Natural Occurring Terpene Cyclic Anhydrides: Biosynthetic Origin and Biological Activities.

Cyclic acid anhydride is a not very widespread structure in nature, but with a determining role in natural products possessing this functionality in their skeleton. To the best of our knowledge, no revision of terpenes containing cyclic anhydrides has been previously reported. The result was that more than 100 terpenic cyclic anhydrides and related compounds were found to be in need of being reported. This review has been systematically organized by terpene skeletons, from the smallest to largest, describing their sources and bioactivities. In addition, different biosynthetic pathways for their final oxidations, namely, routes A, B and C, leading to the formation of these heterocyclic natural products, have been proposed. We have also included the most plausible precursors of these natural products, which mostly happened to be present in the same natural source. Some molecules derived from terpene cyclic anhydrides, such as their natural imide derivatives, have also been described due to their significant biological activity. In this sense, special attention has been paid to cantharidin because of its historical relevance and its broad bioactivity. A plausible biosynthesis of cantharidin has been proposed for the first time. Finally, cyclic anhydride structures that were firstly assigned as anhydrides and later corrected have been also described.

Point-of-Care Ultrasonography to Confirm Endotracheal Tube Placement: A Review for the Emergency Nurse Practitioner.

Ensuring correct placement of the endotracheal tube (ETT) during intubation is an important step to avoid complications. Appropriate placement of the ETT can be challenging and, if done incorrectly, can lead to complications such as hypoxemia, atelectasis, hyperinflation, barotrauma, cardiovascular instability, end organ damage, and even death. Although several procedures exist to help assess ETT confirmation, all have limitations, are not always reliable, and vary in their degree of accuracy. Point-of-care ultrasound (POCUS) has emerged as a useful tool in the emergency department for quick diagnosis and treatment of many emergency conditions (Gonzalez et al., 2020). The purpose of this paper is to describe a systematic approach for the emergency nurse practitioner to use POCUS to assess proper endotracheal placement and the positioning within the trachea based on prior studies that compare this modality to traditional ones.

Deep Learning Applications for Acute Stroke Management.

Brain imaging is essential to the clinical care of patients with stroke, a leading cause of disability and death worldwide. Whereas advanced neuroimaging techniques offer opportunities for aiding acute stroke management, several factors, including time delays, inter-clinician variability, and lack of systemic conglomeration of clinical information, hinder their maximal utility. Recent advances in deep machine learning (DL) offer new strategies for harnessing computational medical image analysis to inform decision making in acute stroke. We examine the current state of the field for DL models in stroke triage. First, we provide a brief, clinical practice-focused primer on DL. Next, we examine real-world examples of DL applications in pixel-wise labeling, volumetric lesion segmentation, stroke detection, and prediction of tissue fate postintervention. We evaluate recent deployments of deep neural networks and their ability to automatically select relevant clinical features for acute decision making, reduce inter-rater variability, and boost reliability in rapid neuroimaging assessments, and integrate neuroimaging with electronic medical record (EMR) data in order to support clinicians in routine and triage stroke management. Ultimately, we aim to provide a framework for critically evaluating existing automated approaches, thus equipping clinicians with the ability to understand and potentially apply DL approaches in order to address challenges in clinical practice. ANN NEUROL 2022;92:574-587.

Asthma academy: A student nurse-led telehealth education program for low-income family caregivers of children with asthma.

AIMS: The aims of the Asthma Academy study were to (1) evaluate the telehealth performance of DNP students, (2) evaluate the perceived learning experience of DNP students and (3) investigate whether an association exists related to student performance and family caregiver outcomes. DESIGN: A descriptive study was conducted with doctor of nursing practice students. METHODS: Students conducted telehealth visits to help family caregivers of children with asthma and were rated on their performance by two faculty members using a rubric. Student perception data were gathered via survey. RESULTS: Out of a total possible score of 15 points, the mean telehealth performance score of students was 13.38 points. Students indicated the telehealth experience was valuable and that they were satisfied with their learning. This model of leveraging telehealth to bridge nursing students to the community may be adapted to help family caregivers of children with various disease foci.

Improving knowledge and decreasing depressive symptoms in caregivers of children with asthma through the asthma academy: A randomized controlled trial.

