Xie Zhixiong

A microcalorimetric method for studying the biological effects of La3+ on Escherichia coli

A microcalorimetric technique based on the bacterial heat-output was explored to evaluate the stimulatory effect of La(3+) on Escherichia coli. The power-time curves of the growth metabolism of E. coli and the effect of La(3+) on it were studied using an LKB-2277 BioActivity Monitor, stopped-flow method, at 37 degrees C. For evaluation of the results, the maximum power (P(max)), the growth rate constants (k) and the heat effects (Q(LOG), Q(STAT)) for the log phase, the stationary phase and the total heat effect (Q(T)) for E. coli were determined. The microcalorimetric method agreed with the conventional methods, such as cell numbers and biomass. La(3+) in the concentration ranges of 0-400 microg/ml has stimulatory effects on E. coli, while La(3+) ion of higher concentrations (>400 microg/ml) can inhibit the growth. This phenomenon is very similar to those observed from the in vitro cells and tissues from animals, plants and some microorganisms by other methods.

Microcalorimetric study of the action of Ce(III) ions on the growth of E. coli.

A microcalorimetric technique based on bacterial heat output was used to evaluate the action of Ce(III) ions on the growth of Escherichia coli. The power-time curves of the growth metabolism of the bacteria were studied in the presence and absence of Ce(III) by means of a LKB-2277 Bioactivity Monitor, by a stopped-flow method at 37°C. For evaluation of the results, the maximum power, Pmax, the growth rate constant k, and the heat effects Qlog, Qstat, and Qtot for the log phase, the stationary phase, and total heat output, respectively, were determined. For comparison, a spectrophotometer was used to estimate the number of cells in the liquid culture. The shape of the bacteria was examined by electron microscopy. We concluded that the presence of cerium ions at concentrations below 350 µg/mL have a stimulatory effect on the growth of E. coli, whereas concentrations at or above 400 µg/mL may have an inhibitory effect.A microcalorimetric technique based on bacterial heat output was used to evaluate the action of Ce(III) ions on the growth of Escherichia coli. The power-time curves of the growth metabolism of the bacteria were studied in the presence and absence of Ce(III) by means of a LKB-2277 Bioactivity Monitor, by a stopped-flow method at 37 degrees C. For evaluation of the results, the maximum power, Pmax, the growth rate constant k, and the heat effects Qlog, Qstat, and Qtot for the log phase, the stationary phase, and total heat output, respectively, were determined. For comparison, a spectrophotometer was used to estimate the number of cells in the liquid culture. The shape of the bacteria was examined by electron microscopy. We concluded that the presence of cerium ions at concentrations below 350 microg/mL have a stimulatory effect on the growth of E. coli, whereas concentrations at or above 400 microg/mL may have an inhibitory effect.

Effects of La3+ on growth, transformation, and gene expression of Escherichia coli.

Rare earth elements have been emitted into the environment largely as fertilizer components. This has caused much fear about whether they would influence our environment, especially on the metabolism and genetics of microorganisms. In this article, the trivalent ion of a rare earth element, lanthanum, was studied for the effects on growth, transformation, and gene expression of Escherichia coli. The results showed that La3+ at concentrations from 50 to 150 µg/mL stimulated the endogenic metabolism and ectogenic metabolism, but had few effects on gene expression. La3+ at lower concentrations from 0.5 to 30 µg/mL inhibit intensively E. coli-absorbing external DNA, decreasing the transformation efficiency. It is also supported by observations using transmission electron microscopy. Our results are significant in understanding the function of rare earth elements to microorganisms and assessing the risk of application of rare earth compounds.

Microcalorimetric studies of the action of Er3+ on Halobacterium halobium R1 growth.

A microcalorimetric technique was used to evaluate the influence of Er3+ on Halobacterium halobium R1 growth. By means of a LKB-2277 Bioactivity Monitor ampoule method, we obtained the thermogenic curves of H. halobium R1 growth at 37°C. In order to analyze the results, the relationship between k and C was obtained. The addition of Er3+ in low concentration cause a decrease of the maximum heat production Pmax and growth rate constants k; however, Er3+ in a high concentration might promote growth of H. halobium R1. When Er3+ is in a much higher concentration, the growth of H. halobium R1 is inhibited completely. For comparison, the shapes of H. halobium R1 cells were observed by means of transmission electron microscope (TEM). According to the thermogenic curves and TEM photos of H. halobium R1 under different conditions, it is clear that the metabolic mechanism of H. halobium R1 growth has been changed with the addition of Er3+.

Live cell synthesis of inorganic nanomaterials

纳米材料由于优异的光学、电学、磁学等性质, 而被广泛应用于生物检测、示踪、光电转换及光热治疗等研究中. 通过调节纳米材料的组成、结构、尺寸及形貌等, 可以有效地调控纳米材料的性能, 已发展的化学合成方法在实现纳米材料性能的调控方面取得了很大进展. 随着化学、材料学及生物学等多学科的交叉, 人们开始探索在纳米材料的合成中利用生物体系的调控网络来进行合成控制, 以期更精确地控制纳米材料的结构及其性质, 从而出现了纳米材料的活细胞合成方法. 由于活细胞内的反应均受到精确调控, 如果能被科学地利用, 将可望实现纳米材料组成、结构、尺寸、形貌和性质的控制.

Effects of La3+ on the competence of Escherichia coli as studied by microcalorimetry

A series of microcalorimetric experiments were performed to investigate the effect of La3+ on the formation of the competent state of Escherichia coli HB101 by using a LKB-2277 BioActivity Monitor at 37°C. The thermogenic curves in the absence and in the presence of La3+ were obtained. Based on these curves, we calculated that the total heat effects (QT) and the maximal power (Pmax) in the presence and absence of La3+. Our experiments indicate that the total heat effects in the presence of a low concentration of La3+ (≤ 100 µg/mL) are greater than those in the absence of La3+. Their trends are similar with respect to the increasing concentration of La3+. To the contrary, when the concentration of La3+ is greater than 100 µg/mL, the total heat effects decrease with the increasing concentration of La3+. Therefore, in the latter case, La3+ has inhibitory effects on the formation of competence. Our experimental results suggest that the La3+ ion in the environmental ecosystem can facilitate the formation of competence of E. coli HB101 and further stimulate the transfer of genetic materials between organisms.A series of microcalorimetric experiments were performed to investigate the effect of La(3+) on the formation of the competent state of Escherichia coli HB101 by using a LKB-2277 BioActivity Monitor at 37 C. The thermogenic curves in the absence and in the presence of La(3+) were obtained. Based on these curves, we calculated that the total heat effects (Q(T)) and the maximal power (P(max)) in the presence and absence of La(3+). Our experiments indicate that the total heat effects in the presence of a low concentration of La(3+) (</= 100 microg/mL) are greater than those in the absence of La(3+). Their trends are similar with respect to the increasing concentration of La(3+). To the contrary, when the concentration of La(3+) is greater than 100 microg/mL, the total heat effects decrease with the increasing concentration of La(3+). Therefore, in the latter case, La(3+) has inhibitory effects on the formation of competence. Our experimental results suggest that the La(3+) ion in the environmental ecosystem can facilitate the formation of competence of E. coli HB101 and further stimulate the transfer of genetic materials between organisms.