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The Actinomycete Gordonia amicalis HS-11 produced orange pigments when cultivated on n -hexadecane as the sole carbon source. When cells of this pigmented bacterium were incubated with 1 mM chloroauric acid (HAuCl 4 ) or silver nitrate (AgNO 3 ), pH 9.0, at 25 °C, gold and silver nanoparticles, respectively, were obtained in a cell associated manner. It was hypothesized that the pigments present in the cells may be mediating metal reduction reactions. After solvent extraction and High Performance Liquid Chromatography, two major pigments displaying UV–vis spectra characteristic of carotenoids were isolated. These were identified on the basis of Atmospheric Pressure Chemical Ionization Mass Spectrometry (APCI-MS) in the positive mode as 1′-OH-4-keto-γ-carotene (Carotenoid K) and 1′-OH-γ-carotene (Carotenoid B). The hydroxyl groups present in the carotenoids were eliminated under alkaline conditions and provided the reducing equivalents necessary for synthesizing nanoparticles. Cell associated and carotenoid stabilized nanoparticles were characterized by different analytical techniques. In vitro free radical scavenging activities of cells (control, gold and silver nanoparticle loaded), purified carotenoids and carotenoid stabilized gold and silver nanoparticles were evaluated. Silver nanoparticle loaded cells and carotenoid stabilized silver nanoparticles exhibited improved nitric oxide (NO) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activities compared to their control and gold counterparts. This paper thus reports cell associated nanoparticle synthesis by G. amicalis , describes for the first time the role of carotenoid pigments in metal reduction processes and demonstrates enhanced free radical scavenging activities of the carotenoid stabilized nanoparticles. [ABSTRACT FROM AUTHOR]

A bacterial isolate obtained from an oil-contaminated soil sample was identified as Gordonia amicalis on the basis of morphological features, biochemical traits and 16S rRNA gene sequence. The cell free supernatant (CFS) of this bacterium (cultivated on n -hexadecane) when incubated with 1 mM chloroauric acid (HAuCl 4 ) or silver nitrate (AgNO 3 ) at pH 9.0 in a boiling water bath mediated the synthesis of gold and silver nanoparticles, respectively. It was hypothesized that the CFS contained some thermostable biomolecule that mediated metal reduction reactions. Extraction of CFS with chloroform:methanol (2:1), subsequent column chromatography and thin layer chromatography led to the activity-guided purification of a glycolipid. The glycolipid was hydrolysed and the glycone (glucose) and aglycone components (three saturated fatty acids (myristic, palmitic and stearic) were identified by gas chromatography mass spectrometry. The reduction of glucose to gluconic acid under alkaline conditions provided the reducing equivalents needed for nanoparticle synthesis. The purified glycolipid and CFS mediated nanoparticles were characterized by using a UV–vis spectrophotometer, X-ray diffractometer and Transmission Electron Microscope. The nanoparticles displayed free radical scavenging activities. This paper thus highlights nanoparticle synthesis by a hitherto unreported actinomycete culture, identifies the biomolecule involved in the process and describes the associated antioxidant activity. [ABSTRACT FROM AUTHOR]

Yarrowia lipolytica is a dimorphic, non-pathogenic, ascomycetous yeast species with distinctive physiological features and biochemical characteristics that are significant in environment-related matters. Strains naturally present in soils, sea water, sediments and waste waters have inherent abilities to degrade hydrocarbons such as alkanes (short and medium chain) and aromatic compounds (biphenyl and dibenzofuran). With the application of slow release fertilizers, design of immobilization techniques and development of microbial consortia, scale-up studies and in situ applications have been possible. In general, hydrocarbon uptake in this yeast is mediated by attachment to large droplets (via hydrophobic cell surfaces) or is aided by surfactants and emulsifiers. Subsequently, the internalized hydrocarbons are degraded by relevant enzymes innately present in the yeast. Some wild-type or recombinant strains also detoxify nitroaromatic (2,4,6-trinitrotoluene), halogenated (chlorinated and brominated hydrocarbons) and organophosphate (methyl parathion) compounds. The yeast can tolerate some metals and detoxify them via different biomolecules. The biomass (unmodified, in combination with sludge, magnetically-modified and in the biofilm form) has been employed in the biosorption of hexavalent chromium ions from aqueous solutions. Yeast cells have also been applied in protocols related to nanoparticle synthesis. The treatment of oily and solid wastes with this yeast reduces chemical oxygen demand or value-added products (single cell oil, single cell protein, surfactants, organic acids and polyalcohols) are obtained. On account of all these features, the microorganism has established a place for itself and is of considerable value in environment-related applications. [ABSTRACT FROM AUTHOR]