Testing the limits of biological tolerance to arsenic in a fungus isolated from the River Tinto

The Tinto river in Spain, with its high acidity and heavy metal concentrations (As, Cu, Cr, Zn), is an example of an environment hostile to life. Yet despite these extreme conditions, the site possesses a great diversity of eukaryotic life forms. We report the isolation of a filamentous fungus able to grow at 200 mM arsenic ( approximately 15 000 p.p.m.), i.e. a concentration 20-fold above that withstood by the reference microorganisms Escherichia coli, Saccharomyces cerevisiae and Aspergillus nidulans, and 200 times greater than that tolerated by Aspergillus niger. Based on morphological, physiological and genotypic criteria, the strain belongs to the genus Aspergillus. High concentrations of the metalloid induced vacuolation, suggesting that this organelle is someway connected to arsenic tolerance. Concentrations that are lethal to other organisms do not stress Aspergillus sp. P37. The fungus was capable of removing arsenic from culture media. In addition to arsenic hyper-resistance, it also displayed a polyresistant phenotype to copper and chromium.     

A numeric study of the noise-induced tremor in a mathematical model of the stretch reflex

A mathematical model of the stretch reflex for the cat soleus muscle is presented. The time-delay differential equations of the model are solved using the fourth-order Runge-Kutta algorithm, introducing a Gaussian-noise term to simulate the environmental noise. The muscle response dynamics are then studied under various levels of average muscle activation. Finally, the feasibility of explaining the so-called physiological tremor from the properties of the stretch reflex mechanisms is discussed by comparing our results with reported experimental evidence.     

Reverse-flow island sural flap

The reverse flow island sural flap is presented as an alternative to flaps currently used for reconstruction of small and medium substance losses in the distal third of the leg, ankle, and heel. This is a random type of flap, based on the reverse flow of the superficial sural artery, which mainly depends on the anatomy of the perforators of the peroneal artery system.The anatomic structures that constitute the pedicle are the superficial and deep fascias, the sural nerve, the short saphenous vein, and the superficial sural artery. The skin island and the subcutaneous cellular tissue complement the flap proper. This skin island was demarcated at any point of the median or distal thirds of the leg, having the short saphenous vein and the sural nerve on its central axis. The distal dissection limit of the pedicle is located 5 centimeters above the lateral malleolus. This limit is established so as to ensure the integrity of the perforators from the principal arteries of the leg, mainly the peroneal artery, responsible for the reverse flow nourishing the flap. These perforators will affect anastomoses with the superficial sural artery in charge of irrigating the structures compounding the flap.A total of 71 patients were operated on with this technique, some of them with basic pathologic abnormalities limiting the distal blood flow, such as diabetes mellitus, and some others having proven vascular insufficiency or displaying unstable areas attributable to problems such as pseudarthrosis and osteomyelitis, which needed to be covered. Fifteen flaps (21.1 percent) suffered partial necrosis, which did not compromise the final result, and another three (4.2 percent) showed total loss. The flap in question has great mobility and versatility, allowing the treatment of specific areas of the lower limb, without sacrificing important arteries or mobilizing structures that might bring about functional deficits.