Phylogenetic relationships of nonaxenic filamentous cyanobacterial strains based on 16S rRNA sequence analysis

In order to determine the nearly complete 16S rRNA gene sequences of cyanobacteria originating from nonaxenic cultures, a cyanobacterium-specific oligonucleotide probe was developed to distinguish polymerase chain reaction (PCR) products of the cyanobacterial rRNA operons from those resulting from amplification of contaminating bacteria. Using this screening method the 16S rRNA genes of four nonaxenic filamentous cyanobacterial strains belonging to the generaLeptolyngbya andOscillatoria were cloned and sequenced. For the genusLeptolyngbya, the 16S rRNA sequence of the axenic strain PCC 73110 was also determined. Phylogenetic trees were constructed based on complete and partial sequences. The results show that the strainsLeptolyngbya foveolarum Komárek 1964/112,Leptolyngbya sp. VRUC 135 Albertano 1985/1, andLeptolyngbya boryanum PCC 73110 belong to the same cluster. StrainOscillatoria cf.corallinae SAG 8.92, which contains the rare photosynthetic pigment CU-phycoerythrin, is not closely related to other CU-phycoerythrin-containing cyanobacteria.Oscillatoria agardhii CYA 18, which is a representative of planktonicOscillatoria species that form toxic blooms in Norwegian inland waters, has no close relatives in the tree.     

Molecular Fingerprinting of Cyanobacteria from River Biofilms as a Water Quality Monitoring Tool

Benthic cyanobacterial communities from Guadarrama River (Spain) biofilms were examined using temperature gradient gel electrophoresis (TGGE), comparing the results with microscopic analyses of field-fixed samples and the genetic characterization of cultured isolates from the river. Changes in the structure and composition of cyanobacterial communities and their possible association with eutrophication in the river downstream were studied by examining complex TGGE patterns, band extraction, and subsequent sequencing of 16S rRNA gene fragments. Band profiles differed among sampling sites depending on differences in water quality. The results showed that TGGE band richness decreased in a downstream direction, and there was a clear clustering of phylotypes on the basis of their origins from different locations according to their ecological requirements. Multivariate analyses (cluster analysis and canonical correspondence analysis) corroborated these differences. Results were consistent with those obtained from microscopic observations of field-fixed samples. According to the phylogenetic analysis, morphotypes observed in natural samples were the most common phylotypes in the TGGE sequences. These phylotypes were closely related to Chamaesiphon, Aphanocapsa, Pleurocapsa, Cyanobium, Pseudanabaena, Phormidium, and Leptolyngbya. Differences in the populations in response to environmental variables, principally nutrient concentrations (dissolved inorganic nitrogen and soluble reactive phosphorus), were found. Some phylotypes were associated with low nutrient concentrations and high levels of dissolved oxygen, while other phylotypes were associated with eutrophic-hypertrophic conditions. These results support the view that once a community has been characterized and its genetic fingerprint obtained, this technique could be used for the purpose of monitoring rivers.     

Shotgun metagenomics and microscopy indicate diverse cyanophytes,other bacteria,and microeukaryotes in the epimicrobiota of a northern Chilean wetland Nostoc (Cyanobacteria)

