Dimensional rearrangement of rod-shaped bacteria following nutritional shift-up. II. Experiments with Escherichia coliBr

The dimensions of Escherichia coli$\text{B}\text{r}$ (strain H266) in transition between two states of balanced growth, were determined from electron micrographs of fixed cells by sampling the culture at various times following nutritional shift-up from a doubling time of 72 min to one of 24 min. Mean cell length rises immediately and overshoots its final steady-state value, cell diameter increases monotonically; both approach their asymptotic levels only after several hours.The results are compared with the dimensions predicted by each of two models of cell growth and morphogenesis in rod-shaped bacteria. The first attributes cell elongation to circular zones that double in number at a particular time during the cell cycle and which act at rates proportional to the growth rate; the second is similar, except that it considers surface growth rather than length extension as the active process, length being determined passively. Two possibilities are examined, that the zonal growth rate adjusts immediately to the new growth conditions, and that it does so gradually.The experimental data appear consistent with the gradual response version of the surface growth model.     

Unit cell transormations in yeast phenylalanine transfer RNA crystals

The orthorhombic unit cell of crystalline yeast phenylalanine transfer RNA has dimensions $\text{a = 33}\text{A}\text{?}$, $\text{b = 56}\text{A}\text{?}$ and $\text{c = 161}\text{A}\text{?}$. When the mother liquor dries partially, a series of transformations takes place in which the a and b axes change very little but the c axis decreases abruptly first to 128 Å and then to 109 Å. In a closely related orthorhombic cell in a different space group the c axis is 104 Å. Although there is some loss in resolution in these smaller unit cells, the over-all distribution of scattering intensity does not change substantially. This suggests that the tRNA molecules can slide together along the c axis without a substantial change in internal structure.     

Observations on the existence of lower threshold and upper critical food concentrations for the copepod Acartia tons a Dana

Acartia tonsa Dana represents a genus of temperate-tropical inshore copepods which, by virtue of its high biomass and rapid generation times, may be assumed to be an important planktonic primary consumer in terms of total production world-wide; its grazing response to different food concentrations is little known. Using wide ranges of concentrations of phytoplankton cultures, we have found that A. tonsa has a maximum grazing rate of ≈ 10.0 μg chl $\text{a}\text{1}$, decreasing to zero below 1.0 μg chl $\text{a}\text{1}$. This was confirmed using the more limited range of naturally-occurring particulate material. Although grazing rate became progressively reduced above 10 μg chl $\text{a}\text{1}$, ingestion rates continued to increase over the next order of magnitude of food concentration. It appears that A. tonsa is rarely exposed to food concentrations in its natural environment (as measured by conventional techniques) high enough to stimulate the maximum grazing effort. On the other hand, it is suggested that the continued increase of ingestion rates in the laboratory at much higher concentrations may indicate an adaptive mechanism associated with the encountering of ephemeral micro-patches of such concentrations, which would permit rapid filling of an empty gut in an energy-efficient manner. Fecal pellet production was also measured and shown to be a good indicator of ingestion rate.     

An ultrastructural examination of everted rat jejunum

Male, albino, Sprague-Dawley rats were sacrificed by cervical separation. Segments of jejunum were excised, everted and examined with the electron microscope. Examination of tissue fixed immediately after eversion revealed the following changes as compared to non-everted segments fixed $\text{in}$$\text{situ}$ and $\text{in}$$\text{vitro}$: 1) an increase in the length of microvilli from (mean ± S. E.) 0.991 ± 0.011μ for normal tissue to 1.389 ± 0.023μ for everted tissue, 2) an increase in width of microvilli from (mean ± S. E.) 0.089 ± 0.001μ for normal tissue to 0.097 ± 0.001μ for everted tissue, 3) an increase in length and number of lateral membrane interdigitations, and 4) the appearance of intercellular “lakes” in the lateral spaces. The above changes are in those structures hypothesized to be involved with salt and water transport across epithelia and may reflect altered transport rates $\text{in}$$\text{vitro}$ as compared to $\text{in}$$\text{vivo}$.     

