The effects of immobilization on the biochemical,physiological and morphological features of Anabaena azollae

Anabaena azollae, a presumptive isolate from Azolla filiculoides, was immobilized in polyurethane foam, hydrophilic polyvinyl foam and alginate. When viewed by low-temperature scanning electron microscopy a thick mucilage layer covered the surface of both cells and matrix; this closely resembles the mode of attachment of the symbiont Anabaena in the Azolla leaf cavity. The heterocyst frequency of the immobilized A. azollae doubled relative to free-living cells and reached a level of 14–17%. Immobilization induced increases in both hydrogen production via nitrogenase or hydrogenase and in the rates and stabilization of acetylene reduction (N₂-fixation). Ammonia production by immobilized cells with L-methionine-D,L-sulfoximine (MSX) is greater than that of freeliving cells. Immobilized cells without MSX were, however, able to excrete ammonium at lower rates thus emulating the characteristic of the symbiotic cyanobacteria (A. azollae) in the leaf cavity of Azolla.Abbreviations Chl chlorophyll - GS glutamine synthetase - MSX L-methionine-D,L-sulfoximine - SEM scanning electron microscopy - PU polyurethane - PV polyvinyl     

The effect of immobilization on carbon flow through Anabaena variabilis and A. azollae

Immobilization in polyvinyl foam resulted in an increased carbon fixation and release of fixed carbon in Anabaena variabilis while in A. azollae both processes decreased.     

The effect of immobilization on carbon flow through Anabaena variabilis and A. azollae

Immobilization in polyvinyl foam resulted in an increased carbon fixation and release of fixed carbon in Anabaena variabilis while in A. azollae both processes decreased. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of immobilization of cyanobacteria in solid matrix on ammonia excretion and nitrogen fixing activity

Summary The algal symbiont of Azolla - Anabaena azollae (AS-DS) and free-living A.variabilis (SAo) colonized and immobilized well in all the solid matrices such as hollow fibre, polyurethane foam, cotton and silk cotton. Biomass production was more under immobilized state than under free-living state. Heterocyst frequency, nitrogen fixing activity and ammonia excretion were significantly higher under immobilized state than under free-living conditions.     

Efficacy of New Inexpensive Cyanobacterial Biofertilizer Including its Shelf-life

Summary Four cyanobacterial inoculants all significantly increased grain and straw yield of rice either alone or in combination with chemical fertilizer. A saving of 25 kg N ha⁻¹ can be attained through cyanobacterial fertilization. Tobacco waste-based cyanobacterial biofertilizer was best in performance. Cyanobacterial acetylene reducing activity in vivo varied from 144 to 255 μmol C₂H₄ m⁻² h⁻¹ in different treatments, being highest for tobacco-based cyanobacterial biofertilizer integrated with 50% chemical N. The nutrient balance for total N, available N, total P and available P was found positive in biofertilizer- and chemical fertilizer-treated plots. The total and available K showed negative balance in all the treatments. The shelf-life of cyanobacterial biofertilizer can be augmented by selecting translucent packing material, dry mixing and paddy straw as a carrier. Dry mixing and a mixing ratio of 50:50 (carrier:cyanobacteria) gave better inoculum loading and shelf-life. Decrease in cyanobacterial population was least in dried cyanobacterial flacks, indicating a possibility of developing cyanobacterial biofertilizer without carrier mixing at the time of production.     

The Effects of Immobilization on Photosynthesis,Growth, Nitrogen Fixation and Ammonium Ion Excretion of Mutant and Wild Type Cells of Anabaena variabilis

