Rice-field Cyanobacterium Research Articles

Distribution of nitrogen-fixing cyanobacteria (Nostocaceae) during rice cultivation in fertilized and unfertilized paddy fields

This study describes the development of nitrogen-fixing cyanobacteria (Nostocaceae) during different stages of rice seedlings plantation in fertilized and unfertilized paddy fields in north Bihar, India. A heterogeneous population of cyanobacteria was randomly harvested around day 20, 40 and 60 of rice seedlings plantation, and the diversity was analyzed. Thirtytwo species (7 genera) were identified from unfertilized fields, of which Anabaena was represented by 12 species, Anabaenopsis and Aulosira by 3 each, Cylindrospermum by 4, Nostoc by 8 and Aphanizomenon and Nodularia by 1 species each. However, fertilized fields contained only 25 species (7 genera), of which 8 each belonged to Nostoc and Anabaena, 3 to Cylindrospermum, 2 to each Anabaenopsis and Aulosira and 1 to each Aphanizomenon and Nodularia. Although Nostoc and Anabaena were dominant in both fertilized and unfertilized paddy fields, a marked decrease in nitrogen-fixing cyanobacteria was recorded from fertilized fields. In both treatments, the diversity of nitrogen-fixing cyanobacteria was at a maximum around day 60 after seedling plantation. The current study concludes that there is a negative effect of nitrogenous fertilizers on the development of heterocystous cyanobacteria in rice fields. It is proposed that early appearing efficient nitrogen-fixers should be used as nitrogen fertilizers in the management for better establishment and exploitation of heterocystous cyanobacteria for sustainable agricultural practices.

Molecular characterization and the effect of salinity on cyanobacterial diversity in the rice fields of Eastern Uttar Pradesh, India

BackgroundSalinity is known to affect almost half of the world's irrigated lands, especially rice fields. Furthermore, cyanobacteria, one of the critical inhabitants of rice fields have been characterized at molecular level from many different geographical locations. This study, for the first time, has examined the molecular diversity of cyanobacteria inhabiting Indian rice fields which experience various levels of salinity.ResultsTen physicochemical parameters were analyzed for samples collected from twenty experimental sites. Electrical conductivity data were used to classify the soils and to investigate relationship between soil salinity and cyanobacterial diversity. The cyanobacterial communities were analyzed using semi-nested 16S rRNA gene PCR and denaturing gradient gel electrophoresis. Out of 51 DGGE bands selected for sequencing only 31 which showed difference in sequences were subjected to further analysis. BLAST analysis revealed highest similarity for twenty nine of the sequences with cyanobacteria, and the other two to plant plastids. Clusters obtained based on morphological and molecular attributes of cyanobacteria were correlated to soil salinity. Among six different clades, clades 1, 2, 4 and 6 contained cyanobacteria inhabiting normal or low saline (having EC < 4.0 ds m-1) to (high) saline soils (having EC > 4.0 ds m-1), however, clade 5 represented the cyanobacteria inhabiting only saline soils. Whilst, clade 3 contained cyanobacteria from normal soils. The presence of DGGE band corresponding to Aulosira strains were present in large number of soil indicating its wide distribution over a range of salinities, as were Nostoc, Anabaena, and Hapalosiphon although to a lesser extent in the sites studied.ConclusionLow salinity favored the presence of heterocystous cyanobacteria, while very high salinity mainly supported the growth of non-heterocystous genera. High nitrogen content in the low salt soils is proposed to be a result of reduced ammonia volatilization compared to the high salt soils. Although many environmental factors could potentially determine the microbial community present in these multidimensional ecosystems, changes in the diversity of cyanobacteria in rice fields was correlated to salinity.

Comparative toxicity of bentazon and molinate on growth, photosynthetic pigments, photosynthesis, and respiration of the Portuguese ricefield cyanobacterium Nostoc muscorum

Bentazon and molinate are selective herbicides recommended for integrated weed management in rice. Their toxicity on growth and some biochemical and physiological parameters of Nostoc muscorum, an abundant cyanobacterium in Portuguese rice fields, was evaluated under laboratory conditions during time- and concentration-dependent exposure for 72 h. Results showed that toxic concentrations (0.75-2 mM) of both herbicides have pleiotropic effects on the cyanobacterium. Molinate was more toxic than bentazon to growth, respiration, chlorophyll-a, carotenoids, and phycobiliproteins contents. Protein content was increased by both herbicides although the effect was particularly evident with higher concentrations of molinate (1.5-2 mM). The herbicides had contrasting effects on carbohydrates content: molinate increased this organic fraction whereas bentazon decreased it. Photosynthesis and respiration were inhibited by both herbicides.

