Cooperation of two opposite flagella allows high-speed swimming and active turning in zoospores

Phytophthora species cause diseases in a large variety of plants and represent a serious agricultural threat, leading, every year, to multibillion dollar losses. Infection occurs when these biflagellated zoospores move across the soil at their characteristic high speed and reach the roots of a host plant. Despite the relevance of zoospore spreading in the epidemics of plant diseases, it is not known how these zoospores swim and steer with two opposite beating flagella. Here, combining experiments and modeling, we show how these two flagella contribute to generate thrust when beating together, and identify the mastigonemes-attached anterior flagellum as the main source of thrust. Furthermore, we find that steering involves a complex active process, in which the posterior flagellum is stopped, while the anterior flagellum keeps on beating, as the zoospore reorients its body. Our study is a fundamental step towards a better understanding of the spreading of plant pathogens’ motile forms, and shows that the motility pattern of these biflagellated zoospores represents a distinct eukaryotic version of the celebrated “run-and-tumble” motility class exhibited by peritrichous bacteria.

Windrow temperatures and chemical properties during active and passive aeration composting of beef cattle feedlot manure

Windrow composting emerged in the mid-1990s as an alternative manure-handling practice in Alberta’s cattle feedlot industry. This study compared two composting methods: active (turning) and passive aeration. Temperatures were monitored over the first 90 d and chemical properties over 188 d of composting. Pre- vs. post-turning sampling of the active treatment was also compared. Mean daily temperature was warmest at the bottom windrow location (53.6ºC) and coolest at the top (46.4ºC) in the active treatment, but warmest at the top (44.1ºC) and coolest at the bottom (33.9ºC) in the passive treatment. Final compost from the passive treatment had significantly higher total N (TN), total C (TC), electrical conductivity (EC), Na, and Cl than the active treatment. There were no significant treatment effects on C:N ratio, NH4-N, NO3-N, total P (TP), Kelowna-extractable P (KEP), pH, Ca, Mg or K. Both treatments showed substantial and non-significantly different C (71–80%) and N (44–58%) losses. Pre- versus post-turning sampling showed significant differences for some compost parameters, notably soluble salts. After the thermophilic phase, the passive treatment appeared only partially composted. Additional disadvantages of the passive treatment included lower windrow temperatures, which may fail to reduce pathogens, and higher EC, which could potentially limit the end use of passively aerated compost. Key words: Cattle manure, composting, active aeration, passive aeration, nutrients

Spatial orientation in the lamprey. I. Control of pitch and roll

Two major tasks must be fulfilled during locomotion: propulsion and spatial orientation. In the lamprey, the propulsive force is generated by laterally directed body undulations propagated from the rostral to the caudal end of the body. The neuronal networks underlying this basic locomotor pattern have been described in considerable detail. The present study was undertaken to provide the necessary behavioural background for parallel studies of the vestibular neuronal networks responsible for spatial orientation during locomotion. The following results were obtained. 1. The lamprey actively stabilized its pitch angle during swimming and usually kept a linear trajectory in the sagittal plane, despite large changes in the speed of swimming. During repeated tests, a certain preferred pitch angle could be maintained over a period of several minutes, even if the initial starting angle of the animal was changed considerably. 2. Two different strategies were observed for active turning in the downward direction: a smooth turn accomplished by weak ventral flexion of the whole body, and a sharp turn accomplished by localized ventral flexion of a region of the body just posterior to the gills. 3. The lampreys were oriented with the dorsal side up while swimming at any pitch angle. The control systems for pitch and roll can thus operate independently. When swimming, lampreys kept the tail region flexed somewhat ventrally. This body configuration will cause lateral movements of the tail to generate a torque that rotates the body around its longitudinal axis. This mechanism is presumably used to correct deviations from the dorsal-side-up orientation. After amputation of the dorsal and tail fins, lampreys maintained a proper spatial orientation during swimming. 4. After a unilateral labyrinthectomy, swimming lampreys continuously rolled towards the lesioned side. Unilaterally labyrinthectomized animals displayed a tonic twisting of the body into a helical shape. This presumably represents an additional strategy for performing roll turns. Bilaterally labyrinthectomized animals never maintained a linear trajectory in any plane, but turned continuously in all directions.