Ammonium ion photoproduced by nitrogen-fixing cyanobacteria is formed from water, air nitrogen and solar energy under normal temperature and atmospheric pressure. It is reported here that the mutant and its parent wiid type cells of Anabaena variabilis from Shanmugan lab were immobilized into the polyurethane foams. The growth curves measured by cell counting, O.D750 measurement and ch]orophyll a determination showed that the growth of the immobilized wild type cells was more rapid than the immobilized mutant cells, and for both two types of cells the free-living cells grew better than the immobilized ones. The nitrogenase activity (reduction of C2H2) was 44% greater in immobilized mutant cells and 232% greater in immobilized wild type cells than both free-living cells, respectively. Free-living cells of wild type A. variabilis almost did not excrete any ammonium ion and the immobilized cells of the wild type had the ammonium ion excretion activity similar to that of the free-living mutant cells. Moreover, immobilization stimulated the activity of ammonium ion excretion 55.6% greater than the free-living cells, in the mutant strain. The fluorescence enhancement induced by DCMU (3-(3,4-dichlor-benzene)-1, 1-dimethl urea) indicated the photosynthetic capability of wild type ceils in both free-living and immobilized states were higher than that of the mutant cells, and the free-living cells of both two types of cells had higher capability than the immobilized cells. The fluorescence emission spectra at 77K showed that there were four peak emission: F646(F645 or F650) and F662(F664 or F665) from phycobilin, F693(F698,F700 or F702) from PS Ⅱ and F732(F728 or F733 from PS Ⅰ In both two types of immobilized cells the photosynthetic light energy distribution tended to be in PS Ⅰ and it seems to be benefitlal for the nitrogenase activity and ammonium ion excretion. SEM observation indicated that the shape and size of the immobilized cells remained unchanged incompared with the free-living cells, However, the surface of the immobilized cells had accumulated some mucilage, and particularly, the film of mucilage coated both surface of the mutant cells and the foam matrix.     

Effect of Aluminum Phosphate on Alkaline Phosphatase Activity of Polyurethane Foam Immobilized Cyanobacteria

The impact of insoluble phosphorus such as aluminum and rock phosphate on alkaline phosphatase activity of polyurethane foam immobilized cyanobacteria was assessed. Polyurethane foam immobilized Nodularia recorded the highest alkaline phosphatase activity of 9.04 (m. mol p-nitrophenol released h^–1 mg^–1 protein) in vitro. A higher concentration of aluminum phosphate was recorded a 25% reduction in alkaline phosphatase activity, ammonia content, and available phosphorus in culture filtrate of polyurethane foam immobilized cyanobacteria. In general, immobilized cyanobacteria exhibited a higher alkaline phosphatase activity in rock phosphate than aluminum phosphate.     

Yield of submerged paddy and uptake of Zn,P and N as affected by liming and Zn fertilizers

The effects of CaCO₃, Zn sources and levels on the yield of submerged paddy and uptake of Zn, P and N to paddy were studied in green-house at Haryana Agricultural University, Hissar. Powdered CaCO₃ was mixed at 0,4 and 8 per cent and Zn was added at 0,5 and 10 ppm through ZnSO₄.7H₂O, ZnO and Zn EDTA separately. Dry weight at tillering and heading and grain and straw at maturity decreased significantly with 4 and 8 per cent CaCO₃ in comparison to the control. Increasing Zn application increased the dry weight and grain yield. Zn EDTA gave highest yield of paddy followed by ZnSO₄.7H₂O and ZnO.Increasing the application of CaCO₃ from 0–8 per cent decreased the concentration and uptake of Zn and increasing Zn application from 0–10 ppm increased concentration and uptake of Zn in paddy at tillering, heading and maturity. Zn EDTA gave the highest concentration and uptake of Zn followed by ZnSO₄.7H₂O and ZnO. There was interaction between Zn sources and CaCO₃.The concentration and uptake of N and P in paddy dry matter at tillering and heading and straw and grain at maturity decreased as compared to control with increasing CaCO₃ addition. The concentration and uptake of N increased and that of P decreased in paddy dry matter straw and grain with increasing Zn application. The highest concentration of N was observed with ZnO, followed by ZnSO₄.7H₂O and Zn EDTA. But highest uptake of N was observed with Zn EDTA followed by ZnSO₄.7H₂O and ZnO. As regards concentration and uptake of P, it was highest with ZnO followed by ZnSO₄.7H₂O and Zn EDTA.     

Cyanobacteria in Uruguayan rice fields: diversity, nitrogen fixing ability and tolerance to herbicides and combined nitrogen

It has been established that cyanobacteria play a vital role in the maintenance of flooded rice field fertility. To evaluate the potential use of nitrogen-fixing cyanobacteria as a natural biofertilizer for rice in Uruguay, the diversity, abundance and nitrogen fixing ability of these microorganisms were studied in the field and in the laboratory. The effect of urea fertilization on population density and diversity of heterocystous cyanobacteria was determined on a 3-year assay. The highest number of cyanobacteria, 1.6x10(4) CFU x m(-2), was found at the control 8 weeks after flooding. About 90% of the heterocystous cyanobacteria found in both treatments belong to the genera Nostoc and Anabaena. Maximal nitrogenase activity was reached after 12 weeks of flooding in both treatments, with an average of about 20 micromol C2H4 x m(-2) x h(-1). To improve the understanding of the environmental factors that can limit nitrogenase activity in rice fields, two of the most abundant cyanobacteria isolates were tested for tolerance to combined nitrogen and two herbicides. In both isolates 0.2 mM ammonium inhibited nitrogenase activity after 24 h of culture. The addition of field-recommended doses of quinclorac and propanil affected oxygen photoevolution but nitrogenase activity was only inhibited by propanil.     

