Biotransformation of mercury by bacteria isolated from a river collecting cinnabar mine waters

One hundred six strains of aerobic bacteria were isolated from the Fiora River which drains an area of cinnabar deposits in southern Tuscany, Italy. Thirty-seven of the strains grew on an agar medium containing 10g/ml Hg (as HgCl₂) with all of these strains producing elemental mercury. Seven of the 37 strains also degraded methylmercury. None of 106 sensitive and resistant strains produced detectable monomethylmercury although 15 strains produced a benzene-soluble mercury species. Two strains of alkylmercury (methyl-, ethyl- and phenylmercury) degrading bacteria were tested for the ability to degrade several other analogous organometals and organic compounds, but no activity was detected toward these compounds. Mercury methylation is not a mechanism of Hg resistance in aerobic bacteria from this environment. Growth of bacteria on the agar medium containing 10g/ml HgCl₂ was diagnostic for Hg detoxification based on reduction.     

Photosynthetic properties of leaves of a yellow green mutant of wheat compared to its wild type

We investigated several photosynthetic parameters of a virescent mutant of durum wheat and of its wild-type. Electron transport rate to ferricyanide was the same in the two genotypes when expressed on leaf area basis while O₂ evolution of the leaf tissue in saturating light and CO₂ was slightly higher in the yellow genotype. RuBPCase was also slightly higher. Quantum yield per absorbed light was similar in the two genotypes. P700 and Cyt f were less concentrated in the mutant while PS II was only marginally lower. The light response curve of CO₂ assimilation indicated higher level of photosynthesis of the mutant in high light, which corresponded to a lower non-photochemical quenching compared to the wild-type. It is concluded that the reaction centres, cyt f and chlorophyll are not limiting factors of electron transport in wheat seedlings and that electron transport capacity is in excess with respect to that needed for driving photosynthesis. Since the differences in photosynthesis reflect differences in RuBPCase activity, it is suggested that this enzyme limits photosynthesis in wheat seedlings also at high light intensities.Abbreviations cyt f cytochrome f - chl chlorophyll - PS II photosystem II - Pn_max maximum photosynthesis - RuBCase Ribulose, 1-5,bisphosphate carboxylase     

Viability of an ectomycorrhizal fungus during cross-flow filtration

Factors affecting the viability and infectivity of an ectomycorrhizal fungus during moderate concentration by cross-flow filtration were determined. Mycelial suspensions were concentrated with three commercial membrane filters (Prostak Millipore Co., M14 Tech-Sep Co. and Ceraflo Norton Co.) under aseptic conditions. Medium components may reduce the filtration rate due to their low solubility. An antifoam agent did not reduce the average flux rates as much as did the malt extract. Clear unobstructed channels (I.D. 6mm) of the tubular modules (Tech-Sep) gave the best results both in terms of performance (filtration rate) and cell viability. Shear stresses caused by pumping and flow through narrow retentate channels were probably responsible for lowering viability and infectivity. There was no linear relationship between permeate fluxes and cell concentration. There is an optimum pore size both in terms of performance (filtration rate) and cell viability. Physical blockage of large pores by hyphae could explain lower permeate flux rates than those obtained with lower pore sizes membranes.     

On the solution of mathematical models of herd immunity in human helminth infections

The general solution of the mathematical model of herd immunity to human helminth infections recently proposed by Anderson and May [3] is obtained. The numerical solution of a more accurate biological model is indistinguishable from the corresponding exact solution of a more tractable mathematical model. Computer simulations of some particular cases of this model support the notion that both ecological and immunological factors determine the observed convex patterns of age-prevalence and age-intensity curves of human helminth infections.This work was made thanks to the advise and support of Dr. Robert M. May while the author was Postdoctoral Fellow at Princeton University     

Allelic and Genotypic Composition of Ancestral Spanish and Colonial Californian Gene Pools of Avena Barbata: Evolutionary Implications

Spanish explorers and colonists inadvertently started a massive experiment in evolutionary genetics when they accidentally introduced Avena barbata to California from Spain during the seventeenth and eighteenth centuries. Assays of the Spanish and Californian gene pools of this species for 15 loci show that the present day Spanish gene pool, particularly that of Southwestern Spain, is identical or virtually identical to that of California for five loci and closely similar for nine loci. Despite their similar allelic and single-locus genotypic compositions, the present-day Spanish and Californian gene pools are differently structured on a multilocus genetic basis. Evolutionary implications of these results are discussed.     

Substrate specificity of the agonist-stimulated release of polyunsaturated fatty acids from vascular endothelial cells

Stimulation of vascular endothelial cells with agonists such as histamine and thrombin results in release of arachidonic acid from membrane lipids and subsequent eicosanoid synthesis. As shown previously, the agonist-stimulated deacylation is specific for arachidonate, eicosapentaenoate, and 5,8,11-eicosatrienoate. This study has utilized radiolabeled fatty acids differing in chain length and position of double bonds to further elucidate the fatty acyl specificity of agonist-stimulated deacylation. Replicate wells of confluent human umbilical vein endothelial cells were incubated with 14C-labeled fatty acids and then challenged with histamine, thrombin, or the calcium ionophore A23187. Comparison of the results obtained with isomeric eicosatetraenoic fatty acids with initial double bonds at carbons 4, 5, or 6 indicated that the deacylation induced by all three agonists exhibited marked specificity for the cis-5 double bond. Lack of stringent chain length specificity was indicated by agonist-stimulated release of 5,8,11,14- tetraenoic fatty acids with 18, 19, 20, and 21 carbons. Release of 5,8,14-[14C]eicosatrienoate was two-to threefold that of 5,11,14-[14C]eicosatrienoate, thus indicating that the cis-8 double bond may also contribute to the stringent recognition by the agonist-sensitive phospholipase. The present study has also demonstrated that histamine, thrombin, and A23187 do not stimulate release of docosahexaenoate from endothelial cells.     

Evidence for the formation of covalent bonds between macromolecules in the domain of the wall of Candida albicans mycelial cells

An O-glycosylated mannoprotein, after its incorporation into the wall, showed an increase in its molecular weight, due at least to its association with N-glycosidic sugar chain(s). This was shown by rendering the material soluble after partial degradation of the wall structure. At present it is unknown whether this phenomenon is due to an additional transglycosylation process or whether the partial degradation of the wall solubilizes a supramolecular structure formed between the original O-glycosylated protein which becomes linked either directly or indirectly through a protein to the N-sugar chain(s).     

Transformation of NIH 3T3 cells by overexpression of the normal coding sequence of the rat neu gene.

While the normal human erbB-2 gene is potently transforming when overexpressed in NIH 3T3 cells, its rat homolog, the neu gene, seems to acquire transforming properties only upon alteration of its coding sequence. In this study, we compared the effects of different levels of expression of normal erbB-2 and neu in NIH 3T3 cells. Our results revealed that the normal rat neu gene acts as a potent oncogene when sufficiently overexpressed in NIH 3T3 cells.