Psychrotrophic yeast Yarrowia lipolytica NCYC 789 mediates the synthesis of antimicrobial silver nanoparticles via cell-associated melanin
© Apte et al.; licensee Springer. 2013
Received: 9 April 2013
Accepted: 3 June 2013
Published: 7 June 2013
A psychrotrophic marine strain of the ascomycetous yeast Yarrowia lipolytica (NCYC 789) synthesized silver nanoparticles (AgNPs) in a cell-associated manner. These nanostructures were characterized by UV-Visible spectroscopy and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analysis. The brown pigment (melanin) involved in metal-interactions was obtained from the cells. This extracted pigment also mediated the synthesis of silver nanoparticles that were characterized by a variety of analytical techniques. The melanin-derived nanoparticles displayed antibiofilm activity. This paper thus reports the synthesis of AgNPs by the biotechnologically important yeast Y. lipolytica; proposes a possible mechanism involved in the synthetic process and describes the use of the bio-inspired nanoparticles as antibiofilm agents.
It is a well established fact that nanoparticles of noble metals (gold and silver) exhibit strong antimicrobial properties (Zhou et al. 2012). An increase in the price of gold in the recent past has brought some restriction on the use of nanoparticles of this metal for antimicrobial applications. On the other hand, antimicrobial activity of silver has been documented since a very long time. In the past few decades, the significance of silver nanoparticles (AgNPs) as antimicrobial agents has increased to a great extent (Rai et al. 2009). Compared to metallic silver, AgNPs display higher surface to volume ratio and exhibit enhanced antimicrobial activity. AgNPs are extensively used in the field of medicine (Jain et al. 2009; Ravindra et al. 2010).
The conventional processes for nanoparticle synthesis involve top-down or bottom-up approaches usually employing physical or chemical protocols. However, such processes are often energy-demanding and cost-intensive (Zinjarde, 2012). Moreover, the chemicals used in such procedures are toxic and the size of the nanoparticles is difficult to control. In view of these problems, biological systems have emerged as effective alternatives for the clean and green synthesis of nanostructures (Sharma et al. 2009; Thakkar et al. 2010; Gade et al. 2010). Yarrowia lipolytica is a yeast that is routinely used in the synthesis of citric acid, mannitol and erythritol (Rywińska and Rymowicz 2010; Tomaszewska et al. 2012). The yeast is also associated with different cheese varieties (Lanciotti et al. 2005; Gardini et al., 2006). In some cases, this causes the brown discoloration of cheese (Carreira et al. 1998). The brown color is due to a pigment, melanin (Carreira et al. 2001). It is a well-known fact that fungal melanins have strong anti-oxidant properties that protect them from radiation, high temperature, free radical attack and metals (Fogarty and Tobin 1996 Apte et al. 2013).
During the present study, we put forth the following hypotheses (i) The yeast Y. lipolytica may produce silver nanoparticles (ii) melanin maybe involved in nanoparticle synthesis and (iii) the bio-inspired AgNPs may display antimicrobial activity against pathogenic bacteria. To test the aforementioned hypotheses, we chose a psychrotrophic strain of Y. lipolytica (NCYC 789) hitherto not reported to synthesize AgNPs. This paper describes the conditions for the synthesis of AgNPs (by cells and by melanin isolated from the cells) and their characterization by a variety of analytical techniques. In addition, applications of the melanin-mediated silver nanoparticles as antibacterial and antibiofilm agents against a representative pathogen are also demonstrated.
Materials and methods
Microorganism and culture maintenance
A psychrotrophic strain of Y. lipolytica deposited in National Collection of Yeast Cultures, U.K. as NCYC 789 was used in this study. Stock cultures of the yeast were maintained on MGYP slants containing malt extract, 3.0; glucose, 10.0; yeast extract, 3.0; peptone, 5.0; agar, 25.0 g/l of distilled water and sub-cultured at monthly intervals. The culture was grown at 20°C.
