Bio-gold nanoparticle synthesis by metalophilic bacterium Cupriavidus necator

Gold nanoparticles have potential applications in the areas of medicine, target drug delivery, cancer diagnosis and therapy, electronic, etc. Recently, biological system is considered as an environmental friendly method for synthesis of stable nanoparticles. We demonstrated a biological system for formation of stable gold nanoparticle by using Cupriavidus necator without using additives such as stabilizing agents. The sizes and composition of nanoparticles were characterised by UV-Vis spectrophotometer, transmission electron microscopy, energy dispersive spectra, and Image J software. Stable bio-gold nanoparticle was formed by using metalophilic bacterium Cupriavidus necator. High uniformity was observed in the presence of 1.55 mg/ml dry biomass, ImM Hydrogen tetrachloroaurate and 25 mM formate. Microbial synthesis of nanoparticle, such as gold, is an easy and eco-friendly method to preparation of stable nanoparticles

[Inverted metabolic engineering of E.coli to produce PHB and simplifying of lysis process; using gene E from phage PhiX 174]

The polyhydroxybutyrate biosynthetic genes of Ralstonia eutropha are organized in single operon. There are many studies which show that this operon could be cloned in gram negative bacteria like E.coli. As its original promoter could work efficiently in E.coli, there is no need to change it with host ones. Granule extraction is one of the most important considerations of industrial production of PHB. Solvent base or physical approaches increase the cost of production and compromise the integrity of PHB granules. Therefore, E mediated lysis was used in this study to extract the granules. In this study, the whole operon of PHB from Ralstonia eutropha and E gene from phage phiX174 were obtained by PCR technique, and cloned transferred to E.coli by separate plasmids. To control the lysis process, the chemical inducible system was used. Bacterial cells which have both plasmids could produce high levels of PHB, and their PHB content could be released into the medium, nearly perfectly, at the correct time by adding IPTG as a chemical inducer. This method could be used to produce and extract PHB with more cost effectiveness in industrial scales

Formation of polyhydroxyalkanoates during the dual-nutrient-limited zone by Ralstonia eutropha / 生物工程学报

Polyhydroxyalkanoates (PHAs) are a class of polyesters biosynthesized by microorganisms (esp. Ralstonia eutropha) under an unbalanced growth condition, and which are supposed to partly take the place of traditional plastics made from petroleum in the near future since they are harmless to the environment and biodegradable. Organic acids (mainly butyrate, lactate, propionate and acetate) produced from anaerobic digested food wastes, industrial wastes and sewage may be used as cheap carbon sources since the large amounts of the above wastes disposed by industry and family each year. In order to better understand the process of PHAs formation with acids as carbon sources, so as to increase the yields of PHAs. Biosynthesis of PHAs by R. eutropha during the dual nutrient-limitation-zone was investigated with mixed organic acids (the mass ratio of the four component acids was butyrate: propionate: acetate: lactate = 3: 3: 1: 1, which was simulated as once the result of anaerobic digestion of food wastes) as carbon sources and (NH4)2 SO4 as nitrogen source. Two different manners of maintaining the dual-nutrient-limitation zone were adopted by feeding mixed acids and (NH4 )2SO4 at determined rates to the fermentation culture which were free of carbon sources (manner A) or nitrogen sources (manner B) firstly. The results suggest that, first of all, the meaning of the limitation of mixed acids or (NH4)2 SO4 does not mean to limit the supply of them, but mean to feed as more as possible of carbon and nitrogen sources in order to meet the cell growth and PHAs formation of R. eutropha by the largest extent. However, it's indispensable to make the residual concentration of carbon and nitrogen sources as low as possible since organic acids are inhibitive to the cell growth, and most importantly, only under the presence of nitrogen during the PHAS formation period of the fermentation could R. eutropha produce more PHAs than any other unbalanced growth condition. Secondly, with the increase of the width of the dual-nutrient-limitation zone, the yield of PHAs would also increase, it suggest that most of the PHAs were biosynthesized during the dual-nutrient-limitation zone. Finally, in contrast with the dual-nutrient-limitation manner of limiting the nitrogen source at first (manner B), the dual-nutrient-limitation manner of limiting the carbon source at first (manner A) was more favorable for the production of PHAs, and the maximum production of PHAs of these two manners are 3.72 g/L and 2.55 g/L, respectively. It may be because that PHAs formation required enzymes could not be well developed when R. eutropha grow under the state of nitrogen limitation from the beginning of fermentation. Besides, yield of PHAs produced by the dual-nutrient-limitation fermentation is larger than that of the single-nutrient-limitation batch culture. Therefore, it seems that to increase the output of PHAs production, the strategy of maintaining as wide as possible the width of dual-nutrient (C, N)-limitation zone may be effective.

A suitable procedure to choose antimicrobials as controlling agents in fermentations performed by bacteria

This work evaluated the influence of nitrofurantoin, erythromycin and streptomycin at 50, 25 and 12,5 (per cent) of the minimal inhibitory concentration (MIC) on maximum specific growth rate (µmax) and specific polymer accumulation rate (µPHB) of "Alcaligenes eutrophus", considered resistant to those antimicrobials. Nitrofurantoin strongly affected µmax even at 50(per cent) MIC. Streptomycin moderately affected µmax only at 50(per cent) MIC. Nitrofurantoin showed the most harmful effect on µPHB when 50(per cent) MIC was applied and erythromycin was not harmful.