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Acinetobacter baumannii is recognized as a critical human pathogen by the World Health Organization, and therefore there is increasing interest in studying its biology and pathophysiology. Among other strains, A. baumannii V15 has been extensively used for these purposes. Here, the genome sequence of A. baumannii V15 is presented.

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It is now clearly recognized that light modulates the physiology of many bacterial chemotrophs, either directly or indirectly. An interesting case are bacterial pathogens of clinical relevance. This work summarizes, discusses, and provides novel complementary information to what is currently known about light sensing and responses in critical human pathogens such as Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus. These pathogens are associated with severe hospital and community infections difficult to treat due to resistance to multiple drugs. Moreover, light responses in Brucella abortus, an important animal and human pathogen, are also compiled. Evidence recovered so far indicates that light modulates aspects related to pathogenesis, persistence, and antibiotic susceptibility in these pathogens; such as motility, biofilm formation, iron uptake, tolerance to antibiotics, hemolysis and virulence. The pathogens elicit differential responses to light depending likely on their pathophysiology, ability to cause disease and characteristics of the host. The response to light is not restricted to discrete physiological traits but is global. In higher organisms, light provides spatial and temporal information. Then, it is crucial to understand what information light is providing in these bacterial pathogens. Our current hypothesis postulates that light serves as a signal that allows these pathogens to synchronize their behavior to the circadian rhythm of the host, to optimize infection. Advances on the molecular mechanism of light signal transduction and physiological responses to light, as well as in the relation between light and bacterial infection, would not only enlarge our understanding of bacterial pathogenesis but also could potentially provide alternative treatment options for infectious illnesses.

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We have previously shown that Acinetobacter baumannii as well as other relevant clinical bacterial pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa, perceive and respond to light at 37 °C, the normal temperature in mammal hosts. In this work, we present evidence indicating that the two-component system BfmRS transduces a light signal in A. baumannii at this temperature, showing selective involvement of the BfmR and BfmS components depending on the specific cellular process. In fact, both BfmR and BfmS participate in modulation of motility by light, while only BfmR is involved in light regulation of desiccation tolerance in this microorganism. Neither BfmR nor BfmS contain a photoreceptor domain and then most likely, the system is sensing light indirectly. Intriguingly, this system inhibits blsA expression at 37 °C, suggesting antagonistic functioning of both signaling systems. Furthermore, we present evidence indicating that the phosphorylatable form of BfmR represses motility. Overall, we provide experimental evidence on a new biological function of this multifaceted system that broadens our understanding of A. baumannii's physiology and responses to light.

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Acinetobacter nosocomialis is a Gram-negative opportunistic pathogen, whose ability to cause disease in humans is well recognized. Blue light has been shown to modulate important physiological traits related to persistence and virulence in this microorganism. In this work, we characterized the three Blue Light sensing Using FAD (BLUF) domain-containing proteins encoded in the A. nosocomialis genome, which account for the only canonical light sensors present in this microorganism. By focusing on a light-modulated bacterial process such as motility, the temperature dependence of light regulation was studied, as well as the expression pattern and spectroscopic characteristics of the different A. nosocomialis BLUFs. Our results show that the BLUF-containing proteins AnBLUF65 and AnBLUF46 encode active photoreceptors in the light-regulatory temperature range when expressed recombinantly. In fact, AnBLUF65 is an active photoreceptor in the temperature range from 15°C to 37°C, while AnBLUF46 between 15°C to 32°C, in vitro. In vivo, only the Acinetobacter baumannii BlsA's ortholog AnBLUF65 was expressed in A. nosocomialis cells recovered from motility plates. Moreover, complementation assays showed that AnBLUF65 is able to mediate light regulation of motility in A. baumannii ΔblsA strain at 30°C, confirming its role as photoreceptor and in modulation of motility by light. Intra-protein interactions analyzed using 3D models built based on A. baumannii´s BlsA photoreceptor, show that hydrophobic/aromatic intra-protein interactions may contribute to the stability of dark/light- adapted states of the studied proteins, reinforcing the previous notion on the importance of these interactions in BLUF photoreceptors. Overall, the results presented here reveal the presence of BLUF photoreceptors in A. nosocomialis with idiosyncratic characteristics respect to the previously characterized A. baumannii's BlsA, both regarding the photoactivity temperature-dependency as well as expression patterns, contributing thus to broaden our knowledge on the BLUF family.

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The redox reaction between an excess of quinic acid (QA) and CrVI involves the formation of intermediates, namely, CrIV and CrV species, which in turn react with the organic substrates. As observed with other substrates that have already been studied, CrIV does not accumulate during this reaction because of the rate of the reaction. Its rate of disappearance is several times higher than that of the reaction of CrVI or CrV with QA. Kinetic studies indicate that the redox reaction proceeds via a combined mechanism that involves the pathways CrVI → CrIV → CrII and CrVI → CrIV → CrIII, which is supported by the observation of superoxo-CrIII (CrO2 2+) ions, free radicals, and oxo-CrV species as intermediates and the detection of CrVI ester species. The present study reports the complete rate laws for the QA/chromium redox reaction.