Background: Caregivers of children with asthma demonstrate higher levels of anxious and depressive symptoms when compared to caregivers of healthy children. Objectives: The objectives of this study were to: 1) Evaluate feasibility and acceptability of two nurse-led, remotely offered interventions for caregivers of children with asthma; 2) Compare effectiveness of two interventions (a virtual education session and a virtual education session supplemented with a telehealth visit) in relation to caregiver outcomes, and 3) Assess the preliminary effect of the interventions on caregivers' knowledge of asthma, sleep, anxiety and depressive symptoms. Methods: A mixed methods approach was used inclusive of a qualitative, descriptive design and randomized controlled trial design. Caregivers were provided virtual education and telehealth visits and evaluated from pre-posttest. Results: The intervention was found to be feasible and acceptable. Both the virtual education session and telehealth visit were effective. The intervention had a significant effect on caregiver's asthma knowledge and depressive symptoms (p<.05), but did not affect caregiver's sleep or anxiety. Qualitative analysis of the virtual educational session revealed themes of 1) valuable learning experience, 2) more medication education needed, and 3) appreciated remote format. Qualitative analysis of the telehealth visits revealed themes of 1) educational, helpful, and worthwhile and 2) virtual offering was easy and convenient. Conclusions: Remotely conducted, nurse-led interventions such as virtual education sessions and telehealth visits are a feasible, acceptable, and effective way to improve caregiver outcomes.

Oxidative Degradation of Polypropylene Mesh in E. coli Environment.

Medical implants of polypropylene (PP) are commonly used in many surgical procedures to support tissues. Previous studies on polypropylene meshes removed from patients demonstrated biodegradation relative to the amount of time after implantation. Among the many possible factors, bacterial colonization is believed to be one of the causes for the biodegradation of PP. To gain insights on this hypothesis, PP mesh samples were tested in Luria-Bertani broth (LB) media containing Escherichia coli (E. coli) to observe possible degradation in a controlled single-organism environment. Mesh samples were immersed in either an LB media with E. coli or a control solution, and the biodegradation was measured at 1-, 2-, and 3-month intervals. The samples were then harvested from both LB media with E. coli and the control media for analysis, and results were then compared with pristine polypropylene mesh. The experimental results demonstrate qualitative and quantitative bioerosion, increased oxygen content, and enhanced hydrophilicity over the surface of the mesh structure, thus confirming the oxidative degradation in vitro.

Mentored Training to Increase Diversity among Faculty in the Biomedical Sciences: The NHLBI Summer Institute Programs to Increase Diversity (SIPID) and the Programs to Increase Diversity among Individuals Engaged in Health-related Research (PRIDE).

OBJECTIVE: To report baseline characteristics of junior-level faculty participants in the Summer Institute Programs to Increase Diversity (SIPID) and the Programs to Increase Diversity among individuals engaged in Health-Related Research (PRIDE), which aim to facilitate participants' career development as independent investigators in heart, lung, blood, and sleep research. DESIGN AND SETTING: Junior faculty from groups underrepresented in the biomedical-research workforce attended two, 2-3 week, annual summer research-education programs at one of six sites. Programs provided didactic and/or laboratory courses, workshops to develop research, writing and career-development skills, as well as a mentoring component, with regular contact maintained via phone, email and webinar conferences. Between summer institutes, trainees participated in a short mid-year meeting and an annual scientific meeting. Participants were surveyed during and after SIPID/PRIDE to evaluate program components. PARTICIPANTS: Junior faculty from underrepresented populations across the United States and Puerto Rico participated in one of three SIPID (2007-2010) or six PRIDE programs (2011-2014). RESULTS: Of 204 SIPID/PRIDE participants, 68% were female; 67% African American and 27% Hispanic/Latino; at enrollment, 75% were assistant professors and 15% instructors, with most (96%) on non-tenure track. Fifty-eight percent had research doctorates (PhD, ScD) and 42% had medical (MD, DO) degrees. Mentees' feedback about the program indicated skills development (eg, manuscript and grant writing), access to networking, and mentoring were the most beneficial elements of SIPID and PRIDE programs. Grant awards shifted from primarily mentored research mechanisms to primarily independent investigator awards after training. CONCLUSIONS: Mentees reported their career development benefited from SIPID and PRIDE participation.

A Perspective on Promoting Diversity in the Biomedical Research Workforce: The National Heart, Lung, and Blood Institute's PRIDE Program.

