Abstract
Microbial biosynthesis of metal nanoparticles as needed in catalysis has shown its theoretical ability as an extremely environmentally friendly production method in the last few years, even though the separation of the nanoparticles is challenging. Biosynthesis, summing up biosorption and bioreduction of diluted metal ions to zero valent metals, is especially ecofriendly, when the bioreactor itself is harmless and needs no further harmful reagents. The cyanobacterium Anabaena cylindrica (SAG 1403.2) is able to form crystalline Au0-nanoparticles from Au3+ ions and does not release toxic anatoxin-a. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and laser-induced breakdown spectroscopy (LIBS) are applied to monitor the time-dependent development of gold nanoparticles for up to 40 hours. Some vegetative cells (VC) are filled with nanoparticles within minutes, while the extracellular polymeric substances (EPS) of vegetative cells and the heterocyst polysaccharide layer (HEP) are the regions, where the first nanoparticles are detected on most other cells. The uptake of gold starts immediately after incubation and within four hours the average size remains constant around 10 nm. Analyzing the TEM images with an image processing program reveals a wide distribution for the diameter of the nanoparticles at all times and in all regions of the cyanobacteria. Finally, the nanoparticle concentration in vegetative cells of Anabaena cylindrica is about 50% higher than in heterocysts (HC). These nanoparticles are found to be located along the thylakoid membranes.
Highlights
Precious metallic nanoparticles are of steadily increasing interest since there are widespread possibilities of usage [1,2,3]
In accordance to the study with cyanobacteria Anabaena sp. (SAG 12.82) [29] we show in this study for another cyanobacterium, that the vegetative cells are more important as location for nanoparticle biosynthesis than the heterocysts
The importance of heterocysts for the biosynthesis is discussed widely in the literature, we have shown in a preceding study a contrary relation for Anabaena sp. [29], where vegetative cells have been found to be the cells in which nanoparticles are mainly formed
Summary
Precious metallic nanoparticles are of steadily increasing interest since there are widespread possibilities of usage [1,2,3]. Instead of using conventional chemical pathways the implementation of microbiological methods is environmentally friendly, especially when the bioreactor itself is harmless and in general since no further harmful reagents are needed, even sustainable [10,11,12]. The reduction of Au3+ by means of enzymes like hydrogenase [31,32,33] and nitrogenase [23] is another prominent example. In case of nitrogenase the reduction of elemental nitrogen to ammonium [34,35] generates the electrons which are required for the reduction of harmful (possibly cytotoxic) metal ions to their zero valent form
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