Occurrence and Localization of Phycoerythrin in Symbiotic Nostoc of Cycas revoluta and in the Free-Living Isolated Nostoc 7422

The phycobiliprotein phycoerythrin was localized in symbiotic and free-living Nostoc of the cycad Cycas using immunocytochemistry. In symbiotic Nostoc, phycoerythrin was associated with the thylakoid membranes of vegetative cells and absent from heterocysts. Similar cellular/subcellular localization was observed between symbiotic Nostoc and the free-living Cycas isolate Nostoc 7422.     

Restriction mapping of genomic DNA from five cyanophages infecting the heterocystous cyanobacteria Nostoc and Anabaena

The positions of the cleavage sites of several restriction endonucleases were mapped in DNA isolated from the cyanophages A-1L, A-4L, AN-10, AN-13 and AN-23, which were replicated in Anabaena PCC 7120. Similarities within the maps show AN-13 and AN-23 to be closely related strains. A-1L and AN-10 also appear to be related, but show more divergence. The maps of A-1L and AN-10 are circular, apparently as the result of circular permutation of sequences. The maps of the other cyanophages are linear.     

Environmental Factors Shape the Community of Symbionts in the Hoopoe Uropygial Gland More than Genetic Factors

Exploring processes of coevolution of microorganisms and their hosts is a new imperative for life sciences. If bacteria protect hosts against pathogens, mechanisms facilitating the intergenerational transmission of such bacteria will be strongly selected by evolution. By disentangling the diversity of bacterial strains from the uropygium of hoopoes (Upupa epops) due to genetic relatedness or to a common environment, we explored the importance of horizontal (from the environment) and vertical (from parents) acquisition of antimicrobial-producing symbionts in this species. For this purpose, we compared bacterial communities among individuals in nonmanipulated nests; we also performed a cross-fostering experiment using recently hatched nestlings before uropygial gland development and some nestlings that were reared outside hoopoe nests. The capacity of individuals to acquire microbial symbionts horizontally during their development was supported by our results, since cross-fostered nestlings share bacterial strains with foster siblings and nestlings that were not in contact with hoopoe adults or nests also developed the symbiosis. Moreover, nestlings could change some bacterial strains over the course of their stay in the nest, and adult females changed their bacterial community in different years. However, a low rate of vertical transmission was inferred, since genetic siblings reared in different nests shared more bacterial strains than they shared with unrelated nestlings raised in different nests. In conclusion, hoopoes are able to incorporate new symbionts from the environment during the development of the uropygium, which could be a selective advantage if strains with higher antimicrobial capacity are incorporated into the gland and could aid hosts in fighting against pathogenic and disease-causing microbes.     

The Biogeography and Phylogeny of Unicellular Cyanobacterial Symbionts in Sponges from Australia and the Mediterranean

The distribution, host associations, and phylogenetic relationships of the unicellular cyanobacterial symbionts of selected marine sponges were investigated with direct 16s rDNA sequencing. The results indicate that the symbionts of the marine sponges Aplysina aerophoba, Ircinia variabilis, and Petrosia ficiformis from the Mediterranean, four Chondrilla species from Australia and the Mediterranean, and Haliclona sp. from Australia support a diversity of symbionts comprising at least four closely related species of Synechococcus. These include the symbionts presently described as Aphanocapsa feldmannii from P. ficiformis and Chondrilla nucula. A fifth symbiont from Cymbastela marshae in Australia is an undescribed symbiont of sponges, related to Oscillatoria rosea. One symbiont, Candidatus Synechococcus spongiarum, was found in diverse sponge genera in the Mediterranean Sea and the Indian, Pacific, and Southern oceans, whereas others were apparently more restricted in host association and distribution. These results are discussed in terms of the biodiversity and biogeographic distributions of cyanobacterial symbionts.This revised version was published online in November 2004 with corrections to Volume 48.     

