Nickel accumulation and nickel oxalate precipitation by Aspergillus niger.

A strain of Aspergillus niger isolated from a metal-contaminated soil was able to grow in the presence of cadmium, chromium, cobalt, copper, and unusually high levels of nickel on solid (8.0 mM) and in liquid (6.5 mM) media. This fungus removed >98% of the nickel from liquid medium after 100 h of growth but did not remove the other metals, as determined by inductively coupled plasma spectroscopy. Experiments with non-growing, live fungal biomass showed that nickel removal was not due to biosorption alone, as little nickel was bound to the biomass at the pH values tested. Furthermore, when the protonophore carbonyl cyanide p-(trifluoremetoxy) phenyl hydrazone (FCCP) was added to the actively growing fungus nickel removal was inhibited, supporting the hypothesis that energy metabolism is essential for metal removal. Analytical electron microscopy of thin-sectioned fungal biomass revealed that metal removed from the broth was localized in the form of small rectangular crystals associated with the cell walls and also inside the cell. X-ray and electron diffraction analysis showed that these crystals were nickel oxalate dihydrate.

Kinetics of toluene degradation by a nitrate-reducing bacterium isolated from a groundwater aquifer.

Groundwater from a xylene-contaminated acquifer was enriched in the laboratory in the presence of toluene, xylenes, ethylbenzene, and benzene. A pure culture that degrades toluene and m-xylene under nitrate-reducing conditions was isolated. Fatty acid analysis, 16S rRNA sequencing, and morphological traits indicate that the isolate was a strain of Azoarcus tolulyticus. The kinetics of toluene degradation under nitrate-reducing conditions by this isolate was determined. Nitrate reduction does not proceed beyond nitrite. Nitrate and toluene are substrate limiting at low concentrations, whereas toluene, nitrate, and nitrite are inhibitory at high concentrations. Several inhibition models were compared to experimental data to represent inhibition by these substrates. A kinetic model for toluene and nitrate degradation as well as for cell growth and nitrite production was developed and compared to experimental data. The results of this work may find important application in the remediation of groundwater aquifers contaminated with aromatic hydrocarbons.

Bioavailability of selenium accumulated by selenite-reducing bacteria.

The bioavailability of selenium (Se) was determined in bacterial strains that reduce selenite to red elemental Se (SeO). A laboratory strain of Bacillus subtilis and a bacterial rod isolated from soil in the vicinity of the Kesterson Reservoir, San Joaquin Valley, CA, (Microbacterium arborescens) were cultured in the presence of 1 mM sodium selenite (Na2SeO3). After harvest, the washed, lyophilized B. Subtilis and M. arborescens samples contained 2.62 and 4.23% total Se, respectively, which was shown to consist, within error, entirely of SeO. These preparations were fed to chicks as supplements to a low-Se, vitamin E-free diet. Three experiments showed that the Se in both bacteria had bioavailabilities of approx 2% that of selenite. A fourth experiment revealed that gray SeO had a bioavailability of 2% of selenite, but that the bioavailability of red SeO depended on the way it was prepared (by reduction of selenite). When glutathione was the reductant, bioavailability resembled that of gray SeO and bacterial Se; when ascorbate was the reductant, bioavailability was twice that level (3-4%). These findings suggest that aerobic bacteria such as B. subtilis and M. arborescens may be useful for the bioremediation of Se-contaminated sites, i.e., by converting selenite to a form of Se with very low bioavailability.

A crystalline inclusion in sieve element nuclei of Amsinckia. I. The inclusion in differentiating cells.

The presence of usually single, elongated, compound crystalloids in nuclei of sieve elements is an outstanding characteristic of the phloem of Amsinckia douglasiana A. DC. (Boraginaceae). The crystalloid consists of two components forming alternating panels, or blocks, that extend through the entire length of the crystalloid and radiate from the centre where one of the components predominates. Three to seven panels for each component were recorded. One component consists of 4-sided tubules closely packed in highly ordered aggregates, the other of wider 6-sided tubules rather loosely arranged in paracrystalline aggregates. The crystalloid arises at the beginning of sieve element differentiation. Aggregates of 4-sided tubules appear first. In plants infected with the curly top virus, the crystalloids do not differ from those in non-infected controls in structure and conformation. But because the phloem in infected plants is hyperplastic, with most of the cells differentiating as sieve elements, the crystalloids are far more abundant in diseased than in healthy plants.

A crystalline inclusion in sieve element nuclei of Amsinckia. II. The inclusion in maturing cells.

The compounds crystalloids formed in sieve element nuclei of Amsinckia douglasiana A. DC. (Boraginaceae) during differentiation of the cell become disaggregated during the nuclear breakdown characteristic of a maturing sieve element. The phenomenon occurs in both healthy and virus-infected plants. The crystalloid component termed cy, which is loosely aggregated, separates from the densely aggregated component termed cx and disperses. The cx component may become fragmented, or broken into large pieces, or remain intact after the cell matures. After their release from the nucleus both crystalloid components become spatially associated with the dispersed P-protein originating in the cytoplasm, but remain distinguishable from it. The component tubules of P-protein are hexagonal in transections and are somewhat wider than the 6-sided cy tubules. The cx tubules are much narrower than the P-protein or the cy tubules and have square transections. Both the P-protein and the products of disintegrated crystalloids accumulate at sieve plates in sieve elements subjected to sudden release of hydrostatic pressure by cutting the phloem. The question of categorizing the tubular components of the nuclear crystalloid of a sieve element with reference to the concept of P-protein is discussed.

Effect of powdery mildew infection on photosynthesis by leaves and chloroplasts of sugar beets.

Chloroplasts isolated from powdery mildew-infected (Erysiphe polygoni DC) sugar beet leaves (Beta vulgaris L) showed a reduction in the rate of electron transport and in the accompanying ATP formation in noncyclic photophosphorylation (water as electron donor, NADP as electron acceptor) and little or no change in the rate of ATP formation in cyclic photophosphorylation catalyzed by phenazine methosulfate. The inhibition of noncyclic photophosphorylation appeared to lead in the parent leaves to a decreased rate of photosynthetic CO(2) assimilation and a shift in products resulting in a relative increase of amino acids. These changes were accompanied by alterations in chloroplast ultrastructure and by a reduction in the activity of enzymes necessary for the formation of organic acids (phosphoenolpyruvate carboxylase and malate dehydrogenase). These results are similar to the findings of Montalbini and Buchanan (1974 Physiol. Plant Pathol. 4: 191-196) with chloroplasts from rust-infected Vicia faba leaves.