Synthesis of silver nanoparticles by Y. lipolytica NCYC 789
Yeast cells were inoculated in YNB glucose (yeast nitrogen base, 7.0; glucose, 10.0 g/l distilled water) and incubated on a shaker (130 rpm, 48 h, 20°C). The culture broth was centrifuged (6000 × g, 10 min, 10°C) and the cell pellets were washed thrice to remove residual glucose. Fixed numbers of cells (1010cells/ml estimated by counting on a Neubauer chamber) were re-suspended in 20 ml of aqueous AgNO3 solutions to achieve final concentrations of 1.0, 2.0, 3.0 or 4.0 mM. The mixtures were incubated in dark on a shaker (130 rpm, 120 h, 20°C). Aliquots were withdrawn and the contents were centrifuged as described above. The re-suspended cell pellet and the cell-free medium were monitored for the presence of intracellular or extracellular silver nanoparticles, respectively, by measuring the UV-Visible spectra. All experiments were carried out in triplicates and representative data is presented here.
Extraction of melanin from yeast cells
The melanin was extracted by following the standard procedure described earlier (Ito et al. 2007 Apte et al. 2013). Briefly, yeast cells were grown at 20°C for 72 h and the biomass was harvested by centrifugation (8000 × g, 15 min, 10°C). The washed cell pellets were dried in an oven to constant weight. Ethanol (10 ml) was added to 600 mg of dry cells and the test tubes were incubated at 60°C for 3 h. The contents were centrifuged, washed twice with distilled water and dried for 24 h at 95°C. The pellet was resuspended in 4 ml of 6 mol/l HNO3 and heated at 70°C for 3 h. This mixture was centrifuged and the supernatant was removed. The pellet was washed twice with distilled water. The melanin was extracted by boiling in 10 ml of 0.5 mol/l NaOH for 20 min. The resulting solution was passed through a 0.22 μ membrane filter to remove undigested debris and quantified by referring to a standard graph.
Synthesis of AgNPs by melanin
AgNPs were synthesized by incubating extracted melanin with silver nitrate solutions. To check the effect of melanin content on nanoparticle synthesis, varying concentrations of the pigment (100, 150, 250, 500 μg) were incubated with 1 ml of 2.5 mM AgNO3 solutions. To enhance the reaction, the mixture was heated at 100°C for 10 min. Visual changes and UV–vis spectra were recorded. To check the effect of silver nitrate on nanoparticle synthesis, 2.5, 3.3, 5.0 and 10.0 mM of the silver salt were incubated with 500 μg/ml of melanin. All experiments were carried out in triplicates with two biological replicates and representative data is present here.
Characterization of the AgNPs
The reaction mixtures were monitored over a period of time and visual observations were recorded. Cell control reactions lacked the silver salt and salt controls lacked the biomass. A Jasco V-530 spectrophotometer was used for UV-Visible spectroscopy measurements. AgNPs synthesized by the extracted melanin were also characterized similarly. Washed yeast cells or the melanin-mediated AgNPs were coated onto glass pieces and thoroughly dried. XRD measurements of thin films of yeast cells exposed to AgNO3 were carried out in the transmission mode on a D8 Advanced Brucker instrument with Cu Kα radiation using λ = 1.54˚A. SEM-EDS analysis was performed on air-dried, platinum-coated cell samples using an analytical SEM (JEOL JSM-6360A) equipped with EDS. All these samples were also analyzed in triplicates and representative micrographs are included here. In order to determine the functional groups involved in nanoparticle synthesis, FTIR spectroscopy was carried out as described earlier (Bankar et al. 2010a.) The melanin-derived AgNPs were also characterized in a similar manner. For transmission electron microscope (TEM) observations, samples were coated on carbon-coated copper grids (200 μm × 200 μm mesh size) and images were obtained on a TECNAI G2 20U-Twin (FEI, Netherlands) electron microscope.
Antimicrobial and antibiofilm activities of nanoparticles
Antimicrobial activity of the melanin-mediated AgNPs against a representative pathogen Salmonella paratyphi MTCC 735 was checked by the disc diffusion method as described earlier (Bankar et al. 2010b). The extracted melanin was used as a control. The plates were incubated at 37°C for 24 h and zones of inhibition were checked. The effect of nanoparticles on biofilm formation by S. paratyphi in microtitre plates was also evaluated. To each well, 200 μl of nutrient broth, NB (containing yeast extract, 3.0; peptone, 5.0; sodium chloride, 5.0 g/l of distilled water), 5 μl of culture (106 cells/ml) and 20 μl nanoparticles (derived from reaction mixtures containing 500 μg of melanin and 5.0 mM AgNO3) were added. In control wells, the nanoparticles were excluded. After incubation for 24 or 48 h, the supernatant was removed and plates were washed with phosphate buffer saline. The biofilm growth was stained with crystal violet, and quantification was done as reported earlier (Dusane et al. 2011). In the graph related to this data, mean values of triplicate experiments are plotted and error bars indicate standard deviation.