Growth,photosynthesis, nitrogen fixation and carbohydrate production by a unicellular cyanobacterium,Synechococcus sp. (Cyanophyta)

A polymer-producing strain of unicellular cyanobacteria, Synechococcus sp., was isolated from a coastal lagoon in Florida. This strain, designated BG0011, excreted a highly viscous polysaccharide. Maximum observed growth rates for BG0011 were 2.5 div. day^-2. BG0011 also exhibited nitrogen fixation (nitrogenase) activity under aerobic conditions and grew at near maximum rates in medium lacking reduced nitrogen. Growth and carbohydrate production were enhanced by carbon dioxide enrichment. Rheological study of the extracellular polysaccharide revealed a viscosity versus shear rate curve similar in shape to that of xanthan gum. Maximum observed rate of carbohydrate production was 1 g dry weight liter^-1 month^-1.     

Transport of molybdate in the cyanobacterium Anabaena variabilis ATCC 29413

Heterocyst-forming filamentous cyanobacteria, such as Anabaena variabilis ATCC 29413, require molybdenum as a component of two essential cofactors for the enzymes nitrate reductase and nitrogenase. A. variabilis efficiently transported (99)Mo (molybdate) at concentrations less than 10(-9) M. Competition experiments with other oxyanions suggested that the molybdate-transport system of A. variabilis also transported tungstate but not vanadate or sulfate. Although tungstate was probably transported, tungsten did not function in place of molybdenum in the Mo-nitrogenase. Transport of (99)Mo required prior starvation of the cells for molybdate, suggesting that the Mo-transport system was repressed by molybdate. Starvation, which required several generations of growth for depletion of molybdate, was enhanced by growth under conditions that required synthesis of nitrate reductase or nitrogenase. These data provide evidence for a molybdate storage system in A. variabilis. NtcA, a regulatory protein that is essential for synthesis of nitrate reductase and nitrogenase, was not required for transport of molybdate. The closely related strain Anabaena sp. PCC 7120 transported (99)Mo in a very similar way to A. variabilis.     

Efficiency of rice fertilization schedules including cyanobacteria under soil application of phosphate and molybdate

Productive tillering, grain and straw yields and N-contents of indica rice IR-28 were increased more by urea fertilizer at 48 or 96 kg N/ha along with Inoculation by cyanobacteria than by using 144 kg N/ha without inoculation. Fertilizer N-use efficiency was increased by the cyanobacteria and decreased with increasing amount of urea fertilizer. Further enhancement was obtained by soil application of calclum superphosphate at 36 kg P₂O₅/ha or sodium molybdate at 1 ppm Mo along with cyanobacteria and/or urea. Application of phosphate, however, slightly diminished the enhancement by molybdate.The author is with the Sakha Agricultural Research Station, Kafr El-Sheikh, Egypt.     

ORGANIZATION OF THE nif GENES OF THE NONHETEROCYSTOUS CYANOBACTERIUM TRICHODESMIUM SP. IMS101

An approximately 16-kb fragment of the Trichodesmium sp. IMS101 (a nonheterocystous filamentous cyanobacterium) "conventional" nif gene cluster was cloned and sequenced. The gene organization of the Trichodesmium and Anabaena variabilis vegetative ( nif 2 ) nitrogenase gene clusters spanning the region from nif B to nif W are similar except for the absence of two open reading frames (ORF3 and ORF1) in Trichodesmium . The Trichodesmium nif EN genes encode a fused Nif EN polypeptide that does not appear to be processed into individual Nif E and Nif N polypeptides. Fused nif  EN genes were previously found in the A. variabilis nif 2 genes, but we have found that fused nif EN genes are widespread in the nonheterocystous cyanobacteria. Although the gene organization of the nonheterocystous filamentous Trichodesmium nif gene cluster is very similar to that of the A. variabilis vegetative nif 2 gene cluster, phylogenetic analysis of nif sequences do not support close relatedness of Trichodesmium and A. variabilis vegetative ( nif 2 ) nitrogenase genes.     