Theory of biological similarity revisited

A unified theory of biological similarity is proposed, based on dimensional analysis (mass M, length L, diameter D, time T) and on three postulates: (1) the constancy of body density in terrestrial mammals; (2) the elastic similarity criterion (Rashevsky and McMahon) where $\text{L ∝ D}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$; and (3) the proportionality between length (L) and time (T), which is valid for relaxation oscillators. The postulated theoretical model provides a satisfactory correlation (r = 0·9937) between the predicted reduced exponent (b) and 96 allometric exponents (b) obtained from experimental data concerning a number of morphologic and physiologic parameters in animals of different size.The reformulation of a theory of biological similarity is posited mainly for the “internal” organization of organisms, whereas a “mechanical” similarity should be applied when inertial forces are present during animal locomotion (kinematics).Since biological rhythmicity is based on relaxation oscillators (T ∝ L), while in “mechanical” similarity the pendulum ($\text{T ∝ L}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) is the paradigm of a self-sustained oscillation, these two are the limits of a continuous spectrum of similarity criteria, where the exponent of the time dimension (T) is the essential factor.The four-dimensional nature of biological space is discussed (W ∝ L⁴), and due to the postulated isometry of length (L) and time (T), periodic phenomena conform to $\text{T ∝ W}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$.     

Relations between enzymatic and association reactions in the development of bovine fibrin clot structure

Development of fibrin clot structure was examined at pH 7.0, Γ/2 0.15, and 29 °C as a function of thrombin and fibrinogen concentrations. Parameters for the release of Apeptides, to give $\text{?}{}_{\mathrm{<mtext>A</mtext>}}$ were evaluated. Characteristics of time dependencies of development of turbidity, 90 ° light scattering, network, and compactible network were established. Mean mass/length ratios of fibrin in developing and mature networks were determined. Relationships between results combined with an inferred dependence of lateral interaction on release of B-peptides are used to disclose a model in which a protofibril network is formed first and the intrinsic length of this network (i.e., length exclusive of overlap or loose ends) determines network length, thus mean mass/length ratio, at maturity. Statements regarding initial protofibril network are: (i) A dominant group of $\text{?}{}_{\mathrm{<mtext>A</mtext>}}$-protofibrils appears first. With decreasing rate of production of $\text{?}{}_{\mathrm{<mtext>A</mtext>}}$ their average length increases and number decreases. (ii) Slower release of B-peptides produces $\text{?}{}_{\mathrm{<mtext>AB</mtext>}}$ whose fraction $\text{θ}{}_{\mathrm{<mtext>AB</mtext>}}\text{=}\text{?}{}_{\mathrm{<mtext>AB</mtext>}}\text{(?}{}_{\mathrm{A}}\text{+?}{}_{\mathrm{AB}}$) determines the occurrence of protofibril regions capable of contributing to a lateral interaction sufficiently stable for the formation of network. (iii) When dominant protofibrils attain a minimum combination of average length, number concentration, and frequency of occurrence of capable regions, an initial protofibril network is rapidly generated. (iv) Capable regions near protofibril ends are preferentially involved in initial network formation. (v) The initial network mesh size is large compared to average concomitant free protofibril length. (vi) With B-peptide release dependent on prior A-peptide release, protofibrils in the initial network have the highest capable region frequency, and this is maintained as lateral interaction progresses. Then, fibrin which is free at initial network formation and fibrin which is produced subsequently interact mainly to increase the mean mass/length ratio of initial network elements.     

The electron transfer in the membranes of endoplasmic reticulum. A quantitative estimation of cytochrome b5 content in the NADPH- and NADH-oxidation chains.

The phenomenon of induction of the NADPH-specific hydroxylase system by sodium phenobarbital was used to determine the content of cytochrome b₅ in each microsomal electron-transfer chain. It turned out that the specific activities of NADPH-dependent reductases and the cytochrome P-450 quantity were increased approximately 1.86 times and the activities of NADH-dependent reductases were somewhat decreased (0.89 times) in microsomes of induced rats. It is assumed that a subfraction of cytochrome b₅ included in the NADPH-oxygenase complex is induced together with the other carriers of the chain. The second subfraction of the hemoprotein, in the course of induction, behaves as a typical component of the NADH-oxidizing complex. On the basis of the data obtained, the calculation was made, which showed that the NADPH-oxidation chain contains from $\text{1}\text{5}$ to $\text{1}\text{3}$ of the total microsomal cytochrome b₅ pool.     

