Claudia P Saavedra

Universidad Andrés Bello | UNAB · Facultad de Ciencias Biológicas

The Atacama Desert is the oldest and driest desert on Earth, encompassing great temperature variations, high ultraviolet radiation, drought, and high salinity, making it ideal for studying the limits of life and resistance strategies. It is also known for harboring a great biodiversity of adapted life forms. While desertification is increasing as a...

La pandemia de la COVID-19 parecía haber dejado claro no sólo para los organismos gubernamentales, sino para la sociedad en su conjunto, la importancia de la ciencia1. Nuestra revista publicó varias editoriales explicando y fundamentando la necesidad de la autonomía sanitaria cuyo requisito principal es la existencia de un sistema científico sólido...

The Atacama Desert is the oldest and driest desert on Earth, with environmental conditions including great temperature variations, high UV-radiation, drought, high salinity, making it a natural laboratory to study the limits of life and resistance strategies. However, it shows great biodiversity harboring vast forms of adapted life and can be used...

Rare-earth elements (REEs) are crucial metals with limited global availability due to their indispensable role in various high-tech industries. As the demand for rare-earth elements continues to rise, there is a pressing need to develop sustainable methods for their recovery from secondary sources. Focusing on Exiguobacterium sp. SH31, this researc...

The Salar de Huasco (SH) salt lake in northern Chile is an extreme environment characterized by high atmospheric pressure, UV radiation, salinity, variable temperatures, and the presence of heavy metals, including arsenic. Exiguobacterium bacteria have adapted to thrive in these challenging conditions and possess various resistance mechanisms, incl...

Microorganisms are the most diverse life form on the planet and are critical for maintaining the geochemical cycles, especially in extreme environments. Bacterial communities are dynamic and respond directly to changes in abiotic conditions; among these communities, poly-extremophiles are particularly sensitive to perturbations due to their high sp...

The presence of mobile genetic elements in Salmonella isolated from a chicken farm constitutes a potential risk for the appearance of emerging bacteria present in the food industry. These elements contribute to increased pathogenicity and antimicrobial resistance through genes that are related to the formation of biofilms and resistance genes conta...

Butyrate is a microbiota-produced metabolite, sensed by host short-chain fatty acid receptors FFAR2 (Gpr43), FFAR3 (Gpr41), HCAR2 (Gpr109A), and Histone deacetylase (HDAC) that promotes microbiota-host crosstalk. Butyrate influences energy uptake, developmental and immune response in mammals. This microbial metabolite is produced by around 79 anaer...

Background Salmonella Typhimurium is a Gram-negative pathogen that causes a systemic disease in mice resembling typhoid fever. During its infective cycle, S. Typhimurium is phagocytized by macrophages and proliferates inside a Salmonella -containing vacuole where Salmonella is exposed and survives oxidative stress induced by H 2 O 2 through modulat...

Arsenic is a highly toxic metalloid of major concern for public safety. However, microorganisms have several resistance mechanisms, particularly the expression of arsenic pumps is a critical component for bacterial ability to expel it and decrease intracellular toxicity. In this study, we aimed to characterize the biochemical, structural, and genom...

Arsenopyrite is the most abundant arsenic-bearing sulfide mineral in the lithosphere, usually associated with sulfide gold ores. The recovery of this highly valuable metal is associated with the release of large quantities of soluble arsenic. One way to mitigate the effects of high concentrations of arsenic in solution is to immobilize it as scorod...

The extreme environmental conditions and lack of water on the soil surface in hyperarid deserts hamper microbial life, allowing only highly specialized microbial communities to the establish colonies and survive. Until now, the microbial communities that inhabit or have inhabited soils of hyperarid environments at greater depths have been poorly st...

Salmonella comprises over 2500 serotypes and foodborne contamination associated with this pathogen remains an important health concern worldwide. During the last decade, a shift in serotype prevalence has occurred as traditionally less prevalent serotypes are increasing in frequency of infections, especially those related to poultry meat contaminat...

As microbial communities inhabiting extreme environments are fundamental for maintaining ecosystems, many studies concerning composition, functionality, and interactions have been carried out. However, much is still unknown.

Microbial communities inhabiting extreme environments like Salar de Huasco (SH) are adapted to thrive while exposed to several abiotic pressures and the presence of toxic elements like arsenic (As). Hence, we aimed to uncover the role of arsenic in shaping bacterial composition, structure, and functional potential in five different sites in this Al...

Oxidative stress is the main mechanism behind efficient disinfectants, causing damage in bacterial macromolecules. Importantly, bacteria activate resistance mechanisms in response to damage generated by oxidative stress. Strategies allowing pathogens to survive oxidative stress are highly conserved among microorganisms. Many of these strategies ent...

