Comparison of definitions of the lag phase and the exponential phase in bacterial growth

M.H. ZWIETERING, F.M. ROMBOUTS AND K. VAN 'T RIET. 1992. Different definitions of the lag time and of the duration of the exponential phase can be used to calculate these quantities from growth models. The conventional definitions were compared with newly proposed definitions. It appeared to be possible to derive values for the lag time and the duration of the exponential phase from the growth models, and differences between the various definitions could be quantified. All the different values can be calculated from the growth parameters μ _m , and a. Therefore, it appeared to be unnecessary to use complicated mathematical equations: simple equations were adequate. For the Gompertz model the conventional definition of the lag time did not differ appreciably from the newly proposed definition. The end-point of the exponential phase and thus the duration of the exponential phase differed considerably for the two definitions. For the logistic model the two definitions lead to considerable differences for all quantities. It is recommended that the conventional definition is used for calculating the lag time. For the duration of the exponential phase it is recommended that the new definition is used. The value can be calculated, however, directly from the conventional growth parameters.     

Exogenous androgens decrease the length of the luteal phase and increase the length of the follicular phase

This study investigated the effects of exogenous androgens on the menstrual cycle of eight transsexual females. It was found that the luteal phase decreased from 13.7 +/- 0.8 to 11.6 +/- 0.8 days, whereas the follicular phase increased in length from 13.5 +/- 0.6 to 15.3 +/- 0.6 days. With the testosterone levels attained in venous blood (+/- 4.5 nmol/l) ovulation continued, judged by the rise of basal body temperature and the increase of oestrogen and progesterone blood levels. These results relate hyperandrogenism to luteal insufficiency.     

Conversion of the beckman liquid phase sequencer to a gas-liquid phase sequencer

As an effective aid to extend the microsequencing capabilities the Beckman protein/peptide sequenator Series 890C has been successfully converted to a gas-liquid system, in which coupling buffer 25% trimethylamine was employed as a gas, and heptafluorobutyric acid as a liquid. The system has been found to be efficient for microsequencing (less than 100 pmol). The details of mechanical, plumbing, and other minor changes are described in this paper along with the results of sequencing proteins and peptides, directly and from blots.     

Gas phase infrared spectra via the phase integration quasi-classical method

We apply the recently developed phase integration method (PIM) (Monteferrante et al. Mol Phys. 2011;109:3015–3027) to the calculation of infrared spectra of gas phase molecules. The PIM combines a generalised Monte Carlo sampling of the exact thermal density of the system with classical molecular dynamics to obtain approximate time quantum correlation functions. To describe the molecules, we adopt very simple analytical potentials that have, however, proved interesting, and surprisingly challenging, benchmarks for approximate quantum dynamical schemes. We show that, in contrast with two other commonly applied methods, our spectra do not exhibit spurious features or unphysical shifts depending on the temperature. Identifying the positions of the peaks requires only a few tens of trajectories, while an accurate evaluation of the relative intensities of the peaks is computationally more demanding.     

Comparison of definitions of the lag phase and the exponential phase in bacterial growth.

Different definitions for the lag time and of the duration of the exponential phase can be used to calculate these quantities from growth models. The conventional definitions were compared with newly proposed definitions. It appeared to be possible to derive values for the lag time and the duration of the exponential phase from the growth models and differences between the various definitions could be quantified. All the different values can be calculated from the growth parameters microm, lambda and alpha. Therefore, it appeared to be unnecessary to use complicated mathematical equations; simple equations were adequate. For the Gompertz model the conventional definition of the lag time did not differ appreciably from the newly proposed definition. The end-point of the exponential phase and thus the duration of the exponential phase differed considerably for the two definitions. For the logistic model the two definitions lead to considerable differences for all quantities. It is recommended that the conventional definition is used for calculating the lag time. For the duration of the exponential phase it is recommended that the new definition is used. The value can be calculated, however, directly from the conventional growth parameters.     

Properties of bilayer membranes in the phase transition or phase separation region

The increase in passive permeability of bilayer membranes near the phase transition temperature is usually explained as caused by either the increase in the amount of ‘boundary lipid’ present in the membrane, or by the increase in lateral compressibility of the membrane. Since both the amount of ‘boundary lipid’ and the lateral compressibility show a similar anomaly near the transition temperature, it is difficult to distinguish experimentally between the two proposed mechanisms.We have examined some details of both of the proposed pictures. The fluid-solid boundary energy, neglected in previous work, has been computed as a function of the domain size. For a single component uncharged lipid bilayer, the results rule out the existence of even loosely defined solid domains in a fluid phase, or vice versa. Thermodynamic fluctuations, which are responsible for anomalous behaviour near the phase transition temperature, are not intense enough to approximate the formation of a domain of the opposite phase.Turning next to lateral compressibility of bilayer membranes we have considered two-component mixtures in the phase separation region. We present the first calculation of lateral compressibility for such systems. The behaviour shows interesting anomalies, which should correlate with existing and future data on transport across membranes.     

