Occurrence of leu(+) revertants under starvation cultures in Escherichia coli is growth-dependent

BACKGROUND: Many investigations have reported that advantageous mutations occurred more frequently under selective conditions than those under non-selective conditions. This phenomenon is referred to as adaptive mutation. Their characteristics are that adaptive mutations are directed and growth-independent. The idea of directed adaptive mutation had been objected by some reports, however, the idea of growth-independent adaptive mutation has been held till today. RESULTS: In this paper, we have observed that under leucine starvation conditions, leu(+) revertants accumulated as a function of time; leu(-) to leu(+) reverse mutation rates and frequencies were higher than those under non starvation conditions; and no divided cells could be monitored by the penicillin method. These results were similar to the time-dependent manner of adaptive mutation from previous reports. However, leucine concentration determinate experiments revealed that certain traces of leucine, which leaked from the E. coli cells, was almost always present in the culture. More numbers of leu(+) revertants appeared when the similar cultures were dropped in small areas on the selective plates than when spread on the whole selective plates. These results have shown that mutations under leucine starving conditions are growth-dependent. Fluctuation analysis of leu(+) revertants indicated that leu(-)leu(+) mutation occurred spontaneously and randomly. In addition, the spectra of leuB gene in the revertants proved that mutations under selective conditions were not specific or directed. CONCLUSIONS: The above investigations led to the conclusion (1) that the occurrence of leu(+) mutations under starvation conditions was growth-dependent. The occurence mutations was also similar to that under non-starvation conditions (2). Under starvation conditions the mutation rates were higher, and was not constant during the long process

Thermal Analysis and Junction Temperature Estimation under Different Ambient Temperatures Considering Convection Thermal Coupling between Power Devices

The convection thermal coupling between adjacent power devices in power converters is dependent on the ambient temperature. When the ambient temperature changes, the convection thermal coupling also changes. This results in an inaccurate thermal model that causes errors in the prediction of the thermal distribution and junction temperature based on a fixed ambient temperature for power devices in converters application. To solve this variable-ambient-temperature-related issue, a thermal coupling experiment for semiconductor power devices (the MOSFET and diode) was performed to discuss the influence of the thermal coupling effect between adjacent devices and the FEM (Finite Element Method) thermal models for the power devices considering the convection thermal coupling are established. Through these simulations, the junction temperatures of devices under different ambient temperatures were obtained, and the relationships between the junction temperature and ambient temperatures were established. Moreover, the junction temperatures of power devices under different ambient temperatures were calculated and temperature distributions are analyzed in this paper. This method shows a strong significance and has potential applications for high-efficiency and high-power density converter designs

Mutagenicity of Chinese traditional medicine Semen Armeniacae amarum by two modified Ames tests

<p>Abstract</p> <p>Background</p> <p>Semen armeniacae amarum (SAA) is a Chinese traditional medicine and has long been used to control acute lower respiratory tract infection and asthma, as a result of its expectorant and antiasthmatic activities. However, its mutagenicity <it>in vitro </it>and <it>in vivo </it>has not yet been reported. The Ames test for mutagenicity is used worldwide. The histidine contained in biological samples can induce histidine-deficient cells to replicate, which results in more <it>his</it>⁺colonies than in negative control cells, therefore false-positive results may be obtained. So, it becomes a prerequisite to exclude the effects of any residual histidine from samples when they are assayed for their mutagenicity. Chinese traditional herbs, such as SAA, are histidine-containing biological sample, need modified Ames tests to assay their <it>in vitro </it>mutagenicity.</p> <p>Methods</p> <p>The mutagenicity of SAA was evaluated by the standard and two modified Ames tests. The first modification used the plate incorporation test same as standard Ames teat, but with new negative control systems, in which different amounts of histidine corresponding to different concentrations of SAA was incorporated. When the number of his⁺revertants in SAA experiments was compared with that in new negative control, the effect of histidine contained in SAA could be eliminated. The second modification used a liquid suspension test similar to the standard Ames test, except with histidine-rich instead of histidine-limited medium. The aim of this change was to conceal the effect of histidine contained in SAA on the final counting of <it>his</it>⁺revertants, and therefore to exclude false-positive results of SAA in the Ames test. Furthermore, the effect of SAA on chromosomal aberration in mammalian bone marrow cells was tested.</p> <p>Results</p> <p>The standard Ames test showed a positive result for mutagenicity of SAA. In contrast, a negative response was obtained with the modified plate incorporation and modified suspension Ames tests. Moreover, no apparent chromosomal aberrations were observed in mammalian bone marrow cells treated with SAA.</p> <p>Conclusion</p> <p>The standard Ames test was not suitable for evaluating the mutagenicity of SAA, because false-positive result could be resulted by the histidine content in SAA. However, the two modified Ames tests were suitable, because the experimental results proved that the effect of histidine in SAA and therefore the false-positive result were effectively excluded in these two modified Ames tests. This conclusion needs more experimental data to support in the future. Moreover, the experimental results illustrated that SAA had no mutagenicity <it>in vitro </it>and <it>in vivo</it>. This was in agreement with the clinical safety of SAA long-term used in China.</p