Aspiring junior investigators from groups underrepresented in the biomedical sciences face various challenges as they pursue research independence. However, the biomedical research enterprise needs their participation to effectively address critical research issues such as health disparities and health inequities. In this article, we share a research education and mentoring initiative that seeks to address this challenge: Programs to Increase Diversity among Individuals Engaged in Health Related Research (PRIDE), funded by the National Heart, Lung, and Blood Institute (NHLBI). This longitudinal research-education and mentoring program occurs through summer institute programs located at US-based academic institutions. Recruited participants are exposed to didactic and lab-based research-skill enhancement experiences, with year-round mentoring over the course of two years. Mentor-mentee matching is based on shared research interests to promote congruence and to enhance skill acquisition. Program descriptions and sample narratives of participants' perceptions of PRIDE's impact on their career progress are showcased. Additionally, we highlight the overall program design and structure of four of seven funded summer institutes that focus on cardiovascular disease, related conditions, and health disparities. Mentees' testimonials about the value of the PRIDE mentoring approach in facilitating career development are also noted. Meeting the clinical and research needs of an increasingly diverse US population is an issue of national concern. The PRIDE initiative, which focuses on increasing research preparedness and professional development of groups underrepresented in the biomedical research workforce, with an emphasis on mentoring as the critical approach, provides a robust model that is impacting the careers of future investigators.

Exopolysaccharide production in response to medium acidification is correlated with an increase in competition for nodule occupancy.

Sinorhizobium meliloti strains unable to utilize galactose as a sole carbon source, due to mutations in the De-Ley Doudoroff pathway (dgoK), were previously shown to be more competitive for nodule occupancy. In this work, we show that strains carrying this mutation have galactose-dependent exopolysaccharide (EPS) phenotypes that were manifested as aberrant Calcofluor staining as well as decreased mucoidy when in an expR(+) genetic background. The aberrant Calcofluor staining was correlated with changes in the pH of the growth medium. Strains carrying dgoK mutations were subsequently demonstrated to show earlier acidification of their growth medium that was correlated with an increase expression of genes associated with succinoglycan biosynthesis as well as increased accumulation of high and low molecular weight EPS in the medium. In addition, it was shown that the acidification of the medium was dependent on the inability of S. meliloti strains to initiate the catabolism of galactose. To more fully understand why strains carrying the dgoK allele were more competitive for nodule occupancy, early nodulation phenotypes were investigated. It was found that strains carrying the dgoK allele had a faster rate of nodulation. In addition, nodule competition experiments using genetic backgrounds unable to synthesize either succinoglycan or EPSII were consistent with the hypothesis that the increased competition phenotype was dependent upon the synthesis of succinoglycan. Fluorescent microscopy experiments on infected root-hair cells, using the acidotropic dye Lysotracker Red DND-99, provide evidence that the colonized curled root hair is an acidic compartment.

Metabolite profiling of Schizochytrium sp. by GC-MS, an oleaginous microbial source of biodiesel.

The chemical screening carried out on Schizochytrium sp. biomass led the identification of 24 types of organic compounds belonging to n-alkanes, 1-alkenes, 1-alkanols, free fatty acids, methyl and ethyl esters of saturated and unsaturated fatty acids, saturated tri- and diglycerides, unsaturated monoglycerides, wax esters, sterols, triterpenes, and mono- and sesquiterpenes. Moreover, a sample containing fully saturated ethyl biodiesel was obtained experimentally with a yield of 28.72% w/w of the crude extract, and an average chain length of 15.52 carbons. This strain produced no toxins, but showed important nutrients, making it potentially applicable to the field of functional food, and biodiesel production.

Metabolite profiling of Schizochytrium sp. by GC-MS, an oleaginous microbial source of biodiesel

The chemical screening carried out on Schizochytrium sp. biomass led the identification of 24 types of organic compounds belonging to n-alkanes, 1-alkenes, 1-alkanols, free fatty acids, methyl and ethyl esters of saturated and unsaturated fatty acids, saturated tri- and diglycerides, unsaturated monoglycerides, wax esters, sterols, triterpenes, and mono- and sesquiterpenes. Moreover, a sample containing fully saturated ethyl biodiesel was obtained experimentally with a yield of 28.72% w/w of the crude extract, and an average chain length of 15.52 carbons. This strain produced no toxins, but showed important nutrients, making it potentially applicable to the field of functional food, and biodiesel production.

Objective Structured Clinical Examination as an educational initiative for summative simulation competency evaluation of first-year student registered nurse anesthetists' clinical skills.