Models for cultural inheritance. I. Group mean and within group variation

Evolution of a cultural trait has been considered at a theoretical level. Cultural evolution is to be kept distinct from biological evolution, but the discrimination of the two may be difficult in actual cases. In cultural evolution, not only the parents of an individual but also other members of the group, contribute directly to determining the value of a trait in the individual. The cumulative effect of members of the group other than the parents has been called the group effect g. The expected value of the trait of an individual in the next generation has been assumed in the model to be the weighted mean of the individual value (as determined by the trait values in the parent or parents plus a random contribution $\text{E}$ the new variation per generation), and the group mean value, the individual and the group contributions being weighted as (1 ? g) to g. Effects of age and peers and of generations earlier than parental have also been analyzed.It has been demonstrated that, if g is different from zero and positive, however small, in spite of new variation arising at every generation the variation of the trait within the group will stabilize at a finite level. The stable amount of the variation depends on the mode of transmission, which has been considered here to be either uniparental or biparental, on the value of g, on the size of the group if the progeny size is not constant, and on the amount of new variation produced per generation. Independent groups will differentiate one from the other randomly, at a rate which is a function of the mode of transmission (uni or biparental), the g value, and the size of the group. Ways to study discontinuous traits have been given. If discontinuity arises from imposition of a perceptive threshold on the existing variation, and therefore the variate is not truly discontinuous, its behavior is still predictable by the same rules, and a transformation for study of the frequencies of observations above or below threshold has been given, which permits the prediction of the trend of changes with time. A truly discontinuous character will undergo fixation of one or other character state, as for alleles in random genetic drift, but the rate of fixation will be decreased by group action.     

Crystallographic study of plastocyanins

Crystals of plastocyanins from pea and corn leaves have been obtained. Both are suitable for X-ray structure analysis with a resolution up to 1.8 Å. The crystal form of plastocyanin from pea leaves belongs to the space group P2₁2₁2₁ with unit cell dimensions: $\text{a = 49.0}\text{A}\text{?}\text{, b = 53.3}\text{A}\text{?}\text{, c = 82.6}\text{A}\text{?}$. The assumed number of protein molecules per asymmetric unit of the unit cell is two. Crystals of the oxidized (Cu²⁺) and reduced (Cu⁺) forms are isomorphic. No essential differences in spot intensities for the main zone with a resolution of 3 Å were revealed. The crystal form of plastocyanin from corn leaves belongs to the space group P1 with unit cell parameters: $\text{a = 24.8}\text{A}\text{?}\text{, b = 30.0}\text{A}\text{?}\text{, c = 58.5}\text{A}\text{?}$ and α = 96° 10′, β = 87°08′, γ = 78°40′. The assumed number of protein molecules per asymmetric unit is two.     

Estimation of mutation rates in cultured mammalian cells

The factors that affect reliable estimations of mutation rates (μ) in cultured mammalian somatic cell populations by fluctuation analysis are studied experimentally and statistically. We analyze the differential effect of the final cell population size in each culture (N_t) and the number of parallel cultures (C) on the variation in the rate estimates ($\text{μ}$) inferred from the P₀ method. The analysis can be made after the derivation of the variance of $\text{μ}$, which is a measure of variation of $\text{μ}$ for a given combination of N_t and C in a number of repeat experiments. The variance of $\text{μ}$ is inversely proportional to C and to the square of N_t. N_t determines the probability of occurrence of mutation in a cell culture. By influencing the size of P₀, N_t also determines whether a rate estimate is obtainable from the experiment. Since P_o is estimated from the fraction of cultures containing no mutation in a set of C cultures, C becomes a determining factor for the accuracy of $\text{μ}$. The rate estimated from $\text{P}\text{?}{}_0$ is biased, but the bias is in general 2 orders of magnitude smaller than $\text{μ}$. By the selection of an appropriate combination of N_t and C for the experiment, this bias can be reduced even further.Based on the notion of comparing two proportions, we propose a test statistic and have applied it to experimental results for a test of equality of mutation rates in different cell lines. This development places the comparison of mutation rates on a statistical basis.     

