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

Abstract

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.

Travelling Expenses: The Energy Cost of Diel Vertical Migrations of Epipelic Microphytobenthos

“…Vertical community migration movements upward and downward are typically completed in 20 min (Hopkins and Drum, 1966 and references therein) but recently Cartaxana et al (2016) reported the beginning of downward migration almost 2 h before tidal flooding. Maximum gliding speed reported for diatoms was ∼20 µm s −1 (Yamaoka et al, 2016) (Table 1), but this was attained in the very specific situation of gliding in the colonial species Bacillaria paxillifera. Murase et al (2011) refer maximum gliding speed an order of magnitude lower (1-2 µm s −1 ) and Wang et al (2013) cast doubts in the capacity of the 2016Bacillaria paxillifera 20 Colonial diatom; adjacent cells glide over each other Kooistra et al (2003) Toxarium undulatum 3.5 Maximum speed of 6 µm s −1 was observed, but only for 10 s; speeds of 0.5-2 µm s −1 were more common.…”

“…where σ ∼ 1 in the case of highly directional vertical motion and σ ≫ 1 for the case of highly chaotic or bidirectional-gliding motion (Yamaoka et al, 2016). Concrete estimations of E S h x(s), y(s), z(s) , as well as σ and A m , may be obtained on the basis of various stochastic models describing, to one degree or another, the real movement of different types of diatoms in accordance to their "decision making" and the sediment granularity or by analysis of recorded diatom tracks.…”

“…Plot (A) represents a m (σ ) for the group of relatively fast and large diatoms: Navicula viridula, migrating with the locomotion speed v l = 30.5 µm s −1 (Edgar, 1979) and having the mean surface area of valve face of its cells = 519 µm 2 (Diatoms org, 2020a); Bacillaria paxillifera of v l = 20 µm s −1 (Yamaoka et al, 2016) and = 485 µm 2 (Diatoms org, 2020b); and the model diatom of v l = 10 µm s −1 and = 1,000 µm 2 (Edgar, 1982). For this group the specific energy expenditure a m varies from ca.…”

“…Latrunculin A and B inhibit actin assemblage, since they form an incompetent complex with monomeric actin, leading to F-actin depolymerization (Coué et al, 1987;Ayscough et al, 1997). In fact, in B. paxillifer, the actin bundles along the raphe disappeared after a short treatment (1 min) with latrunculin B and reappeared shortly after the removal of this drug (Yamaoka et al, 2016). However, it is not possible to exclude additional indirect effects of latrunculin in diatom motility, e.g., impairing the transport of secretion vesicles to the raphe (Poulsen et al, 1999), as postulated in the model of Edgar. In any case, cumulative evidence points to a key role of the raphe in the mechanism of locomotion.…”

Towards a digital diatom: image processing and deep learning analysis ofBacillaria paradoxadynamic morphology

“…that each colony is a multicellular organism). Cellular biology work that has been done on the movement of Bacillaria [6][7][8], is neither computational in nature nor at the whole-organism level.…”