Ultrastructure, Molecular Phylogenetics, and Chlorophyll a Content of Novel Cyanobacterial Symbionts in Temperate Sponges

Marine sponges often harbor photosynthetic symbionts that may enhance host metabolism and ecological success, yet little is known about the factors that structure the diversity, specificity, and nature of these relationships. Here, we characterized the cyanobacterial symbionts in two congeneric and sympatric host sponges that exhibit distinct habitat preferences correlated with irradiance: Ircinia fasciculata (higher irradiance) and Ircinia variabilis (lower irradiance). Symbiont composition was similar among hosts and dominated by the sponge-specific cyanobacterium Synechococcus spongiarum. Phylogenetic analyses of 16S-23S rRNA internal transcribed spacer (ITS) gene sequences revealed that Mediterranean Ircinia spp. host a specific, novel symbiont clade ("M") within the S. spongiarum species complex. A second, rare cyanobacterium related to the ascidian symbiont Synechocystis trididemni was observed in low abundance in I. fasciculata and likewise corresponded to a new symbiont clade. Symbiont communities in I. fasciculata exhibited nearly twice the chlorophyll a concentrations of I. variabilis. Further, S. spongiarum clade M symbionts in I. fasciculata exhibited dense intracellular aggregations of glycogen granules, a storage product of photosynthetic carbon assimilation rarely observed in I. variabilis symbionts. In both host sponges, S. spongiarum cells were observed interacting with host archeocytes, although the lower photosynthetic activity of Cyanobacteria in I. variabilis suggests less symbiont-derived nutritional benefit. The observed differences in clade M symbionts among sponge hosts suggest that ambient irradiance conditions dictate symbiont photosynthetic activity and consequently may mediate the nature of host-symbiont relationships. In addition, the plasticity exhibited by clade M symbionts may be an adaptive attribute that allows for flexibility in host-symbiont interactions across the seasonal fluctuations in light and temperature characteristic of temperate environments.     

Variation of Microcystin Content of Cyanobacterial Blooms and Isolated Strains in Lake Grand-Lieu (France)

Abstract Cyanobacterial blooms were sampled at five locations in Lake Grand-Lieu on seven different occasions during May–October 1994. Strains of Microcystis aeruginosa and Anabaena circinalis were isolated from the samples. Microcystins were detected in freeze-dried field samples and the isolated strains by HPLC. The toxins were present in the blooms sampled between June and October. The microcystin content in the blooms varied with site and time, from undetectable concentrations to 0.23 mg g⁻¹. The highest concentrations of microcystin were found in blooms sampled in September. Microcystin-LR and microcystins with retention times close to the retention time of [Dha⁷]microcystin-RR (probably varieties of microcystin-RR) were found in the field samples. Sixteen of the 98 isolated M. aeruginosa strains and 2 of the 24 A. circinalis strains produced microcystins. The total amount of microcystins varied from undetectable concentrations to 5.06 mg g⁻¹ in the M. aeruginosa isolates, and from undetectable concentrations to 1.86 mg g⁻¹ in the A. circinalis strains. Microcystin-LR was the main toxin found in strains of M. aeruginosa, but was not present in strains of A. circinalis. Both microcystin-producing strains and strains that did not produce microcystin coexisted in the bloom samples. Received: 23 January 1997; Accepted: 25 March 1997     

Paracrystalline inclusions in various isolates of the blue-green bacteria Nostoc and Anabaena.

A number of different crystalline inclusions were observed in various isolates of Anabaena and Nostoc. Membrane-limited crystalline bodies were observed in 7 of 20 isolates of Anabaena and 19 of 29 isolates of Nostoc. These are spherical, single membrane-limited bodies from 0.6 to 0.1 micron in diameter. In most of the isolates they contained needle-like crystals 20 A in thickness and up to 80 nm in length. In 9 of the isolates the inclusions contained granular and fibrillar material. The number of bodies per cell varied in the different isolates from only a few, observed in many sections, up to 5 in a single section of A. subtropica (B1618). Crystalloids were observed in the cytoplasm of Anabaena sp. (1551), N. calcicola (B382), Nostoc sp. (588), and N. punctiforme (1629). In Anabaena sp. (1551) the roughly cuboidal inclusions 0.6 micron in diameter were composed of 100 A thick osmiophilic striations spaced to produce a 150 A periodicity. In Nostoc sp. (588) the elongate, 0.1 micron by 2.5 micron, crystalloids were composed of 100 A thick osmiophilic striations spaced to produce a 200 A periodicity. N. punctiforme (1629) and N. calciola (B382) contained intrathylakoidal crystalloids which consisted of short curved segments with 100 A thick osmiophilic striations producing a 200 A periodicity. Granular areas were observed in 2 isolates of Anabaena and 5 of Nostoc. These bodies found in various locations in the cells, were interpreted to be elongate structures 0.2 micron thick, 1.2 micron long and about 5 micron in depth. These inclusions were composed of 15 nm diameter granules which in some section planes appeared in rows spaced 20 nm apart. Spherical bodies up to 0.7 micron in diameter and of medium electron density were observed in 4 isolates of Anabaena and 2 of Nostoc. Convoluted inclusions were found in N. calcicola (B382) and Anabaena sp. (1551). These roughly spherical bodies up to 0.8 micron in diameter contain lighter swirled areas.     