Crystallographic study of the large tryptic fragments of elongation factor G from Escherichia coli

Crystals of N- and C-terminal fragments of elongation factor G (EF-G) from Escherichia coli have been grown from the preparations obtained by limited tryptic hydrolysis. Molecular masses of these fragments are equal to about 49,000 and 25,000, respectively. In the form of an additive complex they appear to be a major part of the native spatial structure of EF-G (Alakhov et al., 1979). Crystals of N-terminal fragment belong to space group P4₁2₁2 or P4₃2₁2 with unit cell dimensions $\text{a = b = 76.6}\text{A}\text{?}\text{and}\text{c = 191.6}\text{A}\text{?}$. Crystals of C-terminal fragment belong to space group P4₁22 or P4₃22 with unit cell dimensions $\text{a = b = 77.1}\text{A}\text{?}\text{and}\text{c = 75.0}\text{A}\text{?}$. In both cases the assumed number of protein molecules per asymmetric part of the unit cell is one.     

Ecological investigations on the zooplankton community of Balsfjorden,northern Norway: Generation cycles,and variations in body weight and body content of carbon and nitrogen related to overwintering and reproduction in the copepod Calanus finmarchicus (Gunnerus)

The generation cycles of Calanus finmarchicus (Gunnerus) are described together with the seasonal variations in length, wet wt, dry wt, carbon content, nitrogen content and $\text{C}\text{N}$ ratio in copepodite stage IV, V and stage VI males and females from Balsfjorden (69°21′N: 19°06′E), a subarctic fjord in northern Norway. C. finmarchicus overwinters in copepodite stage IV (≈ 20%) or V (≈80%) and produces one generation a year. Variations in body weight and body content of carbon and nitrogen in the different copepodite stages showed a pronounced seasonal pattern. For instance, the $\text{C}\text{N}$ ratio was lowest (4.9) in adult females during the spawning period. Copepodite stage IV and V had higher $\text{C}\text{N}$ values in summer and autumn (12 to 14) than in spring (8 to 10). Variations in length, weight and chemical composition revealed that the overwintering stock of C. finmarchicus went through two growth phases during this period. From September to January no significant changes in the measured variables were detected. During the second phase of the overwintering period, January to April, the different stages showed a profound decrease in weight and change in chemical composition. This seemed to be connected with the onset of sexual differentiation in stage V starting in January, subsequent moulting into adults and gonad maturation in these adults. These results are further discussed in relation to the different prevailing hypotheses concerning overwintering strategy in Calanus species.     

Optimal patch use in a stochastic environment

This paper considers an animal foraging on prey which are distributed in well-defined patches. It is assumed that the environment may be stochastic and that the animal can gain information on patch type as it forages. The foraging policy which maximises mean reward rate for the environment is characterised in terms of a function of state called the potential function. This policy is shown to be given by the rule: continue foraging on the present patch while the potential is positive, when the potential falls to zero move on to the next patch. Let r denote the current reward rate on a patch and let γ denote the maximum mean reward rate for the environment. It is shown that r ? γ if it is optimal to leave. Conditions which ensure r < γ are also given. For a large class of environments the optimal policy is stated in terms of a revised reward rate r?, and is given by the rule: continue on the present patch while $\text{r}\text{?}\text{> γ}$, when r? falls to γ move on to the next patch. Finally, it is shown that the stay time on a patch is a decreasing function of γ.     

Experimental studies on supercooling in two Antarctic micro-arthropods

Samples of mites and Collembola which had been acclimated at 5°C and provided with natural foods were cooled at four constant cooling rates: 1, $\text{1}\text{2}$, $\text{1}\text{4}$, $\text{1}\text{8}\text{deg min}{}^{\mathrm{?1}}$ and ca 20 deg min^?1, and their individual supercooling points measured. Frequency distributions of supercooling points comprised not less than 84 (Alaskozetes antarcticus) and 96 (Cryptopygus antarcticus) individuals in each case. Two modal groups were displayed in these distributions, which were widely separated in temperature and termed low group and high group. In Alaskozetes a trough between ?3 and ?4°C was present in the high-group distribution, which may be due to a lack of a certain class of nucleators. The highest temperatures at which animals froze occurred at the slowest cooling rate ($\text{1}\text{8}\text{deg min}{}^{\mathrm{?1}}$), whereas rapid cooling removed the trough to form a single high-group peak. In Cryptopygus, the high groups were narrow and peaked (<2 deg wide) at all cooling rates, with a downward shift of ca 1 deg between the rates $\text{1}\text{8}$ and $\text{1}\text{2}\text{deg min}{}^{\mathrm{?1}}$. Both species showed a trend towards a lower mean low-group supercooling point at faster rates of cooling, but these were not significant. Regressions of cooling rate on individual low-group supercooling points (≥?20°C) for both species showed a significant negative correlation, which did not differ between species. The distribution of the deviations about each rate-defined mean in the low group for each species was skewed to the right, with 88% occurring between ±2 deg of the means. It is suggested that minor deviations (e.g. halving or doubling of the cooling rate) do not affect the resultant supercooling points at non-constant cooling rates, but a rate of 1 deg min^?1 is to be preferred.     