The antibiofilm activity of the AgNPs on a glass surfaces was also evaluated. In sterile Petri dishes, 20 ml NB, 5 μl of culture (106cells/ml) and 200 μl of different concentrations of AgNPs (derived from reaction mixtures containing 500 μg of melanin and 2.5, 5.0 or 10.0 mM AgNO3) were added. Appropriate control experiments were also performed. The Petri plates were incubated for 48 h at 37°C after which, the slides were washed with distilled water, stained with acridine orange and observed under a fluorescent microscope (Axio Scope-A1 equipped with photographic attachment ProgRes ® Capture Pro 2.7 and software AxioVison Rel. 4.8).
Visual observations and UV-Visible spectroscopic studies
Y. lipolytica cells synthesized AgNPs when incubated with silver nitrate. Control cells without AgNO3 did not show a characteristic brown color. Since cell pellets were brown and the cell-free supernatants did not display any color, it was concluded that the AgNPs were cell-associated. The UV-visible spectra of reaction mixtures after 120 h showed characteristic peaks at around 410 nm (data not shown). As the content of the silver salt was increased, there was a gradual increase in the intensity of the color and the peaks.
Characterization of nanoparticles by XRD and SEM-EDS
On the basis of these results and the fact that cell-associated silver nanoparticles have limited applications, a set of experiments was designed to isolate and extract the cell-associated biopolymer, melanin and to employ this in AgNP synthesis. Melanin isolated from cells was used to synthesize AgNPs in a form which was free of the cells. The effect of varying concentrations of melanin on AgNP synthesis was studied. A yellow color was observed with 100 and 150 μg of melanin while characteristic brown colors were observed with 250 and 500 μg of melanin when 2.5 mM of AgNO3 was used. The UV-Visible spectra also displayed characteristic peaks at around 410 nm for these concentrations. The effect of silver nitrate concentration on nanoparticle synthesis was also studied. As the concentration of silver salt was increased, the intensity of the brown color gradually increased.
SEM-EDS and TEM analysis of melanin mediated silver nanoparticles
Different strains of Y. lipolytica play an important role in biotechnology (Fickers et al. 2005; Beopoulos et al. 2010). A tropical marine isolate of Y. lipolytica has been reported to mediate the synthesis of gold nanoparticles (Agnihotri et al. 2009; Apte et al. 2013). Some strains of this yeast are also psychrotrophic in nature (Ross and Morris 1965; Margesin et al. 2003) Psychrophiles and psychrotrophs are an important group of microorganisms that have several important applications (Feller and Gerday 2003; Bankar et al. 2009; Sa´nchez et al. 2009). Recently, there has been a report on the synthesis of silver nanoparticles by psychrophilic bacteria (Shivaji et al. 2011). To the best of our knowledge there are no reports on the synthesis of nanoparticles by cold-adapted yeasts and thus this investigation was taken up. The psychrotrophic strain of Y. lipolytica NCYC 789 synthesized silver nanoparticles in a cell-associated manner. Some fungi such as Phaenerochaete chrysosporium and Neurospora crassa are also reported to synthesize nanostructures in this manner (Vigneshwaran et al. 2006; Castro-Longoria et al. 2011). The XRD profiles confirmed the crystalline nature of the silver nanoparticles associated with the cells. The peaks could be indexed to the (111), (200) and (220) facets of crystalline silver (Figure 1). Lactobacillus fermentum mediated silver nanoparticles are also known to exhibit such patterns (Sintubin et al. 2009). SEM observations in the current investigation match with those of other microbial systems that synthesize nanoparticles in a cell-associated manner. For example there is a report on Penicillium sp. reducing silver and gold ions to nanostructures on the cell surface similar to the present results (Du et al. 2010).
The significance of different functional groups in nanoparticle synthesis has been reported earlier. In the metal-reducing bacterium, Shewanella oneidensis MR-1, carbonyl, hydroxyl, amide and carboxyl were involved in the nanoparticle synthetic process (Suresh et al. 2010). In the current investigation, the nature of the cell surface was characterized and functional groups involved in AgNP synthesis were determined by FTIR analysis. The involvement of phenolic, hydroxyl and amino groups in nanoparticle synthesis was implicated.
