U L (u + l)

Distribution by Scientific Domains

Selected Abstracts

Phosphate regulates uranium(VI) toxicity to Lemna gibba L. G3

Martin Mkandawire
Abstract The influence of phosphate on the toxicity of uranium to Lemna gibba G3 was tested in semicontinuous culture with synthetic mine water developed as an analogue of surface water of two abandoned uranium mining and ore processing sites in Saxony, Germany. Six concentrations of uranium were investigated under five different supply regimes of PO43, at constant pH (7.0 0.5) and alkalinity (7.0 1.6 mg L,1 total CO32,). The results showed significant inhibition of specific growth rates in cultures exposed to the highest uranium concentrations (3500 and 7000 ,g U L,1) at lowest PO43, supply of 0.01 mg L,1. An increase of phosphate concentration from 0.01 to 8.0 mg L,1 resulted in an increase of EC50 from 0.9 0.2 to 7.4 1.9 mg L,1 (significant with Student's t test, P > 0.05). The accumulation of uranium in L. gibba increased exponentially with the increase in uranium concentration in cultures with 0.01 and 0.14 mg PO43, L,1. Accumulation also increased significantly when PO43, supply was increased from 0.14 to 1.36 mg PO43, L,1 for all uranium concentrations. However, as the supply of PO43, gradually increased from 1.36 to 8.0 mg PO43, L,1, uranium bioaccumulation increased slightly but insignificantly before leveling off. Uranium speciation modeling with PhreeqC geochemical code predicted increases in the proportions of uranyl phosphate species when PO43, concentrations increase in the media. Most of these uranyl phosphate species have a high probability of precipitation [saturation indices (SI) > 0.93]. Therefore, the alleviation of uranium toxicity to L. gibba with phosphates is due to interactions among components of the media, mainly uranyl and phosphate which results in precipitation. Consequently, bioavailable fractions of uranium to L. gibba are reduced. This might explain lack of consistent EC50 values for uranium to most aquatic organisms. 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 9,16, 2007. [source]

A cost-effective cane molasses medium for enhanced cell-bound phytase production by Pichia anomala

A. Vohra
Abstract Aim:, Formulation of an inexpensive cane molasses medium for improved cell-bound phytase production by Pichia anomala. Methods and Results:, Cell-bound phytase production by Pichia anomala was compared in synthetic glucose,beef extract and cane molasses media. The yeast was cultivated in 250 ml flasks containing 50 ml of the medium, inoculated with a 12 h-old inoculum (3 106 CFU ml,1) and incubated at 25C for 24 h at 250 rev min,1. Different cultural parameters were optimized in cane molasses medium in batch fermentation. The cell-bound phytase content increased significantly in cane molasses medium (176 U g,1 dry biomass) when compared with the synthetic medium (100 U g,1 dry biomass). In fed-batch fermentation, a marked increase in biomass (20 g l,1) and the phytase yield (3000 U l,1) were recorded in cane molasses medium. The cost of production in cane molasses medium was 0006 per 1000 U, which is much lower when compared with that in synthetic medium (025 per 1000 U). Conclusions:, An overall 866% enhancement in phytase yield was attained in optimized cane molasses medium using fed-batch fermentation when compared with that in synthetic medium. Furthermore, the production in cane molasses medium is cost-effective. Significance and Impact of the Study:, Phytase yield was improved in cane molasses when compared with the synthetic medium, and the cost of production was also significantly reduced. This enzyme can find application in the animal feed industry for improving the nutritional status of feed and combating environmental pollution. [source]

pH Control of the production of recombinant glucose oxidase in Aspergillus nidulans

R. Luque
Abstract Aims:, Recombinant Aspergillus nidulans sVAL040, capable of synthesizing and secreting glucose oxidase derived from Aspergillus niger was used to study the influence of pH and carbon source on enzyme production. Methods and Results:, Glucose oxidase gene (goxC) was expressed under transcriptional regulation by using the promoter of A. nidulans xlnB gene (encoding an acidic xylanase). A maximum specific glucose oxidase activity of approx. 10 U mg,1 protein and a maximum volumetric productivity of 299 U l,1 h,1 were obtained at pH 55, after 80 h of growth by using xylose as inducer. Enzyme volumetric productivity increased when xylans were used instead of xylose; however, specific glucose oxidase activity did not differ significantly. Conclusions:, Specific GOX activity obtained at pH 55 are two to three times more than those previously described for goxC multicopy transformants of A. nidulans. Xylans were a more powerful inducer than xylose although fungal growth was lower when the polymers were used. Significance and Impact of the Study:, The obtained results by using xlnB promoter in A. nidulans could be useful in improving heterologous enzyme production by using genetic- and process-engineering strategies. [source]

Effect of culturing processes and copper addition on laccase production by the white-rot fungus Fomes fomentarius MUCL 35117

M. Neifar
Abstract Aim:, To produce high laccase activities from the white-rot fungus Fomes fomentarius. Methods and Results:, Different culturing methods, viz, cell immobilization on stainless steel sponges and plastic material and solid-state fermentation (SSF) using wheat bran as substrate were used for laccase production by the white-rot fungus F. fomentarius. The SSF study expresses the highest laccase activities, nearly to 6400 U l,1 after 13 days of laboratory flasks cultivation. When the wheat bran medium was supplemented with 2 mmol l,1 copper sulfate, laccase activity increased by threefold in comparison to control cultures, reaching 27 864 U l,1. With the medium thus optimized, further experiments were performed in a 3 l fixed-bed bioreactor (working volume 15 l) leading to a laccase activity of about 6230 U l,1 on day 13. Conclusions:, The results obtained clearly showed the superiority of wheat bran for laccase production over stainless steel sponges and plastic material. Supplementing the wheat bran solid medium with 2 mmol l,1 copper sulfate allowed obtaining high activities at flask scale. The system was scaled to fixed-bed laboratory reactor. Significance and Impact of the Study:, The high enzyme production along with the low-cost of the substrate, showed the suitability of the system F. fomentarius, SSF for industrial purposes. [source]