Effect of zinc,phosphorus and nitrogen on tryptophan concentration in rice grains grown on limed and unlimed soils

Summary The effects of Zn, P, N and CaCO₃ on tryptophan concentration in rice grain were studied in greenhouse at Haryana Agricultural University. Zinc application upto 20 ppm increased tryptophan concentration in rice grain. Zn-EDTA gave highest increase followed by ZnSO₄ and then ZnO. Liming at the rate of 4 and 8 per cent decreased tryptophan concentration significantly. Phosphorus application upto 100 ppm also decreased tryptophan significantly but Zn in combination with P increased tryptophan and overcame negative effect of P. Nitrogen application upto 120 ppm increased tryptophan concentration. There was positive interaction between Zn and N. Ammonium sulphate gave highest tryptophan followed by ammonium nitrate and then urea. The tryptophan concentration ranged between 766 ppm and 2011 ppm in paddy grain. The lowest tryptophan concentration was in the plants treated with 8 per cent lime in absence of added Zn and highest with 10 ppm Zn through Zn-EDTA. Department of Soils.     

秸秆还田与氮肥施用对稻田温室气体排放的影响

秸秆还田与氮肥施用是农田生态系统中碳氮元素的两大主要补给途径,其在调控稻田甲烷(CH₄)和氧化亚氮(N₂O)排放以及水稻产量方面具有重要作用。以往的研究主要关注秸秆还田或氮肥施用单因素对稻田温室气体排放的影响,而双因素互作对甲烷和氧化亚氮排放的影响尚未明确。同时,在秸秆还田条件下如何进行合理的氮肥施用鲜有深入研究。本研究基于3个氮肥处理(0、180、360 kg N/hm²)和3个秸秆还田处理(0、2.25、3.75 t/hm²)进行多年水稻田间定位试验,研究结果表明:CH₄季节累积排放随秸秆还田量增加而增加,与施氮量无显著正相关关系;N₂O季节累积排放随施氮量增加而增加,与秸秆还田量无显著正相关关系;秸秆还田对于产量的影响具有不确定性,两年均在秸秆不还田+不施氮处理(S0N0)出现最低产量,2021与2022年最低产量分别为5740.64和4903.75 kg/hm²。2021与2022年最高产量分别在秸秆不还田+高氮(S0N2)和高量秸秆还田+高氮(S2N2)出现,分别为10938.48和10384.83 kg/hm²。同时,本研究发现在低量秸秆还田条件下,在碳足迹(CF, Carbon Footprint)方面,施氮量为251 kg N/hm²时碳足迹达到最低点,为1.01 kg C/kg;而在生态经济净收益(NEEB, Net Ecosystem Economic Benefits)方面,施氮量为294 kg N/hm²时生态经济净收益达到最高点,为11778.15 元/hm²。为协同生态经济净收益与碳排放,在低量秸秆还田(S1)下,配合251-294 kg N/hm²的施氮量为最优施肥方案。研究结果为指导稻田温室气体减排、实现稻田碳中和以及农田管理提供了理论支撑,为实现水稻的高产稳产与低碳生产科学依据。     

Regulation of nitrogenase levels in Anabaena sp. ATCC 33047 and other filamentous cyanobacteria

Incubation in the dark of photoautotrophically grown N₂-fixing heterocystous cyanobacteria leads to a loss of nitrogenase activity. Original levels of nitrogenase activity are rapidly regained upon re-illumination of the filaments, in a process dependent on de novo protein synthesis. Ammonia, acting indirectly through some of its metabolic derivatives, inhibits the light-promoted development of nitrogenase activity in filaments of Anabaena sp. ATCC 33047 and several other cyanobacteria containing mature heterocysts. The ammonia-mediated control system is also operative in N₂-fixing filaments in the absence of any added source of combined nitrogen, with the ammonia resulting from N₂-fixation already partially inhibiting full expression of nitrogenase. High nitrogenase levels, about two-fold higher than those in normal N₂-fixing Anabaena sp. ATCC 33047, are found in cell suspensions which have been treated with the glutamine synthetase inhibitor l-methionine-d,l-sulfoximine or subjected to nitrogen starvation. Filaments treated in either way are insensitive to the ammonia-promoted inhibition of nitrogenase development, although this insensitivity is only transitory for the nitrogen-starved filaments, which become ammonia-sensitive once they regain their normal nitrogen status.Abbreviations Chl chlorophyll - EDTA ethylenediaminetetraacetic acid - MSX l-methionine-d,l-sulfoximine     

