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Life came to depend on iron as a cofactor for many essential enzymatic reactions. However, once the atmosphere was oxygenated, iron became both scarce and toxic. Therefore, complex mechanisms have evolved to scavenge iron from an environment in which it is poorly bioavailable, and to tightly regulate intracellular iron contents. In bacteria, this is typically accomplished with the help of one key regulator, an iron-sensing transcription factor. While Gram-negative bacteria and Gram-positive species with low guanine-cytosine (GC) content generally use Fur (ferric uptake regulator) proteins to regulate iron homeostasis, Gram-positive species with high GC content use the functional homolog IdeR (iron-dependent regulator). IdeR controls the expression of iron acquisition and storage genes, repressing the former, and activating the latter in an iron-dependent manner. In bacterial pathogens such as Corynebacterium diphtheriae and Mycobacterium tuberculosis, IdeR is also involved in virulence, whereas in non-pathogenic species such as Streptomyces, it regulates secondary metabolism as well. Although in recent years the focus of research on IdeR has shifted towards drug development, there is much left to learn about the molecular mechanisms of IdeR. Here, we summarize our current understanding of how this important bacterial transcriptional regulator represses and activates transcription, how it is allosterically activated by iron binding, and how it recognizes its DNA target sites, highlighting the open questions that remain to be addressed.

Pseudomonas aeruginosa is an opportunistic pathogen able to infect any human tissue. One of the reasons for its high adaptability and colonization of host tissues is its capacity of maintaining iron homeostasis through a wide array of iron acquisition and removal mechanisms. Due to their ability to cause life-threatening acute and chronic infections, especially among cystic fibrosis and immunocompromised patients, and their propensity to acquire resistance to many antibiotics, the World Health Organization (WHO) has encouraged the scientific community to find new strategies to eradicate this pathogen. Several recent strategies to battle P. aeruginosa focus on targeting iron homeostasis mechanisms, turning its greatest advantage into an exploitable weak point. In this review, we discuss the different mechanisms used by P. aeruginosa to maintain iron homeostasis and the strategies being developed to fight this pathogen by blocking these mechanisms. Among others, the use of iron chelators and mimics, as well as disruption of siderophore production and uptake, have shown promising results in reducing viability and/or virulence of this pathogen. The so-called ‘Trojan-horse’ strategy taking advantage of the siderophore uptake systems is emerging as an efficient method to improve delivery of antibiotics into the bacterial cells. Moreover, siderophore transporters are considered promising targets for the developing of P. aeruginosa vaccines.

Extracytoplasmic function (ECF) sigma factors are subunits of the RNA polymerase specialized in activating the transcription of a subset of genes responding to a specific environmental condition. The signal-transduction pathways where they participate can be activated by diverse mechanisms. The most common mechanism involves the action of a membrane-bound anti-sigma factor, which sequesters the ECF sigma factor, and releases it after the stimulus is sensed. However, despite most of these systems following this canonical regulation, there are many ECF sigma factors exhibiting a non-canonical regulatory mechanism. In this review, we aim to provide an updated and comprehensive view of the different activation mechanisms known for non-canonical ECF sigma factors, detailing their inclusion to the different phylogenetic groups and describing the mechanisms of regulation of some of their representative members such as EcfG from Rhodobacter sphaeroides, showing a partner-switch mechanism; EcfP from Vibrio parahaemolyticus, with a phosphorylation-dependent mechanism; or CorE from Myxococcus xanthus, regulated by a metal-sensing C-terminal extension.

