Role of the lipB gene product in the folding of the secreted lipase of Pseudomonas glumae

The LipB protein of Pseudomonas glumae is essential for the production of active extracellular lipase encoded by the lipA gene. When lipase is overproduced in P. glumae in the absence of a functional lipB gene, the enzyme accumulates intracellularly in an inactive conformation. Heterologous expression of the lipase in Pseudomonas aeruginosa, Bacillus subtilis and Escherichia coli indicated that LipB is not directly involved in the trans location of the lipase across the inner or outer membrane. However, the presence of LipB was essential for obtaining active lipase and had a profound influence on the stability of the protein to proteolytic degradation. Inactive iipase, produced in the absence of LipB could be activated in vitro by unfolding and refolding, which demonstrates that LipB activity is not responsible for an essential covalent modification of the enzyme. We propose that LipB is a lipase-specific foldase. Furthermore, proper folding of the lipase in the periplasm appears to be essential for Xcp-mediated translocation across the outer membrane.     

Seed- versus transplant-based eelgrass (Zostera marina L.) restoration success in a temperate marine lake

Despite active seagrass restoration gaining traction as a tool to halt and reverse worldwide seagrass losses, overall success remains limited. Restoration strategies, through seeding or transplantation, face different environmental bottlenecks that limit success. Choosing the most appropriate strategy of the two for a specific location, however, is hampered by lack of direct practical comparisons between strategies within a single system. To investigate potential life stage dependent bottlenecks, we compared seed-based and transplant-based restoration of Zostera marina in the subtidal saltwater Lake Grevelingen. Our results demonstrate that seedling recruitment was negatively impacted by bioturbation from the lugworm Arenicola marina and sediment movement due to hydrodynamic exposure. Transplant-based restoration was clearly more successful but surprisingly best predicted by leaf gluing by the ragworm Platynereis dumerilii. This previously undescribed interaction caused seagrass leaves to clump and reduce effective photosynthetic surface and leaf movement. We suggest that the observed behavior of these worms may result from a lack of foodweb interactions, illustrating the importance of  trophic control for seagrass restoration. Thus, in addition to recognizing life stage dependent environmental bottlenecks for restoration strategy selection, seagrass restoration may also require the active recovery of their associated food webs.     

SPATIAL AND TEMPORAL DEVELOPMENT OF IRON(III) REDUCTASE ACTIVITY IN ROOT SYSTEMS OF PISUM SATIVUM (FABACEAE) CHALLENGED WITH IRON-DEFICIENCY STRESS

The development of plasma membrane-associated iron(III) reductase activity was characterized in root systems of Pisum sativum during the first 2 wk of growth, as plants were challenged with iron-deficiency stress. Plants of a parental genotype (cv. Sparkle) and a functional iron-deficiency mutant genotype (E107) were grown hydroponically with or without supplemental iron. Iron(III) reductase activity was visualized by placing the roots in an agarose matrix containing 0.2 idm Fe(III)-ethylenediaminetetraacetic acid and 0.3 mM Na₂-bathophenanthrolinedisulfonic acid (BPDS). Red staining patterns, resulting from the formation of Fe(II)-BPDS, were used to identify iron(III)-reducing regions. Iron(III) reduction was extensive on roots of E107 as early as d 7, but not until d 11 for -Fe-treated Sparkle. Roots of +Fe-treated Sparkle showed limited regions of reductase activity throughout the period of study. For secondary lateral roots, iron(III) reduction was found for all growth types except + Fe-treated Sparkle. Treating Sparkle plants alternately to a cycle of iron deficiency, iron sufficiency, and iron deficiency revealed that reductase activity at a given root zone could be alternatively present, absent, and again present. Our results suggest that for Pisum roots grown under the present conditions, iron-deficiency stress induces the activation of iron(III) reductase capacity within 2 d.     

Characterization and prevalence of pigments in the muscle of hawkfish (Cheilodactylus bergi)

Melanin pigment was prevalent in skeletal muscle of 338 out of 1079 Cheilodactylus bergi sampled from the Argentine-Uruguay Common Fisheries Zone. A higher proportion of males than of females was pigmented, and only in males did that proportion increase with body length. No parasites were found in the muscle.     

Blood-Brain Barrier Transport of Basic Amino Acids Is Selectively Inhibited at Low pH

The transport of amino acids across the blood-brain barrier was measured with the single-pass carotid injection method. The pH of the injected bolus varied between 4.5 and 8.5. Arginine and lysine uptakes were inhibited 24% at pH 5.5 and 59% at pH 4.5. The uptakes of 2-aminobicyclo (2,2,1) heptane-2-carboxylic acid and phenylalanine were unaffected at this pH. There were also no changes observed in choline, glucose, or butanol transport. The Ki of arginine transport inhibition by H+ was 2.4 +/- 0.5 microM; i.e., pH 5.6 +/- 0.1. No change with pH occurred in the Km of arginine transport, while a significant decrease (p less than 0.01) was observed in the Vmax (10.2 +/- 2.3 nmol min-1 g-1 and 5.6 +/- 2.3 nmol min-1 g-1 at pH 7.5 and pH 5.5, respectively). This noncompetitive inhibition was found to be transient as arginine uptake at pH 7.5; it was measured by carotid injection 30 sec following a previous bolus which was buffered to pH 4.5, and was not significantly different from the control. This selective inhibition of the blood-brain barrier basic amino acid carrier demonstrates the advantage of the carotid injection approach in exposing the capillary exchange site to extreme alterations in chemical composition which could not be tolerated systemically.     

Effects of 3-aminobenzamide on DNA synthesis and cell cycle progression in Chinese hamster ovary cells

3-Aminobenzamide (3AB), an inhibitor of poly(ADP-ribose) polymerase, is a potent inducer of sister chromatid exchanges (SCEs). Because of the possible relation between SCEs and DNA synthesis, the effects of 3AB on DNA synthesis and cell cycle progression in Chinese hamster ovary (CHO) cells were examined. Unlike all other SCE-inducing agents whose effects on DNA synthesis have been studied, short term exposures (30–120 min) of 3AB did not inhibit the overall rate of DNA synthesis and this result was independent of the amount of bromodeoxyuridine (BrdU) in the DNA. Longer exposure times (>24 h) did result in an extended S phase, but this was not due to an effect on the rate of DNA chain elongation. 3AB also delayed the entry of cells into S phase. The overall cell cycle delay was dose dependent, approaching 9 h after a 54 h exposure to 10 mM 3AB. Earlier reports that 3AB is neither mutagenic nor cytotoxic were confirmed. Thus 3AB acts to increase SCE frequency by a mechanism distinct from that which causes cytotoxicity and mutagenicity, and does not involve any inhibition in the rate of DNA chain growth.