As stated earlier, strains of Y. lipolytica are known to produce melanin (Carreira et al. 1998; Carreira et al. 2001). In addition, this pigment plays an important role in the sequestration of heavy metals and in the synthesis of gold nanoparticles (Bankar et al. 2009; Apte et al. 2013). We hypothesized that cell-associated melanin maybe mediating the reduction of silver ions to elemental silver nanoparticles on account of the following properties displayed by melanins (i) They are natural biopolymers of phenolic compounds (Jacobson, 2000) (ii) they exhibit strong anti-oxidant properties (Commoner et al. 1954; Doering et al. 1999) and (iii) the quinonic residues present in melanin can interchange between the hydroxyquinone and quinone forms (Horak and Gillette 1971). It is a well-established fact that hydroxyquinone-quinone transformations mediate nanoparticle synthesis (Duran et al. 2011). In the current study, the FTIR spectra of the control and silver-laden cells revealed that phenolic, hydroxyl and amide groups are involved in the process of AgNPs synthesis (Figure 3). The SEM images also indicated a cell-surface location of the silver nanostructures (Figure 2a and b, white arrows). Since melanin is known to be associated with cell wall of fungi (Jacobson, 2000), we thought that this pigment may be contributing towards AgNP synthesis in this yeast as well. The isolated melanin also mediated the synthesis of silver nanoparticles. The observations on the effect of salt concentration on nanoparticle synthesis by the yeast cells as well as by the isolated melanin are consistent with earlier results on the use of other biological material for AgNP synthesis (Bankar et al. 2010b). Although the size was determined to be 15 nm on the basis of the TEM images, in SEM images the AgNPs aggregated into dendrites and large structures as an outcome of the sample preparation procedure (Figure 4a and b). Silver nanoparticles synthesized by physical and chemical methods have an inherent property to assemble into larger structures (He et al. 2003; Tang et al. 2009).
Effectiveness of silver nanoparticles as antibacterial agents has been analyzed by a variety of techniques (Kim et al. 2011). Since several pathogenic bacteria exhibit the biofilm mode of growth (Hoiby et al. 2010), the role of the silver nanoparticles as antibiofilm agents was investigated. The antibiofilm activity displayed by the melanin induced AgNPs are consistent with the observations on other types of nanoparticles being effective against pathogens such as P. aeruginosa and Staphylococcus epidermidis (Kalishwaralal et al. 2010). The melanin-inspired AgNPs were thus effective in inhibiting the biofilm growth of a representative pathogen. The AgNPs obtained in the cell-free form could be in the future functionalized by a variety of techniques to enhance their antimicrobial activity (Veerapandian and Yun 2011).
In conclusion, we state that the biotechnologically significant yeast could effectively synthesize AgNPs. We have described the role of a natural biopigment (melanin) in the synthetic process. Cell-associated nanoparticles often pose problems during subsequent applications. This method of using melanin permitted the synthesis of nanoparticles in the free form. The melanin derived AgNPs were effective at disrupting biofilms of a representative pathogen S. paratyphi on polystyrene as well as glass surfaces. These nanoparticles are being differentially functionalized to enhance their antimicrobial activity.
The authors thank University of Pune for financial support under the BCUD Project Budget and Institutional Research Fund. They also thank University Grants Commission, New Delhi for support under UPE phase II.