The use of microorganisms in mining processes is a technology widely employed around the world. Leaching bacteria are characterized by having resistance mechanisms for several metals found in their acidic environments, some of which have been partially described in the Acidithiobacillus genus (mainly on ferrooxidans species). However, the response...

Polyextremophilic bacteria can thrive in environments with multiple stressors such as the Salar de Huasco (SH). Microbial communities in SH are exposed to low atmospheric pressure, high UV radiation, wide temperature ranges, salinity gradient and the presence of toxic compounds such as arsenic (As). In this work we focus on arsenic stress as one of...

ABSTRACT In the absence of a consensus protocol to slow down the current SARS- CoV2 spread, policymakers are in need of real-time indicators to support decisions in public health matters. The Basic Reproduction Number ($R_0$) represents viral spread rate and can be dramatically modified by the application of effective public control measures. Howe...

In the absence of a consensus protocol to slow down the spread of SARS-CoV-2, policymakers need real-time indicators to support decisions in public health matters. The Effective Reproduction Number (Rt) represents the number of secondary infections generated per each case and can be dramatically modified by applying effective interventions. However...

Ciprofloxacin is the choice treatment for infections caused by Salmonella Typhi, however, reduced susceptibility to ciprofloxacin has been reported for this pathogen. Considering the decreased approbation of new antimicrobials and the crisis of resistance, one strategy to combat this problem is to find new targets that enhances the antimicrobial ac...

Salmonella Typhimurium, a bacterial pathogen with high metabolic plasticity, can adapt to different environmental conditions; these traits enhance its virulence by enabling bacterial survival. Neutrophils play important roles in the innate immune response, including the production of microbicidal reactive oxygen species (ROS). In addition, the myel...

Exiguobacterium is a polyextremophile bacterial genus with a physiology that allows it to develop in different adverse environments. The Salar de Huasco is one of these environments due to its altitude, atmospheric pressure, solar radiation, temperature variations, pH, salinity, and the presence of toxic compounds such as arsenic. However, the phys...

Currently, Salmonella enterica serovar Typhimurium (S. Typhimurium), is a major global public health problem, which has caused food-borne illnesses in many countries. Today, with the extensive use of antimicrobials, antimicrobial resistance is increasing at a serious rate in S. Typhimurium isolates. The present study sought the role of cysteine (Cy...

Dr. Ana Inostroza should be included in the author byline. They should be listed as the fourth author, and their affiliation is 1: Laboratorio de Microbiología Molecular, Departamento de Ciencias Biológicas, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile. The contributions of this author are as follows: acquisition of da...

Salmonella enterica Serovar Typhimurium (S. Typhimurium) is an intracellular bacterium that overcomes host immune system barriers for successful infection. The bacterium colonizes the proximal small intestine, penetrates the epithelial layer, and is engulfed by macrophages and neutrophils. Intracellularly, S. Typhimurium encounters highly toxic rea...

Variation of 16S under oxidative stress. Kegg Pathway illustration of data obtained in whole transcriptome analyses of the parental strain S. Typhimurium 14028s. Data extracted from RNA-seq analyses of each strain under 1.56 mM of H2O2 and 1.0075 mM of NaOCl separately. Green boxes indicate repression; red boxes indicate induction of the particular...

Stability of tested housekeeping genes. The abundance of transcripts of 16S, talB, gyrB, rpoB, ftsZ, secA, gmk, and glnA under hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl), as FPKM (Fragments per kilo base per million [mapped reads]) values, was used to calculated fold change expression between the conditions: under 1.56 mM of H2O2 (gre...

CFUs recovered from eukaryotic cells treated with 5 μM cytochalasin D. Strains from S. Typhimurium were incubated at a MOI of 100 with (A) macrophages and (B) bone-marrow derived neutrophils and CFU was recovered as indicated in Materials and Methods in gentamicin protection assays. Values represent Colony Forming Units (CFU) recovered of each stra...

Relative expression of genes in the S. Typhimurium 14028s, ΔarcA, and ΔarcB strains inside RAW 264.7 cells. *p<0,05; **p<0,01; ***p<0,001. One Way ANOVA with Bonferroni post-test comparing mutant strains vs wild type strain in 1 hpi and 3 hpi separately. Data are from 5 biological replicates with 3 technical replicates per experiment. (TIF)

Competitive infection assays. Competitive infections were performed as described before by Evans et al., 2011 [34]. Animals where infected orally (p.o.) of i.p with a 1:1 mixture of S. Typhimurium 14028 and the arcA mutant. Mice were sacrificed at 4 or 6 days p.i and liver and spleen were collected for processing. CI index was calculated as describ...

