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Recent studies have expanded the genomic contours of the Acidithiobacillia, highlighting important lacunae in our comprehension of the phylogenetic space occupied by certain lineages of the class. One such lineage is ‘Igneacidithiobacillus’, a novel genus-level taxon, represented by ‘Igneacidithiobacillus copahuensis’ VAN18-1T as its type species, along with two other uncultivated metagenome-assembled genomes (MAGs) originating from geothermally active sites across the Pacific Ring of Fire. In this study, we investigate the genetic and genomic diversity, and the distribution patterns of several uncharacterized Acidithiobacillia class strains and sequence clones, which are ascribed to the same 16S rRNA gene sequence clade. By digging deeper into this data and contributing to novel MAGs emerging from environmental studies in tectonically active locations, the description of this novel genus has been consolidated. Using state-of-the-art genomic taxonomy methods, we added to already recognized taxa, an additional four novel Candidate (Ca.) species, including ‘Ca. Igneacidithiobacillus chanchocoensis’ (mCHCt20-1TS), ‘Igneacidithiobacillus siniensis’ (S30A2T), ‘Ca. Igneacidithiobacillus taupoensis’ (TVZ-G3 TS), and ‘Ca. Igneacidithiobacillus waiarikiensis’ (TVZ-G4 TS). Analysis of published data on the isolation, enrichment, cultivation, and preliminary microbiological characterization of several of these unassigned or misassigned strains, along with the type species of the genus, plus the recoverable environmental data from metagenomic studies, allowed us to identify habitat preferences of these taxa. Commonalities and lineage-specific adaptations of the seven species of the genus were derived from pangenome analysis and comparative genomic metabolic reconstruction. The findings emerging from this study lay the groundwork for further research on the ecology, evolution, and biotechnological potential of the novel genus ‘Igneacidithiobacillus’.

Lake Caviahue (37° 50 ‘S and 71° 06’ W; Patagonia, Argentina) is an extreme case of a glacial, naturally acidic, aquatic environment (pH ~ 3). Knowledge of the bacterial communities in the water column of this lake, is incipient, with a basal quantification of the bacterioplankton abundance distribution in the North and South Basins of Lake Caviahue, and the described the presence of sulfur and iron oxidizing bacteria in the lake sediments. The role that bacterioplankton plays in nutrient utilization and recycling in this environment, especially in the phosphorus cycle, has not been studied. In this work, we explore this aspect in further depth by assessing the diversity of pelagic, littoral and sediment bacteria, using state of the art molecular methods and identifying the differences and commonalties in the composition of the cognate communities. Also, we investigate the interactions between the sediments of Lake Caviahue and the microbial communities present in both sediments, pore water and the water column, to comprehend the ecological relationships driving nutrient structure and fluxes, with a special focus on carbon, nitrogen, and phosphorus. Two major environmental patterns were observed: (a) one distinguishing the surface water samples due to temperature, Fe2+, and electrical conductivity, and (b) another distinguishing winter and summer samples due to the high pH and increasing concentrations of N-NH4+, DOC and SO42−, from autumn and spring samples with high soluble reactive phosphorus (SRP) and iron concentrations. The largest bacterial abundance was found in autumn, alongside higher levels of dissolved phosphorus, iron forms, and increased conductivity. The highest values of bacterial biomass were found in the bottom strata of the lake, which is also where the greatest diversity in microbial communities was found. The experiments using continuous flow column microcosms showed that microbial growth over time, in both the test and control columns, was accompanied by a decrease in the concentration of dissolved nutrients (SRP and N-NH4+), providing proof that sediment microorganisms are active and contribute significantly to nutrient utilization/mobilization.