- Agnihotri M, Joshi S, Kumar AR, Zinjarde S, Kulkarni S: Biosynthesis of gold nanoparticles by the tropical marine yeast Yarrowia lipolytica NCIM 3589. Mater Lett 2009, 63: 1231–1234. 10.1016/j.matlet.2009.02.042View ArticleGoogle Scholar
- Apte M, Girme G, Nair R, Bankar A, Kumar AR, Zinjarde S: Melanin mediated synthesis of gold nanoparticles by Yarrowia lipolytica . Mater Lett 2013, 95: 149–152.View ArticleGoogle Scholar
- Bankar AV, Kumar AR, Zinjarde SS: Environmental and industrial applications of Yarrowia lipolytica . Appl Microbiol Biotechnol 2009, 84: 847–865. 10.1007/s00253-009-2156-8PubMedView ArticleGoogle Scholar
- Bankar AV, Joshi BS, Kumar AR, Zinjarde SS: Banana peel extract mediated synthesis of gold nanoparticles. Colloids Surf B 2010, 80: 45–50. 10.1016/j.colsurfb.2010.05.029View ArticleGoogle Scholar
- Bankar A, Joshi B, Kumar AR, Zinjarde S: Banana peel extract mediated novel route for the synthesis of silver nanoparticles. Colloids Surf A 2010, 368: 58–63. 10.1016/j.colsurfa.2010.07.024View ArticleGoogle Scholar
- Beopoulos A, Desfougeres T, Sabirova J, Zinjarde S, Nicaud JM: The hydrocarbon degrading oleaginous yeast Yarrowia lipolytica . In Handbook of hydrocarbons and lipid biology. Edited by: Timmis KN. Heidelberg: Springer-Verlag Berlin; 2010:2111–2121.View ArticleGoogle Scholar
- Carreira A, Ferreira LM, Loureiro V: Production of brown tyrosine pigments by the yeast Yarrowia lipolytica . J Appl Microbiol 2001, 90: 372–379. 10.1046/j.1365-2672.2001.01256.xPubMedView ArticleGoogle Scholar
- Carreira A, Paloma L, Loureiro V: Pigment producing yeasts involved in the brown surface discoloration of ewes’ cheese. Int J Food Microbiol 1998, 41: 223–230. 10.1016/S0168-1605(98)00054-3PubMedView ArticleGoogle Scholar
- Castro-Longoria E, Vilchis-Nestor AR, Avalos-Borja M: Biosynthesis of silver, gold and bimetallic nanoparticles using the filamentous fungus Neurospora crassa . Colloids Surf B 2011, 83: 42–48. 10.1016/j.colsurfb.2010.10.035View ArticleGoogle Scholar
- Commoner B, Townsend J, Pike GE: Free radicals in biological materials. Nature 1954, 174: 689–691. 10.1038/174689a0PubMedView ArticleGoogle Scholar
- Doering TL, Nosanchuk JD, Roberts WK, Casadevall A: Melanin as a potential cryptococcal defense against microbicidal proteins. Med Mycol 1999, 37: 175–181.PubMedView ArticleGoogle Scholar
- Du L, Xian L, Feng JX: Rapid extra-/intracellular biosynthesis of gold nanoparticles by the fungus Penicillium sp. J Nanopart Res 2010, 13: 921–930.View ArticleGoogle Scholar
- Duran N, Marcato PD, Duran M, Yadav A, Gade A, Rai M: Mechanistic aspects in the biogenic synthesis of extracellular metal nanoparticles by peptides, bacteria, fungi, and plants. App Microbiol Biotechnol 2011, 90: 1609–1624. 10.1007/s00253-011-3249-8View ArticleGoogle Scholar
- Dusane DH, Pawar VS, Nancharaiah YV, Venugopalan VP, Kumar AR, Zinjarde SS: Anti-biofilm potential of a glycolipid surfactant produced by a tropical marine strain of Serratia marcescens . Biofouling 2011, 27: 645–654. 10.1080/08927014.2011.594883PubMedView ArticleGoogle Scholar
- Feller G, Gerday C: Psychrophilic enzymes: hot topics in cold adaptation. Nat Rev Microbiol 2003, 1: 200–208. 10.1038/nrmicro773PubMedView ArticleGoogle Scholar
- Fickers P, Benetti PH, Wache´ Y, Marty A, Mauersberger S, Smit MS, Nicaud JM: Hydrophobic substrate utilization by the yeast Yarrowia lipolytica , and its potential applications. FEMS Yeast Res 2005, 5: 527–543. 10.1016/j.femsyr.2004.09.004PubMedView ArticleGoogle Scholar
- Fogarty RV, Tobin JM: Fungal melanins and their interactions with metals. Enz Microb Technol 1996, 19: 311–317. 10.1016/0141-0229(96)00002-6View ArticleGoogle Scholar
