Colonial Strains Research Articles

Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria Microcystis aeruginosa.

In the context of global change and enhanced toxic cyanobacterial blooms, cyanobacterial transfer to estuaries islikely to increase in frequency and intensity and impact animal and human health. Therefore, it is important to evaluate the potential of their survival in estuaries. In particular, we tested if the colonial form generally observed in natural blooms enhanced the resistance to salinity shock compared to the unicellular form generally observed in isolated strains. We tested the impact of salinity on two colonial strains of Microcystis aeruginosa, producing different amounts of mucilage by combining classical batch methods witha novel microplate approach. We demonstrate that the collective organization of these pluricellular colonies improves their ability to cope with osmotic shock when compared to unicellular strains. The effect of a sudden high salinity increase (S ≥ 20) over 5 to 6 days had several impacts on the morphology of M. aeruginosa colonies. For both strains, we observed a gradual increase in colony size and a gradual decrease in intercellular spacing. For one strain, we also observed a decrease in cell diameter with an increase in mucilage extent. The pluricellular colonies formed by both strains could withstand higher salinities than unicellular strains studied previously. In particular, the strain producing more mucilage displayed a sustained autofluorescence even at S = 20, a limit that is higher than the most robust unicellular strain. These results imply survival and possible M. aeruginosa proliferation in mesohaline estuaries.

Influence of N ∶P ratio on the phosphorus accumulation and distribution of <i>Microcystis</i> and <i>Scenedesmus</i>

太湖水体氮浓度及氮磷比的改变可能影响藻类对磷元素的赋存及分配，进而影响水体总磷浓度. 为此，本研究选取常见蓝藻(群体微囊藻和单细胞微囊藻)和绿藻(斜生栅藻)，设置低氮磷比(N ∶P=2)和高氮磷比(N ∶P=20)培养实验，分析藻体胞内磷(INT-P)和胞外磷(EPS-P)含量、形态及分布，探究氮磷比对藻体磷元素赋存及分配的影响. 结果表明：低氮磷比组斜生栅藻和群体微囊藻的藻体磷(CTP，即INT-P与EPS-P之和)显著增加，分别为高氮磷比组的2.7和1.4倍. 斜生栅藻和群体微囊藻EPS-P含量(约占CTP的80%)分别增加了3.1和0.48倍，而INT-P含量对氮磷比无明显响应. 低氮磷比组的斜生栅藻和群体微囊藻EPS含量分别增加了51.7% 和63.5%. 此外，微囊藻的CTP与EPS-P主要以可交换态活性磷存在，而INT-P主要以铁铝结合态磷存在. 本研究发现低氮磷比促进了藻类EPS分泌，导致EPS-P升高，显著增加了藻体颗粒态磷的含量. 这或许是近年来太湖水体总磷波动的原因之一.;Variations of nitrogen (N) concentration and the ratio of N to phosphorus (P) in Lake Taihu may impact P accumulation and allocation of algal cells, and even influence total P concentration in water. In this study, common cyanobacteria (colonial and unicellular Microcystis strains) and a green alga (Scenedesmus obliquus) were cultured in different N ∶P groups (N ∶P=2 and N ∶P=20). Changes in their P forms, content, and distribution (intracellular P (INT-P) and extracellular P (EPS-P)) were explored. Results showed that the total cellular P contents (CTP, including INT-P and EPS-P) of S. obliquus and colonial Microcystis in the low N ∶P group were 2.7 and 1.4 times higher than those in the high N ∶P group, respectively. In the low N ∶P group, EPS-P occupied about 80% of the CTP. Particularly, EPS-P contents of the low-N ∶P treated S. obliquus and colonial Microcystis increased by 3.1 and 0.48 times higher than those of the high N ∶P group. In the low N ∶P groups, EPS content of S. obliquus and colonial Microcystis increased by 51.7% and 63.5%, respectively. However, changes of INT-P were not significant in both species. Moreover, CTP and EPS-P mainly existed as NH₄Cl-P, while INT-P was mainly found as Fe/Al-P. These findings revealed that low N ∶P ratio affects the P accumulation and distribution patterns of algal cells, by promoting EPS secretion and EPS-P accumulation. It may be a potential reason for total P fluctuation in the water of Lake Taihu.