Prokaryotic Nostoc, one of the world's most conspicuous and widespread algal genera (similar to eukaryotic algae, plants, and animals) is known to support a microbiome that influences host ecological roles. Past taxonomic characterizations of surface microbiota (epimicrobiota) of free‐living Nostoc sampled from freshwater systems employed 16S rRNA genes, typically amplicons. We compared taxa identified from 16S, 18S, 23S, and 28S rRNA gene sequences filtered from shotgun metagenomic sequence and used microscopy to illuminate epimicrobiota diversity for Nostoc sampled from a wetland in the northern Chilean Altiplano. Phylogenetic analysis and rRNA gene sequence abundance estimates indicated that the host was related to Nostoc punctiforme PCC 73102. Epimicrobiota were inferred to include 18 epicyanobacterial genera or uncultured taxa, six epieukaryotic algal genera, and 66 anoxygenic bacterial genera, all having average genomic coverage ≥90X. The epicyanobacteria Geitlerinemia, Oscillatoria, Phormidium, and an uncultured taxon were detected only by 16S rRNA gene; Gloeobacter and Pseudanabaena were detected using 16S and 23S; and Phormididesmis, Neosynechococcus, Symphothece, Aphanizomenon, Nodularia, Spirulina, Nodosilinea, Synechococcus, Cyanobium, and Anabaena (the latter corroborated by microscopy), plus two uncultured cyanobacterial taxa (JSC12, O77) were detected only by 23S rRNA gene sequences. Three chlamydomonad and two heterotrophic stramenopiles genera were inferred from 18S; the streptophyte green alga Chaetosphaeridium globosum was detected by microscopy and 28S rRNA genes, but not 18S rRNA genes. Overall, >60% of epimicrobial taxa were detected by markers other than 16S rRNA genes. Some algal taxa observed microscopically were not detected from sequence data. Results indicate that multiple taxonomic markers derived from metagenomic sequence data and microscopy increase epimicrobiota detection.     

MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF PLANKTONIC CYANOBACTERIA FROM BELGIUM AND LUXEMBOURG1

For the first time in Belgium and Luxembourg, the diversity and taxonomy of 95 cyanobacterial strains isolated from freshwater blooms were assessed by the comparison of phenotypes and partial 16S rRNA gene sequences. The results showed the high diversity of nanoplanktonic, picoplanktonic, and benthic–periphytic cyanobacteria accompanying the main bloom‐forming taxa. Indeed, besides 15 morphotypes of bloom‐forming taxa, seven non‐bloom‐forming planktonic morphotypes and 11 morphotypes from benthic–periphytic taxa were isolated in culture from the plankton samples of 35 water bodies. The bloom‐forming strains belonged to the genera Microcystis, Woronichinia, Planktothrix, Anabaena, and Aphanizomenon, whereas the other strains isolated from the same samples were assigned to the nanoplanktonic Aphanocapsa, Aphanothece, Snowella, and Pseudanabaena; to the picoplanktonic Cyanobium; and to the benthic–periphytic Geitlerinema, Komvophoron, Leptolyngbya, Lyngbya, Phormidium, Calothrix, Nostoc, and Trichormus. The results supported both the polyphyletism of genera such as Aphanocapsa, Aphanothece, Leptolyngbya, Geitlerinema, Anabaena, and Aphanizomenon as well as the validity of genera such as Microcystis, Planktothrix, and Pseudanabaena with gas vesicles and cells constricted at the cross wall. The results obtained showed the close relationship between Snowella and Woronichinia for which very few sequences exist. The first sequence of Komvophoron appeared poorly related to other available cyanobacterial sequences. Although in a few cases a good agreement existed between phenotypic and genotypic features, there was generally a discrepancy. Strains with identical morphotypes show small differences in the 16S rRNA sequences, which might be related to the different chemical properties of their habitats. The results showed the importance of the polyphasic approach in order to improve the taxonomy of cyanobacteria.     

DNA amplification fingerprinting as a tool for checking genetic purity of strains in the cyanobacterial inoculum

Summary The electrophoretic patterns for 17 different cyanobacterial cultures derived from 6 different decamer primers were analysed to provide diagnostic fingerprints for each culture and their genetic distances based on RAPD markers.The primer OPB 09 produced a maximum of 24 amplified products. The primers OPB 09, OPG 04 and OPAH 02 generated markers specific for Nostoc cultures. Westiellopsis was found to be distinct from other cyanobacterial cultures in the RAPD profile obtained with the primer OPAH 02. The primer OPF 03 generated specific markers for Tolypothrix tenuis. Fischerella cultures could be identified with the primers OPB 09, OPAG 03 and OPF 05. The study revealed that these RAPD markers could be further used to identify and establish the genetic purity of the strains in the cyanobacterial inoculum. There was a similarity of 60–90% within Westiellopsis cultures. Nostoc cultures shared 50–80% similarity with Westiellopsis cultures. Anabaenacultures were similar to Westiellopsiscultures by 60–70. The markers produced for each culture were also applied to phylogenetic analysis to infer genetic relatedness in this group of prokaryotes. The dendrogram analysis clearly revealed that free-living cyanobacterial cultures are closely related to each other and are distinct from the symbiotic forms.     