Induction of fertile oestrus in seasonally anoestrous ewes with low doses of Gn-RH

Oestrus, conception and lambing performance were assessed in progesterone-primed seasonally anoestrous ewes induced to ovulate with gonadotrophin-releasing hormone (Gn-RH), which was administered intravenously for 48 h as either injections of 250 ng at 2-h intervals (n = 15) or as a continuous infusion at the rate of 125 ng/h (n = 12) or 250 ng/h (n = 12).In $\text{14}\text{15}$ of the ewes injected with Gn-RH, a preovulatory LH peak was recorded at a mean time interval of 33.9 ± 1.8 h after the start of treatment. All ewes displayed oestrus and all ovulated, with a mean ovulation rate of 1.67 ± 0.13. Eleven ewes were diagnosed as pregnant and subsequently lambed. Following infusion of Gn-RH, preovulatory LH peaks were recorded in $\text{21}\text{24}$ ewes at a mean time of 36.1 ± 2.9 h (125 ng/h) and 34.7 ± 2.0 h (250 ng/h). All but two of the ewes displayed oestrus and $\text{23}\text{24}$ ovulated. The group mean ovulation rates of 1.27 ± 0.14 (125 ng/h) and 1.75 ± 0.22 (250 ng/h) were not significantly different. Eleven of the 22 ewes mated were diagnosed as pregnant and produced live lambs.These results suggest that fertility of Gn-RH-induced ovulations in seasonally anoestrous ewes is comparable to that apparent in ewes ovulating spontaneously during the breeding season.     

Rate and diel periodicity of pheromone emission from female gypsy moths, (Lymantria dispar) determined with a glass-adsorption collection system

The rate of pheromone emission from wild and laboratory-reared gypsy moth (Lymantria dispar) (Lepidoptera: Lymantriidae) virgin females was determined with an all-glass aeration apparatus. This device incorporated a bed of 1-mm glass beads to extract entrained pheromone from the air flowing over the protruded gland. The temporal pattern of emission was established by monitoring individual females after eclosion for 24 consecutive 2-hr intervals.At a constant 24°C, both wild and laboratory females exhibited a similar diel periodicity of pheromone emission. The mean release rate increased after onset of photophase, generally attained maximal levels between 1600 and 2200 hr and declined during scotophase. Pheromone was released continuously and the mean daily emission increased with age for both wild and laboratory moths. The mean emission rate over the 48-hr monitoring interval was $\text{15.4 ng}\text{2 hr}$ for wild females vs $\text{14.7 ng}\text{2 hr}$ for laboratory moths. The peak emission from 2-day-old laboratory moths was ca.$\text{28 ng}\text{2 hr}$ compared with the ca.$\text{25 ng}\text{2 hr}$ released by their wild counterparts.The calling periodicity of laboratory females was determined at a constant 24°C and under a natural temperature rhythm. At 24°C, the proportion of females calling exceeded 45% throughout the diel period, whereas under the temperature rhythm, calling was virtually eliminated by temperatures below 15°C, indicating that temperature acts as an exogenous cue to modify the expression of the calling rhythm and thus potentially the periodicity of pheromone emission.     

