Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state

The genes for cellobiose utilization are normally cryptic in Escherichia coli. The cellobiose system was used as a model to understand the process by which silent genes are maintained in microbial populations. Previously reported was (1) the isolation of a mutant strain that expresses the cellobiose-utilization (Cel) genes and (2) that expression of those genes allows utilization of three beta- glucoside sugars: cellobiose, arbutin, and salicin. The Cel gene cluster has now been cloned from that mutant strain. In the course of locating the Cel genes within the cloned DNA segment, it was discovered that inactivation of the Cel-encoded hydrolase rendered the host strain sensitive to all three beta-glucosides as potent inhibitors. This sensitivity arises from the accumulation of the phosphorylated beta- glucosides. Because even the fully active genes conferred some degree of beta-glucoside sensitivity, the effects of cellobiose on a series of five Cel+ mutants of independent origin were investigated. Although each of those strains utilizes cellobiose as a sole carbon and energy source, cellobiose also acts as a potent inhibitor that reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand, wild-type strains that cannot utilize cellobiose are not inhibited. The observation that the same compound can serve either as a nutrient or as an inhibitor suggests that, under most conditions in which cellobiose will be present together with other resources, there is a strong selective advantage to having the cryptic (Cel0) allele. In those environments in which cellobiose is the sole, or the best, resource, mutants that express the genes (Cel+) will have a strong selective advantage. It is suggested that temporal alternation between these two conditions is a major factor in the maintenance of these genes in E. coli populations. This alternation of environments and fitnesses was predicted by the model for cryptic-gene maintenance that was previously published.      

Comparison of effects of sustained isocapnic hypoxia on ventilation in men and women

Sajkov, Dimitar, Alister Neill, Nicholas A. Saunders, and R. Douglas McEvoy. Comparison of the effects of sustained isocapnichypoxia on ventilation in men and women. J. Appl.Physiol. 83(2): 599-607, 1997.Sleep-relatedrespiratory disturbances are more common in men than in premenopausalwomen. This might, in part, be due to different susceptibilities to therespiratory depressant effects of hypoxia. Therefore, we comparedventilation during 10 min of baseline room-air breathing and 20-minsustained isocapnic hypoxia (fractional inspiredO₂ = 11%, arterial saturation ofO₂  80%) followed by 10 min ofbreathing 100% O₂ in 10 normal men and in 10 women in the follicular phase of the menstrual cycle. Control measurements were made during two transitions from room air (10 min) to 100% O₂ (10 min) andaveraged. Inspired minute ventilation(I) after2 min of hypoxia was the same in men and women [131 ± 6.1%baseline for men, 136 ± 7.7% baseline for women; not significant(NS)] and declined to the same level after 20 min (115 ± 5.0% baseline for men, 116 ± 6.6% baseline for women; NS)associated with a similar decline in inspiratory time and tidal volume.Breathing frequency did not change.I decreased transiently during subsequent 100%O₂ breathing in both men and women, associated with reduced frequency and duty cycle and increased expiratory time. The fall inI wassignificantly greater than that observed during control hyperoxiaexperiments in men but not in women. We conclude that ventilatoryresponses to sustained isocapnic hypoxia do not differ between awakehealthy men and women in the follicular phase of their menstrual cycle.However, after termination of isocapnic hypoxia, men appear to depress their ventilation to a greater degree than women.

     

Effects of gaseous anaesthetics and inert gases on the phase transition in smectic mesophases of dipalmitoyl phosphatidylcholine

The phase transition in smectic mesophases of dipalmitoyl phosphatidylcholine was studied under high pressures of helium (340 atm), nitrogen (340 atm), nitrous oxide (43 atm), cyclopropane (4.4 atm) and $\text{n-}\text{propane}$ (8.2 atm), using a turbidimetric technique. Helium and nitrogen increased the transition temperature by 0.021 and 0.006°C/atm, respectively, compared with 0.024°C/atm for hydrostatic pressure. Nitrous oxide reduced the transition by 0.58°C/atm. The hydrocarbon gases spread the transition width and lowered the transition temperature with increasing effect at higher doses. Comparisons with other membrane probes are made and the concentration of gases in the bilayer which lower the transition temperature by 1°C are estimated, in mol%: He, 10.2; N₂, 13.2; N₂O, 9.04; $\text{n-}\text{C}{}_3\text{H}{}_8$, 6.3 and cyclopropane, 12.8.     