Genotypic and Phenotypic Diversity of Cyanobacteria in Biological Soil Crusts of the Succulent Karoo and Nama Karoo of Southern Africa

Biological soil crusts (BSCs) are communities of cryptogamic organisms, occurring in arid and semiarid regions all over the world. Based on both morphological identification and genetic analyses, we established a first cyanobacterial inventory using the biphasic approach for BSCs within two major biomes of southern Africa. The samples were collected at two different sites in the Succulent Karoo and one in the Nama Karoo. After cultivation and morphological identification, the 16S rRNA gene was sequenced from the cyanobacterial cultures. From the soil samples, the DNA was extracted, and the 16S rRNA gene sequenced. All the sequences of the clone libraries from soil and cultures were compared with those of the public databases. Forty-five different species were morphologically identified in the samples of the Succulent Karoo (observatories of Soebatsfontein and Goedehoop). Based on the genetic analyses, 60 operational taxonomic units (OTUs) were identified for the Succulent Karoo and 43 for the Nama Karoo (based on 95 % sequence similarity). The cloned sequences corresponded well with the morphologically described taxa in cultures and sequences in the public databases. Besides known species of typical crust-forming cyanobacterial genera (Microcoleus, Phormidium, Tolypothrix and Scytonema), we found sequences of so far undescribed species of the genera Leptolyngbya, Pseudanabaena, Phormidium, Oscillatoria, Schizothrix and Microcoleus. Most OTUs were restricted to distinct sites. Grazed soils showed lower taxa numbers than undisturbed soils, implying the presence of early successional crust types and reduced soil surface protection. Our combined approach of morphological identification and genetic analyses allowed both a taxa inventory and the analysis of species occurring under specific habitat conditions.     

Phylogeny of culturable cyanobacteria from Brazilian mangroves

The cyanobacterial community from Brazilian mangrove ecosystems was examined using a culture-dependent method. Fifty cyanobacterial strains were isolated from soil, water and periphytic samples collected from Cardoso Island and Bertioga mangroves using specific cyanobacterial culture media. Unicellular, homocytous and heterocytous morphotypes were recovered, representing five orders, seven families and eight genera (Synechococcus, Cyanobium, Cyanobacterium, Chlorogloea, Leptolyngbya, Phormidium, Nostoc and Microchaete). All of these novel mangrove strains had their 16S rRNA gene sequenced and BLAST analysis revealed sequence identities ranging from 92.5 to 99.7% when they were compared with other strains available in GenBank. The results showed a high variability of the 16S rRNA gene sequences among the genotypes that was not associated with the morphologies observed. Phylogenetic analyses showed several branches formed exclusively by some of these novel 16S rRNA gene sequences. BLAST and phylogeny analyses allowed for the identification of Nodosilinea and Oxynema strains, genera already known to exhibit poor morphological diacritic traits. In addition, several Nostoc and Leptolyngbya morphotypes of the mangrove strains may represent new generic entities, as they were distantly affiliated with true genera clades. The presence of non-ribosomal peptide synthetase, polyketide synthase, microcystin and saxitoxin genes were detected in 20.5%, 100%, 37.5% and 33.3%, respectively, of the 44 tested isolates. A total of 134 organic extracts obtained from 44 strains were tested against microorganisms, and 26% of the extracts showed some antimicrobial activity. This is the first polyphasic study of cultured cyanobacteria from Brazilian mangrove ecosystems using morphological, genetic and biological approaches.     