- Gade AK, Bonde P, Ingle AP, Marcato PD, Duran N, Rai MK: Exploitation of Aspergillus niger for synthesis of silver nanoparticles. J Biobased Mater Bioener 2008, 2: 243–247. 10.1166/jbmb.2008.401View ArticleGoogle Scholar
- Gade A, Ingle A, Whiteley C, Rai M: Mycogenic metal nanoparticles: progress and applications. Biotechnol Lett 2010, 32: 593–600. 10.1007/s10529-009-0197-9PubMedView ArticleGoogle Scholar
- Gardini F, Tofalo R, Belletti N, Iucci L, Suzzi G, Torriani S, Guerzoni ME, Lanciotti R: Characterization of yeasts involved in the ripening of Pecorino Crotonese cheese. Food Microbiol 2006, 23: 641–648. 10.1016/j.fm.2005.12.005PubMedView ArticleGoogle Scholar
- He R, Qian X, Yin J, Zhu Z: Formation of silver dendrites under microwave irradiation. Chem Phys Lett 2003, 369: 454–458. 10.1016/S0009-2614(02)02036-5View ArticleGoogle Scholar
- Hoiby N, Bjarnsholt T, Givskov M, Molin S, Ciofu O: Antibiotic resistance of bacterial biofilms. Int J Antimicrob Agents 2010, 35: 322–332. 10.1016/j.ijantimicag.2009.12.011PubMedView ArticleGoogle Scholar
- Horak V, Gillette JR: A study of the oxidation-reduction state of synthetic 3, 4-dihydroxy-DL-phenylalanine melanin. Mol Pharm 1971, 7: 429–433.Google Scholar
- Ito H, Inouhe M, Tohoyama H, Joho M: Characteristics of copper tolerance in Yarrowia lipolytica . Biometals 2007, 20: 773–780. 10.1007/s10534-006-9040-0PubMedView ArticleGoogle Scholar
- Jacobson ES: Pathogenic roles for fungal melanins. Clin Microbiol Rev 2000, 13: 708–717. 10.1128/CMR.13.4.708-717.2000PubMed CentralPubMedView ArticleGoogle Scholar
- Jain J, Arora S, Rajwade JM, Omray P, Khandelwal S, Paknikar KM: Silver nanoparticles in therapeutics: development of an antimicrobial gel formulation for topical use. Mol Pharm 2009, 6: 1388–1401. 10.1021/mp900056gPubMedView ArticleGoogle Scholar
- Kalishwaralal K, Manikanth SB, Pandian SRK, Deepak V, Gurunathan S: Silver nanoparticles impede the biofilm formation by Pseudomonas aeruginosa and Staphylococcus epidermidis . Colloids Surf B 2010, 79: 340–344. 10.1016/j.colsurfb.2010.04.014View ArticleGoogle Scholar
- Kim SW, Baek Y-W, An Y-J: Assay-dependent effect of silver nanoparticles to Escherichia coli and Bacillus subtilis . Appl Microbiol Biotechnol 2011, 92: 1045–1052. 10.1007/s00253-011-3611-xPubMedView ArticleGoogle Scholar
- Kumar GC, Mamidyala SK: Extracellular synthesis of silver nanoparticles using culture supernatant of Pseudomonas aeruginosa . Colloids Surf B 2011, 84: 462–466. 10.1016/j.colsurfb.2011.01.042View ArticleGoogle Scholar
- Lanciotti R, Vannini L, Lopez CC, Gobbetti M, Guerzoni ME: Evaluation of the ability of Yarrowia lipolytica to impart strain-dependent characteristics to cheese when used as a ripening adjunct. Int J Dairy Technol 2005, 58: 89–99. 10.1111/j.1471-0307.2005.00197.xView ArticleGoogle Scholar
- Margesin R, Gander S, Zacke G, Gounot AM, Schinner F: Hydrocarbon degradation and enzyme activities of cold-adapted bacteria and yeasts. Extremophiles 2003, 7: 451–458. 10.1007/s00792-003-0347-2PubMedView ArticleGoogle Scholar
- Rai M, Yadav A, Gade A: Silver nanoparticles as a new generation of antimicrobials. Biotechnol Adv 2009, 27: 76–83. 10.1016/j.biotechadv.2008.09.002PubMedView ArticleGoogle Scholar
- Ravindra S, Mohan YM, Reddy NN, Raju KM: Fabrication of antibacterial cotton fibres loaded with silver nanoparticles via “Green Approach”. Colloids Surf A 2010, 367: 31–40. 10.1016/j.colsurfa.2010.06.013View ArticleGoogle Scholar