Population Genetic Variation in the Tree Fern Alsophila spinulosa (Cyatheaceae): Effects of Reproductive Strategy

Background

Essentially all ferns can perform both sexual and asexual reproduction. Their populations represent suitable study objects to test the population genetic effects of different reproductive systems. Using the diploid homosporous fern Alsophila spinulosa as an example species, the main purpose of this study was to assess the relative impact of sexual and asexual reproduction on the level and structure of population genetic variation.

Methodology/Principal Findings

Inter-simple sequence repeats analysis was conducted on 140 individuals collected from seven populations (HSG, LCH, BPC, MPG, GX, LD, and ZHG) in China. Seventy-four polymorphic bands discriminated a total of 127 multilocus genotypes. Character compatibility analysis revealed that 50.0 to 70.0% of the genotypes had to be deleted in order to obtain a tree-like structure in the data set from populations HSG, LCH, MPG, BPC, GX, and LD; and there was a gradual decrease of conflict in the data set when genotypes with the highest incompatibility counts were successively deleted. In contrast, in population ZHG, only 33.3% of genotypes had to be removed to achieve complete compatibility in the data set, which showed a sharp decline in incompatibility upon the deletion of those genotypes. All populations examined possessed similar levels of genetic variation. Population ZHG was not found to be more differentiated than the other populations.

Conclusions/Significance

Sexual recombination is the predominant source of genetic variation in most of the examined populations of A. spinulosa. However, somatic mutation contributes most to the genetic variation in population ZHG. This change of the primary mode of reproduction does not cause a significant difference in the population genetic composition. Character compatibility analysis represents an effective approach to separate the role of sexual and asexual components in shaping the genetic pattern of fern populations.     

Genetic Diversity in the Lactose Operons of Lactobacillus helveticus Strains and Its Relationship to the Role of These Strains as Commercial Starter Cultures

Two novel insertion sequence elements, ISLhe1 and ISLhe15, were located upstream of the genes encoding the β-galactosidase enzyme in Lactobacillus helveticus commercial starter strains. Strains with the IS982 family element, ISLhe1, demonstrated reduced β-galactosidase activity compared to the L. helveticus type strain, whereas strains with the ISLhe15 element expressed β-galactosidase in the absence of lactose.     

Determinative Value of a Portion of the nifH Sequence for the Genera Nostoc and Anabaena (Cyanobacteria)

The taxonomic positions of Nostoc and Anabaena strains are currently disputed. We selected three Nostoc and Anabaena strains, using the classic criteria of morphology and life cycle. DNA sequences of a part of the nifH gene were determined from these strains and aligned with homologous sequences from 10 other Nostoc/Anabaena strains in the public databases. Phylogenetic reconstructions were carried out to test the consistency of the taxonomic placement of these strains. The phylogenetic trees do not separate these strains into distinct groups. Our results are in agreement with other molecular-based phylogenies that also fail to differentiate the Nostoc-Anabaena groups. The data suggest that the currently recognized genera Nostoc and Anabaena may in fact belong within a single, broadly defined genus. Received: 14 February 2000 / Accepted: 21 March 2000     

葡萄糖和氢对Gunnera／Nostoc固氮共生体固氮活力的影响

Ｇｕｎｎｅｒａ／Ｎｏｓｔｏｃ固氮共生体固氮相对效率（ＲＥ）可在０．２６～０．８０之间变动,而不是一个常数。外加１．５％葡萄糖液可使其固氮活力提高约１００％,同时也使组织的呼吸速率提高了近１６０％。加外源Ｈ２可使其固氮活力提高近１００％,但却使组织的呼吸速率降低了近５０％。正常生长条件下的组织净放Ｈ２量较低．而外源２％葡萄糖液可使组织净放Ｈ２量提高近２倍。外加５ｍｍｏｌ／Ｌ的ＮＨ１Ｃｌ溶液可使其固氮活力下降约７０％。故认为Ｇｕｎｎｅｒａ／Ｎｏｓｔｏｃ共生体固氮活力受碳水化合物供应状况及比代谢两者构成的“还原力库”或“电子库”的调节,在此“还原力库”中,Ｈ２代谢起到了一个“中间调节者”的作用。     