Role of diversity-generating retroelements for regulatory pathway tuning in cyanobacteria

BackgroundCyanobacteria maintain extensive repertoires of regulatory genes that are vital for adaptation to environmental stress. Some cyanobacterial genomes have been noted to encode diversity-generating retroelements (DGRs), which promote protein hypervariation through localized retrohoming and codon rewriting in target genes. Past research has shown DGRs to mainly diversify proteins involved in cell-cell attachment or viral-host attachment within viral, bacterial, and archaeal lineages. However, these elements may be critical in driving variation for proteins involved in other core cellular processes.ResultsMembers of 31 cyanobacterial genera encode at least one DGR, and together, their retroelements form a monophyletic clade of closely-related reverse transcriptases. This class of retroelements diversifies target proteins with unique domain architectures: modular ligand-binding domains often paired with a second domain that is linked to signal response or regulation. Comparative analysis indicates recent intragenomic duplication of DGR targets as paralogs, but also apparent intergenomic exchange of DGR components. The prevalence of DGRs and the paralogs of their targets is disproportionately high among colonial and filamentous strains of cyanobacteria.ConclusionWe find that colonial and filamentous cyanobacteria have recruited DGRs to optimize a ligand-binding module for apparent function in signal response or regulation. These represent a unique class of hypervariable proteins, which might offer cyanobacteria a form of plasticity to adapt to environmental stress. This analysis supports the hypothesis that DGR-driven mutation modulates signaling and regulatory networks in cyanobacteria, suggestive of a new framework for the utility of localized genetic hypervariation.

Cell wall surface layer (S-layer) promotes colony formation in Microcystis: comparison of S-layer characteristics between colonial and unicellular forms of Microcystis and function conformation.

Colony is a key to Microcystis becoming a dominant population and forming blooms. To find the mechanism of colony formation, we investigated cell wall structures of colonial and unicellular strains. Results showed that colonial strains had significant surface layer protein (S-layer) on the surface of cells than unicellular strains by transmission electron microscopy. Western blot showed colonial strains had more S-layer than the unicellular strains. When the S-layer gene (GenBank accession number CAO89090.1) of Microcystis aeruginosa PCC7806 was expressed in Synechocystis sp. PCC6803, PCC6803 aggregated into colonial morphology. The results indicated that the S-layer could promote colony formation in Microcystis. Based on the S-layer sequences of PCC6803 and PCC7806, nine S-layer genes in other Microcystis strains were screened from the GenBank. Sequence comparing showed that the S-layers conserved regions were all located in N-terminal. The S-layers contain repeats-in-toxin (RTX) sequences with Ca2+-binding site, and their amino acid composition, hydrophobicity, isoelectric point, etc. were consistent with the characteristics of RTX-type S-layer in bacteria.

Colony formation in two Microcystis morphotypes: Effects of temperature and nutrient availability

The ability of Microcystis to form large colonies is a key trait that contributes to competition ability over other phytoplankton and facilitates the formation of surface scums in many freshwater systems. The effect of temperature and nutrients on this trait, however, is far from clear and needs further investigation, especially under a warmer climate and nutrient overloading in aquatic systems globally. In this study, two colonial strains of Microcystis (M. wesenbergii and M. ichthyoblabe) originally isolated from Lake Taihu in China, were used to investigate cyanobacterial aggregation under a range of temperatures (15–30 °C), phosphorus availability (0.004–8 mg P L−1), and nitrogen availability (0.04–40 mg N L−1). The mechanism of colony formation in Microcystis was determined based on growth rates and extracellular polysaccharide (EPS) contents. The colony size of both strains increased significantly when the temperature rose from 15 to 25 °C. A further increase in temperature from 25 to 30 °C, however, reduced the colony size of M. ichthyoblabe significantly, and, in contrast, increased the colony size of M. wesenbergii. Higher phosphorus availability promoted the formation of larger colonies in both strains. In comparison, nitrogen had no significant effect on the colony size. Furthermore, although EPS was a significant contributor to the formation of large colonies in colonial Microcystis, growth rate was a dominant driving factor in this process. The findings of this study highlight that warmer temperatures and phosphorus enrichment might enhance surface Microcystis scums directly through increasing the colony size. This study also provides new insights into the mechanism of colony formation in Microcystis.

