Killing of Escherichia coli cells modulated by components of the stability system ParD of plasmid R1

Summary The proteins P10 and P12 have been shown to be gene products of a new stability system, ParD, of plasmid R1. It is now shown that an R1 miniplasmid, pAB112, carrying a trans-complementable amber mutation in the gene of the P10 protein, is lethal for the host in the absence of suppression. This lethal effect is suppressed in a supF background and also by deletions in pAB112 that affect the gene of the P12 protein. These data indicate that the P12 protein has a lethal effect on the host and that this effect is neutralized by the P10 protein. The possibility that the stabilization conferred by the ParD system could be due to a counterselection, mediated by P12, of cells that lose the plasmid at cell division, is discussed.     

Models of growth with density regulation in more than one life stage

Discrete-time models of growth of populations with nonoverlapping generations and density regulation in two life stages are studied. It is assumed that there is no delay in the effects of density. Assigning exponential, linear, or hyperbolic functions to describe the dependence of preadult survival and fecundity on density, nine models are obtained. The dynamics of the model resulting from using the exponential function to describe the density dependence of both preadult survival and fecundity is analyzed: for large values of the intrinsic rate of increase there may exist up to three equilibrium population sizes, two stable. This indicates that a life history with two episodes of density regulation can give origin to alternative stable states. The models are fitted to recruitment data from growth experiments of Drosophila laboratory populations obtained with the Serial Transfer System Type 2 (Ayala et al., 1973. Theor. Pop. Biol. 4, 331-356) and collected by other authors. The results of the fittings suggest that this recruitment data can be adequately described with the models.     

Inhibitory activity of antibiotic-producing marine bacteria against fish pathogens

The activity of antibiotic-producing marine bacteria was assayed against bacterial fish pathogens belonging to the genera Vibrio, Aeromonas, Pasteurella, Edwardsiella, Yersinia and Pseudomonas with the aim of evaluating the possible use of these marine strains for controlling epizootics in aquaculture. Inhibition tests on solid medium showed that, in general, the majority of fish bacteria were strongly sensitive to the marine bacteria. Only two strains ( Edwardsiella tarda and Pseudomonas aeruginosa ), were resistant to all the antibiotic-producing strains. The results of antagonism assays in sea water, however, varied according to the fish pathogens examined. Experiments conducted using cell-free supernatant fluids of marine bacteria demonstrated the involvement of antibiotic substances in the inhibition of fish pathogens.     

Biological effects of human gastrin I and II chemically modified at the C-terminal tetrapeptide amide.

Binding to gastrin receptors and gastric acid secretion experiments were performed with gastrin derivatives modified at the C-terminal tetrapeptide amide from HG-13 sequence. 1. When the ultimate phenylalanine amide was replaced by a phenethylester or a phenetylamide moiety, the resulting compound bound to gastrin receptors (Kd approximately 10 nM) and exhibited antagonist activity on gastrin-induced acid secretion in the anesthetized rat. 2. Changing the peptide bond between Trp and Leu residues to a -omega(CH2-NH)- bond resulted in a compound which also bound to gastrin receptors (Kd approximately 10 nM) but presented agonist activity on acid secretion in the rat. In contrast, when the peptide bond between Leu and Asp residues was replaced by a -omega(CH2-NH)- bond, the resulting compound was devoid of any affinity for gastrin receptor (Kd greater than 10(-6) M) and of any biological activity. 3. The HG-13 derivatives were synthesized in sulfated and unsulfated forms: O-sulfation of the HG-13 tyrosine residue did not change its intrinsic in vivo activity but enhanced its affinity for gastrin receptors (Kd approximately 0.3 nM). On the contrary, O-sulfation of the various chemically modified HG-13 had no significant effect in either in vitro or in vivo experiments. 4. Finally, no significant difference between binding on parietal (F3) and nonparietal (F1) cells was observed, in agreement with the presence of a gastrin-type receptor in these two cell populations.     

3-Mercaptopropionic acid administration increases the affinity of [H]Quinuclidinyl benzilate binding to membranes of the striatum and cerebellum

It is known that quinuclidinyl benzilate (QNB) binds specifically and with high affinity to the cholinergic muscarinic receptor and that behaves as a potent antagonist of this receptor.

We have analysed -[³H]QNB binding to rat CNS membranes after the administration of the convulsant 3-mercaptopropionic acid (MP) (150 mg·kg⁻¹, i.p.). The studies were done in rats killed at two stages: during and after seizures. No changes in [³H]QNB binding to hippocampus and cerebral cortex membranes were found. [³H]QNB binding increased about 40 and 80% in striatum and cerebellum membranes, respectively. The changes were observed both in seizure and postseizures states. The study was extended to the assay of [³H]QNB binding kinetic constants in the anatomical areas modified by the convulsant. The analysis of the saturation curves indicated an increase in the binding affinity but no change in the number of binding sites. Hill number values were near the unit suggesting a non-cooperative interaction between the ligand and the receptor, and the labelling of a homogeneous population of receptor sites.

The results suggest the participation of some cholinergic pathways in the development and maintenance of MP-induced seizures.     

Collagen increases the synthesis of membrane-associated proteoglycans produced by Sertoli cells.

Sertoli cells in culture produce two isoforms of proteoglycans which are found in the culture medium and associated with the cell membrane. The amount of both types of proteoglycans increased when Sertoli cells were plated on type I collagen-coated dishes as compared to uncoated dishes. The effect is due to an increase in the synthesis of proteoglycans rather than a diminished rate of degradation of these molecules. The collagen substrate also affects the distribution of these macromolecules; an increase in the amount of membrane-associated proteoglycans occurs at the expense of the proteoglycans released to the culture medium.     

Vaccinia virus preferentially enters polarized epithelial cells through the basolateral surface.

The uptake of vaccinia virus in polarized epithelial cells was studied to determine whether the site of entry was confined to either the apical or the basolateral membrane. Virus infection was monitored with a recombinant vaccinia virus carrying the luciferase reporter gene. Using cell lines MDCK and MDCK-D11, a clonal line with high transepithelial electrical resistance, we determined that vaccinia virus preferentially enters through the basolateral membrane. The possibility that there is a polarized cell surface distribution of vaccinia virus receptors which may be involved in systemic poxvirus infections is discussed.     

In situ diel variation in gut pigment contents of Ceriodaphnia sp. in stratification and destratification periods

The short-term, in situ diel grazing of Ceriodaphnia sp. duringperiods of stratification and mixing was investigated usingthe technique of fluorimetric analysis of the gut pigments.There were considerable seasonal differences in feeding behaviourIn mixing, when the concentration of chlorophyll a in the watercolumn was high and Ceriodaphnia abundance was low, gut pigmentcontents showed clear diel variation patterns, probably dueto diel variations of the high values of feeding activity observedin the 24 hour cycle The maximum values were found at dawn.On the other hand, no diel variations in gut pigment were observedduring periods of stratification and while the amounts of pigmentsin the water and in the gut were very low, species abundancewas high. Taking into account the ambient conditions, the authorsdiscuss the possibility that the change of feeding of the Ceriodaphniasp. observed when the environment changed from a mixing periodto one of stratification represents a change from herbivorousto detritivorous behavior.