An investigation of the involvement of cytoskeletal structures and secretion in gliding motility of the marine diatom, Amphora coffeaeformis

Motion analysis and ultrastructural study of a colonial diatom, Bacillaria paxillifer

The pennate diatom, Bacillaria paxillifer, forms a colony in which adjacent cells glide smoothly and almost continuously, yet no obvious apparatus driving the movement, such as flagella or cilia, is observed. Thus far, neither the mechanism nor physiological significance of this movement has been well understood. Here, we report quantitative analysis of the gliding motion of B. paxillifer and morphological analysis of this diatom with light and electron microscopes. The gliding of pairs of adjacent B. paxillifer cells in a colony was cyclic with rather constant periods while the average gliding period varied from a few seconds to multiples of 10 s among colonies. The gliding was compromised reversibly by inhibitors for actin and myosin, suggesting involvement of the actomyosin system. Indeed, we observed two closely apposed actin bundles near the raphe by fluorescence-labeled phalloidin staining. Using electron microscopy, we observed filamentous structures that resemble the actin bundles seen with fluorescence microscopy, and we also found novel electron-dense structures located between the plasma membrane and these actin-like filaments. From these and other observations, we suggest that B. paxillifer also uses actin bundles and propose a putative myosin as a molecular motor in the gliding of unicellular diatoms.

Underwater locomotion strategy by a benthic pennate diatom Navicula sp

The mechanism of diatom locomotion has been widely researched but still remains a hypothesis. There are several questionable points on the prevailing model proposed by Edgar, and some of the observed phenomena cannot be completely explained by this model. In this paper, we undertook detailed investigations of cell structures, locomotion, secreted mucilage, and bending deformation for a benthic pennate diatom Navicula species. According to these broad evidences, an updated locomotion model is proposed. For Navicula sp., locomotion is realized via two or more pseudopods or stalks protruded out of the frustules. The adhesion can be produced due to the pull-off of one pseudopod or stalk from the substratum through extracellular polymeric substances. And the positive pressure is generated to balance the adhesion because of the push-down of another pseudopod or stalk onto the substratum. Because of the positive pressure, friction is generated, acting as a driving force of locomotion, and the other pseudopod or stalk can detach from the substratum, resulting in the locomotion. Furthermore, this model is validated by the force evaluation and can better explain observed phenomena. This updated model would provide a novel aspect on underwater locomotion strategy, hence can be useful in terms of artificial underwater locomotion devices.

Antibiotic from the marine environment with antimicrobial fouling activity

The degradation in performance of submerged marine structures through their colonization by micro- and macrobiota is well known. Historically, toxic surface coatings have been used to control both types of fouling. Legislative requirements worldwide now require alternative non- or minimally toxic coatings to be used. Here we report on the potential for synthetic 2-pentyl-4-quinolinol (PQ), an antibiotic from an Alteromonas sp., as a candidate antifoulant. Hundred micromolar PQ reduces the growth of four marine diatoms that usually grow as biofilms. Furthermore, PQ inhibits the initial adhesive process in Amphora coffeaeformis in a logarithmic dose-dependent manner, but not the adhesion of a Navicula sp., indicating differing adhesive processes in these two diatoms. Treatment of established biofilms with PQ causes a rapid and complete loss of motility in both Amphora and Navicula and eventually, as seen by Sytox Green staining, cell death, and lysis. We conclude that PQ, or one of its chemical analogues, holds promise as an antifoulant molecule for inclusion in marine surface coating.

Use of fluorophore-conjugated lectins to study cell-cell interactions in model marine biofilms

Biofilms dominated by pennate diatoms are important in fields as diverse as ship biofouling and marine littoral sediment stabilization. The architecture of a biofilm depends on the fact that much of its mass consists of extracellular polymers. Although most illuminated biofilms in nature are dominated by phototrophs, they also contain heterotrophic bacteria. Given the close spatial association of the two types of organisms, cell-cell interaction is likely. Fluorophore-conjugated lectins were used to demonstrate the sites of the various extracellular polymers in three species of diatoms. Based on their lectin staining properties, the polymers in different species appeared to be similar, but their involvement in the process of attachment to a surface differed. In a coculture Pseudoalteromonas sp. strain 4 or its sterilized spent medium reduced the ability of Amphora coffeaeformis and Navicula sp. strains 1 and D to adhere, inhibited motility, and caused agglutination and eventually diatom cell lysis. Diatoms could be protected from the negative effects of the bacterial spent medium if D-galactose or mannan was included in the incubation medium. The active principle of the spent medium is probably a lectin/agglutinin that is able to bind to the extracellular polymers of the diatoms that are involved in adhesion and motility. Awareness of interactions of this type is important in the study of natural biofilms.

