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The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans , A. thiooxidans and A. caldus cells to sublethal Cd 2+ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360 nm and a broad emission spectra between 450 and 650 nm when excited at 370 nm, both characteristic of CdS QDs. Average sizes of 6 and 10 nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H 2 S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5–5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms. [ABSTRACT FROM AUTHOR]

An integrated process based on the concomitant role of non-ionic surfactants as cell disrupters and organic extractants of intracellular antioxidants is proposed for the first time in this work. The lytic effect of two common families of surfactants on the cell walls of the microalga Tetraselmis suecica has been initially evaluated. The antioxidant extraction based on aqueous two-phase systems (ATPS) was proposed using different potential salting out agents such as sodium inorganic and organic salts in aqueous solutions of the selected surfactants. The extraction efficiency was ascertained for the most representative biomolecules previously detected in this microalga: α-tocopherol, β-carotene and gallic acid. The viability of the process was checked in real lyophilized microalga samples, yielding higher antioxidant activity than that provided by an ultrasound-based conventional method. [ABSTRACT FROM AUTHOR]

Previous studies demonstrated that it is possible to optimize Oreochromis mossambicus fry production in a recirculating system by means of supplemented diets with Artemia's cysts. In the present work, productive yields of Oreochromis niloticus, species kind highly cultured in México and worldwide, and O. mossambicus fry are reported in order to know the possible differences on growth and survival. Tilapia fry with a mean wet weight of 0.011 ± 0.002 and 0.017 ± 0.005 g(O. niloticus and O. mossambicus, respectively), were fed with a dietary inclusion of 10% of decapsulated Artemia cysts (QDS) in a starter commercial diet, during the first month of exogenous feeding after yolk absorption. Fry were reared in a recirculating system at a stocking density of 5 org/l (5000 org/m3). Diet was given at a daily feeding rate of 25% of body biomass, four times a day. Final mean weight and survival for O. niloticus and O. mossambicus were 1.31 ± 0.15 and 1.60 ± 0.22 g, and 90 % y 97.5 %, respectively. There were no significant differences (p > 0.05) in final yields (mean weight, length, biomass/l, daily weight gain, specific growth, feed conversion and survival) between species. The results suggests that an inclusion of 10% of QDS in the hatchery diet may improve growth performance of both Oreochomis species under similar management conditions. Technical and economic considerations should be carefully reviewed before using QDS at commercial level. [ABSTRACT FROM AUTHOR]