Mycosporine-like amino acids (MAAs) profile of a rice-field cyanobacterium Anabaena doliolum as influenced by PAR and UVR

The mycosporine-like amino acid (MAA) profile of a rice-field cyanobacterium, Anabaena doliolum, was studied under PAR and PAR + UVR conditions. The high-performance liquid chromatographic analysis of water-soluble compounds reveals the biosynthesis of three MAAs, mycosporine-glycine (lambda (max) = 310 nm), porphyra-334 (lambda (max) = 334 nm) and shinorine (lambda (max) = 334 nm), with retention times of 4.1, 3.5 and 2.3 min, respectively. This is the first report for the occurrence of mycosporine-glycine and porphyra-334 in addition to shinorine in Anabaena strains studied so far. The results indicate that mycosporine-glycine (monosubstituted) acts as a precursor for the biosynthesis of the bisubstituted MAAs shinorine and porphyra-334. Mycosporine-glycine was under constitutive control while porphyra-334 and shinorine were induced by UV-B radiation, indicating the involvement of UV-regulated enzymes in the biotransformation of MAAs. It seems that A. doliolum is able to protect its cell machinery from UVR by synthesizing a complex set of MAAs and thus is able to survive successfully during the summer in its natural brightly lit habitats.

Differential sensitivity of five cyanobacterial strains to ammonium toxicity and its inhibitory mechanism on the photosynthesis of rice-field cyanobacterium Ge–Xian–Mi ( Nostoc)

Effects of two fertilizers, NH 4Cl and KCl, on the growth of the edible cyanobacterium Ge–Xian–Mi ( Nostoc) and four other cyanobacterial strains were compared at pH 8.3 ± 0.2 and 25 °C. Their growth was decreased by at least 65% at 10 mmol L −1 NH 4Cl but no inhibitory effect was observed at the same level of KCl. Meanwhile, the strains exhibited a great variation of sensitivity to NH 4 + toxicity in the order: Ge–Xian–Mi > Anabaena azotica FACHB 118 > Microcystis aeruginosa FACHB 905 > M. aeruginosa FACHB 315 > Synechococcus FACHB 805. The 96-h EC 50 value for relative growth rate with regard to NH 4 + for Ge–Xian–Mi was 1.105 mmol L −1, which was much less than the NH 4 + concentration in many agricultural soils (2–20 mmol L −1). This indicated that the use of ammonium as nitrogen fertilizer was responsible for the reduced resource of Ge–Xian–Mi in the paddy field. After 96 h exposure to 1 mmol L −1 NH 4Cl, the photosynthetic rate, F v/ F m value, saturating irradiance for photosynthesis and PSII activity of Ge–Xian–Mi colonies were remarkably decreased. The chlorophyll synthesis of Ge–Xian–Mi was more sensitive to NH 4 + toxicity than phycobiliproteins. Thus, the functional absorption cross section of Ge–Xian–Mi PSII was increased markedly at NH 4Cl levels ≥1 mmol L −1 and the electron transport on the acceptor side of PSII was significantly accelerated by NH 4Cl addition ≥3 mmol L −1. Dark respiration of Ge–Xian–Mi was significantly increased by 246% and 384% at 5 and 10 mmol L −1 NH 4Cl, respectively. The rapid fluorescence rise kinetics indicated that the oxygen-evolving complex of PSII was the inhibitory site of NH 4 +.

Effects of intense PAR and UV radiation on photosynthesis, growth and pigmentation in the rice-field cyanobacterium Anabaena sp.

The relative importance of photosynthetically active radiation and UV on photoinhibition has been studied in the cyanobacterium Anabaena sp. by measuring the effective quantum yield, growth, pigmentation and fluorescence emission.

Wavelength-dependent induction of a mycosporine-like amino acid in a rice-field cyanobacterium, Nostoc commune: role of inhibitors and salt stress.

Wavelength-dependent induction of a mycosporine-like amino acid (MAA) was studied in a nitrogen-fixing rice-field cyanobacterium, Nostoc commune. HPLC studies showed the presence of shinorine, a bisubstituted MAA containing both glycine and serine groups and having an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665; all Schott filter series) clearly indicated that MAAs were induced by UV-B radiation, while UV-A and PAR had very little effect on MAA induction in this organism. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the derived action spectrum also revealed the induction of MAAs to be UV-B dependent with a prominent peak at 290 nm and a second small peak at 310 nm. Various concentrations (50-300 mM) of NaCl were used to test whether another common stress factor, such as osmotic stress, also induces MAAs, as has been reported for other cyanobacterial species. The results indicate that cells grown at high concentration of NaCl but without UV-B did not show any MAA induction. In order to elucidate the possible photoreceptors, the effects of various inhibitors/quenchers on the induction of MAAs were studied. There was a marked reduction in the amount of MAA when the cells were irradiated with UV-B in the presence of inhibitors of the shikimate pathway (glyphosate, 1 mM), photosynthesis [3-(3,4-dichlorophenyl)-1,1-dimethylurea, 20 microM], protein synthesis (chloramphenicol, 25 microg ml(-1)), pterin synthesis (N-acetylserotonin, 5 mM, and 2,4-diamino-6-hydroxypyrimidine, 5 mM) and a quencher of the excited state of flavins and pterins (phenylacetic acid, 1 mM).

