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.

Microgrooves and fluid flows provide preferential passageways for sperm over pathogen Tritrichomonas foetus

Successful mammalian reproduction requires that sperm migrate through a long and convoluted female reproductive tract before reaching oocytes. For many years, fertility studies have focused on biochemical and physiological requirements of sperm. Here we show that the biophysical environment of the female reproductive tract critically guides sperm migration, while at the same time preventing the invasion of sexually transmitted pathogens. Using a microfluidic model, we demonstrate that a gentle fluid flow and microgrooves, typically found in the female reproductive tract, synergistically facilitate bull sperm migration toward the site of fertilization. In contrast, a flagellated sexually transmitted bovine pathogen, Tritrichomonas foetus, is swept downstream under the same conditions. We attribute the differential ability of sperm and T. foetus to swim against flow to the distinct motility types of sperm and T. foetus; specifically, sperm swim using a posterior flagellum and are near-surface swimmers, whereas T. foetus swims primarily via three anterior flagella and demonstrates much lower attraction to surfaces. This work highlights the importance of biophysical cues within the female reproductive tract in the reproductive process and provides insight into coevolution of males and females to promote fertilization while suppressing infection. Furthermore, the results provide previously unidentified directions for the development of in vitro fertilization devices and contraceptives.

The Autofluorescent Substance in the Posterior Flagellum of Swarmers of the Brown Alga Scytosiphon lomentaria

The flagellar autofluorescent substance of the brown alga Scytosiphon lomentaria , which is probably involved in the photoreception of the phototaxis of flagellate cells, was investi­ gated. 4′,5′-Cyclic FMN (1) was isolated from the extract of whole mature plants for the first time as a natural product. Since the concentration of 4′,5′-cyclic FMN (1) was considerably low in vegetative plants, which do not contain fluorescent flagella, this substance is consid­ered to correspond to the flagellar fluorescent substance.

The ultrastructure of the R.S. zoospore of the Chytridiomycete Physoderma gerhardti

The fine structure of the zoospore of Physoderma gerhardti Schroeter is described. It possesses a single very large lipid body (sometimes accompanied by several smaller ones) situated laterally to the nuclear cap – nucleus complex and is associated with electron-dense material (the microbody) and the single large posteriorly located mitochondrion. The single posterior flagellum proximally terminates in a kinetosome just short of the posterior cone-shaped end of the nucleus. The kinetosome lies in a deep groove in the mitochondrion and is associated with this organelle by striated rootlets. The kinetosome terminates in electron-dense material from which an array of microtubules arises. These microtubules run along the sides of the cone-shaped nucleus and nuclear cap. There is an accessory centriole lying close to and more or less parallel with the kinetosome. The cytoplasm contains a small amount of smooth endoplasmic reticulum and several inclusion bodies in the anterior region and several small vacuoles in the posterior region of the cell. The general internal organization of the zoospore of Physoderma gerhardti more nearly resembles that of a blastocladiaceous fungus than of any chytrid thus far investigated.

THE FLAGELLATION, MOVEMENT, AND ENCYSTMENT OF SOME PHYCOMYCETOUS ZOOSPORES

The anterior flagellum of the zoospores of Phytophthora fragariae, P. megasperma, P. cambivora, Saprolegnia parasitica, Achlya americana, and Pythium aphanidermatum projects straight in front of the zoospore and never moves except during encystment whereas the posterior flagellum is active during the swimming period. In the secondary zoospore the anterior and posterior flagella are attached a short distance apart in the center of the depression on the concave side and respectively pass forward and backward through a groove and form a central axis about which the zoospore rotates. Hyaline vesicles which also have been called beads or paddles form at the base of the flagella at the beginning of encystment and glide part or all the way down the flagella. Movement of flagella after they are released from the zoospore is reported for the first time. Encystment may result from contact stimulus except in the case of Allomyces anomalus. A filament on which vesicles may occur may be secreted or retracted by the Allomyces zoospore.

On the Structure, Division, and Systematic Position of Trichomonas vaginalis Donné, with a Note on its Methods of Feeding

1. Trichomonas vaginalis has been cultivated on various media and a simple method of maintaining cultures on Boeck and Drbohlav's egg-Ringer-albumen medium is described. 2. The feeding methods of the flagellates in culture have been studied and some evidence of extracellular digestion is recorded. 3. When cultivated on media deficient in carbohydrate, T. vaginalis is reduced to the dimensions of T. hominis, but when adequately fed it maintains its distinctively larger size. Out of forty-eight strains of T. vaginalis, only two developed in culture the long undulating membrane and free posterior flagellum typical of T. hominis in nature. 4. The structure of T. vaginalis has been reinvestigated. (i) It differs constantly and significantly from the intestinal trichomonads of man in size, nuclear organization, and the form of the axostyle and basal fibre, (ii) It also differs from T. hominis in the characters of its parabasal apparatus and cytoplasmic inclusions, and, in nature, in the length of its undulating membrane and in lacking a free posterior flagellum, but for reasons discussed in the text these points are at present considered less reliable in diagnosis than those given under 4 (i). 5. It is concluded that T. vaginalis is a species distinct from all other human trichomonads. 6. The method of division has been described. In general, it follows the same course as T. hominis, but separation of the old, and growth of the new, cytoplasmic structures occurs somewhat later in T. vaginalis, and the old axostyle is retained throughout division. There are five chromosomes, formed during prophase from aggregations of extra-karyosomatic granules.