The effect of ethanol on the phase transition temperature and the phase structure of monounsaturated phosphatidylcholines

Previous studies from our laboratories have delineated the relationship between the acyl chain asymmetry of mixed-chain phosphatidylcholines, C(X):C(Y)PC, and the effect of ethanol concentration, [EtOH], on the main phase transition temperature, T(m), and the phase structure of the lipid bilayer composed of C(X):C(Y)PC using differential scanning calorimetry and X-ray diffraction techniques [Huang and McIntosh, Biophys. J. 72 (1997) 2702--2709]. In the present work, we have extended these studies to characterize the effect of [EtOH] on the T(m) and the phase structure of the lipid bilayer composed of sn-1 saturated/sn-2 monounsaturated phosphatidylcholines with various positions of the cis double bond. Specifically, five positional isomers of 1-eicosanoyl-2-eicosenoyl-sn-glycero-3-phosphocholines, C(20):C(20:1 Delta(n))PC with n=5, 8, 11, 13 and 17, were synthesized and studied. For C(20):C(20:1 Delta(n))PC with n=5 and 8, results from the calorimetric experiments showed that in response to various concentrations of ethanol, the change in T(m) of the lipid bilayer composed of monounsaturated lipids was characterized by a sigmoidal or biphasic profile in the plot of T(m) versus [EtOH]. In contrast, a continuous depression of the T(m) by ethanol was observed calorimetrically for C(20):C(20:1 Delta(n))PC with n> or =11. The X-ray diffraction experiments further demonstrated that C(20):C(20:1 Delta(5))PC and C(20):C(20:1 Delta(8))PC can undergo the ethanol-induced gel-to-fully interdigitated phase transition at T相似文献   

New evidence for gel-liquid crystalline phase coexistence in the ripple phase of phosphatidylcholines

Experimental evidence supporting the hypothesis of gel-liquid crystalline phase coexistence in the stable ripple phase of diacylphosphatidylcholines has been obtained from time-resolved X-ray small- (SAXS) and wide-angle diffraction (WAXS) in the millisecond to second time domain. The pretransition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) exhibits a thin lamellar liquid crystalline intermediate phase (designated L_α*) if driven far away from equilibrium by an infrared temperature jump (T-jump) technique. The findings can be described by a two-step model. (1) Instantaneously with the T-jump, an anomalously thin lamellar liquid crystalline intermediate phase (d = 5.6–5.8 nm) forms, coexisting with the original gel-phase L_β′. Within the first seconds, the lamellar repeat distance of the intermediate increases to a value of about 6.7 nm. A closer examination of these kinetics reveals two relaxation components: a fast process, proceeding within tenths of a second, and a slow process, on the time scale of a few seconds. (2) Finally, both the liquid crystalline and the gel-phase relax into the stable ripple phase P_β′. The total process time of the transition is nearly independent of the addition of NaCl, but varies strongly with the chain length of the lecithin species. Received: 24 November 1999 / Revised version: 25 February 2000 / Accepted: 25 February 2000     

Defective S phase chromatin assembly causes DNA damage,activation of the S phase checkpoint,and S phase arrest

The S phase checkpoint protects the genome from spontaneous damage during DNA replication, although the cause of damage has been unknown. We used a dominant-negative mutant of a subunit of CAF-I, a complex that assembles newly synthesized DNA into nucleosomes, to inhibit S phase chromatin assembly and found that this induced S phase arrest. Arrest was accompanied by DNA damage and S phase checkpoint activation and required ATR or ATM kinase activity. These results show that in human cells CAF-I activity is required for completion of S phase and that a defect in chromatin assembly can itself induce DNA damage. We propose that errors in chromatin assembly, occurring spontaneously or caused by genetic mutations or environmental agents, contribute to genome instability.     

Cytophotometric evaluation of the transition of cells from the G0 phase to the G1 phase of the cell cycle

Feulgen stained nuclei of PHA-stimulated human blood lymphocytes were used for cytophotometric chromatin pattern analysis. Similar distributions of low optical density values indicating the predominance of diffuse chromatin were obtained for G1, S and G2 cells. Condensed chromatin was predominant in G0 and M nuclei. Integral versus average optical densities scatter plots analyses permitted one to distinguish cells undergoing different phases of cell cycle including G0 and G1.     

A rapid,simplified medium for converting the mycelial phase of Blastomyces dermatitidis to the yeast phase

Summary The twenty-two isolates ofB. dermatitidis used in this study were converted to their yeast phase more readily on the cottonseed medium than on any of the other three media used in this experiment.The dextrose concentration and pH level do not seem to be factors in the conversion process when this medium is used.The advantages of this medium are discussed.From the Communicable Disease Center, Public Health Service, United States Department of Health, Education, and Welfare.     

Measuring the kinetics of membrane phase transitions

This article presents a brief review of literature on the physical chemistry of lipid phase transitions with emphasis on their kinetic properties. The theoretical foundations of perturbation techniques, and specifically the volume-perturbation technique are discussed in some detail. These are presented as a rationale for, and introduction to, a volume-perturbation kinetic calorimeter that we have constructed for measurement of the kinetics of lipid phase transitions. The instrument has been applied to study the gel-liquid crystalline phase transition in a variety of phospholipid bilayer systems. The design and implementation of the volume-perturbation calorimeter are presented along with a discussion of the techniques of data analysis. Finally, we present typical results obtained with this methodology for a multilamellar vesicle dispersion of dipalmitoylphosphatidylcholine.