Polychromatic action spectrum for the induction of a mycosporine-like amino acid in a rice-field cyanobacterium, Anabaena sp.

A polychromatic action spectrum for the induction of an ultraviolet-absorbing/screening mycosporine-like amino acid (MAA) has been determined in a filamentous and heterocystous nitrogen-fixing rice-field cyanobacterium, Anabaena sp. High-performance liquid chromatographic (HPLC) studies revealed the presence of only one type of MAA, which was identified as shinorine, a bisubstituted MAA containing both glycine and serine groups having a retention time at 2.8 min and an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665 and a broad-band filter, UG 11) clearly revealed that the induction of the MAA takes place only in the UV range. Photosynthetic active radiation (PAR) had no significant impact on MAA induction. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the action spectrum also showed the induction of MAA to be UV dependent peaking in the UV-B range at around 290 nm. The results indicate that the studied cyanobacterium, Anabaena sp. may protect itself from deleterious short wavelength solar radiation by its ability to synthesize a mycosporine-like amino acid in response to UV-B radiation and thereby screen the negative effects of UV-B.

Induction of a mycosporine-like amino acid (MAA) in the rice-field cyanobacterium Anabaena sp. by UV irradiation

An ultraviolet-absorbing mycosporine-like amino acid (MAA) has been detected in a filamentous and heterocystous cyanobacterium, Anabaena sp., isolated from a rice paddy field near Varanasi, India. The MAA is isolated and purified by high-performance liquid chromatography. Only one MAA is detected with a retention time of around 2.8 min and an absorption maximum at 334 nm. The MAA is identified as shinorine, a bisubstituted MAA containing both glycine and serine groups. There is an increase in the amount of MAA when the cultures are exposed to photosynthetically active radiation and ultraviolet radiation (PAR+UV) in comparison with the cultures exposed to PAR only. This shows that UV stress induces the synthesis of MAA in this cyanobacterium and thus may protect the organism against deleterious high solar radiation, particularly during summer seasons in the tropics.

Effects of ultravjolet-B radiation in three rice field cyanobacteria

Summary The effects of artificial ultraviolet-B (UV-B; 280-315 nm; 2.5 Wm −2 ) radiation on survival, growth, pigmentation, and total protein profile have been studied in three cyanobacterial strains, Nostoc sp., Calothrix pulvinata and Plectonema boryanum , isolated from rice (paddy) fields in India. Differential sensitivity of individual species to UV-B irradiation were recorded in this investigation. P. boryanum failed to survive 180 min of UV-B irradiation, whereas the brown Nostoc sp. and C. pulvinata survived the same duration of irradiation. Growth patterns of the organisms treated with UV-B revealed that Nostoc sp. was comparatively more tolerant than C. pulvinata and P. boryanum . Phycocyanin (K max 620 nm) was severely affected by UV-B irradiation in all strains; the degree of pigment bleaching was most pronounced in P. boryanum followed by C. pulvinata and Nostoc sp. Phycoerythrin(λ max 560 nm) was also bleached considerably in Nostoc sp. and C. pulvinata; P. boryanum does not contain phycoerythrin. There was also a significant drop in the absorption of Chl a after UV-B irradiation in all strains. Fluorescence emission decreased considerably in all organisms with increasing UV-B irradiation time. SDS-PAGE analyses of the total protein profile of the organisms showed a linear decrease in the protein content with increasing UV-B irradiation time. Complete loss of most of the protein bands occurred after UV-B irradiation of 60 min in P. boryanum and 120 min in C. pulvinata , whereas there was only little effect in the brown Nostoc sp. even after 180 min of UV-B irradiation. Phycoerythrin (26 kDa) in Nostoc sp. was less affected by UV-B irradiation than phycocyanin (20 kDa) in P. boryanum .

Effects of UV radiation on the rice field cyanobacterium, Aulosira fertilissima

The effects of UV radiation (5 W m −2) were studied in the cyanobacterium, Aulosira fertilissima. The organism was found to be sensitive to UV-B and, to a lesser extent, UV-A. Absorption spectra showed that the pigment content, particularly phycocyanin, severely decreased following UV exposures; the effect was more pronounced with UV-B than with UV-A. The organism was also very sensitive to solar radiation, and complete bleaching of the cells occurred following exposure of 2–3 hr. The absorption and fluorescence emission spectra of crude pigments after 3 hr of UV-B exposure (5 W m −2) decreased significantly, suggesting the loss of effective energy transfer from the accessory pigments to PS-II. SDS-PAGE analysis of the total protein profile of cells treated with UV-B showed a decrease in the protein content with increasing exposure time. Substantial decrease in the protein bands occurred after 3 hr of UV-B exposure (5 W m −2), particularly of those between 14.2 and 45 kDa.

