Algal Viruses: The (Atomic) Shape of Things to Come

Abstract

Visualization of algal viruses has been paramount to their study and understanding. The direct observation of the morphological dynamics of infection is a highly desired capability and the focus of instrument development across a variety of microscopy technologies. However, the high temporal (ms) and spatial resolution (nm) required, combined with the need to operate in physiologically relevant conditions presents a significant challenge. Here we present a short history of virus structure study and its relation to algal viruses and highlight current work, concentrating on electron microscopy and atomic force microscopy, towards the direct observation of individual algae⁻virus interactions. Finally, we make predictions towards future algal virus study direction with particular focus on the exciting opportunities offered by modern high-speed atomic force microscopy methods and instrumentation.

Keywords: algal virus; atomic force microscopy; electron microscopy; imaging; infection dynamics; virus structure.

Figure 1

Cryoelectron microscopy map of Paramecium bursaria chlorella virus-1, used with permission and adapted from Zhang et al. [23].

Figure 2

(a) Schematic diagram of a high speed-atomic force microscope created by O. Payton. Adapted from [42]; (b) Colourised electron microscopy image of an atomic force microscopy cantilever (scale bar 10 µm), the imaging tip is visible at the apex of the sharp, pyramidal structure at the free end of the cantilever. Image by Steve Gschmeissner.

Figure 3

Selected AFM image of PBCV-1, used with permission from Kuznetsov et al. [51].

Figure 4

Selected contact mode HS-AFM frame of Emiliania huxleyi cell surface captured at 0.5 s per frame by the authors. Variations in height are likely due to membrane ruffles, localised variation in membrane lipid composition/size and their associated membrane proteins.

Figure 5

Selected tapping mode HS-AFM frame of COS-7 cell surface captured at 6 s per frame, used with permission from Shibata et al. [84]. (max height 45 nm, scale bar 500 nm) This is a single image from a series that shows membrane pit closure over 78 s.

Figure 6

(a) Selected contact mode HS-AFM frame of disrupted Emiliania huxleyi Virus 86 spilling its genomic content captured at 0.5 s per frame by the authors (max height 37.1 nm); (b) Selected AFM image of PBCV-1 DNA pre proteinase K treatment, used with permission and adapted from Wulfmeyer et al. [106] (scale bar 100 nm, max height 2.4 nm). Arrows show ([a]-putative) DNA associated proteins.