Abstract The recent revision of the Acidithiobacillia class using genomic taxonomy methods has shown that, in addition to the existence of previously unrecognized genera and species, some species of the class harbor levels of divergence that are congruent with ongoing differentiation processes. In this study, we have performed a subspecies-level analysis of sequenced strains of Acidithiobacillus ferrooxidans to prove the existence of distinct sublineages and identify the discriminant genomic/genetic characteristics linked to these sublineages, and to shed light on the processes driving such differentiation. Differences in the genomic relatedness metrics, levels of synteny, gene content, and both integrated and episomal mobile genetic elements (MGE) repertoires support the existence of two subspecies-level taxa within A. ferrooxidans. While sublineage 2A harbors a small plasmid related to pTF5, this episomal MGE is absent in sublineage 2B strains. Likewise, clear differences in the occurrence, coverage and conservation of integrated MGEs are apparent between sublineages. Differential MGE-associated gene cargo pertained to the functional categories of energy metabolism, ion transport, cell surface modification, and defense mechanisms. Inferred functional differences have the potential to impact long-term adaptive processes and may underpin the basis of the subspecies-level differentiation uncovered within A. ferrooxidans. Genome resequencing of iron- and sulfur-adapted cultures of a selected 2A sublineage strain (CCM 4253) showed that both episomal and large integrated MGEs are conserved over twenty generations in either growth condition. In turn, active insertion sequences profoundly impact short-term adaptive processes. The ISAfe1 element was found to be highly active in sublineage 2A strain CCM 4253. Phenotypic mutations caused by the transposition of ISAfe1 into the pstC2 encoding phosphate-transport system permease protein were detected in sulfur-adapted cultures and shown to impair growth on ferrous iron upon the switch of electron donor. The phenotypic manifestation of the △pstC2 mutation, such as a loss of the ability to oxidize ferrous iron, is likely related to the inability of the mutant to secure the phosphorous availability for electron transport-linked phosphorylation coupled to iron oxidation. Depletion of the transpositional △pstC2 mutation occurred concomitantly with a shortening of the iron-oxidation lag phase at later transfers on a ferrous iron-containing medium. Therefore, the pstII operon appears to play an essential role in A. ferrooxidans when cells oxidize ferrous iron. Results highlight the influence of insertion sequences and both integrated and episomal mobile genetic elements in the short- and long-term adaptive processes of A. ferrooxidans strains under changing growth conditions.

Membrane vesicles (MVs) are envelope-derived extracellular sacs that perform a broad diversity of physiological functions in bacteria. While considerably studied in pathogenic microorganisms, the roles, relevance, and biotechnological potential of MVs from environmental bacteria are less well established. Acidithiobacillaceae family bacteria are active players in the sulfur and iron biogeochemical cycles in extremely acidic environments and drivers of the leaching of mineral ores contributing to acid rock/mine drainage (ARD/AMD) and industrial bioleaching. One key aspect of such a role is the ability of these bacteria to tightly interact with the mineral surfaces and extract electrons and nutrients to support their chemolithotrophic metabolism. Despite recent advances in the characterization of acidithiobacilli biofilms and extracellular matrix (ECM) components, our understanding of its architectural and mechanistic aspects remains scant. Using different microscopy techniques and nano-tracking analysis we show that vesiculation is a common phenomenon in distant members of the Acidithiobacillaceae family, and further explore the role of MVs in multicellular colonization behaviors using ‘Fervidacidithiobacillus caldus’ as a bacterial model. Production of MVs in ‘F. caldus’ occurred in both planktonic cultures and biofilms formed on sulfur surfaces, where MVs appeared individually or in chains resembling tube-shaped membranous structures (TSMSs) important for microbial communication. Liquid chromatography–mass spectrometry data and bioinformatic analysis of the MV-associated proteome revealed that ‘F. caldus’ MVs were enriched in proteins involved in cell–cell and cell–surface processes and largely typified the MVs as outer MVs (OMVs). Finally, microbiological assays showed that amendment of ‘F. caldus’ MVs to cells and/or biofilms affects collective colonizing behaviors relevant to the ecophysiology and applications of these acidophiles, providing grounds for their exploitation in biomining.