The effect of weak auxins on the growth of blue-green algae

Summary 5-Hydroxy indole-3-acetic acid promoted the growth (increase in dry weight) of Anacystis nidulans, Chlorogloea fritschii, Phormidium foveolarum, Nostoc muscorum and Tolypothrix tenuis. 5-Hydroxy tryptamine stimulated the growth of Chlorogloea fritschii and Nostoc muscorum. Phenyl-acetic acid promoted the growth of Nostoc muscorum and Tolypothrix tenuis. Tryptophol stimulated the growth of Chlorogloea fritschii, it failed to stimulate the growth of Nostoc muscorum. Isatin promoted the growth of Anacystis nidulans and Chlorogloea fritschii 2, 3, 5-triidobenzoic acid inhibited the growth of Anacystis nidulans, Chlorogloea fritschii, Phormidium foveolarum, Nostoc muscorum and Tolypothrix tenuis.     

Development of a Universal Microarray Based on the Ligation Detection Reaction and 16S rRNA Gene Polymorphism To Target Diversity of Cyanobacteria

The cyanobacteria are photosynthetic prokaryotes of significant ecological and biotechnological interest, since they strongly contribute to primary production and are a rich source of bioactive compounds. In eutrophic fresh and brackish waters, their mass occurrences (water blooms) are often toxic and constitute a high potential risk for human health. Therefore, rapid and reliable identification of cyanobacterial species in complex environmental samples is important. Here we describe the development and validation of a microarray for the identification of cyanobacteria in aquatic environments. Our approach is based on the use of a ligation detection reaction coupled to a universal array. Probes were designed for detecting 19 cyanobacterial groups including Anabaena/Aphanizomenon, Calothrix, Cylindrospermopsis, Cylindrospermum, Gloeothece, halotolerants, Leptolyngbya, Palau Lyngbya, Microcystis, Nodularia, Nostoc, Planktothrix, Antarctic Phormidium, Prochlorococcus, Spirulina, Synechococcus, Synechocystis, Trichodesmium, and Woronichinia. These groups were identified based on an alignment of over 300 cyanobacterial 16S rRNA sequences. For validation of the microarrays, 95 samples (24 axenic strains from culture collections, 27 isolated strains, and 44 cloned fragments recovered from environmental samples) were tested. The results demonstrated a high discriminative power and sensitivity to 1 fmol of the PCR-amplified 16S rRNA gene. Accurate identification of target strains was also achieved with unbalanced mixes of PCR amplicons from different cyanobacteria and an environmental sample. Our universal array method shows great potential for rapid and reliable identification of cyanobacteria. It can be easily adapted to future development and could thus be applied both in research and environmental monitoring.     

A retained viability index (RVI10) for evaluation of a cyanobacterial powder fertilizer

The preparation of a dry and powder fertilizer based on five nitrogen-fixing cyanobacterial strains is described. Tolypothrix tenuis and Nostoc muscorum resisted the drying and milling processes and showed a suitable recovering capacity in liquid media of different pH and salinity. Although a decrease in the cellular viability was observed with the storage time, the biomass of Nostoc muscorum retained viability for 16 months. The results were evaluated in terms of the retained viability index (RVI₁₀) specifically designed for the fertilizer material.     