Sterol biosynthesis: Establishment of the structure of 3β-p-bromobenzoyloxy-5α-cholest-8(14)-en-15β-ol

Previous studies have established that hydride reduction of 3β-benzoyloxy-5α-cholest-8(14)-en-15-one yields two epimers (at C-15) of 5α-cholest-8(14)-en-3β,15-diol which were designated as diol A and B. Efficient enzymatic conversion of both compounds to cholesterol was observed. To determine the absolute configuration of the 15-OH function in the two compounds, the 3β-p-bromobenzoyl ester of diol B was prepared from 3β-p-bromobenzoyloxy-5α-cholest-8(14)-en-15-one by reduction with sodium borohydride. Crystals of the derivative were found to belong to the space group P1, with unit cell parameters; $\text{a = 9.24}\text{A}\text{?}$, $\text{b = 12.61}\text{A}\text{?}$, $\text{c = 7.03}\text{A}\text{?}$, α = 93.05°, β = 100.27°, γ = 90.82°, and one molecule per unit cell. Least-squares refinement of the structure was carried out to final R value of 0.14. The configuration of the hydroxyl group at the 15 position of diol B has been determined to be β.     

Tyrocidine A: crystal growth and preliminary x-ray diffraction data.

Tyrocidine A was crystallized from 2-methyl-2,4-pentanediol and water, or methanol, to yield crystals that are large enough for X-ray diffraction studies. Four crystals were examined; three were in equilibrium with mother liquor and the fourth was air-dried. They belong to the rhombohedral space group R32. Parameters of the hexagonal cell of the fully solvated crystals vary slightly and are approximately $\text{a = 34}\text{A}\text{?}\text{and}\text{c = 50}\text{A}\text{?}$. The asymmetric unit consists of one molecule of tyrocidine and several molecules of 2-methyl-2,4-pentanediol. Air-dried crystals appear to contain about half the number of solvent molecules. Three-dimensional X-ray diffraction data showing a maximum resolution of $\text{s = (1.7}\text{A}\text{?}\text{)}{}^{\mathrm{?1}}$ have been recorded.     

Disequilibrium among several linked neutral genes in finite population 1. mean changes in disequilibrium

Formulae are developed for computing changes in expected values in a finite population of linkage disequilibrium among neutral genes from more than two loci, although the exact analysis is taken up to only six loci. An essentially haploid model is used. As with two loci, the three-locus disequilibrium declines exponentially at all generations, but for m > 3 loci a matrix has to be constructed to give joint changes in the m-locus disequilibrium and products of disequilibria with fewer loci, for example of two $\text{m}\text{2}\text{-}\text{locus}$ disequilibria. The asymptotic rates of change in multilocus disequilibria depend on the arrangement of genes on the chromosome as well as its total length, but the initial rate of breakdown of disequilibrium from a line cross base is less dependent on the arrangement. With equally spaced loci the asymptotic rate of breakdown of m locus disequilibrium is roughly proportional to m. Although mutation and interference are excluded from the main analysis, it is shown how they can be incorporated.     

DNA synthesis during the division cycle of three substrains of Escherichia coliBr

The relationship between chromosome replication and the bacterial division cycle has been examined in three substrains of Escherichia coli$\text{B}\text{r}$ obtained from different sources and designated $\text{B}\text{r}$ A, $\text{B}\text{r}$ F and $\text{B}\text{r}$ K. At growth rates greater than 1.0 doubling per hour (μ > 1.0), the time for a round of chromosome replication (C) was 42 minutes in all three substrains, but the time between the end of a round and cell division (D) was 22 minutes in $\text{B}\text{r}$ A, 16 minutes in $\text{B}\text{r}$ F and 14 minutes in $\text{B}\text{r}$ K. At slower growth rates C and D increased, but to significantly different extents in the three substrains. When μ = 0.5, C and D were approximately 80 and 40 minutes in $\text{B}\text{r}$ A, 60 and 20 minutes in $\text{B}\text{r}$ F, and 70 and 20 minutes in $\text{B}\text{r}$ K.As a consequence of the lengths of the C and D periods in the three stocks of E. coli$\text{B}\text{r}$, the patterns of chromosome replication during the division cycle differed. The most obvious difference was that E. coli$\text{B}\text{r}$ F and E. coli$\text{B}\text{r}$ K possessed periods devoid of DNA synthesis at both the beginning and the end of the division cycle during slow growth, whereas E. coli$\text{B}\text{r}$ A contained only one period devoid of DNA synthesis at the end of the cycle.