Homeoviscous theory under pressure: II. The molecular order of membranes from deep-sea fish

The molecular order of brain and liver membranes isolated from deep sea and continental shelf fish species have been estimated and compared using the fluorescence polarization technique in order to determine whether life in a high pressure habitat is associated with an adjustment of membrane order. Fish were trawled at depths between 200 m and 4000 m, liver and brain membranes were fractionated, and fluorescence polarization was measured at 4°C and ambient pressure. Polarization of the brain myelin fraction provided a statistically significant regression with depth of capture ($\text{P<0.001}$) with a slope of ?0.004 km^?1. This change in polarization with depth was sufficient to offset approximately half of the pressure-induced increase in polarization and thus represents the first structural evidence of homeoviscous adaptation to pressure. Polarization of the brain synaptic and liver mitochondrial fraction was not significantly related to depth. This may be due, at least in part, to a high individual variability of polarization compared to laboratory-acclimated freshwater fish.     

Ixodes ricinus and Borrelia burgdorferi sensu lato in the Royal Parks of London,UK

Experimental and Applied Acarology - Assessing the risk of tick-borne disease in areas with high visitor numbers is important from a public health perspective. Evidence suggests that tick presence,...     

Transfected HEK293 Cells Expressing Functional Recombinant Intercellular Adhesion Molecule 1 (ICAM-1) – A Receptor Associated with Severe Plasmodium falciparum Malaria

Intercellular adhesion molecule 1 (ICAM-1) is a membrane-bound glycoprotein expressed on endothelial cells and cells of the immune system. Human ICAM-1 mediates adhesion and migration of leucocytes, and is implicated in inflammatory pathologies, autoimmune diseases and in many cancer processes. Additionally, ICAM-1 acts as receptor for pathogens like human rhinovirus and Plasmodium falciparum malaria parasites. A group of related P. falciparum erythrocyte membrane protein 1 (PfEMP1) domains, the DBLβ, mediates ICAM-1 binding of P. falciparum-infected erythrocytes. This ICAM‑1-binding phenotype has been suggested to be involved in the development of cerebral malaria. However, more studies identifying cross-reactive antibody and ICAM-1-binding epitopes and the establishment of a clinical link between DBLβ expression and e.g. cerebral malaria are needed before the DBLβ domains can be put forward as vaccine candidates and go into clinical trials. Such studies require availability of functional recombinant ICAM-1 in large quantities. In this study, we compared recombinant ICAM-1 expressed in HEK293 and COS-7 cells with mouse myeloma NS0 ICAM-1 purchased from a commercial vendor in terms of protein purity, yield, fold, ability to bind DBLβ, and relative cost. We present a HEK293 cell-based, high-yield expression and purification scheme for producing inexpensive, functional ICAM‑1. ICAM-1 expressed in HEK293 is applicable to malaria research and can also be useful in other research fields.     

The effects of dietary flaxseed on the Fischer 344 rat: II. Liver gamma-glutamyltranspeptidase activity

The effect of 10% flax chow consumption from the 30th to the 130th day after birth was examined in male Fischer 344 rats. The effects of both the high lignan/high oil Norlin strain and a high lignan/low oil Solin strain of flaxseed were compared. Physically and behaviourally there were no differences in rats belonging to the three dietary groups at any time. At 50 and 100 days of dietary exposure, blood glucose levels were the same in Norlin and Solin flax chow-fed and as well as regular chow-fed rats; there were no signs of toxicity in the Norlin and Solin flax-fed rats since their plasma levels of alanine aminotransferase were the same and equal to those of regular chow-fed rats. The activity of gamma-glutamyltranspeptidase (gammaGT) displayed an increase in the liver homogenates of flax chow-fed rats. This increase was the same in Norlin and Solin flax-fed rats at 50 and 100 days. Thus the liver effect was not oil, but lignan, likely secoisolariciresinol diglucoside (SDG), induced and was effected early on, and sustained, after flax exposure. The degree of heat activation of liver homogenate gammaGT was the same in regular chow-fed and flax chow-fed rats. Compared to liver homogenate gammaGT activity, the soluble form of gammaGT was expressed at very low levels while the plasma membrane-bound form of gammaGT was expressed at very high levels in rat liver in both regular chow-fed and flax chow-fed rats. There was no effect of flax feeding on the soluble form of liver gammaGT which was expressed at a very low level. Flax feeding effected an increase in the activity of gammaGT in isolated plasma membrane fractions which mirrored that in liver homogenates: the same degree of increase was seen in Norlin flax chow-fed and Solin flax chow-fed rats. Flax consumption effects an increase in the activity of liver gammaGT at the level of the plasma membrane which is lignan dependent, physiologically relevant and may be linked to hepatoprotection against injury through an increase in reduced glutathione.     

