The nature of the voltage-dependent conductance induced by alamethicin in black lipid membranes

Summary Alamethicin induces a conductance in black lipid films which increases exponentially with voltage. At low conductance the increase occurs in discrete steps which form a pattern of five levels, the second and third being most likely. The conductance of each level is directly proportional to salt concentration, inversely proportional to solution viscosity, and nearly independent of voltage.The probability distribution of the five steps is not a function of voltage, but as the voltage is increased, more levels begin to appear. These can be explained as super-positions of the original five, both in position and relative probability.This suggests that the five levels are associated with a physical entity which we call a pore. This point of view is confirmed by the following measurements. The kinetic response of the current to a voltage step is first order, and shows an exponential increase in rate of pore formation and an exponential decrease in rate of pore disappearance with voltage. If these rates are statistical, the number of pores should fluctuate about a voltage-dependent mean. High conductance current fluctuations are too large to be explained by fluctuation in the number of pores alone. But if fluctuations among the five levels are included, the magnitude of the fluctuations at high conductance is accurately predicted.Alamethicin adsorbs reversibly to the membrane surface, and the conductance at a fixed voltage depends on the ninth power of alamethicin concentration and on the fourth power of salt concentration, in the aqueous phase. In our bacterial phosphatidyl ethanolamine membranes, alamethicin added to one side of the membrane produces elevated conductance only when the voltage on that side is increased.On leave of absence from the Facultad de Ciencias, Universidad de Chile, Santiago de Chile.     

Rhizosphere bacteria of maize with chitinolytic activity and its potential in the control of phytopathogenic fungi

The chitinase enzyme was identified in isolated bacteria of maize rhizosphere as well as its potential for the biological control of fungi associated at seeds of the same plant. The production of chitinase enzyme was found in the genera identified as Acinetobacter, Bacterium, Burkholderia, Paenibacillus, Pseudomonas, Rhizobium, Shewanella, Sphingomonas and Stenotrophomonas. Bacterial isolates with ability to degrade fungal mycelium from maize fungi as Fusarium and Alternaria among others, were detected. Bacterial chitinase activity and the presence of the chiA gene were determined. The inoculation of chitinolytic bacteria showed a positive effect in the control of fungi in maize seeds. The results support the potential use of chitinase enzyme producing bacteria on the control of phytopathogenic fungi.     

Introgression and selection shaped the evolutionary history of sympatric sister‐species of coral reef fishes (genus: Haemulon)

Closely related marine species with large overlapping ranges provide opportunities to study mechanisms of speciation, particularly when there is evidence of gene flow between such lineages. Here, we focus on a case of hybridization between the sympatric sister‐species Haemulon maculicauda and H. flaviguttatum, using Sanger sequencing of mitochondrial and nuclear loci, as well as 2422 single nucleotide polymorphisms (SNPs) obtained via restriction site‐associated DNA sequencing (RADSeq). Mitochondrial markers revealed a shared haplotype for COI and low divergence for CytB and CR between the sister‐species. On the other hand, complete lineage sorting was observed at the nuclear loci and most of the SNPs. Under neutral expectations, the smaller effective population size of mtDNA should lead to fixation of mutations faster than nDNA. Thus, these results suggest that hybridization in the recent past (0.174–0.263 Ma) led to introgression of the mtDNA, with little effect on the nuclear genome. Analyses of the SNP data revealed 28 loci potentially under divergent selection between the two species. The combination of mtDNA introgression and limited nuclear DNA introgression provides a mechanism for the evolution of independent lineages despite recurrent hybridization events. This study adds to the growing body of research that exemplifies how genetic divergence can be maintained in the presence of gene flow between closely related species.     

The lysophosphatidic acid receptor LPA1 links pulmonary fibrosis to lung injury by mediating fibroblast recruitment and vascular leak

Aberrant wound-healing responses to injury have been implicated in the development of pulmonary fibrosis, but the mediators directing these pathologic responses have yet to be fully identified. We show that lysophosphatidic acid levels increase in bronchoalveolar lavage fluid following lung injury in the bleomycin model of pulmonary fibrosis, and that mice lacking one of its receptors, LPA1, are markedly protected from fibrosis and mortality in this model. The absence of LPA1 led to reduced fibroblast recruitment and vascular leak, two responses that may be excessive when injury leads to fibrosis rather than to repair, whereas leukocyte recruitment was preserved during the first week after injury. In persons with idiopathic pulmonary fibrosis, lysophosphatidic acid levels in bronchoalveolar lavage fluid were also increased, and inhibition of LPA1 markedly reduced fibroblast responses to the chemotactic activity of this fluid. LPA1 therefore represents a new therapeutic target for diseases in which aberrant responses to injury contribute to fibrosis, such as idiopathic pulmonary fibrosis.     

Optimal Performance of the Tryptophan Operon of E. coli: A stochastic,Dynamical, Mathematical-Modeling Approach

In this work, we develop a detailed, stochastic, dynamical model for the tryptophan operon of E. coli, and estimate all of the model parameters from reported experimental data. We further employ the model to study the system performance, considering the amount of biochemical noise in the trp level, the system rise time after a nutritional shift, and the amount of repressor molecules necessary to maintain an adequate level of repression, as indicators of the system performance regime. We demonstrate that the level of cooperativity between repressor molecules bound to the first two operators in the trp promoter affects all of the above enlisted performance characteristics. Moreover, the cooperativity level found in the wild-type bacterial strain optimizes a cost-benefit function involving low biochemical noise in the tryptophan level, short rise time after a nutritional shift, and low number of regulatory molecules.     

Molecular cloning and characterization of two novel autophagy-related genes belonging to the ATG8 family from the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Rhipicephalus (Boophilus) microplus is an obligate haematophagous arthropod and the major problem for cattle industry due to economic losses it causes. The parasite shows a remarkable adaptability to changing environmental conditions as well as an exceptional ability to survive long-term starvation. This ability has been related to a process of intracellular protein degradation called autophagy. This process in ticks is still poorly understood and only few autophagy-related (ATG) genes have been characterized. The aim of the present study was to examine the ESTs database, BmiGI, of R. microplus searching for ATG homologues. We predicted five putative ATG genes, ATG3, ATG4, ATG6 and two ATG8s. Further characterization led to the identification of RmATG8a and RmATG8b, homologues of GABARAP and MAP1LC3, respectively, and both of them belonging to the ATG8 family. PCR analyses showed that the expression level of RmATG8a and RmATG8b was higher in egg and larval stages when compared to ovary and midgut from adult ticks. This up-regulation coincides with the period in which ticks are in a starvation state, suggesting that autophagy is active in R. microplus.