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.      

The binding and catalytic activities of forms of ligandin after modification of its thiol groups.

Ligandin (glutathione S-transferase B, EC 2.5.1.18)was treated with p-mercuribenzoate, N-(4-dimethylamino-3,5-dinitrophenyl)-maleimide, 5,5,-dithiobis-(2-nitrobenzoic acid), N-ethylmaleimide, iodoacetamide or iodoacetate. Although performic acid oxidation revealed the presence of four cysteines, p-mercuribenzoate and N-(4-dimethylamino-3,5-dinitrophenyl)maleimide, the most effective of the reagents studied, reacted with only three residues. N-Ethylmaleimide and 5,5'-dithiobis-(2-nitrobenzoic acid) each reacted with two cysteines: iodoacetamide reacted with only one cysteine and iodoacetate was essentially unreactive. Modification of three thiol groups decreased both the enzymic and binding activities of ligandin although the number of binding sites was unaffected. Modification of only one or two of the thiol groups had little effect on the ligandin activities. It therefore appears that there is a thiol group in the common hydrophobic-ligand- and substrate-binding site of ligandin. Ligandin was separated into two fractions on CM-cellulose. Both fractions gave the same results with p-mercuribenzoate and iodoacetamide.     

The phytogeography and genetic diversity of the weedy hydrophyte,Pistia stratiotes L.

Biological Invasions - Understanding the origins and genetic relationships of invasive, non-native species is critical to informing conservation and management practices. Pistia stratiotes is one...     

Modelling the production and transport of dissolved organic carbon in forest soils

DyDOC describes soil carbon dynamics, with a focus on dissolved organic carbon (DOC). The model treats the soil as a three-horizon profile, and simulates metabolic carbon transformations, sorption reactions and water transport. Humic substances are partitioned into three fractions, one of which is immobile, while the other two (hydrophilic and hydrophobic) can pass into solution as DOC. DyDOC requires site-specific soil characteristics, and is driven by inputs of litter and water, and air and soil temperatures. The model operates on hourly and daily time steps, and can simulate carbon cycling over both long (hundreds-to-thousands of years) and short (daily) time scales. An important feature of DyDOC is the tracking of ¹⁴C, from its entry in litter to its loss as DO¹⁴C in drainage water, enabling information about C dynamics to be obtained from both long-term radioactive decay, and the characteristic ¹⁴C pulse caused by thermonuclear weapon testing during the 1960s ("bomb carbon"). Parameterisation is performed by assuming a current steady state. Values of a range of variables, including C pools, annual DOC fluxes, and ¹⁴C signals, are combined into objective functions for least-squares minimisation. DyDOC has been applied successfully to spruce forest sites at Birkenes (Norway) and Waldstein (Germany), and most of the parameters have similar values at the two sites. The results indicate that the supply of DOC from the surface soil horizon to percolating water depends upon the continual metabolic production of easily leached humic material. In contrast, concentrations and fluxes of DOC in the deeper soil horizons are controlled by sorption processes, involving comparatively large pools of leachable organic matter. Times to reach steady state are calculated to be several hundred years in the organic layer, and hundreds-to-thousands of years in the deeper mineral layers. It is estimated that DOC supplies 89% of the mineral soil carbon at Birkenes, and 73% at Waldstein. The model, parameterised with "steady state" data, simulates short-term variations in DOC concentrations and fluxes, and in DO¹⁴C, which are in approximate agreement with observations.     

Crescentic glomerulonephritis--a manifestation of a nephritogenic Th1 response?

