Cluster of type IV secretion genes in Helicobacter pylori's plasticity zone

Some genes present in only certain strains of the genetically diverse gastric pathogen Helicobacter pylori may affect its phenotype and/or evolutionary potential. Here we describe a new 16.3-kb segment, 7 of whose 16 open reading frames are homologs of type IV secretion genes (virB4, virB7 to virB11, and virD4), the third such putative secretion gene cluster found in H. pylori. This segment, to be called tfs3, was discovered by subtractive hybridization and chromosome walking. Full-length and truncated tfs3 elements were found in 20 and 19%, respectively, of 94 strains tested, which were from Spain, Peru, India, and Japan. A tfs3 remnant (6 kb) was found in an archived stock of reference strain J99, although it was not included in this strain's published genome sequence. PCR and DNA sequence analyses indicated the following. (i) tfs3's ends are conserved. (ii) Right-end insertion occurred at one specific site in a chromosomal region that is varied in gene content and arrangement, the "plasticity zone." (iii) Left-end insertion occurred at different sites in each of nine strains studied. (iv) Sequences next to the right-end target in tfs3-free strains were absent from most strains carrying full-length tfs3 elements. These patterns suggested insertion by a transposition-like event, but one in which targets are chosen with little or no specificity at the left end and high specificity at the right end, thereby deleting the intervening DNA.     

The Klebsiella pneumoniae wabG gene: role in biosynthesis of the core lipopolysaccharide and virulence

To determine the function of the wabG gene in the biosynthesis of the core lipopolysaccharide (LPS) of Klebsiella pneumoniae, we constructed wabG nonpolar mutants. Data obtained from the comparative chemical and structural analysis of LPS samples obtained from the wild type, the mutant strain, and the complemented mutant demonstrated that the wabG gene is involved in attachment to alpha-L-glycero-D-manno-heptopyranose II (L,D-HeppII) at the O-3 position of an alpha-D-galactopyranosyluronic acid (alpha-D-GalAp) residue. K. pneumoniae nonpolar wabG mutants were devoid of the cell-attached capsular polysaccharide but were still able to produce capsular polysaccharide. Similar results were obtained with K. pneumoniae nonpolar waaC and waaF mutants, which produce shorter LPS core molecules than do wabG mutants. Other outer core K. pneumoniae nonpolar mutants in the waa gene cluster were encapsulated. K. pneumoniae waaC, waaF, and wabG mutants were avirulent when tested in different animal models. Furthermore, these mutants were more sensitive to some hydrophobic compounds than the wild-type strains. All these characteristics were rescued by reintroduction of the waaC, waaF, and wabG genes from K. pneumoniae.     

Tumor cytotoxicity by endothelial cells. Impairment of the mitochondrial system for glutathione uptake in mouse B16 melanoma cells that survive after in vitro interaction with the hepatic sinusoidal endothelium

High GSH content associates with high metastatic activity in B16-F10 melanoma cells cultured to low density (LD B16M). GSH homeostasis was investigated in LD B16M cells that survive after adhesion to the hepatic sinusoidal endothelium (HSE). Invasive B16M (iB16M) cells were isolated using anti-Met-72 monoclonal antibodies and flow cytometry-coupled cell sorting. HSE-derived NO and H(2)O(2) caused GSH depletion and a decrease in gamma-glutamylcysteine synthetase activity in iB16M cells. Overexpression of gamma-glutamylcysteine synthetase heavy and light subunits led to a rapid recovery of cytosolic GSH, whereas mitochondrial GSH (mtGSH) further decreased during the first 18 h of culture. NO and H(2)O(2) damaged the mitochondrial system for GSH uptake (rates in iB16M were approximately 75% lower than in LD B16M cells). iB16M cells also showed a decreased activity of mitochondrial complexes II, III, and IV, less O(2) consumption, lower ATP levels, higher O(2) and H(2)O(2) production, and lower mitochondrial membrane potential. In vitro growing iB16M cells maintained high viability (>98%) and repaired HSE-induced mitochondrial damages within 48 h. However, iB16M cells with low mtGSH levels were highly susceptible to TNF-alpha-induced oxidative stress and death. Therefore depletion of mtGSH levels may represent a critical target to challenge survival of invasive cancer cells.     