Development of a universal microarray based on the ligation detection reaction and 16S rrna gene polymorphism to target diversity of cyanobacteria

The cyanobacteria are photosynthetic prokaryotes of significant ecological and biotechnological interest, since they strongly contribute to primary production and are a rich source of bioactive compounds. In eutrophic fresh and brackish waters, their mass occurrences (water blooms) are often toxic and constitute a high potential risk for human health. Therefore, rapid and reliable identification of cyanobacterial species in complex environmental samples is important. Here we describe the development and validation of a microarray for the identification of cyanobacteria in aquatic environments. Our approach is based on the use of a ligation detection reaction coupled to a universal array. Probes were designed for detecting 19 cyanobacterial groups including Anabaena/Aphanizomenon, Calothrix, Cylindrospermopsis, Cylindrospermum, Gloeothece, halotolerants, Leptolyngbya, Palau Lyngbya, Microcystis, Nodularia, Nostoc, Planktothrix, Antarctic Phormidium, Prochlorococcus, Spirulina, Synechococcus, Synechocystis, Trichodesmium, and Woronichinia. These groups were identified based on an alignment of over 300 cyanobacterial 16S rRNA sequences. For validation of the microarrays, 95 samples (24 axenic strains from culture collections, 27 isolated strains, and 44 cloned fragments recovered from environmental samples) were tested. The results demonstrated a high discriminative power and sensitivity to 1 fmol of the PCR-amplified 16S rRNA gene. Accurate identification of target strains was also achieved with unbalanced mixes of PCR amplicons from different cyanobacteria and an environmental sample. Our universal array method shows great potential for rapid and reliable identification of cyanobacteria. It can be easily adapted to future development and could thus be applied both in research and environmental monitoring.     

Phylogenetic relationships between geographically separate Phormidium cyanobacteria: is there a link between north and south polar regions?

We present a phytogeographical comparison between polar (Arctic and Antarctic) and non-polar strains of the cyanobacterial genus Phormidium, which plays a key role in Arctic and Antarctic ecosystems as primary producer. A total of 26 Phormidium strains were studied using a polyphasic approach, 18 from Arctic (Svalbard, Ellesmere Island and Scandinavian Arctic—Abisko) and Antarctic (Antarctic Peninsula—King George and James Ross Island) regions, and 8 from temperate sites (mostly situated in Central Europe). A phylogenetic tree was constructed and compared with similar 16S rRNA sequences retrieved from Genbank. Within the Phormidium autumnale cluster, genetic similarity of 16S rDNA was more related to geographical proximity of strain origin than to morphological similarity. No genetic identity of Phormidium strains from north and south polar regions was found. The cluster Phormidium autumnale apparently belongs to generic entities in which geographical limitation plays a prominent role. However, the cyanobacterial strains found in Europe suggest that the distribution areas of some Phormidium cyanobacteria overlap. The Phormidium autumnale cluster is evidently a very characteristic type and represents an isolated clade within the traditional genus Phormidium. According to morphological features and the structure of trichomes, it is most similar and thus probably belongs to the genus Microcoleus.     

Studies on the hormonal relationships of algae in pure culture

Summary The effect of potential precursors of Indole-3-acetic acid (IAA) on the growth (increase in dry weight) of Anacystis nidulans, Chlorogloea fritschii, Phormidium foveolarum, Nostoc muscorum and Tolypothrix tenuis have been investigated under as sterile conditions as possible.Tryptamine showed a marked stimulation of growth indicating its possible conversion to IAA. Tryptophan at a hormonal concentration promoted growth in only 1 species, Chlorogloea fritschii. Indole stimulated the growth of Chlorogloea fritschii, Nostoc muscorum and Tolypothrix tenuis. Anthranilic acid promoted the growth of Nostoc muscorum, it failed to stimulate the growth of Chlorogloea fritschii. Anthranilonitrile promoted the growth of Nostoc muscorum and Chlorogloea fritschii. -Alanine promoted the growth of Nostoc muscorum, Tolypothrix tenuis and Chlorogloea fritschii at hormonal concentrations.     