The use of simulation to imitate real-life scenarios reaches back many centuries. In the last decade, the use of simulation in healthcare has gained acceptance as a valuable tool for teaching and learning technical and nontechnical skills in healthcare. The use of simulation technology has moved medical education from the standard of pen and paper examinations to the assessment of clinical competency before caring for patients. The old thinking of "see one, do one, teach one" is behind us as healthcare works to create a culture of safety that holds healthcare personnel accountable. A current use of testing clinical competence is the use of Objective Structured Clinical Examination (OSCE) by physician training programs. As a testing tool, the OSCE has great potential to assess the clinical competence of students before they enter the clinical setting. The nurse anesthesia program at the authors' university has moved toward creating a formal assessment to ensure clinical competence of their student registered nurse anesthetists. In this article, we describe the development and implementation of an OSCE to ensure clinical competence of first-year student registered nurse anesthetists before they begin their clinical training.

Determinants of blood lead levels in children: a cross-sectional study in the Canary Islands (Spain).

The adverse effects of lead exposure on children are well known. Low blood lead levels (BLL) produce neurodevelopmental delay and cognitive disorders. However, since BLL thresholds for adverse effects on children's health are not known, the children population at risk of excessive lead exposure still has to be identified. This study was aimed at evaluating BLL in a children population of Gran Canaria (Canary Islands, Spain). Up to our knowledge, this is the first study to report on BLL in this population. Lead was identified and quantified in blood samples of 120 children, by means of Graphite furnace atomic absorption spectrometry (GFAAS). Lead was undetected in 80% of samples; BLL was 1 to 5 µg/dl in 15% of samples, and higher than 5 µg/dl in more than 4% of samples. BLL values in the evaluated children were low and similar to those described for other populations in Western countries. However, samples with the highest contamination (those in percentile 95) reached BLLs as high as 5.2 µg/dl. Positive associations were found between BLL and recent immigration (children adopted from non-western countries), and between BLL and parental smoking in children with low weight at birth. Since lead exposure in childhood may be a causative factor in adverse health trends - especially those involving the neurological system - and since threshold values for adverse lead effects are unknown, our finding that around 20% of the studied children had BLL higher than 1 µg/dl are of concern. Enhancing preventive measures for reducing lead exposure in children from the Canary Islands deserves further study.

Complex regulation of symbiotic functions is coordinated by MucR and quorum sensing in Sinorhizobium meliloti.

In Sinorhizobium meliloti, the production of exopolysaccharides such as succinoglycan and exopolysaccharide II (EPS II) enables the bacterium to invade root nodules on Medicago sativa and establish a nitrogen-fixing symbiosis. While extensive research has focused on succinoglycan, less is known concerning the regulation of EPS II or the mechanism by which it mediates entrance into the host plant. Previously, we reported that the ExpR/Sin quorum-sensing system is required to produce the symbiotically active low-molecular-weight fraction of this exopolysaccharide. Here, we show that this system induces EPS II production by increasing expression of the expG-expC operon, encoding both a transcriptional regulator (ExpG) and a glycosyl transferase (ExpC). ExpG derepresses EPS II production at the transcriptional level from MucR, a RosR homolog, while concurrently elevating expression of expC, resulting in the synthesis of the low-molecular-weight form. While the ExpR/Sin system abolishes the role of MucR on EPS II production, it preserves a multitude of other quorum-sensing-independent regulatory functions which promote the establishment of symbiosis. In planktonic S. meliloti, MucR properly coordinates a diverse set of bacterial behaviors by repressing a variety of genes intended for expression during symbiosis and enhancing the bacterial ability to induce root nodule formation. Quorum sensing precisely modulates the functions of MucR to take advantage of both the production of symbiotically active EPS II as well as the proper coordination of bacterial behavior required to promote symbiosis.

Efecto inhibidor del aceite de trementina sobre el desarrollo de larvas de Aedes aegypti (Diptera: Culicidae) / Inhibitory effect of turpentine oil on Aedes aegypti (Diptera: Culicidae) larvae growth

