Disturbance and Seasonal Dynamics of Mycorrhizae in a Tropical Deciduous Forest in Mexico1

Mycorrhizal fungi were sampled in a deciduous tropical forest on the Pacific coast of Mexico during different seasons and in natural treefall gaps and pastures. All 12 plant species sampled in the forest were arbuscular mycorrhizal. The percent root infection and spore production were closely related to the phenology of the plants. Most tree species and all herbaceous species had the highest infection in the summer rainy season, but two species, Opuntia excelsa and Jacquinia pungens, had highest infection in the dry season. Unusually high rainfall during the dry season was associated with increased infection but not increased spore production. Spore density was low for all species at all sample times, except at the beginning of the July 1993 rainy season in, when we observed up to 28 spores/g soil. The percent cover of shrubs or herbs did not increase in gaps after two years, and we observed no colonizing seedlings. No plant species with cover higher than 2.7 percent occurred exclusively in gaps or forest. The percent mycorrhizal infection did not differ significantly between gaps and forest. Spore counts were as high in the gaps as in the forest in two of the three gaps but lower in the third gap. The lack of significant response of plants in these gaps after two years differed from the rapid response in tropical rainforests. It is likely related to the small size of the gaps and to light infiltration to the forest floor. Pastures were dominated by two species of exotic grasses and one species of mycorrhizal fungus, whereas forests had 15 fungal species. The slow regrowth of vegetation in gaps was not limited by mycorrhizal fungi, since they were still abundant after the treefalls, but recovery in pastures could be affected by low fungal diversity and dominance of grasses.     

Structure of the Shigella dysenteriae haem transport locus and its phylogenetic distribution in enteric bacteria

The ability to transport and use haemin as an iron source is frequently observed in clinical isolates of Shigella spp. and pathogenic Escherichia coli . We found that many of these haem-utilizing E. coli strains contain a gene that hybridizes at high stringency to the S. dysenteriae type 1 haem receptor gene, shuA . These shuA -positive strains belong to multiple phylogenetic groups and include clinical isolates from enteric, urinary tract and systemic infections. The distribution of shuA in these strains suggests horizontal transfer of the haem transport locus. Some haem-utilizing pathogenic E. coli strains did not hybridize with shuA , so at least one other haem transport system is present in this group. We also characterized the chromosomal region containing shuA in S. dysenteriae . The shuA gene is present in a discrete locus, designated the haem transport locus, containing eight open reading frames. Several of the proteins encoded in this locus participate with ShuA in haem transport, as a Salmonella typhimurium strain containing the entire haem transport locus used haem much more efficiently than the same strain containing only shuA . The haem transport locus is not present in E. coli K-12 strains, but the sequences flanking the haem transport locus in S. dysenteriae matched those at the 78.7 minute region of E. coli K-12. The junctions and flanking sequences in the shuA -positive pathogenic E. coli strains tested were nearly identical to those in S. dysenteriae , indicating that, in these strains, the haem transport locus has an organization similar to that in S. dysenteriae , and it is located in the same relative position on the chromosome.     

Artificial endosperm of Cleopatra tangerine zygotic embryos: a model for somatic embryo encapsulation

Synthetic seed technology may be of value in breeding programs and allow the propagation of many elite genotype-derived plants in a short time. In this work, a range of artificial endosperm treatments of Cleopatra tangerine zygotic embryos were evaluated for suitability for encapsulation of somatic embryos. Different complexing ions in the form of alginate capsules, zeolite as an ion exchanger and the relationship between capsule-nutrient gel on germination of zygotic embryos, were evaluated. Artificial endosperm assays showed that abscisic acid (1 μM) and mannitol (0.25 M) delayed germination and conversion of zygotic embryos, whereas amino acid supplements (proline, glutamic acid and arginine) accelerated the conversion process. An artificial endosperm was used to encapsulate somatic and zygotic embryos. After encapsulation, zygotic embryos germinated after four days of culture while somatic embryos germinated asynchronously after 20 days. Somatic embryo-derived plantlets showed greater vigour than zygotic embryo-derived plantlets. Results showed that this artificial endosperm is adequate for Cleopatra tangerine somatic embryo germination and conversion into plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fungal post-treatment of pulp mill effluents for the removal of recalcitrant pollutants