Crescentic glomerulonephritis (GN) is the histopathological correlate of the clinical syndrome of rapidly progressive glomerulonephritis. Glomerular crescent formation complicates proliferative forms of GN and indicates severe disease with a poor renal prognosis. In the past 10 years evidence from experimental models of GN and from human disease has accumulated suggesting that crescentic glomerulonephritis is a manifestation of a delayed type hypersensitivity (DTH)-like response to nephritogenic antigens. The elucidation of T helper 1 (Th1) and Th2 subsets in mice and in humans has led to the hypothesis that crescentic GN is a manifestation of a Th1 predominant DTH mediated immune response. Recent experiments performed mainly in a murine model of crescentic glomerulonephritis have tested this hypothesis. Crescent formation in this model is substantially interleukin (IL)-12 and interferon-gamma (IFN-gamma) dependent. Administration of IL-12, deletion of endogenous IL-4 or IL-10 results in enhanced disease, while administration of exogenous IL-4 and/or IL-10 reduces crescentic injury. These findings, together with the available evidence from human studies (examining the pattern of immune effectors in glomeruli, data on cytokine production by peripheral blood mononuclear cells and case reports of the induction of proliferative and/or crescentic GN by administration of IFN-gamma or IL-2) suggest that human crescentic GN is manifestation of a Th1 mediated DTH-like nephritogenic immune response.     

��-arrestin Kurtz inhibits MAPK and Toll signalling in Drosophila development

β‐Arrestins have been implicated in the regulation of multiple signalling pathways. However, their role in organism development is not well understood. In this study, we report a new in vivo function of the Drosophila β‐arrestin Kurtz (Krz) in the regulation of two distinct developmental signalling modules: MAPK ERK and NF‐κB, which transmit signals from the activated receptor tyrosine kinases (RTKs) and the Toll receptor, respectively. Analysis of the expression of effectors and target genes of Toll and the RTK Torso in krz maternal mutants reveals that Krz limits the activity of both pathways in the early embryo. Protein interaction studies suggest a previously uncharacterized mechanism for ERK inhibition: Krz can directly bind and sequester an inactive form of ERK, thus preventing its activation by the upstream kinase, MEK. A simultaneous dysregulation of different signalling systems in krz mutants results in an abnormal patterning of the embryo and severe developmental defects. Our findings uncover a new in vivo function of β‐arrestins and present a new mechanism of ERK inhibition by the Drosophila β‐arrestin Krz.     

The organic carbon dynamics of a moorland catchment in N. W. England

The carbon cycle was quantified in the catchment of Doe House Gill, which drains high-relief moorland, with thin organic-rich soils (leptosols and podzols) 10–25 cm deep, in northern England. The soil C pool of 8,300 g m^-2 is due mainly to humic acid and older humin. If steady state is assumed, and a single soil C pool, the average ¹⁴C content of the whole soil (93% modern) yields a mean carbon residence time of 800 years, although this varied from 300 to 1,600 years in the four samples studied. Stream water fluxes of dissolved and particulate organic carbon (DOC, POC) were 2.5 and 0.4 g m⁻² a⁻¹ respectively in 2002–2003, lower than values for some other upland streams in the UK. The C pool, flux, and isotope data were used, with the assumption of steady state, to calibrate DyDOC, a model that simulates the soil carbon cycle, including the generation and transport of DOC. According to DyDOC, the litter pool (ca. 100 gC m⁻²) turns over quickly, and most (>90%) of the litter carbon is rapidly mineralised. The soil is calculated to gain only 16 gC m⁻² a⁻¹, and to lose the same amount, about 80% as CO₂ and 20% as DOC. From the DO¹⁴C content of 107.5% modern (due to “bomb carbon”) the model could be calibrated by assuming all DOC to come directly from litter, but DOC is more likely a mixture, derived from more than one soil C pool. The seasonal variability exhibited by stream water DOC concentration (maximum in September, minimum in January) is attributed mainly to variations in rainfall and evapotranspiration, rather than in the metabolic production rate of “potential DOC”. The model predicts that, for a Q ₁₀ of 2, the total soil organic C pool would decrease by about 5% if subjected to warming over 200 years. DyDOC predicts higher DOC fluxes in response to increased litter inputs or warming, and can simulate changes in DOC flux due to variations in sorption to soil solids, that might occur due to acidification and its reversal.