INTRODUCCIÓN: en la lucha por la protección del medio ambiente es de vital importancia encontrar formas alternativas de control para el combate de insectos vectores de importancia médica. Una fuente de ello lo constituyen las plantas que posean principios activos potentes y con alta estabilidad química con acción insecticida. OBJETIVO: evaluar la posible existencia de un efecto inhibidor del desarrollo en larvas de Aedes aegypti de un aceite de trementina modificado fotoquímicamente. MÉTODOS: se utilizaron larvas de Ae. aegypti de una cepa susceptible a insecticida criada en el insectario del Instituto de Medicina Tropical. Diariamente durante una semana después de la exposición a la concentración letal que provoca 90 por ciento de mortalidad se contó la mortalidad de larvas y pupas, la cantidad de adultos emergidos y su sexo, además de los adultos que quedaban adheridos a las exuvias. RESULTADOS: se observó una alta mortalidad larval y pupal en los sobrevivientes a la concentración letal que provoca 90 por ciento de mortalidad una semana después a la exposición, se alcanzó 39,46 por ciento de mortalidad. Las larvas que completaron su desarrollo hasta adultos correspondieron a 60,54 por ciento del total de larvas sobrevivientes. La proporción de hembras y machos en el control se comportó de forma muy similar, mientras que en los expuestos se obtuvo un número mayor de machos que de hembras. Al calcular el porcentaje de inhibición de la eclosión, este resultó 36,47 por ciento. CONCLUSIONES: se demostró la actividad del aceite de trementina como larvicida e inhibidor del crecimiento en Ae. aegypti.

INTRODUCTION: in the fight for environmental protection, finding out alternative ways to control vectors that are important from the medical viewpoint is a must. Those plants having potent active principles and high chemical stability to act as pesticides can contribute to this end. OBJECTIVE: to evaluate the possible inhibitory effect of photochemically-modified turpentine oil on Aedes aegypti larvae growth. METHODS: Aedes aegypti larvae of an insecticide-sensitive strain from the insect breeding site located in the Institute of Tropical Medicine were used. During a week after the exposure to the lethal dose causing 90 percent mortality, the mortality indexes of larvae and pupas were recorded as well as the number of emerged adults and their sex in addition to adults stuck to the exuvias. RESULTS: high larval and pupal mortality was observed in the survivors to the lethal dose causing 90 percent mortality after one week of the exposure; mortality index was 39,46 percent. Larvae which managed to grow to become adults amounted to 60,54 percent of the surviving larvae. Female to male ratio was very similar in the control whereas the exposed group showed a higher number of male adults. On estimating the hatching inhibition percentage, it got 36,47 percent. CONCLUSIONS: the activity of turpentine oil as larvicide and Ae. aegypti growth inhibitor was demonstrated.

Chemical sensing in mammalian host-bacterial commensal associations.

The mammalian gastrointestinal (GI) tract is colonized by a complex consortium of bacterial species. Bacteria engage in chemical signaling to coordinate population-wide behavior. However, it is unclear if chemical sensing plays a role in establishing mammalian host-bacterial commensal relationships. Enterohemorrhagic Escherichia coli (EHEC) is a deadly human pathogen but is a member of the GI flora in cattle, its main reservoir. EHEC harbors SdiA, a regulator that senses acyl-homoserine lactones (AHLs) produced by other bacteria. Here, we show that SdiA is necessary for EHEC colonization of cattle and that AHLs are prominent within the bovine rumen but absent in other areas of the GI tract. We also assessed the rumen metagenome of heifers, and we show that it is dominated by Clostridia and/or Bacilli but also harbors Bacteroidetes. Of note, some members of the Bacteroidetes phyla have been previously reported to produce AHLs. SdiA-AHL chemical signaling aids EHEC in gauging these GI environments, and promotes adaptation to a commensal lifestyle. We show that chemical sensing in the mammalian GI tract determines the niche specificity for colonization by a commensal bacterium of its natural animal reservoir. Chemical sensing may be a general mechanism used by commensal bacteria to sense and adapt to their mammalian hosts. Additionally, because EHEC is largely prevalent in cattle herds, interference with SdiA-mediated cattle colonization is an exciting alternative to diminish contamination of meat products and cross-contamination of produce crops because of cattle shedding of this human pathogen.

[Inhibitory effect of turpentine oil on Aedes aegypti (Diptera:Culicidae) larvae growth]. / Efecto inhibidor del aceite de trementina sobre el desarrollo de larvas de Aedes aegypti (Diptera: Culicidae).

