resulted in a 4.5-fold increment of H 2 photoproduction (1.43 μmol H 2 mg −1 dry wt h −1 ) in comparison to cells in Ar:CO 2 gas phase (0.31 μmol H 2 mg −1 dry wt h −1 ). Inhibition of photosystem II by 3(3,4-dichlorophenyl)1,1-dimethyl urea (DCMU) caused an increment of 1.6 and 3.2-fold in Ar:CO 2 and Ar:CO 2 :N 2 , respectively, in comparison to cells incubated in Ar:CO 2 gas phase alone. Simultaneous production of H 2 and NH 4 + was at a maximum when MSX and DCMU were added together in suboptical concentrations. Immobilization of cells in calcium alginate prolonged the duration (12 days) of H 2 evolution and NH 4 − excretion.

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.

Simultaneous photoproduction of hydrogen and ammonia by a non-heterocystous cyanobacterium Plectonema boryanum.

Filamentous, non-heterocystous diazotrophic cyanobacterium Plectonema boryanum simultaneously photoproduced hydrogen (0.30μmol mg-1 dry wth-1) and ammonium (8.2nmol mg-1 dry wth-1) under microaerobic (A:CO2, 96:4, v/v) conditions in the presence of 1mM sulfide. Nitrogen in the gas phase (A:CO2:N2, 72:4:24, v/v) enhanced the process more than two fold. A glutamine synthetase inhibitor, MSX, stimulated ammonium excretion and H2-production and pulses of MSX rather than a single dose favoured both the processes. A higher dose (15μM) in comparison to lower dose (5μM) of MSX, although it stimulated H2-evolution and NH4+-excretion, shortened the duration of both the processes. The stability of both the processes was prolonged in alginate-immobilized cyanobacterial cells besides enhancement in H2-evolution and NH4+-excretion. MSX was less toxic under immobilized state than the free cells.

Growth characteristics of non-heterocystous cyanobacterium Plectonema boryanum with N2 as nitrogen source

Strains of filamentous, non-heterocystous cyanobacteria from the Pasteur Culture Collection (PCC), able to synthesize nitrogenase under anaerobic test conditions, were tested for growth with N2 as sole nitrogen source at low O2 partial pressure (less than 0.05%).

Effect of Sodium on Nitrogen Fixation in Anabaena torulosa and Plectonema boryanum

The cyanobacterium Anabaena torulosa required sodium and molybdenum for nitrogenase activity and diazotrophic growth. Addition of sodium or molybdenum to cultures deficient in either element restored nitrogenase activity. Heterocyst differentiation was unaffected by sodium but molybdenum deficiency enhanced differentiation. The non-heterocystous cyanobacterium Plectonema boryanum 594 also required sodium for nitrogenase activity but synthesized presumptive nitrogenase component I and II proteins during sodium deficiency. The results show that in cyanobacteria nitrogenase is synthesized even in the absence of sodium but functions only in its presence.

Nitrogen-fixing growth by nonheterocystous cyanobacterium Plectonema boryanum

Many oxygen-evolving nonheterocystous cyanobacteria can synthesise nitrogenase1,2, but only a few are able to protect the enzyme from inhibition and denaturation by oxygen3–5. It is difficult to reconcile concomitant oxygenic photosynthesis and the obligately anaerobic process of nitrogen fixation in the remaining strains. One possibility is a temporal separation of the processes: Plectonema boryanum (U. Tex strain 594) has been shown6 to fix nitrogen and then grow oxygenically to the limits of the fixed nitrogen when incubated without combined nitrogen under N2/CO2. Growth was not extensive. Here conditions are described in which the same strain of P. boryanum will simultaneously fix nitrogen and grow extensively, fully pigmented, apparently with sufficient metabolic energy to drive nitrogen fixation.