Mechanism of metal ion biosorption by fungal biomass

Alkali extracted mycelial biomass from Aspergillus niger, referred to as Biosorb, was found to sequester metal ions (Cd²⁺, Cu²⁺, Zn²⁺, Ni²⁺ and Co²⁺) efficiently both from dilute and concentrated solutions upto 10% of its weight (w/w). Sequestration of metal ions from a mixture was also efficient but with attendant antagonisms. The kinetics of metal binding by Biosorb indicated that it is a rapid process and about 70–80% of the metal is removed from solution in 5 min followed by a slower rate. The mechanism of metal binding is shown to be due to exchange of calcium and magnesium ions of the Biosorb during which equimolar concentrations of both the ions were released into the medium. Following this an efficient procedure for the regeneration and reuse of Biosorb was standardized by washing the biosorbent with calcium and magnesium solution (0.1 m). Biosorbents prepared from Neurospora, Fusarium and Penicillium also exhibited similar mechanisms for metal ion binding, though they had a lower metal binding capacity when compared with Biosorb. Chemical modification of carboxylic acid functional groups of the Biosorb resulted in loss of 90% of metal binding capacity which could not be restored even on regeneration. The significance of this finding on the metal sequestration mechanisms of microbial biosorbents is discussed.     

Cobalt transport in nickel-resistant strains ofNeurospora crassa

Uptake of Co²⁺ by three nickel-resistant strains (Ni^R1, Ni^R2, and Ni^R3) ofNeurospora crassa that differed in resistance to Co²⁺ has been studied. Uptake was linear with Co²⁺ concentration (up to 1 mM), with time (up to 6 h), and with pH between 3 and 6. Uptake rates were in the order Ni^R2>Ni^R1>Ni^R3. In all strains, there was gradual increase in Co²⁺ uptake between 10° and 28°C, with a much sharper increase between 28° and 40°C. Metabolic inhibitors decreased Co²⁺ uptake partially in all strains, except for KF in Ni^R3. About 50–80 g Co²⁺/100 mg dry weight was surface bound. Ni²⁺, Zn²⁺, and Mn²⁺ competed with Co²⁺, the effects being strain specific. Mg²⁺ inhibited Co²⁺ uptake in all strains with preformed mycelia. In Ni^R1 and Ni^R2 only with young mycelia (40 h old) was Mg²⁺ inhibitory to Co²⁺ uptake,during growth in the presence of Co²⁺. The results suggested the presence of two transport systems for Co²⁺ in Ni^R1 and Ni^R2, only one of which was sensitive to Mg²⁺; in contrast, Ni^R3 had a single system, which was sensitive to Mg²⁺.     

Studies on copper toxicity in nickel-resistant strains ofNeurospora crassa

Copper toxicity has been studied in three nickel-resistant strains ofNeurospora crassa (Ni^R1, Ni^R2, and Ni^R3). Ni^R1 and Ni^R2, but not Ni^R3, were two-to threefold more sensitive than the parent wild strain (N. crassa EM 5297a) to Cu²⁺ on a normal N medium. On a nitrate N medium, Cu²⁺ was 16-fold more toxic to Ni^R3 because of reduced synthesis of nitrite reductase; Ni^R1 and Ni^R2 were only fivefold more sensitive to Cu²⁺, and nitrite reductase synthesis was unaffected. Mn²⁺ reversed Cu²⁺ toxicity on normal N medium only, in all strains. Fe³⁺ counteracted Cu²⁺ toxicity on nitrate N medium also. It was shown that Cu²⁺ affected Fe³⁺ utilization for nitrite reductase synthesis in Ni^R3 only and that in these Ni²⁺-resistant strains, Fe³⁺ antagonized effects of Cu²⁺, but not of other toxic metal ions.     

On the use of adenovirus dodecahedron as a carrier for glycoconjugate vaccines

Glycoconjugate Journal - Virus-Like Particles (VLPs) have been used as immunogenic molecules in numerous recombinant vaccines. VLPs can also serve as vaccine platform to exogenous antigens, usually...     

