Tyrosine Nitration of Flagellins: a Response of Sinorhizobium meliloti to Nitrosative Stress.

Rhizobia are bacteria which can either live as free organisms in the soil or interact with plants of the legume family with, as a result, the formation of root organs called nodules in which differentiated endosymbiotic bacteria fix atmospheric nitrogen to the plant's benefit. In both lifestyles, rhizobia are exposed to nitric oxide (NO) which can be perceived as a signaling or toxic molecule. NO can act at the transcriptional level but can also modify proteins by S-nitrosylation of cysteine or nitration of tyrosine residues. However, only a few molecular targets of NO have been described in bacteria and none of them have been characterized in rhizobia. Here, we examined tyrosine nitration of Sinorhizobium meliloti proteins induced by NO. We found three tyrosine-nitrated proteins in S. meliloti grown under free-living conditions, in response to an NO donor. Two nitroproteins were identified by mass spectrometry and correspond to flagellins A and B. We showed that one of the nitratable tyrosines is essential to flagellin function in motility.IMPORTANCE Rhizobia are found as free-living bacteria in the soil or in interaction with plants and are exposed to nitric oxide (NO) in both environments. NO is known to have many effects on animals, plants, and bacteria where only a few molecular targets of NO have been described so far. We identified flagellin A and B by mass spectrometry as tyrosine-nitrated proteins in Sinorhizobium melilotiin vivo We also showed that one of the nitratable tyrosines is essential to flagellin function in motility. The results enhanced our understanding of NO effects on rhizobia. Identification of bacterial flagellin nitration opens a new possible role of NO in plant-microbe interactions.

Sinorhizobium meliloti Controls Nitric Oxide-Mediated Post-Translational Modification of a Medicago truncatula Nodule Protein.

Nitric oxide (NO) is involved in various plant-microbe interactions. In the symbiosis between soil bacterium Sinorhizobium meliloti and model legume Medicago truncatula, NO is required for an optimal establishment of the interaction but is also a signal for nodule senescence. Little is known about the molecular mechanisms responsible for NO effects in the legume-rhizobium interaction. Here, we investigate the contribution of the bacterial NO response to the modulation of a plant protein post-translational modification in nitrogen-fixing nodules. We made use of different bacterial mutants to finely modulate NO levels inside M. truncatula root nodules and to examine the consequence on tyrosine nitration of the plant glutamine synthetase, a protein responsible for assimilation of the ammonia released by nitrogen fixation. Our results reveal that S. meliloti possesses several proteins that limit inactivation of plant enzyme activity via NO-mediated post-translational modifications. This is the first demonstration that rhizobia can impact the course of nitrogen fixation by modulating the activity of a plant protein.

Evaluation of the cost and length of hospital stays related to the management of an intestinal Clostridium difficile infection.

INTRODUCTION: Intestinal Clostridium difficile Infection (CDI) treated in hospitals may concern patients whose reason for admission is CDI (primary diagnosis) or who have acquired CDI during their stay (secondary diagnosis). OBJECTIVES: The objective of this study is to evaluate the cost for social security and hospitals and the length of hospital stays related to CDIs as the main reason for admission. METHOD: This study was carried out in 2012 in 13 Belgian hospitals. Cases were selected by using diagnosis recorded in minimum discharge summaries. Pediatric stays are not part of the inclusion criteria (n= 86). RESULTS: The average length of stay (standard deviation) was 13.53 days (11.95). The average cost (standard deviation) covered by social security/hospitals was €5,019.51 / €6,286.39 (9,638.42/ 6,368.45). 7% of patients were admitted to the Intensive Care Unit during hospitalization, for an average duration (standard deviation) of 8.18 days (2.93). The mortality rate was 8.1%. 19.8% of patients used vancomycin during the stay, 43% were treated with metronidazole only, 12.8% used vancomycin and metronidazole and 24.4% do not received vancomycin or metronidazole. No patients received fidaxomycin. CONCLUSION: This study made it possible to approach the cost of CDI as the main reason for admission. Such data should allow contributing to optimally assess both the pharmacoeconomic impact of the implementation of prevention strategies and also therapeutic management making use of more expensive medicinal products but associated with decreased risk of recurrence.

Control of NO level in rhizobium-legume root nodules: not only a plant globin story.

Nitric oxide (NO ) is a gaseous signaling molecule which plays both regulatory and defense roles in animals and plants. In the symbiosis between legumes and rhizobia, NO has been shown to be involved in bacterial infection and nodule development steps as well as in mature nodule functioning. We recently showed that an increase in NO level inside Medicago truncatula root nodules also could trigger premature nodule senescence. Here we discuss the importance of the bacterial Sinorhizobium meliloti flavohemoglobin to finely tune the NO level inside nodules and further, we demonstrate that S. meliloti possesses at least two non redundant ways to control NO and that both systems are necessary to maintain efficient nitrogen fixing activity.