Bacteriophage Transport in Sandy Soil and Fractured Tuff

Bacteriophage transport was investigated in laboratory column experiments using sandy soil, a controlled field study in a sandy wash, and laboratory experiments using fractured rock. In the soil columns, the phage MS-2 exhibited significant dispersion and was excluded from 35 to 40% of the void volume but did not adsorb. Dispersion in the field was similiar to that observed in the laboratory. The phage f2 was largely excluded from the porous matrix of the two fractured-rock cores studied, coming through 1.2 and 2.0 times later than predicted on the basis of fracture flow alone. Because of matrix diffusion, nonsorbing solutes were retarded by over a factor of three relative to fracture flow. The time for a solute tracer to equilibrate with the porous matrix of 6.5-cm-diameter by 25-cm-long cores was measured in days. Results of both granular-medium and fractured-rock experiments illustrate the inability of a solute tracer to provide estimates for dispersion and effective porosity that are applicable to a colloid. Bacteriophage can be used to better estimate the maximum subsurface transport rate of colloidal contaminants through a porous formation.     

Conformational states of beta-lactamase: molten-globule states at acidic and alkaline pH with high salt

We present evidence that beta-lactamase is close to fully unfolded (i.e., random coil conformation) at low ionic strength at the extremes of pH and that the presence of salt causes a cooperative transition to a conformation with the properties of a molten globule, namely, a compact state with native-like secondary structure but disordered side chains (tertiary structure). The conformation of beta-lactamase I from Bacillus cereus was examined over the pH 1.5-12.5 region by circular dichroism (CD), tryptophan fluorescence, dynamic light scattering, and 1-anilino-8-naphthalenesulfonate (ANS) binding. Under conditions of low ionic strength (I = 0.05) beta-lactamase was unfolded below pH 2.5 and above pH 11.5, on the basis of the far-UV and near-UV CD and tryptophan fluorescence. However, at high ionic strength and low pH an intermediate conformation (state A) was observed, with a secondary structure content similar to that of the native protein but a largely disordered tertiary structure. The transition from the unfolded state (U) to state A induced by KCl was cooperative and had a midpoint at 0.12 M KCl (I = 0.17 M) at pH 1.6. A similar conformation (state B) was observed at high pH and high ionic strength. The transition from the alkaline U state to state B induced by KCl at pH 12.2 was cooperative and had a midpoint at 0.6 M KCl (I = 0.65 M). Light scattering measurements showed that state B was compact although somewhat expanded compared to the N state. The compactness of state A could not be determined due to its strong propensity to aggregate.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of glycogen depletion and supercompensation on the physical working capacity at the fatigue threshold

The purpose of this investigation was to determine the effect of glycogen depletion and supercompensation on the physical working capacity at the fatigue threshold (PWCFT). Ten adult males (mean age 23 years, SD 3) volunteered as subjects for this study. During the first laboratory visit the subjects performed a maximal bicycle ergometer test for the determination of maximum oxygen consumption (VO2max). Between 48 and 72 h later, the subjects pedaled to exhaustion at a power output which corresponded to a mean of 76% of VO2max (range, 72-80%) for the purpose of glycogen depletion. For the next 3 days, the subjects were fed a 10.5 MJ.day-1 low carbohydrate diet which consisted of 7.5% carbohydrates, 22.0% protein and 70.5% fat. The subjects then performed an incremental cycle ergometer test to the onset of fatigue or PWCFT, which was estimated from integrated electromyographic voltages of the vastus lateralis muscle. For the next 3 days the subjects were fed a 10.5 MJ high carbohydrate diet which consisted of 72.2% carbohydrates, 12.4% protein and 15.4% fats for the purpose of glycogen supercompensation. The subjects then performed a second PWCFT test. A paired t-test indicated that there was no significant (p greater than 0.05) difference between the means of the PWCFT values (depletion 246 W, SD 30; supercompensation 265 W, SD 28) and they were highly correlated at r = 0.884. The results of this investigation suggested that the methods commonly used to affect glycogen depletion or supercompensation had no effect on PWCFT.     

The development of the sensory organs of the legs in the blowfly,Phormia regina

Summary The development of the sensory neurons of the legs of the blowfly,Phormia regina has been described from the third instar larva to the late pupa using immunohistochemical staining. The leg discs of the third instar larva contain 8 neurons of which 5 come to lie in the fifth tarsomere of the developing leg. Whereas 2 neurons persist at least to the late pupa, the other cells degenerate. The first neurons of gustatory sensilla arise in the fifth tarsomere at about 1.5 h after formation of the puparium. Most of these sensilla, however, appear within a short time period beginning at about 18 h. The femoral chordotonal sensory neurons first appear at the time of formation of the puparium, as a mass of cells situated in the distal femur. During later pupal development 2 groups of these cells come to lie at the femur-trochanter border, where they become the proximal femoral chordotonal organ of the adult; the remaining cells become the distal femoral chordotonal organ. Other scolopidial neurons appear later in development. The nerve pathways of the late pupal leg are established either by the axons of the cells that are present in the larval leg disc or by new outgrowing processes of sensory neurons. In the tibia, the initial direction of new outgrowth differs in different regions of the segment: proximal tibial neurons grow distally, while distal tibial neurons grow initially proximally.     