Allelopathic Activities of Three Emergent Macrophytes on Several Monospecific Cyanobacterial Species and Natural Phytoplankton Assemblages

The extracts of three emergent macrophytes (Acorus calamus, Oenanthe javanica, and Sagittaria sagittifolia) were tested to study their allelopathic activities on unicellular Microcystis aeruginosa, Anabaena flosaquae, Aphanizomenon flosaquae, and natural phytoplankton assemblages. The 72 h EC50 of the most active extracts were measured. The results demonstrated the obvious species-specific activities of macrophytes on algae. Anabaena flosaquae and Aphanizomenon flosaquae was sensitive to the three macrophytes extracts, while unicellular M. aeruginosa was only sensitive to A. calamus and O. javanica extracts under the extracts concentration of 100 mg·L -1 . Only the extract of A. calamus roots showed high growth inhibition on the natural phytoplankton assemblages in Dianchi Lake (Microcystis water bloom). The 72 h EC50 of A. calamus roots hexane extract on unicellular M. aeruginosa was 13.59 mg·L -1 , while that on natural phytoplankton assemblages was 48.75 mg·L -1 . These results demonstrated that the growth inhibitory activities of allelochemicals on unicellular M. aeruginosa cannot instead of the efficacies for controlling Microcystis bloom completely. And according to the different sensitivities of Microcystis species, the colonial Microcystis strains or natural Microcystis bloom will be proposed as the target organism when searching for Microcystis bloom control.

Comparative studies on growth and physiological responses of unicellular and colonial Microcystis aeruginosa to Acorus calamus.

In order to explore the growth inhibition and physiological responses of unicellular and colonial Microcystis aeruginosa during coexistence with Acorus calamus, algal densities, chlorophyll a contents, exopolysaccharide (EPS) concentrations, malondialdehyde (MDA) contents, catalase (CAT) activities, and peroxidase (POD) activities of the two algae strains were analyzed. Although the unicellular and colonial strains of M. aeruginosa were both inhibited by A. calamus, unicellular algae were more sensitive than the colonial algae. The measurement results for EPS, MDA, CAT, and POD showed that unicellular M. aeruginosa had higher levels of stress related damage than colonial strains when they were exposed to the same density of A. calamus, and the cellular defense system of colonial M. aeruginosa was stronger than that of unicellular M. aeruginosa. Natural blooms of Microcystis are typically composed of colonial forms of M. aeruginosa, therefore future efforts to control such blooms, possibly through the development of new algicides, should focus on the unique characteristics of colonial M. aeruginosa strains.

Differences in growth, pigment composition and photosynthetic rates of two phenotypes Microcystis aeruginosa strains under high and low iron conditions

This paper provided insight into the influence of iron on the growth of Microcystis aeruginosa strains related to different phenotypes of this species. In this research it was intended to compare the growth, pigment composition, photosynthetic efficiency and extracellular polysaccharides production of unicellular and colonial strains of M. aeruginosa. A significantly growth inhibition under iron-limited condition on unicellular M. aeruginosa was noted, whereas the colonial strain could maintain a steady growth along with the culture time. This observation was reconfirmed by the content of chlorophyll a. Compared with unicellular strain; the colonial strain exhibited a higher PSII maximum light energy transformation, photosynthetic oxygen evolution and extracellular polysaccharides (EPS) production in iron-limited condition. Further, in order to gain more information about the accessibility of iron in the two phenotypic Microcystis, we found the two strains could produce hydroxamate-type siderophores, the content of siderophores produced by the colonial strain was more than those in unicellular strain under the iron-limited condition. It was interpreted as an adaptation to the dilute environment. Our results demonstrated that the colonial phenotypes possessed stronger ability to endure iron-limited condition than unicellular strain by higher pigment contents, higher photosynthetic activities, higher EPS production and higher siderophores secretion. It might elucidate that the colonial M. aeruginosa bloom can sustain in eutrophic reservoirs and lakes.