The objective of this work was to evaluate the post-treatment of an anaerobic recalcitrant effluent (anaerobically-treated weak black liquor, AnE) in an aerobic, upflow reactor packed with “biocubes” of Trametes versicolor immobilized onto small cubes of holm oak wood. The treated effluent (named anaerobic effluent; AnE) from an anaerobic fluidized bed reactor was fed to an up-flow aerobic fungal packed bed reactor (PBR). Two HRT were tested in this unit, namely 5 and 2.5 days; the PBR operated 60 days at 5-day HRT and 35 days at 2.5-day HRT. The aerobic packed bench scale reactor was a glass column 1.5 L total geometric volume containing 0.75 L biocubes of T. versicolor immobilized onto holm oak wood small cubes of 5 mm side. The reactor was operated at 25 °C. The pH of the AnE was adjusted to 4.5 before feeding; no carbohydrates or other soluble carbon source was supplemented. The fungal packed bed bioreactor averaged organic matter removals of 30% and 32% COD basis, during an experimental run of 60 days at 5-day HRT and 35 days at 2.5-day HRT, respectively. Colour and ligninoids contents were removed at higher percentages (69% and 54% respectively, average of both HRT). There was no significant difference between reactor performance at 5- and 2.5-day HRT, so, operation at 2.5-day HRT is recommended since reactor throughput is double. Activity of manganese peroxidase and laccase was found during the entire operation of the fungal PBR whereas lignin peroxidase activity practically disappeared in the second operation period. In general, enzyme activities were higher in the first period of operation (5-day HRT) than at 2.5-day HRT. To the best of our knowledge, this is one of the few works that demonstrated extended performance (3 months) of a fungal bioreactor for the treatment of a recalcitrant wastewater with no supplementation of glucose or other expensive, soluble carbohydrate.     

Molecular taxonomic identification in the absence of a ‘barcoding gap’: a test with the endemic flora of the Canarian oceanic hotspot

We use a comprehensive subset of Canarian angiosperms corresponding to 23 families, 35 genera and 60 Canarian endemic taxa to test whether this flora is suitable to taxonomic identification with the two proposed plant DNA barcode sequences and whether these sequences may reveal the existence of cryptic species overlooked by morphology. The rate of discrimination success between the insular congeneric samples using the rbcL+matK combination and a ‘character‐based’ approach (where we use only the combination of nucleotide positions in an alignment that allows unambiguous species identification) is higher (82.29%) than that obtained with the ‘distance‐based’ approach (80.20%) used by the CBOL Plant Working Group in 2009 and also when compared with tests conducted in other floras. This suggests that the molecular identification of the Canarian endemic flora can be achieved as successfully as in other floras where the incidence of radiation is not as relevant. The facts that (i) a distance‐based criterion was unable to discriminate between congeneric and conspecific comparisons and (ii) only the character‐based discrimination criterion resolved cases that the distance‐based criterion did not, further support the use of a character discrimination approach for a more efficient DNA barcoding of floras from oceanic islands like the Canaries. Thus, a barcoding gap seems not to be necessary for the correct molecular characterization of the Canarian flora. DNA barcodes also suggest the possible existence of cryptic taxa to be further investigated by morphology and that the current taxonomic status of some of the taxa analysed may need revision.     

Cerebral Circulation Time is Prolonged and Not Correlated with EDSS in Multiple Sclerosis Patients: A Study Using Digital Subtracted Angiography

Literature has suggested that changes in brain flow circulation occur in patients with multiple sclerosis. In this study, digital subtraction angiography (DSA) was used to measure the absolute CCT value in MS patients and to correlate its value to age at disease onset and duration, and to expand disability status scale (EDSS). DSA assessment was performed on eighty MS patients and on a control group of forty-four age-matched patients. CCT in MS and control groups was calculated by analyzing the angiographic images. Lesion and brain volumes were calculated in a representative group of MS patients. Statistical correlations among CCT and disease duration, age at disease onset, lesion load, brain volumes and EDSS were considered. A significant difference between CCT in MS patients (mean = 4.9s; sd = 1.27s) and control group (mean = 2.8s; sd = 0.51s) was demonstrated. No significant statistical correlation was found between CCT and the other parameters in all MS patients. Significantly increased CCT value in MS patients suggests the presence of microvascular dysfunctions, which do not depend on clinical and MRI findings. Hemodynamic changes may not be exclusively the result of a late chronic inflammatory process.