TRK1 encodes a plasma membrane protein required for high-affinity potassium transport in Saccharomyces cerevisiae.

We identified a 180-kilodalton plasma membrane protein in Saccharomyces cerevisiae required for high-affinity transport (uptake) of potassium. The gene that encodes this putative potassium transporter (TRK1) was cloned by its ability to relieve the potassium transport defect in trk1 cells. TRK1 encodes a protein 1,235 amino acids long that contains 12 potential membrane-spanning domains. Our results demonstrate the physical and functional independence of the yeast potassium and proton transport systems. TRK1 is nonessential in S. cerevisiae and maps to a locus unlinked to PMA1, the gene that encodes the plasma membrane ATPase. Haploid cells that contain a null allele of TRK1 (trk1 delta) rely on a low-affinity transporter for potassium uptake and, under certain conditions, exhibit energy-dependent loss of potassium, directly exposing the activity of a transporter responsible for the efflux of this ion.     

The Saccharomyces cerevisiae genome contains functional and nonfunctional copies of transposon Ty1.

Saccharomyces cerevisiae Ty elements are transposons closely related to retroviruses. The DNA sequence of a functional Ty element (TyH3) is presented. The long terminal repeat sequences are different, suggesting that TyH3 is a recombinant Ty element. A chromosomal Ty element near the LYS2 gene, Ty173, was found to be nonfunctional, even though it has no detectable insertions or deletions. The defect in Ty173 transposition is caused by a missense mutation giving rise to a Leu-to-Ile substitution in the TYB (pol) open reading frame. Several chromosomal Ty elements carry this lesion in their DNA, indicating that nonfunctional Ty elements are common in the yeast genome.     

Spectral mechanisms in the tree squirrel retina

Summary The retina of the gray squirrel (Sciurus carolinensis) contains rods and cones in a ratio of about 23. The spectral mechanisms in this retina were examined in behavioral and electrophysiological experiments. Tests of color vision revealed that this animal has a spectral neutral point at about 500 nm and, thus, dichromatic color vision. Recordings made from single optic nerve fibers and results obtained from an analysis of the flicker photometric electroretinogram (ERG) indicated that vision in the gray squirrel is based on three spectral mechanisms. One of these, presumably rod-based, has peak sensitivity at about 502 nm. The other two mechanisms reflect the presence of two classes of cone having average peak sensitivity of about 444 nm and 543 nm.     

Depletion of Brain Glutathione in Preweanling Mice by L-Buthionine Sulfoximine

Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS.     

Oestrogen and progesterone interactions in the control of gonadotrophin and prolactin secretion

Oestrogen and progesterone have marked effects on the secretion of the gonadotrophins and prolactin. During most of the oestrous or menstrual cycle the secretion of gonadotrophin is maintained at a relatively low level by the negative feedback of oestrogen and progesterone on the hypothalamic-pituitary system. The spontaneous ovulatory surge of gonadotrophin is produced by a positive feedback cascade. The cascade is initiated by an increase in the plasma concentration of oestradiol-17 beta which triggers a surge of luteinizing hormone releasing hormone (LHRH) and an increase in pituitary responsiveness to LHRH. The facilitatory action of oestrogen on pituitary responsiveness is reinforced by progesterone and the priming effect of LHRH. How oestrogen and progesterone exert their effects is not clear but the facilitatory effects of oestrogen take about 24 h, and the stimulation of LHRH release is produced by an indirect effect of oestradiol on neurons which are possibly opioid, dopaminergic or noradrenergic and which modulate the activity of LHRH neurons. In the rat, a spontaneous prolactin surge occurs at the same time as the spontaneous ovulatory gonadotrophin surge. The prolactin surge also appears to involve a positive feedback between the brain-pituitary system and the ovary. However, the mechanism of the prolactin surge is poorly understood mainly because the neural control of prolactin release appears to be mediated by prolactin inhibiting as well as releasing factors, and the precise role of these factors has not been established. The control of prolactin release is further complicated by the fact that oestradiol stimulates prolactin synthesis and release by a direct action on the prolactotrophes. Prolactin and gonadotrophin surges also occur simultaneously in several experimental steroid models. A theoretical model is proposed which could explain how oestrogen and progesterone trigger the simultaneous surge of LH and prolactin.