During summer, when oligotrophic conditions prevail offshore in the Mediterranean Sea, enhanced phytoplankton stripes are often observed in nearshore waters. In this study, we examine the cross-shore hydrographic variability and the associated microbial plankton communities in this zone. Detailed cross-shore underway sampling at 47 coastal sites spread along the Balearic and Catalan coasts revealed the widespread existence of narrow bands of warm and decreased salinity water beholding high phytoplankton biomass (up to 50-fold vs. offshore chlorophyll). Most intense physical and biological anomalies along these transects were generally constrained to the first hundred meters from the shoreline (i.e., a transition zone starting at ~400 m). We use Principal Component Analysis (PCA) and k-means cluster analysis to categorize temperature, salinity and chlorophyll (T, S and Chl) in three main types of cross-shore trends. Prevalence of exponential-shaped Chl trends was observed particularly in areas with shoreward directed winds (B1-type). The other two trends (B2 and B3) presented variations offthe coast produced by alongshore structures like river plumes, city outfalls and other features. Exponential-shaped cross-shore chlorophyll distribution (B1-type) accumulated 90% of the total transect Chl variation in the first 367 ± 190 m from the shoreline, whereas this distance was variable in the other profile types. Repeated daily sampling at one site with this transect typology revealed that wind forcing variations produced fast response on cross-shore T and S properties. Chl was less sensitive to changes at this time-scale. Phytoplankton communities exhibited site-dependent responses to the nearshore environment. Pico- and nanoplankton assemblages, typically dominating coastal assemblages during summer in the Mediterranean Sea, showed lower cross-shore variation. Conversely, larger response to nearshore conditions was observed in microplankton populations. These larger cells

During summer, when oligotrophic conditions prevail offshore in the Mediterranean Seea, an alongshore zone with enhanced phytoplankton biomass is ofteen evidenced in these waters. Here, using high continuous measurements of temperature, salinity and fluorrescence as well as discrete samples and primary production experiments, we examine the cross-shore typology and the associated chemical and biological characteristics of these waters. Data from three coastal regions in the NW Mediterranean revealed widespread presence of lower water density bands in the proximity of the shoreline generated by increased warming and groundwater seeps through the coastal sediments. Most often, enhanced phytoplankton biomass (max=9.6 mg Chla m3; up to 16 fold offshore chlorophyll) was associated with these modified waters and exponentially decayed in the offshore direction. Gradient characteristics are highly variable but the main onshore-offshore features, determined by terrestrial loads and hydrodynamics are locally consistent. Important variations were observed in the structure of the communities among nearshore sites which were attributed to variations in the geochemical conditions. Our study argues the relevance of the formation of a groundwater-sustained nearshore niche and its temporal stability for the development of a distinct community which could eventually favor the emergence of harmful algal blooms

El campo experimental Las Margaritas, en la Sierra Nororiental del Estado de Puebla, México, posee extensa superficie y conserva parte de bosque tropical perennifolio, lo que permite que exista in situ el venado cola blanca de la subespecie veraecrucis. Por el método indirecto de conteo de huellas en transectos, se concluyó que el animal se distribuye en 1271,58 ha al norte del predio. La densidad poblacional media de 2,13 individuos/km2; con s= 0,35; y CV= 16,62 p.100. Por lo que la población absoluta se estimó en 27 individuos. También se obtuvo una lista de otras especies de fauna silvestre en el sitio, encontrándose especies en peligro de extinción en México como: Cairina moschata, Micrastur ruficolis, Crax rubra, Amazona oratrix, Ramphastos sulfuratos, Dryocopus lineatus, Leopardus pardalis y Panthera onca. Con respecto a otras regiones de Puebla, se concluye que Las Margaritas tiene alta diversidad biológica representativa del trópico húmedo, el ecosistema más diverso de México; por lo que es un área de gran importancia ecológica. Por lo tanto la investigación, la diversificación experimental biológica, así como la transferencia de tecnología, para la conservación, manejo y aprovechamiento sustentable de su fauna silvestre, por medio del modelo tecnológico de ganadería diversificada, es una alternativa económica, ambiental y social para 816 productores rurales, que puede coadyuvar a futuro a detener y revertir las tendencias de deterioro de los recursos naturales, así como a disminuir los niveles de pobreza y marginación en la Sierra Nororiental de Puebla, México.