Phenotype and temperature affect the affinity for dissolved inorganic carbon in a cyanobacterium Microcystis

The cyanobacterium Microcystis is the most common bloom-forming species in eutrophicated water bodies. Known eco-physiological advantages of this organism help it to compete effectively with other algae and cyanobacteria; however, little is known about the physiological characteristics competence of colonial Microcystis. In the present study, carbonic anhydrase (CA) activity, the affinity for dissolved inorganic carbon (DIC), and the transcription of CA genes were examined in unicellular and colonial Microcystis strains. In comparison with unicellular strains, colonial Microcystis exhibited dramatically higher inorganic carbon affinity at 25 and 35°C, but no significant differences were observed at 15°C. The relative transcription levels of the CA genes icfA1, icfA2, ecaA, and ecaB in all colonial Microcystis were significantly higher than those in unicellular Microcystis at 25 and 35°C. In addition, CA activities of Microcystis increased with temperature, but no significant difference was observed between the unicellular and colonial Microcystis. These results suggest that temperature and phenotypes probably play important roles in the utilization of DIC and trigger the expression of CA genes of Microcystis. The present results may indicate that the capacity for utilizing inorganic carbon plays a role in the persistence or/and succession of different Microcystis blooms.

Role of Cell Hydrophobicity on Colony Formation in Microcystis (Cyanobacteria)

AbstractColony formation is highly import ant for the competitive advantage of the cyanobacterium Microcystis over other phytoplankton species. The laboratory‐grown colonial Microcystis strains isolated from Lake Taihu (China) maintained colonial forms under the low light condition (10 μE m–2 s–1). The cell surface hydrophobicities of the Microcystis colonies were measured by cyanobacterial adherence to xylene in comparison with unicellular Microcystis strains. The cells of the tested colonial strains were all hydrophobic, while the cells of the tested unicellular strains were all hydrophilic. Incubation under the higher light condition (75 μE m–2 s–1) leaded to the significant decrease in the cell hydrophobicities of the colonial Microcystis and the transition from colonial forms to unicellular forms. These findings indicated that the cell hydrophobicity of Microcystis may play a role in cell‐cell adherence and colony formation. Phosphate‐limitation, nitrate‐limitation and pH did not affect cell hydrophobicities of colonial Microcystis. Treatment with proteolytic enzymes had no effect on the cell hydrophobicity, indicating that cell surface proteins did not contribute to high cell hydrophobicity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth inhibition of unicellular and colonial Microcystis strains ( Cyanophyceae) by compounds isolated from rice ( Oryza sativa) hulls

The algicidal effects of crude and pure rice hull extracts on the growth of Microcystis aeruginosa were investigated using cultured unicellular and colonial strains. Upon treatment with rice hull crude extract (RHE), growth inhibition of unicellular M. aeruginosa was much higher than that of colonial M. aeruginosa. However, purified compounds from the crude extract, β-sitosterol-β- d-glucoside and dicyclohexanyl orizane, powerfully inhibited the growth of colonial M. aeruginosa cells. At the same concentrations, the two compounds were almost equipotent (66% and 80% growth inhibition for colonial M. aeruginosa, respectively; P < 0.05). As rice hulls are readily obtainable, and as extracts show high algicidal activity (targeting colonial algae rather than unicellular organisms) at low concentrations, the results suggest that some pure compounds extracted from rice hulls, such as β-sitosterol-β- d-glucoside and dicyclohexanyl orizane, may serve as environmentally friendly agents for controlling the growth of toxic colonial M. aeruginosa in eutrophic waters.