Community phylogenetic analysis of moderately thermophilic cyanobacterial mats from China, the Philippines and Thailand

Most community molecular studies of thermophilic cyanobacterial mats to date have focused on Synechococcus occurring at temperatures of ~50–65°C. These reveal that molecular diversity exceeds that indicated by morphology, and that phylogeographic lineages exist. The moderately thermophilic and generally filamentous cyanobacterial mat communities occurring at lower temperatures have not previously been investigated at the community molecular level. Here we report community diversity in mats of 42–53°C recovered from previously unstudied geothermal locations. Separation of 16S rRNA gene-defined genotypes from community DNA was achieved by DGGE. Genotypic diversity was greater than morphotype diversity in all mats sampled, although genotypes generally corresponded to observed morphotypes. Thirty-six sequences were recovered from DGGE bands. Phylogenetic analyses revealed these to form novel thermophilic lineages distinct from their mesophilic counterparts, within Calothrix, Cyanothece, Fischerella, Phormidium, Pleurocapsa, Oscillatoria and Synechococcus. Where filamentous cyanobacterial sequences belonging to the same genus were recovered from the same site, these were generally closely affiliated. Location-specific sequences were observed for some genotypes recovered from geochemically similar yet spatially separated sites, thus providing evidence for phylogeographic lineages that evolve in isolation. Other genotypes were more closely affiliated to geographically remote counterparts from similar habitats suggesting that adaptation to certain niches is also important.     

Blue-green algae in the sediment of the Lake Brielse Meer

Summary It was demonstrated that the blue-green algaeAphanizomenon flosaquae, Microcystis aeruginosa, Oscillatoria agardhii andO. tenuis are present throughout the year in the sediment of an eutrophic dutch lake.Anabaena flos-aquae does not have a benthic phase.     

Lysis of Aphanizomenon flos-aquae (Cyanobacterium) by a bacterium Bacillus cereus

A phytoplankton-lytic (PL) bacterium, Bacillus cereus, capable of lysing the bloom-forming cyanobacterium Aphanizomenon flos-aquae was isolated from Lake Dianchi of Yunnan province, China. This bacterium showed lytic activities against a wide range of cyanobacteria/algae, including A. flos-aquae, Microcystis viridis, Microcystis wesenbergi, Microcystis aeruginosa, Chlorella ellipsoidea, Oscillatoria tenuis, Nostoc punctiforme, Anabaena flos-aquae, Spirulina maxima, and Selenastrum capricornutum. Chlorophyll a contents, phycocyanin contents, and photosynthetic activities of the A. flos-aquae decreased evidently in an infected culture for a period. Bacterium B. cereus attacked rapidly A. flos-aquae cells by cell-to-cell contact mechanism. It was shown that the lysis of A. flos-aquae began with the breach of the cyanobacterial cell wall, and the cyanobacterial cell appeared abnormal in the presence of the PL bacterium. Moreover, transmission electron microscope examinations revealed that a close contact between the bacterium and the cyanobacterium was necessary for lysis. Some slime extrusions produced from B. cereus assisted the bacterial cells to be in close association with and lyse the cyanobacterial cells. These findings suggested that this bacterium could play an important role in controlling the Aphanizomenon blooms in freshwaters.     

Limnology and cyanobacterial diversity of high altitude lakes of Lahaul-Spiti in Himachal Pradesh,India

Limnological data of four high altitude lakes from the cold desert region of Himachal Pradesh, India, has been correlated with cyanobacterial diversity. Physico-chemical characteristics and nutrient contents of the studied lakes revealed that Sissu Lake is mesotrophic while Chandra Tal, Suraj Tal and Deepak Tal are ultra-oligotrophic. Based on morphology and 16S rRNA gene sequence, a total of 20 cyanobacterial species belonging to 11 genera were identified. Canonical correspondence analysis distinguished three groups of species with respect to their occurrence and nutrient/physical environment demand. The first group, which included Nostoc linckia, N. punctiforme, Nodularia sphaerocarpa, Geitlerinema acutissimum, Limnothrix redekii, Planktothrix agardhii and Plank. clathrata, was characteristic of water with high nutrient content and high temperature. The second group, including Gloeocapsopsis pleurocapsoides, Leptolyngbya antarctica, L. frigida, Pseudanabaena frigida and N. spongiaeforme, occurred in oligotrophic water with high pH and low temperature. The distribution of third group of Cyanobium parvum, Synechocystis pevalekii, L. benthonica, L. foveolarum, L. lurida, L. valderiana, Phormidium autumnale and P. chalybeum could not be associated with a particular environmental condition because of their presence in all sampling sites.     

