Media Optimization for Poly(β-hydroxybutyrate) Production Using Azotobacter Beijerinckii

In the present study, efforts were made to optimize the growth of Azotobacter beijerinckii in the media with essential nutrients for production of PHB. The effects of temperature, agitation rate, carbon and nitrogen source concentrations on microbial grows and PHB production were investigated. Glucose and ammonium chloride were used as carbon and nitrogen source, respectively. The optimal temperature for the growth and PHB synthesis appeared to be 30°C. However, over the range of 25–38°C, the effect of temperature was not very significant. Fermentation under controlled conditions such as agitation rate of 250 rpm, incubated inoculums for 15 h, fermentation temperature at 30°C, and fermentation time of 72 h was performed. Glucose concentration of 30 to 60 g/l with increment of 10 g/l and ammonium chloride in the range of 0.5 to 2 g/l with increment of 0.5 g/l were utilized as carbon and nitrogen sources, respectively. The PHB production was maximized at the desired concentration of glucose (50 g/l) and ammonium chloride (1.5) for carbon and nitrogen sources, respectively. A. beijerinckii exhibited maximum biomass of 17.31 g/l with a PHB concentration of 5.84 g/l. Under the best conditions, PHB constituted up to 34% of dry cell mass after 64 h of culture. The average biomass yield coefficient on glucose was about 0.57 kg/kg.     

Effect of bacterial alginate on growth of mesenchymal stem cells

Abstract

Capsular alginate was synthesized using bacteria Azotobacter agile 12 in order to test its potential for use in biotechnology and tissue engineering. Capsular bacterial alginate was isolated and purified using EDTA treatment and dialysis. Calcium alginate spheres were produced and their effect on growth of mesenchymal stem cells was studied. Bacterial alginate shows significantly lower cytotoxicity than commercial alginate isolated from algae.     

种衣剂对大豆根际固氮菌多样性的影响

利用变性梯度凝胶电泳（DGGE）技术研究宁南霉素、甲霜灵、多克福和咯菌腈4种种衣剂对大豆根际固氮菌多样性的影响。运用nifH基因的特异引物对,将大豆根际土壤总DNA进行PCR扩增后,通过DGGE技术对PCR产物进行分析。结果表明,种衣剂对固氮菌产生了不同程度的抑制作用。对大豆根际固氮菌抑制作用由强到弱的种衣剂品种依次是咯菌腈、甲霜灵、多克福和宁南霉素;种衣剂浓度对大豆根际固氮菌多样性的抑制程度不同,但没有明显规律。     

Bacterial biosynthesis of alginates

Alginates are polysaccharides with many industrial and medical uses, from food additives to encapsulation agents in the emerging transplantation technologies. Alginate is composed of variable proportions of β‐D‐mannuronic acid and α‐L‐guluronic acid linked by 1–4 glycosidic bonds. Traditionally, commercial alginate has been produced by farmed brown seaweeds, but this alginate suffers from heterogeneity in composition and quality partly due to environmental variation. Two bacterial genera, Pseudomonas and Azotobacter, are also capable of producing alginate as an exopolysaccharide. These bacterial alginate producers can provide the means to produce alginates with defined monomer composition and possibly through genetic and protein engineering may allow for the production of ‘tailor made’ bacterial alginates. The paper discusses the mechanisms behind alginate production in bacteria and how they may be used in the commercial production of alginates. Copyright © 2010 Society of Chemical Industry     

Effect of nitrification inhibitors on N-fixing bacteriaRhizobium leguminosarum andAzotobacter chroococcum

The nitrification inhibitor dicyandiamide [DCD] did not inhibit growth and respiration of N-fixing bacteria (Rhizobium leguminosarum andAzotobacter chroococcum) in cell suspensions with concentrations of 400 ppm DCD. Growth ofRhizobium leguminosarum was inhibited by 17% with 100 ppm nitrapyrin (N-Serve), but respiration was not affected. Growth ofAzotobacter chroococcum was inhibited by 10 ppm (10%) and 100 ppm nitrapyrin (50%); in the latter case, respiration was also impaired (36%). Thiourea only caused a minor growth inhibition ofAzotobacter chroococcum with 100 ppm (8%) and had no effect onRhizobium leguminosarum.     

Production and characterisation of alginate from Azotobacter vinelandii

The alginate produced from glucose by Azotobacter vinelandii DSM 576 in the shaken‐flask (SF) scale was characterised in terms of chemical composition and average molecular mass (M_n). Its chemical composition was practically independent of the fermentation time with an average content in uronic acids of 0.66±0.09 g/g, a high proportion of mannuronic acid (M =0.75±0.04) and a mean acetylation degree of 18.5±7.9%. On the contrary, M_n reached a maximum value of ca. 220 kDa after 40–42 h fermentation and then decreased to 60 kDa in the following 20–22 hours. The fermentation process was scaled‐up in a laboratory fermenter (LF) and the kinetics of alginate production was classified of the mixed‐growth ‐associated product formation type with a contribution of non‐growth associated production of the order of 70 or 80% depending on the LF or SF scale used. However, the rate of M_n increase was found to be strictly growth‐associated, since alginate depolymerisation was observed as soon as the exponential cell growth rate stopped and this coincided with ammoniac nitrogen levels smaller than 10–15 g m ⁻³. © 1999 Society of Chemical Industry     

生物可降解塑料聚羟基脂肪酸酯的生产及物性表征

用一株固氮杆菌（ＡｚｏｔｏｂａｔｅｒＶｉｎｄｌａｎｄｉｉＵＷＤ），利用糖蜜生产细菌高分子材料一聚－β－羟基丁酸酯ＰＨＢ，同时在甜菜糖蜜和戊酸培养基中成功地培养ＵＷＤ而得到了一系列不同羟基戊酸酯（ＨＶ）含量的Ｐ（ＨＢ－ｃｏ－ＨＶ）共聚物，并通过以这一系列共聚物的物理性能进行表征，试图寻找单一高分子材料ＰＨＢ与共聚高分子Ｐ（ＨＢ－ｃｏ－ＨＶ）在微观结构上的区别，从而找到改良ＰＨＢ物性的方法。