Ultrastructural localization of uranium biosorption in Penicillium digitatum by stem X-ray microanalysis.

When Penicillium digitatum Saccardo cultures are exposed to aqueous solutions containing soluble uranium salts, considerable amounts of this element are accumulated in the fungal mycelium. The accumulated uranium is retained after thorough rinsing with distilled water but is removed by alkali carbonate solutions. Analysis of thick sections (0.5 microm) of the fungal hyphae with TEM, after incubation in UO(2)Cl(2) solutions of varying concentrations under both light and dark conditions, revealed conspicuous crystal-like deposits in UO(2)Cl(2)-exposed hyphae, but none in the control hyphae. Thick sections were necessary for crystal visualization. Using energy-dispersive X-ray analysis, uranium was detected as the only heavy element in these crystals. Uranium crystal biosorption was localized on the outside surface of the hyphal cell wall (following short exposures to relatively low uranium concentrations) or inside the cell wall (following long exposure to relatively high uranium concentrations). In some cases, crystal-like deposits of uranium salts were located on the outside surface as well as inside the cell.

Photoacoustic study of the green alga Trebouxia in the lichen Ramalina duriaei in vivo.

Photosynthetic parameters of the lichen Ramalina duriael were investigated in vivo, by the photoacoustic method using intensity-modulated exciting light (frequency range 5-300 Hz). The photoacoustic signal in intact lichens was similar in its general characteristics to that obtained from intact leaves of higher plants (Poulet et al., Biochim. Biophys. Acta 724, 433-446, 1983). It included two components interpreted to be due to modulated heat and modulated oxygen evolution. The quantum yield of the oxygen evolution component was maximal in the red spectral region and exhibited the 'red drop' decrease at wavelengths larger than 680 nm, similar to observations in higher plants. In contrast to those however, there was a pronounced decrease in this yield in the region below about 600 nm, indicating that pigments absorbing at shorter wavelengths are inefficient energy transfer agents. Similar results were observed for the quantum yield spectrum of photochemical energy storage. Analysis of oxygen diffusion in the symbiont alga, from the modulation frequency dependence of the ratio of oxygen evolution to photothermal signal component is consistent with an average diffusion path of about 4 µm, compared to a smaller, 1 µm, average diffusion path obtained in green leaves.

Removal of Uranium(VI) from Solution by Fungal Biomass and Fungal Wall-Related Biopolymers.

Penicillium digitatum mycelium can accumulate uranium from aqueous solutions of uranyl chloride. Azide present during the uptake tests does not inhibit the process. Killing the fungal biomass in boiling water or by treatment with alcohols, dimethyl sulfoxide, or potassium hydroxide increases the uptake capability to about 10,000 parts per million (dry weight). Formaldehyde killing does not enhance the uranium uptake. The inference that wall-binding sites were involved led to the testing of uranium uptake by chitin, cellulose, and cellulose derivatives in microcolumns. All were active, especially chitin.

Effect of water regime on carbon isotope composition of lichens.

delta(13)C values of the lichens Ramalina duriaei and Teloschistes villosus collected in their natural habitat were repeatedly measured during 2 years. Results show variations in the stable carbon isotope ratios ((13)C/(12)C). Such variations are correlated to the seasonal rainfall, i.e. low values of delta(13)C of the lichens during the winter and high values of delta(13)C during the dry summer. Relatively low delta(13)C values were obtained also in laboratory experiments with lichens grown under controlled humid conditions and in lichens collected from humid habitats.The variations in carbon isotopes were associated with quantitative metabolic changes. Under humid conditions an increase was obtained in the total amount of the extracted water-soluble fraction of the plant tissues as well as in the relative content of soluble carbohydrates.Analysis of the possible factors which may cause such variations indicates that the quantity of precipitation and the exposure time to high humidity were the main environmental factors causing seasonal variations in the delta(13)C values of the lichens. Such variations are dependent mainly on enzymic reactions and are probably less influenced by purely physicochemical processes. In view of the data presented here the balance between carboxylation and decarboxylation reactions seems to be the major factor for the observed seasonal differences. Winter accumulation of (12)C enriched components causes an over-all decrease in delta(13)C. During the summer, those storage materials are respired with concomitant increase in the delta(13)C of the residual plant material.

Hyphal walls of isolated lichen fungi: autoradiographic localization of precursor incorporation and binding of fluorescein-conjugated lectins.

The hyphal walls of three mycobionts, isolated from the lichens Xanthoria parietina, Tornabenia intricata and Sarcogyne sp. were investigated by two techniques: microautoradiography of fungal colonies exposed to radioactive carbohydrate precursors: and binding, in vivo, of fluorescein conjugated lectins to hyphal walls of such colonies. N-[3H] acetylglucosamine was readily incorporated into tips, young hyphal walls and septa of the three mycobionts and the free-living fungus Trichoderma viride, but not into Phytophthora citrophthora, indicating that chitin is a major component of the mycobionts' hyphal walls. All three mycobionts, but neither of the free-living fungi, incorporated [3H] mannose and [3H] mannitol into their hyphal walls. Fluorescein-conjugated wheat germ agglutinin was bound to the hyphal walls of the three mycobionts and T. viride, but not to the walls of P. citrophthora; the binding pattern was similar to the grain pattern obtained in autoradiographs after short N-[3H]acetylglucosamine labelling. As wheat germ agglutinin binds specifically to chitin oligomers, the lectin binding tests further confirmed that chitin is a mycobiont hyphal wall component. Binding characteristics of several fluorescein-conjugated lectins to the three mycobionts indicated that this technique can yield useful information concerning the chemical composition of hyphal wall surfaces.