Plankton variations in Lake Cote,Costa Rica,from 2002 to 2018

Long-term plankton studies in neotropical lakes are scarce. Here we studied plankton composition in Lake Cote, Costa Rica, twice per year from 2002 to 2018, to monitor changes after it was modified as a reservoir for hydroelectricity in 2003. Plankton variation was examined for a long-term trend and its relationship with basic limnological characteristics of the lake. Phytoplankton was sampled from the surface and with a depth-integrating sampler. Zooplankton was caught with vertical hauls, at the same station at the middle of the lake. A total of 138 taxa of microalgae occurred, most from Chlorophyta and Cyanobacteria, to which dominant species belonged; Aulacoseira granulata was also ubiquitous. A shift in dominance occurred, from Cosmarium asphaerosporum to Aphanothece cf. microscopica, and Aphanocapsa cf. delicatissima. Zooplankton included 23 species of Cladocera, Copepoda, Rotifera, and Chaoborus. Most abundant were Keratella americana, Eubosmina tubicen, and Cyclopoida; Daphnia laevis became abundant after 2007 while E. tubicen declined. There was little correspondence between both planktonic components. Plankton composition was typical of a mesotrophic to eutrophic shallow lake, but changes indicated an increase in stratification, and can be attributed to combined effects of recent warming and outflow management for hydropower production.

     

Freshwater Cladocera (Crustacea, Branchiopoda) in Lake Tonle Sap and its adjacent waters in Cambodia

Sixty species of freshwater Cladocera (Crustacea, Branchiopoda) are recorded from Lake Tonle Sap and its adjacent waters, Cambodia. Four species, Ceriodaphnia laticaudata, Bunops cf. tuberculatus, Leydigia australis, and Chydorus cf. dentifer are newly recorded from Southeast Asia, and occurrence of Macrothrix pholpunthini is secondary confirmed in the world. The present cladoceran fauna is characterized by having rich epiphytic and benthic forms. It can be associated with the shallow and vegetation-rich habitats of the study sites.     

Growth and survival potentials of immobilized diazotrophic cyanobacterial isolates exposed to common ricefield herbicides

Summary The effect of graded concentrations of four common ricefield herbicides (Arozin, Butachlor, Alachlor, 2,4-D) on diazotrophic growth, macromolecular contents, heterocyst frequency and tolerance potentials of Ca-alginate immobilized diazotrophic cyanobacterial isolates Nostoc punctiforme, N. calcicola, Anabaena variabilis, Gloeocapsasp., Aphanocapsa sp. and laboratory strain N. muscorum ISU (Anabaena ATCC 27893) was studied and compared with free-living cultures. Cyanobacterial isolates showed progressive inhibition of growth with increasing dosage of herbicides in both free and immobilized states. There were significant differences in the relative toxicity of the four herbicides. Arozin proved to be more growth toxic in comparison to Alachlor, Butachlor and 2,4-D. Growth performance of the immobilized cyanobacterial isolates under herbicide stress showed a similar diazotrophic growth pattern to free cells with no difference in lethal and sub-lethal dosages. However, at lethal concentrations of herbicides, the immobilized cells exhibited prolonged survivability of 14–16 days as compared to their free-living counterparts (8–12 days). The decline in growth, macromolecular contents and heterocyst frequency was found to be similar in both the states in graded dosages of herbicides. Of the test organisms, A. variabilis showed maximum natural tolerance towards all the four herbicides tested. Evidently immobilization by Ca-alginate seems to provide protection to the diazotrophic cyanobacterial inoculants to a certain extent against the growth-toxic action of herbicides.