Diatom gliding is the result of an actin-myosin motility system

Diatoms are a group of unicellular microalgae that are encased in a highly ornamented siliceous cell wall, or frustule. Pennate diatoms have bilateral symmetry and many genera possess an elongated slit in the frustule called the raphe, a feature synonymous with their ability to adhere and glide over a substratum, a process little understood. We have used cytoskeleton-disrupting drugs to investigate the roles of actin, myosin, and microtubules in diatom gliding or motility. No effect on diatom gliding was observed using the cytochalasins, known actin inhibitors, or the microtubule-inhibitors oryzalin and nocodazole. The latrunculins are a new group of anti-actin drugs, and we show here that they are potent inhibitors of diatom gliding, resulting in the complete disassociation of the raphe-associated actin cables. The recovery of actin staining and motility following latrunculin treatment was extremely fast. Cells exposed to latrunculin for 12 h recovered full function and actin staining within 5 sec of the drug being removed, demonstrating that the molecular components required for this motility system are immediately available. Butanedione monoxime (BDM), a known myosin inhibitor, also reversibly inhibited diatom gliding in a manner similar to the latrunculins. This work provides evidence that diatom gliding is based on an actin/myosin motility system.

A Computer-based image analysis system for biocide screening

A computer-based image analysis system that measures the behavioral response of the marine diatom Amphora coffeaeformis to potentially toxic challenges is described. At any one time the system is capable of measuring in a population of about 80 cells, changes in the number motile, their speed, direction, and if they are turning, their angular velocity and acceleration. Chemical compounds that interfere with the generation of energy, protein or glycoprotein synthesis, calcium homeostasis and cytoskeletal activity, change the motile behavior of the cell. A pre-requisite of motility is that the cells be attached to a substratum. It is proposed that the system, which requires only a 1-2 minute data collection period per replicate, could be used to screen for potential antifouling activity in chemical agents, and it is speculated that it could be used also for measuring the physicochemical interaction between attached motile organisms and their substratum, as well as in environment toxicology measurements.

Podophyllotoxin, steganacin and combretastatin: natural products that bind at the colchicine site of tubulin

A large number of antimicrotubule agents are known that bind to tubulin in vitro and disrupt microtubule assembly in vitro and in vivo. Many of these agents bind to the same site on the tubulin molecule, as does colchicine. Of these, the natural products podophyllotoxin, steganacin and combretastatin are the subjects of this review. For each of these, the chemistry and biochemistry are described. Particular attention is given to stereochemical considerations. Biosynthetic pathways for podophyllotoxin and congeners are surveyed. The binding to tubulin and the effects on microtubule assembly and disassembly are described and compared. In addition, structural features important to binding are examined using available analogs. Several features significant for tubulin interaction are common to these compounds and to colchicine. These are described and the implications for tubulin structure are discussed. The manifold results of applying these agents to biological systems are reviewed. These actions include effects that are clearly microtubule mediated and others in which the microtubule role is less obvious. Activity of some of these compounds due to inhibition of DNA topoisomerase is discussed. The range of species in which these compounds occur is examined and in the case of podophyllotoxin is found to be quite broad. In addition, the range of species that are sensitive to the effects of these compounds is discussed.

Malaria sporozoites release circumsporozoite protein from their apical end and translocate it along their surface

Plasmodium sporozoites, the causative agents of malaria, release circumsporozoite (CS) protein into medium when under conditions simulating those that the parasites encounter in the bloodstream of the vertebrate host. CS protein of the rodent parasite, Plasmodium berghei, is released as the lower molecular weight form, Pb44. This release is substratum- and antibody-independent. Previous studies show that CS protein is released at the trailing, posterior end of motile sporozoites. Video and electron microscopic studies now demonstrate that CS protein is released at the apical end of cytochalasin b-immobilized sporozoites. We propose that CS protein released from the apical end, the leading end of gliding sporozoites, adheres to the sporozoite surface and is translocated posteriorly by a cytochalasin-sensitive and apparently actin-mediated surface motor, which drives gliding motility. This model explains the mechanism of both the circumsporozoite precipitation (CSP) reaction and formation of the CS protein trail by gliding sporozoites.