Comparative studies on physiological responses to phosphorus in two phenotypes of bloom-forming Microcystis

Toxic Microcystis blooms frequently occur in eutrophic water bodies and exist in the form of colonial and unicellular cells. In order to understand the mechanism of Microcystis dominance in freshwater bodies, the physiological and biochemical responses of unicellular ( 4 strains) and colonial ( 4 strains) Microcystis strains to phosphorus ( P) were comparatively studied. The two phenotype strains exhibit physiological differences mainly in terms of their response to low P concentrations. The growth of four unicellular and one small colonial Microcystis strain was significantly inhibited at a P concentration of 0.2 mg l - 1; however, that of the large colonial Microcystis strains was not inhibited. The results of phosphate uptake experiments conducted using P- starved cells indicated that the colonial strains had a higher affinity for low levels of P. The unicellular strains consumed more P than the colonial strains. Alkaline phosphatase activity in the unicellular strains was significantly induced by low P concentrations. Under P- limited conditions, the oxygen evolution rate, Fv/ Fm, and ETRmax were lower in unicellular strains than in colonial strains. These findings may shed light on the mechanism by which colonial Microcystis strains have an advantage with regard to dominance and persistence in fluctuating P conditions.

Response of Microcystis to copper stress – Do phenotypes of Microcystis make a difference in stress tolerance?

To elucidate the role of phenotype in stress-tolerant bloom-forming cyanobacterium Microcystis, two phenotypes of M. aeruginosa – unicellular and colonial strains were selected to investigate how they responded to copper stress. Flow cytometry (FCM) examination indicated that the percents of viable cells in unicellular and colonial Microcystis were 1.92–2.83% and 72.3–97.51%, respectively, under 0.25 mg l −1 copper sulfate treatment for 24 h. Upon exposure to 0.25 mg l −1 copper sulfate, the activities of antioxidative enzyme, such as superoxide dismutase (SOD) and catalase (CAT), were significantly increased in colonial Microcystis compared to unicellular Microcystis. Meanwhile, the values of the photosynthetic parameters ( F v/ F m, ETR max, and oxygen evolution rate) decreased more rapidly in unicellular Microcystis than in colonial Microcystis. The results indicate that colonial Microcystis has a higher endurance to copper than unicellular Microcystis. This suggests that the efficient treatment concentration of copper sulfate as algaecides will be dependent on the phenotypes of Microcystis.

Strategies of Silence: Colonial Strains in Short Stories of the Troubles

This essay finds a resonance between the short story form and familiar features of 'Troubles' writing: the emphasis on reticence and silence, the articulation of historical forces through narrative gaps, the intrusion of political disturbance into the private or domestic realm, the use of symbolism, the attempt to express a social condition through non-mimetic modes. It argues that the short story form both reflects problems of articulation and representation, yet with its characteristically wry, elliptical point of view can be a subversive strategy of understatement. It includes readings of short stories by John Montague, Bernard MacLaverty, Mary Beckett, Anne Devlin, and William Trevor.

Disaggregation of colonies of Microcystis (Cyanobacteria): efficiency of two techniques assessed using an image analysis system

Disaggregation of colonies of Microcystis (Cyanobacteria) into smalleraggregates or single cells is a usefulprocess for improving the accuracy andprecision of cell abundance estimates innatural populations. An image analysissystem was therefore used to assess theefficiency of two techniques,heating/vortexing and grinding, fordisaggregating fixed and live colonies. Eight environmental samples, consisting ofeither colonial or non-colonial strains,were tested in time course experimentsusing each technique by analysing thenumber and total area of the objects (i.e.,cells, clumps of cells, colonies) acquired. The results show that i) image analysis isan efficient tool to compare the efficiencyof disaggregation techniques on colonies ofcyanobacteria, ii) the grinding techniqueis more efficient in disaggregating alltypes of Microcystis colony, withoutsignificant loss, and iii) the heatingtechnique does not work for all types ofcolonies, in particular, compact coloniesfixed with Lugol's iodine solution.

Coincidences of structural and molecular characters in evolutionary lines of cyanobacteria

The traditional system of cyanobacteria based on morphological characters is in agreement with the molecular phylogenetic tree derived from 16S rRNA sequencing only in complicated, morphologically clearly diversified groups (heterocytous orders). The molecular evaluations of simple cyanobacteria yield a mixture of coccoid and filamentous (oscillatorialean) strains indicating the more complicated relations and heterogeneity of these groups. The evaluation of phenotype and molecular markers resulted in several conclusions: (i) The basic fine structures (thylakoidal patterns) are more or less in agreement with clusters derived from molecular sequencing; (ii) the coccoid types are particularly heterogeneous, and different groups of unicellular and colonial strains are more related to different consequent clusters of filamentous cyanobacteria than mutually one to another; (iii) it means, that several phylogenetically separated lines exist in cyanobacteria with more or less congruent type of cell structure; and (iv) each of these lines contains both special coccoid and simple trichal types. The taxonomic classification should be re-evaluated according to mentioned criteria.

