Evidence from field nitrogen balance and 15N natural abundance data for the contribution of biological N2 fixation to Brazilian sugarcane varieties

Aims

In Brazil N fertilization of sugarcane (Saccharum spp.) is low compared to most other countries. ¹⁵N-aided studies and the occurrence of many N₂-fixing bacteria associated with cane plants suggest significant contributions from biological N₂ fixation (BNF). The objective of this study was to evaluate BNF contributions to nine cane varieties under field conditions using N balance and ¹⁵N natural abundance techniques.

Methods

The field experiment was planted near Rio de Janeiro in 1989, replanted in 1999 and harvested 13 times until 2004. Soil total N was evaluated at planting and again in 2004. Samples of cane leaves and weeds for the evaluation of ¹⁵N natural abundance were taken in 2000, 2003 and 2004.

Results

N accumulation of the commercial cane varieties and a variety of Saccharum spontaneum were persistently high and N balances (60 to 107?kg?N ha^?1?yr^?1) significantly (p?<?0.05) positive. The δ¹⁵N of leaf samples were lower than any of the weed reference plants and data obtained from a greenhouse study indicated that this was not due to the cane plants tapping into soil of lower ¹⁵N abundance at greater depth.

Conclusion

The results indicate that the Brazilian varieties of sugarcane were able to obtain at least 40?kg?N ha^?1?yr^?1 from BNF.     

Evaluation of the bioremoval of Cr(VI) and TOC in biofilters under continuous operation using response surface methodology

In the present study, the bioremoval of Cr(VI) and the removal of total organic carbon (TOC) were achieved with a system composed by an anaerobic filter and a submerged biofilter with intermittent aeration using a mixed culture of microorganisms originating from contaminated sludge. In the aforementioned biofilters, the concentrations of chromium, carbon, and nitrogen were optimized according to response surface methodology. The initial concentration of Cr(VI) was 137.35 mg l⁻¹, and a bioremoval of 85.23% was attained. The optimal conditions for the removal of TOC were 4 to 8 g l⁻¹ of sodium acetate, >0.8 g l⁻¹ of ammonium chloride and 60 to 100 mg l⁻¹ of Cr(VI). The results revealed that ammonium chloride had the strongest effect on the TOC removal, and 120 mg l⁻¹ of Cr(VI) could be removed after 156 h of operation. Moreover, 100% of the Cr(VI) and the total chromium content of the aerobic reactor output were removed, and TOC removals of 80 and 87% were attained after operating the anaerobic and aerobic reactors for 130 and 142 h, respectively. The concentrations of cells in both reactors remained nearly constant over time. The residence time distribution was obtained to evaluate the flow through the bioreactors.     

RAPD variation and population genetic structure of Physalaemus cuvieri (Anura: Leptodactylidae) in Central Brazil

Studies about the organization of the genetic variability and population structure in natural populations are used either to understand microevolutionary processes or the effects of isolation by human-inducted landscape modifications. In this paper, we analyzed patterns of genetic population structure using 126 RAPD loci scored for 214 individuals of Physalaemus cuvieri, sampled from 18 local populations. Around 97% of these loci were polymorphic. The among-population variation component (Φ_ST) obtained by AMOVA was equal to 0.101 and θ ^B obtained using a Bayesian approach for dominant markers was 0.103. Genetic divergence, analyzed by Mantel spatial correlogram, revealed only a short-distance significant correlation between genetic and geographic distances. This is expected if low levels of population differentiation, due to high abundance buffering the effect of stochastic processes, are combined with low spatially restricted gene flow. Although this may be consistent with the current knowledge of species’ biology, the spatial distribution of local populations observed in this study also suggest that, at least in part, recent human occupation and habitat fragmentation may also explain part of the interpopulational component of the genetic variation.     

Virulence Factors and Antifungal Susceptibility of Candida albicans Isolates from Oral Candidosis Patients and Control Individuals

Sixty isolates of Candida albicans, 30 obtained from the oral cavity of denture wearers presenting signs of candidosis and 30 obtained from the oral cavity of denture wearers with normal palatal mucosa were assayed for phospholipase and proteinase production, as well as for adherence to buccal epithelial cells. Likewise, susceptibility of the isolates to antifungals was determined by the NCCLS reference method and the E-test method. Proteinase activity was increased among the strains obtained from oral candidosis patients. In contrast, no significant differences between the two groups of isolates were observed in their adherence ability in vitro, in phospholipase production, and susceptibility to antifungal drugs.     