Mechanism of nickel resistance in a cobalt-resistant wall-less mutant of Neurospora crassa (fz; sg; os-1)

A cobalt-resistant wall-less mutant of N. crassa (Cor-sl) characterized previously was also found to be 3-fold more resistant to nickel when compared to the parent wall-less mutant (W-sl). The Cor-sl strain accumulates relatively lower amounts of nickel when compared to W-sl. Sub-cellular fractionation showed significant quantities of nickel to be associated with nuclear and mitochondrial fractions in both the wall-less mutants. However significant differences were observed in vacuolar fractions of W-sl and Cor-sl strains. Fractionation of cell-free extracts on Sephadex G-10 column resolved nickel into two peaks, of which the peak II in Cor-sl constituted 70% of nickel, while the same in W-sl was about 30%. A 3-fold increase in histidine content was observed in case of Cor-sl as compared to W-sl strain, suggesting its role in Ni-resistance.     

Dolichos yellow mosaic virus belongs to a distinct lineage of Old World begomoviruses; its biological and molecular properties

Dolichos yellow mosaic disease (DYMD) affects the production of dolichos in South Asia. Diseased plants produce characteristic bright yellow mosaic patches on the leaves and early infections cause reductions in yield. The putative dolichos yellow mosaic virus (DoYMV) was transmitted poorly (maximum 18.3% transmission) by the whitefly, Bemisia tabaci. DoYMV has a narrow host range and infected only Lablab purpureus and L. purpureus var. typicum out of the 36 species tested. Virus was detected using monoclonal antibodies in a triple‐antibody sandwich enzyme‐linked immunosorbent assay and by PCR. Complete DNA‐A components of DoYMV isolates from Mysore and Bangalore, South India, were sequenced, but several attempts to identify DNA‐B and DNA‐β were unsuccessful. DoYMV isolates shared DNA‐A nucleotide identities of 92.5–95.3% with previously described isolates from North India and Bangladesh. They were most similar to mungbean‐infecting begomoviruses at 61.6–64.4% of DNA‐A nucleotide identities. Phylogenetic analyses of DNA‐A sequences grouped the dolichos‐infecting and mungbean‐infecting begomoviruses into a distinct cluster away from begomoviruses infecting non‐leguminous plants in the Indian subcontinent. Antigenically, legume‐infecting begomoviruses were most similar to each other compared with non‐legume viruses. Collectively, these results indicate that legume‐infecting begomoviruses in the Indian subcontinent belonged to a distinct lineage of Old World begomoviruses.     

Isolation of cinnamoyl CoA reductase and cinnamyl alcohol dehydrogenase gene promoters from <Emphasis Type="Italic">Leucaena leucocephala</Emphasis>, a leguminous tree species,and characterization of tissue-specific activity in transgenic tobacco

Promoter sequences of a 795 bp cinnamoyl CoA reductase (LlCCR) and 1,882 bp cinnamyl alcohol dehydrogenase (LlCAD) genes were isolated from Leucaena leucocephala, a leguminous tree species by genome walking, and analysed using bioinformatics tools. This revealed presence of cis-elements such as AC-boxes, XYLAT, WRKY, and MYB binding sites in addition to CAAT and TATA boxes. For functional characterization, each of LlCCR and LlCAD promoter sequences were fused to β-glucuronidase (GUS) reporter gene, immobilized into pBI101 plasmid, and introduced into tobacco via Agrobacterium tumefaciens strain LBA4404. Histochemical observations of transgenic lines indicated tissue-specific expression of GUS in the vascular tissues of leaves, stems, and roots. These results demonstrate that GUS expression driven by either LlCCR or LlCAD promoters were involved in lignifying tissues, and more specifically in differentiating xylem cells. This observed tissue-specific expression driven by either LlCCR or LlCAD promoters is sufficient for reducing the lignin content only in vascular tissues, thus overcoming the risks and challenges associated with down-regulation of lignin content in whole plants.     