The phylogeny of unicellular, extremely halotolerant cyanobacteria.

We examined the morphology, physiology, and 16S rRNA gene sequences of three culture collection strains and of ten novel isolates of unicellular cyanobacteria from hypersaline environments. The strains were morphologically diverse, with average cell widths ranging from 2.8 to 10.3 micron. There were single-celled, colonial, and baeocyte-forming strains. However, morphological traits were markedly variable with culture conditions. In contrast, all strains displayed extreme halotolerance (growing close to optimally at above 12% salinity); all were obligately marine, euryhaline, and moderately thermophilic; and all shared a suite of chemotaxonomic markers including phycobilins, carotenoids, and mycosporine-like amino acids. 16S rRNA gene sequence analysis indicated that the strains were related to each other. Sequence similarity analysis placed the strains in a monophyletic cluster (which we named the Halothece cluster) apart from all cultured or uncultured, not extremely halotolerant cyanobacteria whose 16S rRNA gene sequences are available in public nucleotide sequence databases. This represents the first case in which a phylogenetically coherent group of cyanobacteria can be defined on the basis of physiology. The Halothece cluster contained two subclusters that may be divergent at the generic level, one encompassing 12 strains (spanning 5% 16S rRNA gene sequence divergence and named the Euhalothece subcluster), and a single deep-branching isolate. Phenotypic characterization of the isolates, including morphological, physiological, and chemotaxonomic traits, did not distinguish these subclusters and only weakly suggested the existence of two separate clades, one encompassing strains of small cell size (cell width < 5 m) and another one encompassing strains of larger cell size.

Protoplast production and transformation of morphological mutants of the Quorn ® myco-protein fungus, Fusarium graminearum A3/5, using the hygromycin B resistance plasmid pAN7–1

A protocol for the generation of high yields of viable protoplasts has been developed for several highly branched (colonial) strains of the Quorn ® myco-protein fungus, Fusarium graminearum A3/5. Driselase was found to produce higher protoplast yields ( ca 10 9 g -1 wet weight) than the other lytic enzymes tested (Glucanex, Novozyme, β-glucuronidase, Sigma lytic enzyme, or ICN lytic enzyme), although yields differed for the various strains. Protoplast regeneration frequencies of 25–50% were observed when glucose (1.0 M) or sucrose (1.0 M) was used as the osmotic stabilizer. A highly branched strain of F. graminearum CC1–5, which grows better in submerged culture than the more sparsely branched wild-type strain (A3/5) was transformed using the hygromycin B resistance plasmid pAN7–1.

Genetic and biochemical characterization of D-arabinose dehydrogenase from Neurospora crassa.

D-Arabinose dehydrogenase has been purified to homogeneity from wild-type Neurospora crassa 74-A (FGSC 262) and from two colonial mutants, col-15a (FGSC 1391) and col-16a (FGSC 1349), found to contain more of the enzyme. The enzymes were characterized by measurement of several kinetic and physicochemical parameters. The enzymes were the same in all characteristics studied thus far. Immunological studied performed with enzyme preparations from the three strains showed antigenic identity and indicated that those colonial strains contain more normal enzyme, rather than the usual amount of an altered "improved" enzyme. Quantitation of the enzyme in crude extracts, performed by single radial immunodiffusion, showed that the colonial strains have twice the level of enzyme as the wild-type strain. Genetic characterization, performed by analysis of meiotic products, heterokaryosis, and reversions, indicated that the difference in D-arabinose dehydrogenase activity detected among the three strains is probably determined by one gene. The genetic control, structural or regulatory of this enzyme activity is different from that determining the morphological alterations exhibited by mutant strains carrying the col-15 or col-16 gene.

Conidiating colonial strains suitable for replication

Conidiating colonial strains suitable for replication