INTRODUCTION: in the fight for environmental protection, finding out alternative ways to control vectors that are important from the medical viewpoint is a must. Those plants having potent active principles and high chemical stability to act as pesticides can contribute to this end. OBJECTIVE: to evaluate the possible inhibitory effect of photochemically-modified turpentine oil on Aedes aegypti larvae growth. METHODS: Aedes aegypti larvae of an insecticide-sensitive strain from the insect breeding site located in the Institute of Tropical Medicine were used. During a week after the exposure to the lethal dose causing 90% mortality, the mortality indexes of larvae and pupas were recorded as well as the number of emerged adults and their sex in addition to adults stuck to the exuvias. RESULTS: high larval and pupal mortality was observed in the survivors to the lethal dose causing 90% mortality after one week of the exposure; mortality index was 39.46%. Larvae which managed to grow to become adults amounted to 60.54% of the surviving larvae. Female to male ratio was very similar in the control whereas the exposed group showed a higher number of male adults. On estimating the hatching inhibition percentage, it got 36.47%. CONCLUSIONS: the activity of turpentine oil as larvicide and Ae. aegypti growth inhibitor was demonstrated.

The low-molecular-weight fraction of exopolysaccharide II from Sinorhizobium meliloti is a crucial determinant of biofilm formation.

Sinorhizobium meliloti is a soil bacterium that elicits the formation of root organs called nodules on its host plant, Medicago sativa. Inside these structures, the bacteria are able to convert atmospheric nitrogen into ammonia, which is then used by the plant as a nitrogen source. The synthesis by S. meliloti of at least one exopolysaccharide, succinoglycan or EPS II, is essential for a successful symbiosis. While exopolysaccharide-deficient mutants induce the formation of nodules, they fail to invade them, and as a result, no nitrogen fixation occurs. Interestingly, the low-molecular-weight fractions of these exopolysaccharides are the symbiotically active forms, and it has been suggested that they act as signals to the host plant to initiate infection thread formation. In this work, we explored the role of these rhizobial exopolysaccharides in biofilm formation and their importance in the symbiotic relationship with the host. We showed that the ExpR/Sin quorum-sensing system controls biofilm formation in S. meliloti through the production of EPS II, which provides the matrix for the development of structured and highly organized biofilms. Moreover, the presence of the low-molecular-weight fraction of EPS II is vital for biofilm formation, both in vitro and in vivo. This is the first report where the symbiotically active fraction of EPS II is shown to be a critical factor for biofilm formation and root colonization. Thus, the ability of S. meliloti to properly attach to root surfaces and form biofilms conferred by the synthesis of exopolysaccharides may embody the main function of these symbiotically essential molecules.

The novel genes emmABC are associated with exopolysaccharide production, motility, stress adaptation, and symbiosis in Sinorhizobium meliloti.

The nitrogen-fixing symbiont Sinorhizobium meliloti senses and responds to constantly changing environmental conditions as it makes its way through the soil in search of its leguminous plant host, Medicago sativa (alfalfa). As a result, this bacterium regulates various aspects of its physiology in order to respond appropriately to stress, starvation, and competition. For example, exopolysaccharide production, which has been shown to play an important role in the ability of S. meliloti to successfully invade its host, also helps the bacterium withstand osmotic changes and other environmental stresses. In an effort to further elucidate the intricate regulation of this important cell component, we set out to identify genetic factors that may affect its production. Here we characterize novel genes that encode a small protein (EmmA) and a putative two-component system (EmmB-EmmC). A mutation in any of these genes leads to increased production of the symbiotically important exopolysaccharide succinoglycan. In addition, emm mutants display membrane-associated defects, are nonmotile, and are unable to form an optimal symbiosis with alfalfa, suggesting that these novel genes may play a greater role in the overall fitness of S. meliloti both during the free-living stage and in its association with its host.

Role of quorum sensing in Sinorhizobium meliloti-Alfalfa symbiosis.

The ExpR/Sin quorum-sensing system of the gram-negative soil bacterium Sinorhizobium meliloti plays an important role in the establishment of symbiosis with its host plant Medicago sativa. A mutant unable to produce autoinducer signal molecules (sinI) is deficient in its ability to invade the host, but paradoxically, a strain lacking the quorum-sensing transcriptional regulator ExpR is as efficient as the wild type. We compared the whole-genome expression profile of the wild-type strain with strains missing one of the quorum-sensing regulatory components to identify genes controlled by the ExpR/Sin system throughout the different phases of the bacterial growth cycle, as well as in planta. Our analyses revealed that ExpR is a highly versatile regulator with a unique ability to show different regulatory capabilities in the presence or absence of an autoinducer. In addition, this study provided us with insight into the plant invasion defect displayed by the autoinducer mutant. We also discovered that the ExpR/Sin quorum-sensing system is repressed after plant invasion. Therefore, quorum sensing plays a crucial role in the regulation of many cell functions that ensures the successful invasion of the host and is inactivated once symbiosis is established.