H2O2 production in Raw 264.7 and bone-marrow-derived murine neutrophils. Phagocytic cells were co-cultured with S. Typhimurium 14028s (white bar), S. Typhimurium ΔarcA (grey bar) and S. Typhimurium ΔarcB (black bar) at 1 hpi, and S. Typhimurium 14028s (blue bar), S. Typhimurium ΔarcA (red bar), and S. Typhimurium ΔarcB (purple bar) at 3 hpi. Quanti...

HOCl production in bone-marrow-derived murine neutrophils. Each phagocyte was co-cultured with S. Typhimurium 14028s/pGLO (white bar), S. Typhimurium ΔarcA/pGLO (grey bar), and S. Typhimurium ΔarcB/pGLO (black bar). The amount of HOCl was quantified by GFP bleaching after cell lysate. *P < 0.05; **P < 0.01, ***P < 0.001 by one-way ANOVA followed by...

Expression of target genes calculated as relative to different housekeeping genes. Comparison between the expression patterns of some of our work target genes (manZ, pmgI, ompD, ompW, sodA, and sipC) in control, H2O2 and NaOCl conditions, normalized with some of the housekeeping genes proposed by Rocha et al., 2015 and talB. Ratios were calculated...

Relative expression of genes in the S. Typhimurium 14028s, ΔarcA, and ΔarcB strains inside RAW 264.7 cells. *p<0,05; **p<0,01; ***p<0,001. One Way ANOVA with Bonferroni post-test comparing mutant strains vs wild type strain in 1 hpi and 3 hpi separately. Data are from 5 biological replicates with 3 technical replicates per experiment. (TIF)

Primers used for qPCR. (PDF)

Poly-extremophiles microorganisms have the capacity to inhabit hostile environments and can survive several adverse conditions that include as variations in temperature, pH, and salinity, high levels UV light and atmospheric pressure, and even the presence of toxic compounds and the formation of reactive oxygen species (ROS). A halotolerant Exiguob...

Salmonella Typhimurium is an intracellular pathogen that is capable of generating systemic fever in a murine model. Over the course of the infection, Salmonella faces different kinds of stressors, including harmful reactive oxygen species (ROS). Various defence mechanisms enable Salmonella to successfully complete the infective process in the prese...

The Atacama Desert hosts diverse ecosystems including salt flats and shallow Andean lakes. Several heavy metals are found in the Atacama Desert, and microorganisms growing in this environment show varying levels of resistance/tolerance to copper, tellurium, and arsenic, among others. Herein, we report the genome sequence and comparative genomic ana...

Salmonella Typhimurium is the etiological agent of gastroenteritis in humans and enteric fever in mice. Inside these hosts, Salmonella must overcome hostile conditions to develop a successful infection, a process in which the levels of porins may be critical. Herein, the role of the Salmonella Typhimurium porin OmpD in the infection process was ass...

Typically, the expression of sRNAs is activated in response to environmental stimuli in order to regulate gene expression through post-transcriptional mechanisms. In the present work we show that the Salmonella Typhimurium paralogous sRNAs RyhB-1 and RyhB-2 are induced in response to the nitrosating agent S-nitrosoglutathione (GSNO). Inactivation o...

As part of the response to specific stress conditions, bacteria express small molecules of non-coding RNA which maintain cellular homeostasis by regulating gene expression, commonly at the post-transcriptional level. Among these, in Salmonella enterica sv. Typhimurium, the paralog small non-coding RNAs RyhB-1 and RyhB-2 play an important role in ir...

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS), which is part of the oxidative burst encountered upon internalization of Salmonella enterica serovar Typhimurium (S. Typhimurium) by phagocytic cells. It has previously been established that, the ArcAB two-component system plays a critical role in ROS resistance, but the genes regulated b...

In response to antibiotics, bacteria activate regulatory systems that control the expression of genes that participate detoxifying these compounds, like multidrug efflux systems. We previously demonstrated that the BaeSR two-component system from S. Typhimurium participates in the detection of ciprofloxacin, a bactericidal antibiotic, and in the po...

OmpW is a minor porin that has been involved in osmoregulation and the uptake of ceftriaxone. Evidence obtained in our laboratory indicates that in S. Typhimurium 14028s its expression is increased by SoxS, upon exposure to paraquat, and is required for the resistance to the toxic compound. SoxS belongs to the AraC family of transcriptional regulat...

