Gene expression kinetics governs stimulus-specific decoration of the Salmonella outer membrane.

Lipid A is the innermost component of the lipopolysaccharide (LPS) molecules that occupy the outer leaflet of the outer membrane in Gram-negative bacteria. Lipid A is recognized by the host immune system and targeted by cationic antimicrobial compounds. In Salmonella enterica serovar Typhimurium, the phosphates of lipid A are chemically modified by enzymes encoded by targets of the transcriptional regulator PmrA. These modifications increase resistance to the cationic peptide antibiotic polymyxin B by reducing the negative charge of the LPS. We report the mechanism by which Salmonella produces different lipid A profiles when PmrA is activated by low Mg2+ versus a mildly acidic pH. Low Mg2+ favored modification of the lipid A phosphates with 4-amino-4-deoxy-l-aminoarabinose (l-Ara4N) by activating the regulatory protein PhoP, which initially increased the LPS negative charge by promoting transcription of lpxT, encoding an enzyme that adds an additional phosphate group to lipid A. Later, PhoP activated PmrA posttranslationally, resulting in expression of PmrA-activated genes, including those encoding the LpxT inhibitor PmrR and enzymes responsible for the incorporation of l-Ara4N. By contrast, a mildly acidic pH favored modification of the lipid A phosphates with a mixture of l-Ara4N and phosphoethanolamine (pEtN) by simultaneously inducing the PhoP-activated lpxT and PmrA-activated pmrR genes. Although l-Ara4N reduces the LPS negative charge more than does pEtN, modification of lipid A phosphates solely with l-Ara4N required a prior transient increase in lipid A negative charge. Our findings demonstrate how bacteria tailor their cell surface to different stresses, such as those faced inside phagocytes.

The biology of the PmrA/PmrB two-component system: the major regulator of lipopolysaccharide modifications.

The ability of gram-negative bacteria to resist killing by antimicrobial agents and to avoid detection by host immune systems often entails modification to the lipopolysaccharide (LPS) in their outer membrane. In this review, we examine the biology of the PmrA/PmrB two-component system, the major regulator of LPS modifications in the enteric pathogen Salmonella enterica. We examine the signals that activate the sensor PmrB and the targets controlled by the transcriptional regulator PmrA. We discuss the PmrA/PmrB-dependent chemical decorations of the LPS and their role in resistance to antibacterial agents. We analyze the feedback mechanisms that modulate the activity and thus output of the PmrA/PmrB system, dictating when, where, and to what extent bacteria modify their LPS. Finally, we explore the qualitative and quantitative differences in gene expression outputs resulting from the distinct PmrA/PmrB circuit architectures in closely related bacteria, which may account for their differential survival in various ecological niches.

Reciprocal control between a bacterium's regulatory system and the modification status of its lipopolysaccharide.

Gram-negative bacteria often modify their lipopolysaccharide (LPS), thereby increasing resistance to antimicrobial agents and avoidance of the host immune system. However, it is unclear how bacteria adjust the levels and activities of LPS-modifying enzymes in response to the modification status of their LPS. We now address this question by investigating the major regulator of LPS modifications in Salmonella enterica. We report that the PmrA/PmrB system controls expression of a membrane peptide that inhibits the activity of LpxT, an enzyme responsible for increasing the LPS negative charge. LpxT's inhibition and the PmrA-dependent incorporation of positively charged L-4-aminoarabinose into the LPS decrease Fe(3+) binding to the bacterial cell. Because Fe(3+) is an activating ligand for the sensor PmrB, transcription of PmrA-dependent LPS-modifying genes is reduced. This mechanism enables bacteria to sense their cell surface by its effect on the availability of an inducing signal for the system regulating cell-surface modifications.

An allele of an ancestral transcription factor dependent on a horizontally acquired gene product.

Changes in gene regulatory circuits often give rise to phenotypic differences among closely related organisms. In bacteria, these changes can result from alterations in the ancestral genome and/or be brought about by genes acquired by horizontal transfer. Here, we identify an allele of the ancestral transcription factor PmrA that requires the horizontally acquired pmrD gene product to promote gene expression. We determined that a single amino acid difference between the PmrA proteins from the human adapted Salmonella enterica serovar Paratyphi B and the broad host range S. enterica serovar Typhimurium rendered transcription of PmrA-activated genes dependent on the PmrD protein in the former but not the latter serovar. Bacteria harboring the serovar Typhimurium allele exhibited polymyxin B resistance under PmrA- or under PmrA- and PmrD-inducing conditions. By contrast, isogenic strains with the serovar Paratyphi B allele displayed PmrA-regulated polymyxin B resistance only when experiencing activating conditions for both PmrA and PmrD. We establish that the two PmrA orthologs display quantitative differences in several biochemical properties. Strains harboring the serovar Paratyphi B allele showed enhanced biofilm formation, a property that might promote serovar Paratyphi B's chronic infection of the gallbladder. Our findings illustrate how subtle differences in ancestral genes can impact the ability of horizontally acquired genes to confer new properties.