Response of a rice field cyanobacterium Anabaena sp. to physiological stressors

The impact of physiological factors such as heat, salinity and L-methionine-DL-sulfoximine (MSO) on growth and total protein profile was studied in a rice field cyanobacterium, Anabaena sp. There was a gradual decrease in growth rate of the organism with increase in incubation time at 47°C; by 168 h of incubation there was essentially no growth. NaCl concentration > 5 mM inhibited growth of the organism, and there was apparently no growth at > 200 mM NaCl-supplemented media. Similarly, growth was inhibited with MSO concentration > 5 μM and there was no growth in cultures treated with > 100 μM MSO. SDS-PAGE protein profile after heat stress revealed a decline in the synthesis of several proteins but at the same time, synthesis of a new set of proteins of approximately 60–65 kDa was induced after 12 and 24 h of incubation and the same was completely eliminated after 96 h of incubation. Cultures treated with 10 mM of NaCl did not show any change in the protein pattern. In contrast, 100 mM NaCl treated cultures elicited a number of new proteins at around 29, 32, 40 and 70 kDa. Most of the protein bands disappeared in the cultures treated with 500 mM NaCl. Cultures treated with 10 μM MSO did not show any change in the appearance of the protein bands, whereas the cultures treated with 100 μM MSO showed a drastic decline in the intensity of all protein bands. The results indicate that different stressors exert specific effects on cyanobacterial protein synthesis.

Isolation and Characterization of Partially Derepressed Mutants of Cyanobacterium Aulosira spec.

Summary The chlorate and L-methionine DL-Sulfoximine resistant mutants were isolated in rice field cyanobacterium Aulosira spec. after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. MSX-resistant mutant was partially blocked in the glutamine synthetase (GS) and exhibited 44.1 % GS transferase activity compared to the parent grown on N2. Unlike its parent, the mutant showed nitrogenase activity of 2.19 nmol/µ g chlorophyll a/h when grown in ammonia. The mutant resistant to both chlorate and JISX (ClrR MSXR) was defective in both nitrate reductase and GS. It possessed only 39.4 % GS transferase activity in NZ grown culture and 6.2 % of nitrate reductase activity in nitrate grown culture as compared to the parent. Unlike its parent this mutant exhibited nitrogenase activity of 2.22 and 4.34 nmol/µg chl - a/h when grown in nitrate and ammonia respectively. The maximum of the GS transferase and nitrogenase activities were observed on N2 grown cultures of parent, MSXR and ClrR MSXR mutants whereas minimum level of GS transferase was noticed in glutamine grown culture.

OCCURRENCE OF NITROGEN-FIXING CYANOBACTERIA IN LOCAL RICE FIELDS OF ORISSA, INDIA

Cyanobacterial diversity occurring in some local rice fields of Orissa, India has been studied in two different seasons and influence of pH, organic carbon (%) and conductivity were correlated on their population. At different locations and seasons the pH of the soil varies from 6.30±0.20 to 6.66±0.305. Conductivity and organic carbon (%) varies from 0.6±0.10 to 0.76±0.152 and 0.56±0.045 to 0.70±0.025 respectively. Altogether 58 taxa belonging to 20 genera were obtained and characterized. Out of these 19 forms were heterocystous and 39 were non-heterocystous. Highest abundance of cyanobacteria was found in order Nostocales which was represented by 15 species. Among the species relative abundance of Oscillatoria chalybea (9.90%) was found to be highest followed by Phormidium purpurascens (8.49%), Cylindrospermum muscicola and Oscillatoria chlorina (8.01%). Highest Shannon's diversity index was recorded in sampling site 1, followed by site 2. Comparatively the diversity index was more during winter than in summer in all the study sites. Highest similarity index (0.174) was found in summer-summer isolates of site 1 and 3. Among the environmental variables (i.e., soil pH, organic carbon (%), conductivity) highly positive correlation was observed between cyanobacterial population and soil pH (r ≥ 9) in all the three sampling sites. The study indicates ubiquitous distribution of cyanobacteria in rice fields and could be exploited for biofertilizer in agriculture. Key words: Cyanobacteria; Rice fields; Abundance; Diversity index; Environmental variablesDOI: 10.3126/eco.v17i0.4120EcoprintAn International Journal of EcologyVol. 17, 2010Page: 77-85Uploaded date: 3 January, 2011