ABSTRACT We present here a comprehensive phylogenomic analysis of Acetobacteraceae, a vast group of alphaproteobacteria that has been widely studied for their economic importance. Our results indicate that the ancestor of Acetobacteraceae most likely was photosynthetic and evolved via a progressive transition from versatile photoferrotrophy to the incomplete oxidation of organic substrates defining acetous physiology. Vestigial signs of photosynthetic carotenoid metabolism are present in non-photosynthetic acetous taxa that have lost cytochrome oxidase, while their sister taxa retain such traits. The dominant terminal oxidase of acetous bacteria, the bo 3 ubiquinol oxidase, is derived from duplication and diversification of operons present in Acidocella taxa that have lost photosynthesis. We analyzed the bioenergetic traits that can compensate for the electron transfer function of photosynthetic reaction centers or constitute alternative pathways for the oxidoreduction of c-type cytochromes, such as iron oxidation. The latter pathway bypasses the deranged cytochrome bc 1 complex that is characteristically present in acidophilic taxa due to the loss of conserved ligands in both the Rieske iron-sulfur protein and cytochrome b subunit. The deranged or non-functional bc 1 complex may be retained for its structural role in stabilizing Complex I. The combination of our phylogenetic analysis with in-depth functional evaluations indicates that the order Acetobacterales needs to be emended to include three families: Acetobacteraceae sensu stricto, Roseomonadaceae fam. nov., and Acidocellaceae fam. nov. IMPORTANCE Acetobacteraceae are one of the best known and most extensively studied groups of bacteria, which nowadays encompasses a variety of taxa that are very different from the vinegar-producing species defining the family. Our paper presents the most detailed phylogeny of all current taxa classified as Acetobacteraceae, for which we propose a taxonomic revision. Several of such taxa inhabit some of the most extreme environments on the planet, from the deserts of Antarctica to the Sinai desert, as well as acidic niches in volcanic sites like the one we have been studying in Patagonia. Our work documents the progressive variation of the respiratory chain in early branching Acetobacteraceae into the different respiratory chains of acidophilic taxa such as Acidocella and acetous taxa such as Acetobacter. Remarkably, several genomes retain remnants of ancestral photosynthetic traits and functional bc 1 complexes. Thus, we propose that the common ancestor of Acetobacteraceae was photosynthetic.

Mobile genetic elements (MGEs) are relevant agents in bacterial adaptation and evolutionary diversification. Stable appropriation of these DNA elements depends on host factors, among which are the nucleoid-associated proteins (NAPs). NAPs are highly abundant proteins that bind and bend DNA, altering its topology and folding, thus affecting all known cellular DNA processes from replication to expression. Even though NAP coding genes are found in most prokaryotic genomes, their functions in host chromosome biology and xenogeneic silencing are only known for a few NAP families. Less is known about the occurrence, abundance, and roles of MGE-encoded NAPs in foreign elements establishment and mobility. In this study, we used a combination of comparative genomics and phylogenetic strategies to gain insights into the diversity, distribution, and functional roles of NAPs within the class Acidithiobacillia with a special focus on their role in MGE biology. Acidithiobacillia class members are aerobic, chemolithoautotrophic, acidophilic sulfur-oxidizers, encompassing substantial genotypic diversity attributable to MGEs. Our search for NAP protein families (PFs) in more than 90 genomes of the different species that conform the class, revealed the presence of 1,197 proteins pertaining to 12 different NAP families, with differential occurrence and conservation across species. Pangenome-level analysis revealed 6 core NAP PFs that were highly conserved across the class, some of which also existed as variant forms of scattered occurrence, in addition to NAPs of taxa-restricted distribution. Core NAPs identified are reckoned as essential based on the conservation of genomic context and phylogenetic signals. In turn, various highly diversified NAPs pertaining to the flexible gene complement of the class, were found to be encoded in known plasmids or, larger integrated MGEs or, present in genomic loci associated with MGE-hallmark genes, pointing to their role in the stabilization/maintenance of these elements in strains and species with larger genomes. Both core and flexible NAPs identified proved valuable as markers, the former accurately recapitulating the phylogeny of the class, and the later, as seed in the bioinformatic identification of novel episomal and integrated mobile elements.

The Cas1 protein is essential for the functioning of CRISPR-Cas adaptive systems. However, despite the high prevalence of CRISPR-Cas systems in thermophilic microorganisms, few studies have investigated the occurrence and diversity of Cas1 across hot spring microbial communities. Phylogenomic analysis of 2,150 Cas1 sequences recovered from 48 metagenomes representing hot springs (42–80°C, pH 6–9) from three continents, revealed similar ecological diversity of Cas1 and 16S rRNA associated with geographic location. Furthermore, phylogenetic analysis of the Cas1 sequences exposed a broad taxonomic distribution in thermophilic bacteria, with new clades of Cas1 homologs branching at the root of the tree or at the root of known clades harboring reference Cas1 types. Additionally, a new family of casposases was identified from hot springs, which further completes the evolutionary landscape of the Cas1 superfamily. This ecological study contributes new Cas1 sequences from known and novel locations worldwide, mainly focusing on under-sampled hot spring microbial mat taxa. Results herein show that circumneutral hot springs are environments harboring high diversity and novelty related to adaptive immunity systems.