An Experimental Test of the Relationship between Genetic Variation and Environmental Variation in Tribolium Flour Beetles

The hypothesis that a component of genetic variation for polygenic fitness traits is maintained by environmental heterogeneity was tested using an experimental system involving two species of flour beetles, Tribolium castaneum and T. confusum. Replicated populations of each species from a number of environmental treatments were analyzed for various fitness components following almost 60 generations of natural selection. Environmental differences consisted of flours of cereals commonly invaded by natural populations of these insects.—Tests for adaptation to environments were based on experiments in which populations were reared factorially on each flour, such that population treatment x flour interactions could be detected. Measurements were made of survival, growth rate, larval weight, pupal weight, developmental time, fecundity of individuals at low density and fecundity and cannibalism at high density in both fresh and conditioned media.—Flour differences were found to have significant effects on most traits. Evidence for significant genetic variation and significant genotype x environment interaction was also found. However, no evidence could be found to support the hypothesis that genetic variation was maintained by environmental heterogeneity in food resources. The absence of adaptation to the experimental treatments despite the presence of genetic variation in fitness components suggests that pleiotropy may assume an important role in determining net fitness values of polygenes.     

Genetic Variation in Activity of the Enzymes of Glycolysis and Gluconeogenesis between Inbred Strains of Mice

Variation in the activity of 21 liver and 15 erythrocyte enzymes between seven inbred strains of mice has been studied in a single area of metabolism, glycolysis and gluconeogenesis. Most of the variation between the strains is genetic. From the variation within and between inbred strains heritabilities (H²) were determined. Out of 35, 26 showed significant values above 0.4. A comparison with previously published work suggests that enzyme activities have mainly dominance and interaction components of variance, and this is discussed in relation to the variation in quantitative characters such as growth. In nine of the pairwise comparisons of the strains, the activity of the enzyme varied more than two-fold. In these cases the genetics and biochemistry of the enzyme was studied; F₂ progeny were produced and assessed for segregation, and the heat stability of the enzyme was determined. No unequivocal segregation was observed, although in one case we found a considerable difference in heat stability. The variations found were not considered to be great enough to be useful as models of human inborn errors of metabolism or to study metabolic control. If such variants are to be found, sources of variation other than inbred strains must be used.     

Genetic transformation of glutamine auxotrophy to prototrophy in the cyanobacterium Nostoc muscorum

Glutamine auxotrophic (Gln ^-) and l-methionine d,l-sulfoximine (MSX) resistant (MSX ^r) mutants of N. muscorum were isolated and characterized for nitrogen nutrition, nitrogenase activity, glutamine synthetase (GS) activity and glutamine amide, -keto-glutarate amido transferase (GOGAT) activity. The glutamine auxotroph was found to the GOGAT-containing GS-defective, incapable of growth with N₂ or NH ₄ ⁺ but capable of growth with glutamine as nitrogen source, thus, suggesting GS to be the primary enzyme of both ammonia assimilation and glutamine formation in the cyanobacterium. The results of transformation and reversion studies suggests that glutamine auxotrophy is the result of a mutation in the gln A gene and that gln A gene can be transferred from one strain to another by transformation.     

The Effect of Some External Factors on Nitrogenase Activity in the Free-Living and Endophytic Nostoc of the Liverwort Blasia pusilla

The effects of pH, light intensity, temperature, oxygen and dehydration on nitrogenase activity in the free-living and endophytic Nostoc sp. of Blasia are described. The endophyte exhibits greater nitrogenase activity at lower pH's than the free-living alga. Maximal activity in the free-living alga is attained at much lower light intensities than those required by the endophyte. Both algae have low activities below 10°C, the free-living alga showing high activity above 12°C and the endophyte above 17°C. Increasing pO₂ levels cause a decrease in activity in both algae. The free-living alga is more tolerant to dehydration than the endophyte, although both algae are protected by mucilage. The results are discussed and possible benefits resulting from the symbiosis, with respect to nitrogen fixation rates, considered.