The genetic diversity of two brazilian vellozia (velloziaceae) with different patterns of spatial distribution and pollination biology

BACKGROUND AND AIMS: The genetic structure and variability of two species of Vellozia (Velloziaceae) with restricted distribution in high-altitude quartzitic fields in south-eastern Brazil were studied. Vellozia epidendroides is short, grows on pebbly or sandy soil, and is pollinated by bees. Vellozia leptopetala is arborescent, grows on rock outcrops, and is pollinated by bees and hummingbirds. Both are self-incompatible and have a short, massive flowering strategy. The study aimed to associate differences in their genetic diversity and structure with their microhabitat distribution and pollination ecology. METHODS: Leaves from 106 and 139 plants of V. epidendroides and V. leptopetala, respectively, were collected from five patches of each species and prepared for electrophoretic analyses. KEY RESULTS: Five enzyme systems could be reliably scored for both species. Vellozia epidendroides showed 100 % of the loci polymorphic for almost all patches. The average number of alleles per locus ranged between 2.2 and 2.4 among patches. The Wright's fixation index (F) for this species was 0.226. A significant (p) value indicates that there is a reasonable genetic divergence among patches. Vellozia leptopetala presented 47.5 % of polymorphic loci. All levels of P, A, A(p) and of heterozygosities were lower than those of V. epidendroides. Vellozia leptopetala showed high inbreeding within patches. CONCLUSIONS: The relatively high values of genetic diversity indices found for V. epidendroides may be associated with its large and widespread populations. On the other hand, the low values of genetic diversity found for V. leptopetala may be related to physical isolation on outcrops and intensive foraging by territorial hummingbirds, which may hinder gene flow among patches, aggravated by the very restricted seed dispersal characteristic of the genus, that facilitates sibling mating. It is important to stress the need to preserve the specific habitats of these species of Vellozia, in particular those of V. leptopetala that has lower genetic diversity and is restricted to rock outcrop environments.     

Mice Immunization with Radioattenuated Yeast Cells of <Emphasis Type="Italic">Paracoccidiodes brasiliensis</Emphasis>: Influence of the Number of Immunizations

Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis, the most prevalent mycosis in Latin America. Up to the moment no vaccine has been reported. The aim of this study was to evaluate the influence of the number of immunizations on the protection elicited by radioattenuated yeast cells of P. brasiliensis. BALB/c mice were divided into two groups that were immunized once (Group 1) or twice (Group 2), respectively. In each group, mice were divided into sub-groups that were challenged 30, 45, or 60 days after the second immunization. Organ colony-forming units (CFUs) was determined 90 days post-challenge. A significant reduction in CFUs recovery was verified in both groups, but it was higher in Group 2. Histologic alterations were observed only in Group 1. The cytokines IL-4, IL-10, and IFN-γ were produced in mice of Group 1. In Group 2, only IFN-γ was significantly detected. IgG2a predominance relative to IgG1 was also observed in Group 2. Altogether, our results indicated that mice immunized once developed a mixed Th1/Th2 response, which was less efficient in the infection control, while a trend to a Th1 pattern was obtained with two immunizations, promoting optimal elimination of P. brasiliensis yeast cells from mice tissues.     

In vitro studies of anticandidal activity of goniothalamin enantiomers

Aims:  The antifungal activity of ( R )-goniothalamin ( 1 ) and ( S )-goniothalamin ( ent - 1 ) was evaluated against six Candida species. The in vitro effect of these compounds on yeast adhesion to human buccal epithelial cells (BEC) and Candida albicans and C. dubliniensis biofilms progression were also investigated.
Methods and Results:  Yeast susceptibility was evaluated by broth microdilution assay and showed that ent - 1 exhibited higher potency against all fungal clinical isolated when compared to compound 1 . Compounds 1 and ent - 1 were as potent as fluconazole in inhibiting the adhesion of C. albicans and C. dubliniensis to BEC. XTT-reducing assay and scanning electron microscopy revealed that 1 and ent - 1 were twice as potent as fluconazole in the inhibition of yeast biofilms progression.
Conclusions:  Our findings indicate that compounds 1 and ent - 1 are potent anticandidal agents.
Significance and Impact of the Study:  This study highlights goniothalamin enantiomers as promising lead compounds for the design of new antifungal with inhibitory activity on yeast adhesion and biofilm progression.     

Genetic control of Eucalyptus urophylla and E. grandis resistance to canker caused by Chrysoporthe cubensis

Chrysophorte cubensis induced canker occurs in nearly all tropical and subtropical regions where eucalypts are planted, causing losses in both wood quality and volume productivity, especially so in the warmer and more humid regions of Brazil. The wide inter and intra-specific genetic variability of resistance to canker among Eucalyptus species facilitates the selection of resistant plants. In this study, we evaluated resistance to this pathogen in five Eucalyptus grandis (G) and 15 E. urophylla (U) trees, as well as in 495 individuals from 27 progenies derived from crosses between the trees. In the field, six-months-old test seedlings were inoculated with C. cubensis. Lesion length in the xylem and bark was measured eight months later. The results demonstrated that xylem lesions could preferentially be used for the selection of resistant clones. Eight trees (7 U and 1 G) were susceptible, and the remainder (8 U and 4 G) resistant. Individual narrow and broad sense heritability estimates were 17 and 81%, respectively, thereby suggesting that canker resistance is quantitative and highly dependent on dominance and epistasis.