Glucose 6-phosphate produced by gluconeogenesis and by glucokinase is equally effective in activating hepatic glycogen synthase

Glucose 6-phosphate (Glc-6-P) produced in cultured hepatocytes by direct phosphorylation of glucose or by gluconeogenesis from dihydroxyacetone (DHA) was equally effective in activating glycogen synthase (GS). However, glycogen accumulation was higher in hepatocytes incubated with glucose than in those treated with DHA. This difference was attributed to decreased futile cycling through GS and glycogen phosphorylase (GP) in the glucose-treated hepatocytes, owing to the partial inactivation of GP induced by glucose. Our results indicate that the gluconeogenic pathway and the glucokinase-mediated phosphorylation of glucose deliver their common product to the same Glc-6-P pool, which is accessible to liver GS. As observed in the treatment with glucose, incubation of cultured hepatocytes with DHA caused the translocation of GS from a uniform cytoplasmic distribution to the hepatocyte periphery and a similar pattern of glycogen deposition. We hypothesize that Glc-6-P has a major role in glycogen metabolism not only by determining the activation state of GS but also by controlling its subcellular distribution in the hepatocyte.     

A review of the world marine gastropod fishery: evolution of catches, management and the Chilean experience

Marine mollusks are among the most importantinvertebrate fisheries in the world. The mainclasses of mollusk fished are Cephalopoda,Bivalvia and Gastropoda. Marine gastropodsrepresent approximately 2% of the mollusksfished in the world. Several species ofgastropods, such as Haliotis spp., Strombus spp., Busycon spp. and Concholepas concholepas, have high economicvalue in international markets and playimportant social roles in small-scale artisanalfisheries. In the past 25 years wild-stockcatches of marine gastropods have increasedfrom 75,000 mt in 1979 to 103,000 mt in 1996.During the same period the countries involvedin gastropod landings rose from 23 to 47.Gastropods are fished mainly in: (1) theAmerican continent, dominated by the extractionof the muricid ``loco', C. concholepas, inChile and Peru; strombid conchs, Strombusspp., in the Caribbean, and abalone, Haliotis spp., in California and the west coastof the Baja California peninsula; (2) Asia andOceania, with the dominate abalone fishery,mainly in Australia and New Zealand, and thehorned turban snail, Turbo truncatus, inJapan and Korea; (3) in Africa and Europe, thedominate species extracted are Haliotismidae, heavily fished in South Africa, and thecommon periwinkle, Littorina littorea,and the whelk Buccinum undatum, which areextracted in Europe. This review summarizes the fishery of abalonespecies in California and the west coast of theBaja California peninsula. We highlightoverfishing situations and the utilization ofadaptive management tools, such as those inoperation in Baja California, where small-scalefisher associations (cooperatives) havereceived exclusive access rights to abaloneextraction within specific fishing zones, since1936. We also review the abalone fishery inAustralia, and the use of IndividualTransferable Quotas (ITQs) and Total AllowableCommercial Catches (TACC), which have been inuse since the mid-1980's. We describe thegastropod fisheries in Chile, mainly C. concholepas, highlighting their economic andsocial importance. We provide information onthe evolution of catches and exports anddiscuss the development of novel managementadaptive tools, such as the implementation ofthe Benthic Regime for Extraction andProcessing (BREP), the introduction ofNon-Transferable Individual Quotas (NTIQs) andterritorial users rights for benthic fisheries,such as the Management and Exploitation Areas(MEAS). Finally, we present and discuss thenecessary steps for the sustainable managementof marine gastropods and other benthic resources.     

Development and validation of a spatially explicit individual-based mixed crop growth model

Spatial disposition of plants in intercrops, and differences in sowing time between species, can strongly affect their ecological interactions and, in consequence, the system’s viability and performance. Empirical exploration of a wide range of spatial and temporal plant arrangements is costly and time-consuming. Modelling the growth of mixed crops is a tool which, combined with empirical tests, can greatly reduce the time and investment required for this task. Spatially explicit, individual-based dynamic models seem well suited for this purpose; their exploration and experimental validation for the case of simple, two-species, artificial plant communities, can also provide further insight as to how the spatial and temporal scales of a plant’s multispecific neighbourhood affect its growth and performance. The aim of this investigation was to further develop a published spatially explicit individual-based mixed crop growth model [Vandermeer, J. H. (1989). The Ecology of Intercropping, Cambridge, U.K.: Cambridge University Press, p. 237], and to validate it experimentally. With this purpose in mind: (1) computer programs to simulate individual plant growth and to perform statistical analysis of both deterministic and stochastic versions of the model were developed; (2) the model was parametrized using a complex experimental diculture with several cohorts and spatial arrangements; (3) the predictive capacity of the model was tested using independent spatio-temporal experimental arrangements; (4) a modified version of the model was written, which abandons the assumption of linearity of the neighbourhood index at the cost of increasing the number of parameters; (5) The performance of stochastic versions of both Vandermeer’s and our modified model were compared, employing a non-parametric measure of goodness of fit. We conclude that this approach to modelling plant growth subject to intra and interspecific competition is a remarkably efficient, general, conceptually elegant, heuristic tool whose predictive power can be further improved when nonlinear terms are introduced into the neighbourhood competition index, as done in our modified version of Vandermeer’s model.