Farmland treatment and utilization of straw pulp mill effluents

Straw pulp production accounts for 74% of the total raw pulp production in China. The pulping waste, containing high contents of silicate and high pH, is difficult to treat. Instead of the conventional alkaline process, ammonia sulfite pulping discharges neutral effluent with nitrogen, phosphorus, potassium, sulfur and organic matter which are potential fertilizers and water resources for agriculture. The effect of effluent from ammonia sulfite pulping on rice growth and yield, was studied in Baigezhuang farm, Hebei province. Diluted rice straw digester waste or composite waste were irrigated on a paddy field. In plot tests, rice output increased by 16.2–25.3% with 0.7–6% pulp digester waste and by 22.9–37.9% with 2.7–5.4% composite waste. In field tests, rice output increased by 8.6–15.9% with 2.7–4.1% composite waste. Due to clean water dilution and paddy purification, the removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solid (SS), sulfide and phenol can reach over 97%. Rice quality also tested had higher protein content than the control. The study suggests that the effluents from ammonia sulfite pulping can be widely used in the farming industry. The ammonia sulfite process is a good approach to overcome pulp pollution in rural areas.     

Methane emission from paddy soils as affected by wheat straw returning mode

To study influence of wheat straw returning mode on CH₄ emission from paddy soils, a field experiment was conducted at Jurong, Jiangsu Province, China in 2006. Five treatments, no wheat straw applied (CK), wheat straw evenly incorporated into the topsoil (WI), wheat straw buried in ditches (WD), wheat straw strip-mulched onto the field surface (WM) and wheat straw burned in-situ (WB), were laid out in a randomized block design. Results showed that seasonal CH₄ emissions ranged from 6.9 to 28.1 g CH₄ m^?2. Wheat straw incorporation significantly increased CH₄ emission. No significant difference was observed between Treatments WI and WD in total CH₄ emission. Compared with Treatment WI, Treatment WM reduced total CH₄ emission by 32% and Treatment WB by 42%. Treatment WM was about 27% higher than Treatment CK in grain yield. Based on the findings, the best management of wheat straw prior to rice cultivation is strip-mulching wheat straw onto the field surface, which largely reduced CH₄ emission from rice fields with no decrease in rice yield.     

The optimized CO2-added ammonia explosion pretreatment for bioethanol production from rice straw

A CO₂-added ammonia explosion pretreatment was performed for bioethanol production from rice straw. The pretreatment conditions, such as ammonia concentration, CO₂ loading level, residence time, and temperature were optimized using response surface methodology. The response for optimization was defined as the glucose conversion rate. The optimized pretreatment conditions resulting in maximal glucose yield (93.6 %) were determined as 14.3 % of ammonia concentration, 2.2 MPa of CO₂ loading level, 165.1 °C of temperature, and 69.8 min of residence time. Scanning electron microscopy analysis showed that pretreatment of rice straw strongly increased the surface area and pore size, thus increasing enzymatic accessibility for enzymatic saccharification. Finally, an ethanol yield of 97 % was achieved via simultaneous saccharification and fermentation. Thus, the present study suggests that CO₂-added ammonia pretreatment is an appropriate process for bioethanol production from rice straw.     

Analogue-resistant mutants of Azotobacter chroococcum derepressed for nitrogenase activity and early ammonia excretion having potential as inoculants for cereal crops

Spontaneous mutants resistant to methionine sulfoximine (Msx), methyl alanine (Mal) and methyl ammonium chloride (Mac) were derived from A. chroococcum strain A103. Msx and Mal-resistant mutants expressed 1.73 to 10.98% of the fully derepressed nitrogenase activity when grown in Burk's medium containing ammonium acetate. Mac-resistant mutants did not express nitrogenase activity in ammonium acetate supplemented medium. The mutants excreted ammonia even after 2 days of growth and some mutants excreted more ammonia as compared to the parent. Selected mutants were inoculated on wheat (Triticum aestivum) and barley (Hordeum vulgare) under field conditions. Majority of the derepressed mutants increased grain yield of wheat and barley varying from 1.2 to 33.3%. However, host-dependent effects on grain yield were observed with different mutants. Two mutants, Mal 27 and Mac 19 showed significant increase in grain yields of both the crops. The results suggest that metabolic analogue-resistant mutants of Azotobacter have potential for use as a biofertilizer for cereal crops.