To survive, Salmonella enterica serovar Typhimurium (S. Typhimurium) must sense signals found in phagocytic cells and modulate gene expression. In the present work, we evaluated the expression and cross-regulation of the transcription factors MarA, Rob, and SoxS in response to NaOCl. We generated strains ΔsoxS and ΔmarA, which were 20 times more se...

Hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) are reactive oxygen species that are part of the oxidative burst encountered by Salmonella enterica serovar Typhimurium (S. Typhimurium) upon internalization by phagocytic cells. In order to survive, bacteria must sense these signals and modulate gene expression. Growing evidence indicates that...

Two-component systems are one of the most prevalent mechanisms by which bacteria sense, respond and adapt to changes in their environment. The activation of a sensor histidine kinase leads to autophosphorylation of a conserved histidine residue followed by transfer of the phosphoryl group to a cognate response regulator in an aspartate residue. The...

Here we demonstrate that OmpD, the most abundant porin in Salmonella enterica serovar Typhimurium, facilitates uptake of hydrogen peroxide (H₂O₂) and that its expression is negatively regulated by ArcA upon peroxide exposure. When exposed to sublethal concentrations of H₂O₂, a S. Typhimurium ompD mutant showed decreased peroxide levels compared to...

Salmonella enterica serovar Typhi (S. Typhi) is the aetiological agent of typhoid fever in humans. This bacterium is also able to persist in its host, causing a chronic disease by colonizing the spleen, liver and gallbladder, in the last of which the pathogen forms biofilms in order to survive the bile. Several genetic components, including the yih...

OmpW of Salmonella enterica serovar Typhimurium has been described as a minor porin involved in osmoregulation, and is also affected by environmental conditions. Biochemical and genetic evidence from our laboratory indicates that OmpW is involved in efflux of and resistance towards paraquat (PQ), and its expression has been shown to be activated in...

The Geobacillus stearothermophilus V cobA gene encoding uroporphyrinogen-III C-methyltransferase (also referred to as SUMT) was cloned into Escherichia coli and the recombinant enzyme was overexpressed and purified to homogeneity. The enzyme binds S-adenosyl-L-methionine and catalyzes the production of III methyl uroporphyrinogen in vitro. E. coli...

The aim was to study the role played by SmvA pump in the efflux of quaternary ammonium compounds (QACs) in Salmonella enterica serovar Typhimurium (Salmonella Typhimurium). Mutants in the smvA, acrB and tolC genes were constructed by the red swap method. P22 was used to transduce tolC to acrB and smvA mutant strains. The susceptibility of these str...

Porins are channels that enable passive diffusion of hydrophilic solutes, nutrients and toxins through the outer bacterial membrane. This explains in part the ability of Gram-negative microorganisms to grow in several different environments, as well as their drug resistance. OmpD is an outer membrane channel that works with the inner membrane pump...

Reactive oxygen species damage intracellular targets and are implicated in cancer, genetic disease, mutagenesis, and aging. Catalases are among the key enzymatic defenses against one of the most physiologically abundant reactive oxygen species, hydrogen peroxide. The well-studied, heme-dependent catalases accelerate the rate of the dismutation of p...

Escherichia coli JM109 cells were modified to express the genes encoded in a 3.8-kb chromosomal DNA fragment from a metalloid-resistant thermophile, Geobacillus stearothermophilus V. Manual headspace extraction was used to collect the gases for gas chromatography with fluorine-induced sulfur chemiluminescence analysis while solid-phase microextract...

The ubiE gene of Geobacillus stearothermophilus V, with its own promoter, was cloned and introduced into Escherichia coli. The cloned gene complemented the ubiE gene deficiency of E. coli AN70. In addition, the expression of this gene in E. coli JM109 resulted in the evolution of volatile selenium compounds when these cells were grown in selenite-...

We have characterized a natural isolate of Staphylococcus epidermidis resistant to heavy metals that carries a small 2391-bp plasmid, pSepCH, encoding the qacC gene. The S. epidermidis qacC gene confers resistance to a number of beta-lactam antibiotics and to ethidium bromide in its natural host and in Escherichia coli K12 and Salmonella enterica s...

We have characterized a natural isolate of Staphylococcus epidermidis resistant to heavy metals that carries a small 2391-bp plasmid, pSepCH, encoding the qacC gene. The S. epidermidis qacC gene confers resistance to a number of β-lactam antibiotics and to ethidium bromide in its natural host and in Escherichia coli K12 and Salmonella enterica sv....