Abstract Background Maintaining a proper supply of soluble histones throughout the cell cycle is important to ensure chromatin and genome stability. Following their synthesis, histones undergo a series of maturation steps to prepare them for deposition onto chromatin. Results Here, we identify the lysine demethylase JMJD1B as a novel player in the maturation cascade that contributes to regulate histone provision. We find that depletion of JMJD1B increases the protein levels of the histone chaperone tNASP leading to an accumulation of newly synthesized histones H3 and H4 at early steps of the histone maturation cascade, which perturbs chromatin assembly. Furthermore, we find a high rate of JMJD1B mutations in cancer patients, and a correlation with genomic instability. Conclusions Our data support a role for JMJD1B in fine-tuning histone supply to maintain genome integrity, opening novel avenues for cancer therapeutics.

Respiration is a major trait shaping the biology of many environments. Cytochrome oxidase containing heme A (COX) is a common terminal oxidase in aerobic bacteria and is the only one in mammalian mitochondria. The synthesis of heme A is catalyzed by heme A synthase (CtaA/Cox15), an enzyme that most likely coevolved with COX. The evolutionary origin of COX in bacteria has remained unknown. Using extensive sequence and phylogenetic analysis, we show that the ancestral type of heme A synthases is present in iron-oxidizing Proteobacteria such as Acidithiobacillus spp. These bacteria also contain a deep branching form of the major COX subunit (COX1) and an ancestral variant of CtaG, a protein that is specifically required for COX biogenesis. Our work thus suggests that the ancestors of extant iron-oxidizers were the first to evolve COX. Consistent with this conclusion, acidophilic iron-oxidizing prokaryotes lived on emerged land around the time for which there is the earliest geochemical evidence of aerobic respiration on earth. Hence, ecological niches of iron oxidation have apparently promoted the evolution of aerobic respiration.

Mobile Genetic Elements (MGEs) are mosaics of functional gene modules of diverse evolutionary origin and are generally divergent from the hosts´ genetic background. Existing biases in base composition and codon usage of these elements` genes impose transcription and translation limitations that may affect the physical and regulatory integration of MGEs in new hosts. Stable appropriation of the foreign DNA depends on a number of host factors among which are the Nucleoid-Associated Proteins (NAPs). These small, basic, highly abundant proteins bind and bend DNA, altering its topology and folding, thereby affecting all known essential DNA metabolism related processes. Both chromosomally- (endogenous) and MGE- (foreign) encoded NAPs have been shown to exist in bacteria. While the role of host-encoded NAPs in xenogeneic silencing of both episomal (plasmids) and integrative MGEs (pathogenicity islands and prophages) is well acknowledged, less is known about the role of MGE-encoded NAPs in the foreign elements biology or their influence on the host's chromosome expression dynamics. Here we review existing literature on the topic, present examples on the positive and negative effects that endogenous and foreign NAPs exert on global transcriptional gene expression, MGE integrative and excisive recombination dynamics, persistence and transfer to suitable hosts and discuss the nature and relevance of synergistic and antagonizing higher order interactions between diverse types of NAPs. Keywords: NAP, Bacterial nucleoid, MGE, HGT, Xenogeneic silencing, Regulatory hierarchies

Abstract Acidithiobacillus thiooxidans CLST is an extremely acidophilic gamma-proteobacteria that was isolated from the Gorbea salt flat, an acidic hypersaline environment in northern Chile. This kind of environment is considered a terrestrial analog of ancient Martian terrains and a source of new material for biotechnological applications. A. thiooxidans plays a key role in industrial bioleaching; it has the capacity of generating and maintaining acidic conditions by producing sulfuric acid and it can also remove sulfur layers from the surface of minerals, which are detrimental for their dissolution. CLST is a strain of A. thiooxidans able to tolerate moderate chloride concentrations (up to 15 g L−1 Cl−), a feature that is quite unusual in extreme acidophilic microorganisms. Basic microbiological features and genomic properties of this biotechnologically relevant strain are described in this work. The 3,974,949 bp draft genome is arranged into 40 scaffolds of 389 contigs containing 3866 protein-coding genes and 75 RNAs encoding genes. This is the first draft genome of a halotolerant A. thiooxidans strain. The release of the genome sequence of this strain improves representation of these extreme acidophilic Gram negative bacteria in public databases and strengthens the framework for further investigation of the physiological diversity and ecological function of A. thiooxidans populations.