The Combined Effects of Amino Acid Substitutions and Indels on the Evolution of Structure within Protein Families

BACKGROUND: In the process of protein evolution, sequence variations within protein families can cause changes in protein structures and functions. However, structures tend to be more conserved than sequences and functions. This leads to an intriguing question: what is the evolutionary mechanism by which sequence variations produce structural changes? To investigate this question, we focused on the most common types of sequence variations: amino acid substitutions and insertions/deletions (indels). Here their combined effects on protein structure evolution within protein families are studied. RESULTS: Sequence-structure correlation analysis on 75 homologous structure families (from SCOP) that contain 20 or more non-redundant structures shows that in most of these families there is, statistically, a bilinear correlation between the amount of substitutions and indels versus the degree of structure variations. Bilinear regression of percent sequence non-identity (PNI) and standardized number of gaps (SNG) versus RMSD was performed. The coefficients from the regression analysis could be used to estimate the structure changes caused by each unit of substitution (structural substitution sensitivity, SSS) and by each unit of indel (structural indel sensitivity, SIDS). An analysis on 52 families with high bilinear fitting multiple correlation coefficients and statistically significant regression coefficients showed that SSS is mainly constrained by disulfide bonds, which almost have no effects on SIDS. CONCLUSIONS: Structural changes in homologous protein families could be rationally explained by a bilinear model combining amino acid substitutions and indels. These results may further improve our understanding of the evolutionary mechanisms of protein structures

Bacterial cell segmentation and imaging processing

Water is essential to life, 72% of the planet earth is covered in water. However, less than 1% is available for drinking, industry and nature. 1 ml of drinking water on average contains 80,000 of bacteria, and some are harmful to human body such as Cryptosporidium, E.coli, Giardia, Hepatitis A, Legionella pneumophila, and Salmonella. Consumption of raw water may cause disease or even death due to waterborne bacterial infection. Monitoring of the water quality is necessary and crucial. My project focus on the detection of Cryptosporidium and Giardia as these microorganisms will highly cause the outbreak of diseases. Cytometer will be used to detect and photograph the various particles found in preconcentrated sample of drinking water, the liquid mixture with sample and fluid is injected into the flow cytometer instrument, ideally the cell will flow through the laser beam one by one and the light scattered is characteristic to the cells and their components. With this flow cytometry technology, thousands of cells can be examined in short time. However, the basic characteristic have to be measured and collated manually. Manual labelling requires the lab user to have the relevant expertise to handle the detection process and measure the samples individually. Repetition of this process and long operation time may lead to human error, this can affect the accuracy of the data and efficiency of the measurement process. With this algorithm implantation, the characteristic of the bacterial image will be measure automatically and collated into excel file for further usage. Follow by the user interface design, the designed software reduce the disadvantage of manual measurement and enhance the data accuracy as well.Bachelor of Engineering (Electrical and Electronic Engineering

<Note>Kinetic Analysis of the Noncompetitive Inhibition of Lignin Peroxidase by Cellobiose : Quinone Oxidoreductase

この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。The steady-state kinetics of the redox interaction between lignin peroxidase (LiP) and cellobiose: quinone oxidoreductase (CBQ) was analyzed. To explain the unique noncompetitive inhibition of LiP by CBQ, a scheme was proposed with a novel equation derived. The inhibition constant here differs from that occurring in the equation for the inhibition of LiP by oxalic acid (OX), in that it involves more parameters

<Original>Lignin Peroxidase-Catalyzed Oxidation of Monomeric Lignin Model Substrates

この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。The substrate specificity of lignin peroxidase (LiP) was investigated by determining the K_ms and V_s of LiP for the four lignin model substrates of 3,4-dimethoxybenzyl alcohol (I), 3,4-dimethoxybenzyl glycerol (II), 3,4,5-trimethoxybenzyl alcohol (III), and 3, 4, 5-trimethoxybenzyl glycerol (IV). The K_ms (μM) and V_s (turnover number, sec^) of LiP were determined. The K_m/V_ values calculated to be 4.7, 18.2, 29.9, and 76.7 for I, II, III, and IV, respectively. Among the substrates tested, I (veratryl alcohol), which is a secondary metabolite of white-rot fungi, was found to be the best substrate for LiP