Ecological role of <Emphasis Type="Italic">Phyllophora antarctica</Emphasis> drift accumulations in coastal soft-sediment communities of McMurdo Sound,Antarctica

At Cape Evans on Ross Island, Antarctica, the rhodophyte Phyllophora antarctica is the dominant primary producer in terms of biomass from 10 to >30 m depth. The vast majority of Phyllophora occurs as accumulations of unattached plants. Whilst decomposition and incorporation of macroalgal drift material into the food web is rapid in temperate ecosystems, we predicted these processes to be slow in Antarctica. We address the functional role of macroalgal detritus in fuelling the biodiversity of benthic communities at Cape Evans during the summers of 2001 and 2002. Specifically we (a) describe the distribution and biomass of attached and drift algae, (b) assess the photosynthetic capacity and degradation of drift accumulations using in situ fluorometry, (c) assess the effect of patches of drift Phyllophora on underlying macrofaunal communities, and, (d) use stable isotopes to investigate the possible uptake of Phyllophora by macrofauna. We found drift Phyllophora accumulations throughout the depth range investigated (3–31 m), with peak biomasses of 140±30 g dwt m^–2 in the 15–25 m depth strata. At this depth stratum Phyllophora was a conspicuous habitat element with the % cover on the seafloor averaging 30%. While initially the drift algal accumulations appeared in good health we measured significant declines in photosynthetic capacity between years suggesting ongoing, albeit slow, degradation of the drift algal accumulations. Our results demonstrate that Phyllophora drift accumulations have a structuring role on soft-sediment communities, which increases in strength with the gradual degradation of the algae. The longevity of Phyllophora is enhanced by secondary metabolites, which serve as protection against grazers, and their extreme shade adaptation. However, our carbon and nitrogen stable isotope data of polychaetes and amphipods associated with Phyllophora suggest that macroalgal detritus enters the food web, and although this process is slow, Phyllophora accumulations might serve to dampen the seasonality in food supply providing higher trophic levels with a more constant food source.     

Wheat Cultivar-Specific Selection of 2,4-Diacetylphloroglucinol-Producing Fluorescent <Emphasis Type="Italic">Pseudomonas</Emphasis> Species from Resident Soil Populations

An emerging body of evidence indicates a role for plant genotype as a determinant of the species and genetic composition of the saprophytic microbial community resident to the rhizosphere. In this study, experiments were conducted to determine the capacity of five different wheat cultivars to enhance resident populations and support introduced strains of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing fluorescent pseudomonads, a group of bacteria known to provide biological control of several soilborne diseases. When soils were cropped with three successive 28-day growth cycles of wheat, the 2,4-DAPG-producing strains were consistently recovered from the rhizosphere of the cultivar Lewjain, and commonly were present at populations higher than those recovered from other wheat cultivars. Based on restriction fragment length polymorphism and sequence analyses of phlD, a key gene involved in 2,4-DAPG production, two previously undefined phlD+ genotypes, referred to as genotypes PfZ and PfY, were discovered. Wheat cultivar Lewjain was the primary source of genotype PfY while cultivar Penawawa yielded the majority of genotype PfZ. Based on 16S rDNA sequence analysis, both new phlD genotypes were classified as P. fluorescens. Comparison of the rhizosphere competence of 2,4-DAPG-producing P. fluorescens Q2-87 (genotype B) and P. fluorescens LR3-A28 (genotype PfY) showed that both strains persisted at similar populations in the rhizosphere of all cultivars tested over a 30 day period when introduced as a seed inoculant. However, when strain LR3-A28 was applied as a soil inoculant, this strain was recovered at higher populations from the rhizosphere of wheat cultivar Lewjain than from the rhizospheres of two other cultivars. No cultivar effects were shown for strain Q2-87. Collectively, these results add further to evidence indicating a degree of specificity in interactions between plant cultivars and specific members of the saprophytic microbial community. Furthermore, as 2,4-DAPG-producing fluorescent Pseudomonas spp. have a central role in the spontaneous reduction in severity of take-all disease of wheat in response to continuous wheat monoculture, we postulate that the use of specific cultivars, such as Lewjain, which possess a superior capacity to enhance resident soil populations of these bacteria may have potential to reduce the length of the monoculture period required to induce natural suppressiveness of soils toward this disease.