Ancestral genes can control the ability of horizontally acquired loci to confer new traits.

Horizontally acquired genes typically function as autonomous units conferring new abilities when introduced into different species. However, we reasoned that proteins preexisting in an organism might constrain the functionality of a horizontally acquired gene product if it operates on an ancestral pathway. Here, we determine how the horizontally acquired pmrD gene product activates the ancestral PmrA/PmrB two-component system in Salmonella enterica but not in the closely related bacterium Escherichia coli. The Salmonella PmrD protein binds to the phosphorylated PmrA protein (PmrA-P), protecting it from dephosphorylation by the PmrB protein. This results in transcription of PmrA-dependent genes, including those conferring polymyxin B resistance. We now report that the E. coli PmrD protein can activate the PmrA/PmrB system in Salmonella even though it cannot do it in E. coli, suggesting that these two species differ in an additional component controlling PmrA-P levels. We establish that the E. coli PmrB displays higher phosphatase activity towards PmrA-P than the Salmonella PmrB, and we identified a PmrB subdomain responsible for this property. Replacement of the E. coli pmrB gene with the Salmonella homolog was sufficient to render E. coli resistant to polymyxin B under PmrD-inducing conditions. Our findings provide a singular example whereby quantitative differences in the biochemical activities of orthologous ancestral proteins dictate the ability of a horizontally acquired gene product to confer species-specific traits. And they suggest that horizontally acquired genes can potentiate selection at ancestral loci.

Evaluation and development of a bone age assessment method in patients with Down syndrome / Avaliação e desenvolvimento de um método de avaliação de idade óssea em portadores de síndrome de Down

The objective of this paper was to evaluate the applicability of the method developed by Caldas to measure the vertebral bone age of Brazilians suffering from Down syndrome. A database comprised of 57 case records of individuals with this syndrome, both male and female, with ages ranging between 5 and 18 years, was used for this purpose. These records had lateral cephalometric radiographs and radiographs of hand and wrist, all of which had been obtained on the same date. There were 48 other records of individuals who did not suffer from Down syndrome. The Tanner and Whitehouse (TW3) method was used to perform the hand and wrist radiographs for obtaining bone age. The Caldas method was employed on the lateral cephalometric radiographs in order to obtain the vertebral bone age. From the information acquired on bone age, vertebral bone age and chronological age, it could be concluded that there is a statistically significant difference between the three ages for both the male and the female control group and for the female Down syndrome group. Therefore, this method was employed only on male Down syndrome individuals. Based on the results, a formula was developed to obtain the bone age for Down syndrome individuals (AU).

O objetivo deste trabalho foi avaliar a aplicabilidade do método desenvolvido por Caldas para medir a idade óssea vertebral em brasileiros, quando empregado em indivíduos portadores da síndrome de Down. Foram estudados 57 prontuários de indivíduos com síndrome de Down, de ambos os sexos, com idades variando entre 5 e 18 anos. Esses prontuários continham radiografias cefalométricas laterais e radiografias de mão e punho, obtidas no mesmo dia, e também foram avaliados 48 prontuários de indivíduos não portadores de síndrome de Down. Para as radiografias de mão e punho, o método de Tanner e Whitehouse (TW3) foi usado para que pudéssemos obter a idade óssea. O método de Caldas foi empregado nas radiografias cefalométricas laterais, e assim obtivemos a idade óssea vertebral. A partir das informações sobre a idade óssea, idade óssea vertebral e idade cronológica, foi verificada uma diferença estatisticamente significativa entre as três faixas etárias para ambos os sexos do grupo controle e grupo com síndrome de Down do sexo feminino. Portanto, este método foi aplicável apenas em indivíduos do sexo masculino portadores da síndrome de Down. Com base nos resultados, uma fórmula para obtenção da idade óssea de indivíduos com síndrome de Down foi desenvolvida (AU).

Verbal and visual short-term memory in children with arithmetic disabilities.

With the exception of the explication of the Nonverbal Learning Disability Syndrome, our knowledge of cognitive characteristics of children with isolated arithmetic (A) disabilities contrasted with those with comorbid arithmetic and reading (AR) disabilities is limited. Of the existing studies, most suggest that visual deficits are characteristic of Subtype A. This study examined short-term memory in 45 children who were classified into these two subtypes. Children in Subtype A displayed better verbal memory on some tasks than children in the AR subtype, but no subtype differences in visual memory were found. Counter to our hypothesis, children in Subtype A did not display relatively poorer visual memory than verbal memory. These results suggest a mixed neuropsychological profile, and the absence of visual short-term memory weaknesses as descriptive of the A subtype.

Mapa de riesgo de los desordenes por deficiencia de yodo(DDI)

La deficiencia de yodo en la dieta constituyó una de las más antiguas e importantes carencias nutricionales a la que fue sometida la mayor parte de la población boliviana