Escherichia coli JM109 cells, expressing the genes encoded in a 3.8-kb chromosomal DNA fragment from Geobacillus stearothermophilus V, produced volatile organotellurium compounds which were released into the headspace gas above liquid cultures when amended with tellurite anions in micromolar amounts. Headspace sampling was achieved using gas-syring...

The cysK gene encoding a cysteine synthase of Geobacillus stearothermophilus V was overexpressed in E. coli and the recombinant protein was purified and characterized. The enzyme is a thermostable homodimer (32 kDa/monomer) belonging to the beta family of pyridoxal phosphate (PLP)-dependent enzymes. UV-visible spectra showed absorption bands at 279...

A 3.8-kb fragment of chromosomal DNA of Geobacillus stearothermophilus V cloned in pSP72 (p1VH) confers resistance to potassium tellurite (K(2)TeO(3)) and to potassium tellurate (K(2)TeO(4)) when the encoded genes are expressed in Escherichia coli K-12. The nt sequence of the cloned fragment predicts three ORFs of 780, 399, and 600 bp, whose encode...

Many eubacteria are resistant to the toxic oxidizing agent potassium tellurite, and tellurite resistance involves diverse biochemical mechanisms. Expression of the iscS gene from Geobacillus stearothermophilus V, which is naturally resistant to tellurite, confers tellurite resistance in Escherichia coli K-12, which is naturally sensitive to telluri...

Determination of the nucleotide sequence of a 4.5-kb chromosomal DNA fragment of Bacillus stearothermophilus LV revealed two open reading frames (ORFs) of 121 and 727 amino acids (aa) that exhibit a high degree of similarity with the cadC and cadA cadmium resistance genes of a number of microorganisms. Transfer and expression of the B. stearothermo...

The nucleotide sequence of a 4,539 bp fragment of Bacillus stearothermophilus V mediating tellurite resistance in Escherichia coli was determined. Four ORFs of more than 150 amino acids encoding polypeptides of 244, 258, 308, and 421 residues were found in the restriction fragment. E. coli cells harboring a recombinant plasmid containing the Ter de...

The nucleotide sequence of a 2837-base pairs (bp) EcoRI-PvuI fragment of Bacillus stearothermophilus LV chromosomal DNA encoding the bstLVIM gene was determined. It revealed a large open reading frame (ORF) of 1737 bp specifying a methylase of 579 amino acid (aa) residues and Mr 66,831. This was in agreement with the size estimated for the M. BstLV...

Structural studies of the proteins of the BstVI restriction-modification system of Bacillus stearothermophilus V were carried out using intrinsic fluorescence techniques. The exposure and environments of their tryptophanyl residues were determined using collisional quenchers. Quenching of BstVI endonuclease by iodide suggested a heterogeneous class...

The restriction endonuclease BstVI from Bacillus stearothermophilus V contains three cysteine residues at positions 134, 167 and 180. Titration of Cys residues with DTNB showed that none of them are involved in disulphide bond formation. Cysteine triplets 134 and 167 were modified by recombinant PCR to introduce a serine residue in each case. The m...

A potassium tellurite-resistance determinant was isolated from Bacillus stearothermophilus V and cloned in Escherichia coli. Transformed cells formed black colonies when grown on solid media containing permissive tellurite concentrations. The resistance determinant was contained in a B. stearothermophilus V chromosomal DNA fragment of 7 kb.

On Nov 6, 2001 this sequence version replaced gi:6165641.

Bacillus stearothermophilus V is a naturally occurring Gram-positive rod which exhibits resistance to potassium tellurite. Crude extracts of this bacterium catalyse the NADH-dependent, protease-sensitive reduction of K2TeO3 in vitro. Two fractions which showed the ability to reduce potassium tellurite (H1 and H2) were obtained. Fraction H1 behaved...

Bacterial restriction and modification systems must be regulated to avoid self-restriction. It is generally accepted that cognate DNA methyltransferases normally protects both, the host's chromosome and extrachromosomal elements from the activity of their endonuclease counterparts. When the bstVIRM genes from Bacillus stearothermophilus V were subc...

The activity of BstVI DNA methyltransferase was monitored during the sporulative cycle of Bacillus stearothermophilus V. Significant methylase activity was found only in bacteria growing vegetatively. This was confirmed by Northern hybridization, which indicated that the bstVIM gene was not transcribed in cells undergoing sporulation. Supporting ev...

The activity of BstVl DNA methyltransferase was monitored during the sporulative cycle of Bacillus stearothermophilus V. Significant methylase activity was found only in bacteria growing vegetatively. This was confirmed by Northern hybridization, which indicated that the bstVIM gene was not transcribed in cells undergoing sporulation. Supporting ev...