Abstract Acidithiobacillus albertensis is an extremely acidophilic, mesophilic, obligatory autotrophic sulfur-oxidizer, with potential importance in the bioleaching of sulfidic metal ores, first described in the 1980s. Here we present the draft genome sequence of Acidithiobacillus albertensis DSM 14366T, thereby both filling a long-standing gap in the genomics of the acidithiobacilli, and providing further insight into the understanding of the biology of the non iron-oxidizing members of the Acidithiobacillus genus. The assembled genome is 3,1 Mb, and contains 47 tRNAs, tmRNA gene and 2 rRNA operons, along with 3149 protein-coding predicted genes. The Whole Genome Shotgun project was deposited in DDBJ/EMBL/GenBank under the accession MOAD00000000.

Cyclic and linear nucleotides are key elements of the signal transduction networks linking perception of the environment to specific cellular behavior of prokaryotes. These molecular mechanisms are particularly important in bacteria exposed to different, and frequently simultaneous, types of extreme conditions. This is the case in acidithiobacilli, a group of extremophilic bacteria thriving in highly acidic biotopes, that must also cope with significant variations in temperature, osmotic potentials and concentrations of various transition metals and metalloids. Environmental cues sensed by bacteria are transduced into differential levels of nucleotides acting as intracellular second messengers, promoting the activation or inhibition of target components and eliciting different output phenotypes. Cyclic (c) di-GMP, one of the most common bacterial second messengers, plays a key role in lifestyle changes in many bacteria, including acidithiobacilli. The presence of functional c-di-GMP-dependent signal transduction pathways in representative strains of the best-known linages of this species complex has been reported. However, a comprehensive panorama of the c-di-GMP modulated networks, the cognate input signals and output responses, are still missing for this group of extremophiles. Moreover, little fundamental understanding has been gathered for other nucleotides acting as second messengers. Taking advantage of the increasing number of sequenced genomes of the taxon, here we address the challenge of disentangling the nucleotide-driven signal transduction pathways in this group of polyextremophiles using comparative genomic tools and strategies. Results indicate that the acidithiobacilli possess all the genetic elements required to establish functional transduction pathways based in three different nucleotide-second messengers: (p)ppGpp, cyclic AMP (cAMP), and c-di-GMP. The elements related with the metabolism and transduction of (p)ppGpp and cAMP appear highly conserved, integrating signals related with nutrient starvation and polyphosphate metabolism, respectively. In contrast, c-di-GMP networks appear diverse and complex, differing both at the species and strain levels. Molecular elements of c-di-GMP metabolism and transduction were mostly found scattered along the flexible genome of the acidithiobacilli, allowing the identification of probable control modules that could be critical for substrate colonization, biofilm development and intercellular interactions. These may ultimately convey increased endurance to environmental stress and increased potential for gene sharing and adaptation to changing conditions.

The dispersal of mobile genetic elements and their gene cargo relies on type IV secretion systems (T4SS). In this work the ICEAfe1 Tra-type T4SS nanomachine, encoded in the publicly available genome of Acidithiobacillus ferrooxidans ATCC 23270TY, was characterized in terms of its organization, conservation, expression and mating bridge formation. Twenty-one conjugative genes grouped in four genetic clusters encode the ICEAfe1 T4SS, containing all the indispensable functions for the formation and stabilization of the pili and for DNA processing. The clusters’ organization resembles that of other mobile genetic elements (such as plasmids and integrative and conjugative elements–ICEs). Sequence conservation, genetic organization and distribution of the tra system in the genomes of other sequenced Acidithiobacillus spp. suggests that the ICEAfe1 T4SS could mediate the lateral gene transfer between related bacteria. All ICEAfe1 T4SS genes are transcriptionally active and expressed from four independent operons. The transcriptional levels of selected marker genes increase in response to Mitomycin C treatment, a DNA damage elicitor that has acknowledged stimulatory effects on excision rates and gene expression of other ICEs, including ICEAfe1. Using a tailor-made pilin-antiserum against ICEAfe1 T4SS TraA pilin and epifluorescence microscopy, the presence of the conjugative pili on the cell surface of A. ferrooxidans could be demonstrated. Additionally, immunodetection assays, by immunogold, allowed the identification of pili-like extracellular structures. Together, the results obtained in this work demonstrate that the ICEAfe1 T4SS is phylogenetically conserved within the taxon, is expressed at mRNA and protein levels in vivo in the A. ferrooxidans type strain, and produces a pili-like structure of extracellular and intercellular localization in this model acidophile, supporting its functionality. Additional efforts will be required to prove conjugation of the ICEAfe1 or parts of this element through the cognate T4SS.