- Rodrigues AG, Ping LY, Marcato PD, Alves OL, Silva MCP, Ruiz RC, Melo IS, Tasic L, De Souza AO: Biogenic antimicrobial silver nanoparticles produced by fungi. Appl Microbiol Biotechnol 2013, 97: 775–782. 10.1007/s00253-012-4209-7PubMedView ArticleGoogle Scholar
- Ross SS, Morris EO: An investigation of the yeast flora of marine fish from Scottish coastal waters and a fishing ground off Iceland. J Appl Microbiol 1965, 28: 224–234. 10.1111/j.1365-2672.1965.tb02147.xView ArticleGoogle Scholar
- Rywińska A, Rymowicz W: High-yield production of citric acid by Yarrowia lipolytica on glycerol in repeated-batch bioreactors. J Ind Microbiol Biotechnol 2010, 37: 431–443. 10.1007/s10295-009-0687-8PubMedView ArticleGoogle Scholar
- Sa´nchez LA, Go´mez FF, Delgado OD: Cold-adapted microorganisms as a source of new antimicrobials. Extremophiles 2009, 13: 111–120. 10.1007/s00792-008-0203-5View ArticleGoogle Scholar
- Sharma VK, Yngard RA, Lin Y: Silver nanoparticles: Green synthesis and their antimicrobial activities. Adv Colloids Interface Sci 2009, 145: 83–96. 10.1016/j.cis.2008.09.002View ArticleGoogle Scholar
- Shivaji S, Madhu S, Singh S: Extracellular synthesis of antibacterial silver nanoparticles using psychrophilic bacteria. Process Biochem 2011, 46: 1800–1807. 10.1016/j.procbio.2011.06.008View ArticleGoogle Scholar
- Sintubin L, Windt WD, Dick J, Mast J, van der Ha D, Verstraete W, Boon N: Lactic acid bacteria as reducing and capping agent for the fast and efficient production of silver nanoparticles. Appl Microbiol Biotechnol 2009, 84: 741–749. 10.1007/s00253-009-2032-6PubMedView ArticleGoogle Scholar
- Sivaraman SK, Elango I, Kumar S, Santhanam V: A green protocol for room temperature synthesis of silver nanoparticles in seconds. Curr Sci 2009, 97: 1055–1059.Google Scholar
- Suresh AK, Pelletier DA, Wang W, Moon JW, Gu B, Mortensen NP, Allison DP, Joy DC, Phelps TJ, Doktycz MJ: Silver nanocrystallites: biofabrication using Shewanella oneidensis , and an evaluation of their comparative toxicity on Gram-negative and Gram-positive bacteria. Env Sci Technol 2010, 44: 5210–5215. 10.1021/es903684rView ArticleGoogle Scholar
- Tang S, Meng X, Lu H, Zhu S: PVP-assisted sonoelectrochemical growth of silver nanostructures with various shapes. Mater Chem Phys 2009, 116: 464–468. 10.1016/j.matchemphys.2009.04.004View ArticleGoogle Scholar
- Thakkar KN, Mhatre SS, Parikh RY: Biological synthesis of metallic nanoparticles. Nanomed: Nanotechnol Biol Med 2010, 6: 257–262. 10.1016/j.nano.2009.07.002View ArticleGoogle Scholar
- Tomaszewska L, Rywińska A, Gładkowski W: Production of erythritol and mannitol by Yarrowia lipolytica yeast in media containing glycerol. J Ind Microbiol Biotechnol 2012, 39: 1333–1343. 10.1007/s10295-012-1145-6PubMed CentralPubMedView ArticleGoogle Scholar
- Veerapandian M, Yun K: Functionalization of biomolecules on nanoparticles: specialized for antibacterial applications. Appl Microbiol Biotechnol 2011, 90: 1655–1667. 10.1007/s00253-011-3291-6PubMedView ArticleGoogle Scholar
- Vigneshwaran N, Kathe AA, Varadarajan PV, Nachane RP, Balasubramanya RH: Biomimetics of silver nanoparticles by white rot Phaenerochaete chrysosporium . Colloids Surf B 2006, 53: 55–59. 10.1016/j.colsurfb.2006.07.014View ArticleGoogle Scholar
- Zhou Y, Kong Y, Kundu S, Cirillo JD, Liang H: Antibacterial activities of gold and silver nanoparticles against Escherichia coli and bacillus Calmette-Guérin. J Nanobiotechnol 2012, 10: 19. 10.1186/1477-3155-10-19View ArticleGoogle Scholar
- Zinjarde SS: Bio-inspired nanomaterials and their applications as antimicrobial agents. Chronicles of Young Scientists 2012, 3: 74–81. 10.4103/2229-5186.94314View ArticleGoogle Scholar
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