Redox-mediated quorum sensing in plants.

The rhizosphere, the narrow zone of soil around plant roots, is a complex network of interactions between plants, bacteria, and a variety of other organisms. The absolute dependence on host-derived signals, or xenognosins, to regulate critical developmental checkpoints for host commitment in the obligate parasitic plants provides a window into the rhizosphere's chemical dynamics. These sessile intruders use H2O2 in a process known as semagenesis to chemically modify the mature root surfaces of proximal host plants and generate p-benzoquinones (BQs). The resulting redox-active signaling network regulates the spatial and temporal commitments necessary for host attachment. Recent evidence from non-parasites, including Arabidopsis thaliana, establishes that reactive oxygen species (ROS) production regulates similar redox circuits related to root recognition, broadening xenognosins' role beyond the parasites. Here we compare responses to the xenognosin dimethoxybenzoquinone (DMBQ) between the parasitic plant Striga asiatica and the non-parasitic A. thaliana. Exposure to DMBQ simulates the proximity of a mature root surface, stimulating an increase in cytoplasmic Ca2+ concentration in both plants, but leads to remarkably different phenotypic responses in the parasite and non-parasite. In S. asiatica, DMBQ induces development of the host attachment organ, the haustorium, and decreases ROS production at the root tip, while in A. thaliana, ROS production increases and further growth of the root tip is arrested. Obstruction of Ca2+ channels and the addition of antioxidants both lead to a decrease in the DMBQ response in both parasitic and non-parasitic plants. These results are consistent with Ca2+ regulating the activity of NADPH oxidases, which in turn sustain the autocatalytic production of ROS via an external quinone/hydroquinone redox cycle. Mechanistically, this chemistry is similar to black and white photography with the emerging dynamic reaction-diffusion network laying the foundation for the precise temporal and spatial control underlying rhizosphere architecture.

Interkingdom Responses to Bacterial Quorum Sensing Signals Regulate Frequency and Rate of Nodulation in Legume-Rhizobia Symbiosis.

Density-dependent phenotypic switching in bacteria, the phenomenon of quorum sensing (QS), is instrumental in many pathogenic and mutualistic behaviors. In many Gram-negative bacteria, QS is regulated by N-acylated-l-homoserine lactones (AHLs). Synthetic analogues of these AHLs hold significant promise for regulating QS at the host-symbiont interface. Regulation depends on refined temporal and spatial models of quorums under native conditions. Critical to this is an understanding of how the presence of these signals may affect a prospective host. We screened a library of AHL analogues for their ability to regulate the legume-rhizobia mutualistic symbiosis (nodulation) between Medicago truncatula and Sinorhizobium meliloti. Using an established QS-reporter line of S. meliloti and nodulation assays with wild-type bacteria, we identified compounds capable of increasing either the rate of nodule formation or total nodule number. Most importantly, we identified compounds with activity exclusive to either host or pathogen, underscoring the potential to generate QS modulators selective to bacteria with limited effects on a prospective host.

Rhinocerebral Mucor circinelloides infection in immunocompromised patient following yogurt ingestion.

The purpose of this case report is to illustrate the cause of this patient's headache and sinus pain in the setting of a unique environmental exposure: the patient ingested yogurt only days before presentation. This particular brand of yogurt caused controversy in early September 2013 when the manufacturer voluntarily recalled all flavors. The yogurt was found to be contaminated with Mucor circinelloides. The recall was triggered by the FDA, after receiving many complaints from consumers affected by temporary gastrointestinal symptoms such as abdominal cramping, diarrhea, and nausea. This patient was diagnosed with Rhinocerebral mucormycosis through fungal culture of the affected area. He was specifically colonized with Mucor circinelloides, a variant that rarely causes disease in humans. According to a literature review, only eight cases of mucormycosis in adults caused by this strain were documented before 2009.

Otalgia associated with migraine.

OBJECTIVE: To investigate the association of otalgia and migraine. STUDY DESIGN: Retrospective survey with evaluation of otalgia response to migraine treatment. Only patients with minimum symptom duration of 3 months, who accepted migraine treatment and had a minimum follow-up of 3 months, were included. SETTING: Single neurotology practice. SUBJECTS: All patients with otalgia in whom other causes of otalgia had been excluded and who were treated with migraine therapies. INTERVENTION: Standard first-line abortive and prophylactic migraine therapies. MAIN OUTCOME MEASURES: Specific clinical data, as well as pretreatment and posttreatment severity scores, were gathered. Response to treatment was assessed by comparing pretreatment and posttreatment symptom scores using paired t test. RESULTS: A total of 26 patients were included. Ninety-two percent responded to migraine therapy with improved symptom frequency, severity, and duration (p < 0.001). Median duration of symptoms was 5 years. Mean delay to response was 2.3 weeks, and mean follow-up was 20 months. Otalgia was the chief complaint in 77%. Pain was dull in 35%, sharp in 19%, throbbing in 19%, and mixed in 27%. Sixty-five percent demonstrated triggerability of otalgia. A total of 65% had International Headache Society migraine. Patients responded to many classes of migraine preventive and abortive medications. CONCLUSION: Otalgia of unclear cause can be related to migraine mechanisms. Our group showed a high prevalence of migraine characteristics, including headache, migraine-associated symptoms, patterns of triggerability, and response to migraine treatment. Clinical criteria for diagnosis of migraine-associated otalgia are suggested for future prospective study.