Extreme acidophiles play central roles in the geochemical cycling of diverse elements in low pH environments. This has been harnessed in biotechnologies such as biomining, where microorganisms facilitate the recovery of economically important metals such as gold. By generating both extreme acidity and a chemical oxidant (ferric iron) many species of prokaryotes that thrive in low pH environments not only catalyze mineral dissolution but also trigger both community and individual level adaptive changes. These changes vary in extent and direction depending on the ore mineralogy, water availability and local climate. The use of indigenous versus introduced microbial consortia in biomining practices is still a matter of debate. Yet, indigenous microbial consortia colonizing sulfidic ores that have been domesticated, i.e., selected for their ability to survive under specific polyextreme conditions, are claimed to outperform un-adapted foreign consortia. Despite this, little is known on the domestication of acidic microbial communities and the changes elicited in their members. In this study, high resolution targeted metagenomic techniques were used to analyze the changes occurring in the community structure of local microbial consortia acclimated to growing under extreme acidic conditions and adapted to endure the conditions imposed by the target mineral during biooxidation of a gold concentrate in an airlift reactor over a period of 2 years. The results indicated that operative conditions evolving through biooxidation of the mineral concentrate exerted strong selective pressures that, early on, purge biodiversity in favor of a few Acidithiobacillus spp. over other iron oxidizing acidophiles. Metagenomic analysis of the domesticated consortium present at the end of the adaptation experiment enabled reconstruction of the RVS1-MAG, a novel representative of Acidithiobacillus ferrooxidans from the Andacollo gold mineral district. Comparative genomic analysis performed with this genome draft revealed a net enrichment of gene functions related to heavy metal transport and stress management that are likely to play a significant role in adaptation and survival to adverse conditions experienced by these acidophiles during growth in presence of gold concentrates.

Rubrerythrins (RBRs) are non-heme di-iron proteins belonging to the ferritin-like superfamily (FLSF). They are involved in oxidative stress defense as peroxide scavengers in a wide range of organisms. The vast majority of RBRs, including classical forms of this protein, contain a C-terminal rubredoxin-like domain involved in electron transport that is used during catalysis in anaerobic conditions. Rubredoxin is an ancient and large protein family of short length (

Se estudió morfología y dieta de dos poblaciones de Liolaemus elongatus del noroeste de la Patagonia, una de ambiente de estepa y otra de bosque. Ambas poblaciones se encuentran separadas por una distanciada de 30 km. Se evaluó la variación entre poblaciones y entre sexos de la coloración y patrón de diseño corporal, los parámetros métricos más relevantes (longitud hocico-cloaca, longitud y ancho de la cabeza y longitud del maxilar), así como de la composición y diversidad de los contenidos digestivos de 22 ejemplares adultos de estepa y 25 de bosque. Las poblaciones difirieron en la coloración, el patrón de diseño y en el tamaño corporal promedio (mayor en la zona de estepa). La variación en la coloración podría estar relacionada con factores genéticos o selectivos. Los valores mayores de tamaño corporal en la estepa podrían representar una disminución de tamaño a mayor altitud. No se encontró dimorfismo sexual en la coloración ni en la longitud hocico-cloaca en ninguna de las dos poblaciones. Respecto a la dieta, se advirtió un predominio de consumo de formícidos en ambas poblaciones. Los vegetales resultaron ser un componente usual, contrastando con las opiniones previas que consideraban a la especie exclusivamente insectívora. La disponibilidad de elementos vegetales podría ser un factor de considerable importancia para determinar la tendencia de esta especie a la omnivoría. Las diferencias en la dieta entre las dos poblaciones analizadas podrían estar relacionadas con diferentes parámetros ecológicos y/o con características intrínsecas de las poblacionesMorphology and diet of two Liolaemus elongatus populations from northwestern Patagonia, consisting of a steppe and a forested patch, and 30 km apart from each other, were studied. The variation between populations and sexes of the coloration and design pattern, the most relevant metrical parameters, and that of composition and diversity of the digestive contents was examined in 22 steppe and 25 forest adult specimens. Populations differed in coloration, design pattern and average body size, with individuals from steppe being larger. Variation in color could be related to either genetic or selective factors. The lower altitude of the steppe zone might account for the bigger size of individuals therein. No sexual dimorphism was detected either in coloration or body size in individuals of both populations. Regarding diet, individuals from both populations appeared to feed mainly on ants (Formicidae). Nonetheless, plant material was frequent, which contradicts previous opinions that considered the species as being exclusively insectivorous. Availability of plants could therefore be a major influence on the tendency of this species towards omnivory. Differences in diet between the two populations could be related to different ecological parameters and/or to intrinsic characteristics of the populations