Mating compatibility, life-history traits, and RAPD-PCR variation in Bemisia tabaci associated with the cassava mosaic disease pandemic in East Africa

The pandemic of a severe form of cassava mosaic virus disease (CMVD) in East Africa is associated with abnormally high numbers of its whitefly vector, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). To determine whether a novel B. tabaci biotype was associated with the CMVD pandemic, reproductive compatibility, fecundity, nymphal development, and random amplified polymorphic DNA (RAPD) variability were examined in, and between, B. tabaci colonies collected from within the CMVD pandemic and non-pandemic zone in Uganda. In a series of reciprocal crosses carried out over two generations among the six CMVD pandemic and four non-pandemic zone cassava B. tabaci colonies, there was no evidence of mating incompatibility. All the crosses produced both female and male progeny in the F₁ and F₂ generations, which in a haplo-diploid species such as B. tabaci indicates successful mating. There also were no significant differences between the sex ratios for the pooled data of experimental crosses, between individuals from two different colonies and control crosses between individuals from the same colony. Only one instance of mating incompatibility occurred in a control cross between cassava B. tabaci from Uganda and cottonB. tabaci from India. Measures of fecundity of the pandemic and non-pandemic zone B. tabaci on four cassava varieties showed no significant differences in their fecundity, nymphal development or numbers surviving to adult eclosion. Cluster analysis of 26 RAPD bands using six 10-mer primers was concordant with the mating results, grouping the pandemic and non-pandemic zone colonies into a single large group, also including a B. tabaci colony collected from cassava in Tanzania. These results suggest that it is unlikely that the severe CMVD pandemic in East Africa is associated with a novel and reproductively isolated B. tabaci biotype.     

Genetic diversity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) populations and presence of the B biotype and a non-B biotype that can induce silverleaf symptoms in squash, in Uganda

The extent of genetic variability and host‐plant distribution of Bemisia tabaci (Gennadius) genotypes colonising cultivated and uncultivated plant species occurring adjacent to cassava fields in selected cassava‐producing areas of Uganda in 2003/04 were investigated using the mitochondrial cytochrome oxidase I (mtCOI) gene as the molecular marker. Eight genotype clusters, Ug1–Ug8, which are supported by high bootstrap values (≥80), at 3–18% nt divergence, were revealed among the collective Ugandan B. tabaci populations. Ug1 and Ug2 (both cassava‐associated) and Ug8 (sweetpotato‐associated) have been reported previously in Uganda. Ug3 was genetically dissimilar to B. tabaci described elsewhere and colonised a single species, Ocimum gratissimum. Ug4–Ug7 formed four closely related subclusters (93–97% nt identity) and diverged by 15–18% from Ug1, Ug2, Ug3 and Ug8, respectively. Ug4 had as its closest relatives (at 97–99% nt identity) the Ivory Coast okra biotype, whereas genotypes Ug5 and Ug6 had as their closest relatives (at 95–99% and 99% nt identity, respectively) the Mediterranean–North Africa–Middle East (MED‐NAFR‐ME) biotypes, which also include the well‐studied B and Q biotypes. Ug7 was closely related (at 98–99% nt identity) to biotype Ms from the Reunion Island in the Indian Ocean. Ug4 colonised Cucurbita pepo, Cucurbita sativus, Leonotis nepetifolia and Pavonia urens, while Ug7 colonised Commelina benghalensis, Gossypium hirsutum and Phaseolus vulgaris. Ug6, the B‐biotype‐like genotype colonised Abelmoschus esculentus and C. benghalensis only. None of Ug4–Ug7 genotypes was found associated with, or colonising, cassava or sweetpotato plants. In addition to colonising sweetpotato, the Ug8 genotypes colonised Lycopersicon esculentum and L. nepetifolia. Ug6 and Ug7, both members of the B biotype/B‐like cluster, induced silverleaf symptoms on Cucurbita sp. The discovery of five previously identified B. tabaci genotype clusters, Ug3–Ug7, in Uganda, among which are some of the world's most economically important biotypes, namely B and Q, is particularly significant in the spread of geminiviruses with devastating effects to crop production in Africa.