BackgroundAcidithiobacillus caldus is a sulfur oxidizing extreme acidophile and the only known mesothermophile within the Acidithiobacillales. As such, it is one of the preferred microbes for mineral bioprocessing at moderately high temperatures. In this study, we explore the genomic diversity of A. caldus strains using a combination of bioinformatic and experimental techniques, thus contributing first insights into the elucidation of the species pangenome.Principal findingsComparative sequence analysis of A. caldus ATCC 51756 and SM-1 indicate that, despite sharing a conserved and highly syntenic genomic core, both strains have unique gene complements encompassing nearly 20% of their respective genomes. The differential gene complement of each strain is distributed between the chromosomal compartment, one megaplasmid and a variable number of smaller plasmids, and is directly associated to a diverse pool of mobile genetic elements (MGE). These include integrative conjugative and mobilizable elements, genomic islands and insertion sequences. Some of the accessory functions associated to these MGEs have been linked previously to the flexible gene pool in microorganisms inhabiting completely different econiches. Yet, others had not been unambiguously mapped to the flexible gene pool prior to this report and clearly reflect strain-specific adaption to local environmental conditions.SignificanceFor many years, and because of DNA instability at low pH and recurrent failure to genetically transform acidophilic bacteria, gene transfer in acidic environments was considered negligible. Findings presented herein imply that a more or less conserved pool of actively excising MGEs occurs in the A. caldus population and point to a greater frequency of gene exchange in this econiche than previously recognized. Also, the data suggest that these elements endow the species with capacities to withstand the diverse abiotic and biotic stresses of natural environments, in particular those associated with its extreme econiche.

The constant emergence of antibiotic multi-resistant pathogens is a concern worldwide. An alternative for bacterial treatment using nM concentrations of tellurite was recently proposed to boost antibiotic-toxicity and a synergistic effect of tellurite/cefotaxime (CTX) was described. In this work, the molecular mechanism underlying this phenomenon is proposed. Global changes of the transcriptional profile of Escherichia coli exposed to tellurite/CTX were determined by DNA microarrays. Induction of a number of stress regulators (as SoxS), genes related to oxidative damage and membrane transporters was observed. Accordingly, increased tellurite adsorption/uptake and oxidative injuries to proteins and DNA were determined in cells exposed to the mixture of toxicants, suggesting that the tellurite-mediated CTX-potentiating effect is dependent, at least in part, on oxidative stress. Thus, the synergistic tellurite-mediated CTX-potentiating effect depends on increased tellurite uptake/adsorption which results in damage to proteins, DNA and probably other macromolecules. Our findings represent a contribution to the current knowledge of bacterial physiology under antibiotic stress and can be of great interest in the development of new antibiotic-potentiating strategies.

Thiol/disulfide systems are involved in the maintenance of the redox status of proteins and other molecules that contain thiol/disulfide groups. Leptospirillum ferriphilum DSM14647, an acidophilic bacterium that uses Fe(2+) as electron donor, and withstands very high concentrations of iron and other redox active metals, is a good model to study how acidophiles preserve the thiol/disulfide balance. We studied the composition of thiol/disulfide systems and their role in the oxidative stress response in this extremophile bacterium. Bioinformatic analysis using genomic data and enzymatic assays using protein extracts from cells grown under oxidative stress revealed that the major thiol/disulfide system from L. ferriphilum are a cytoplasmic thioredoxin system (composed by thioredoxins Trx and thioredoxin reductase TR), periplasmic thiol oxidation system (DsbA/DsbB) and a c-type cytochrome maturation system (DsbD/DsbE). Upon exposure of L. ferriphilum to reactive oxygen species (ROS)-generating compounds, transcriptional activation of the genes encoding Trxs and the TR enzyme, which results in an increase of the corresponding activity, was observed. Altogether these data suggest that the thioredoxin-based thiol/disulfide system plays an important role in redox protection of L. ferriphilum favoring the survival of this microorganism under extreme environmental oxidative conditions.