Secret life of the 'Plastisphere' exposed


Rebecca Pool

Tuesday, December 3, 2019 - 23:15
Microbial communities colonising microplastics collected from the North Atlantic Ocean [Cathleen Schlundt] 
Using novel epifluorescence imaging developed at the Marine Biological Laboratory (MBL), Woods Hole, researchers have unravelled the structure of the microbial communities that coat microplastic trash in the world's oceans.
To study the 'Plastisphere' - microscopic communities on plastic marine debris - Linda Amaral-Zettler from MBL and the Royal Netherlands Institute for Sea Research, and colleagues, used confocal laser-scanning microscopy alongside CLASI-FISH, combinatorial labelling and spectral imaging fluorescence in situ hybridization.
Spatial Structure in the “Plastisphere” [MBL Woods Hole]
The researchers developed a nested probe set consisting of three existing phylogenetic probes and four newly designed probes, based on fluorophore‐labelled oligonucleotides, that could target known bacterial groups. 
According to the researchers, this nested approach allowed them to identify the spatial organisation of microbes on the plastic samples, differentiating seven major microbial groups simultaneously in one image.
The structure of microbial communities colonizing microplastics collected from the North Atlantic Ocean (Vineyard Sound, Woods Hole, Mass.) This image reveals the phylogenetic affiliations of different bacterial groups. Large ellipsoid and pennate yellow cells= diatoms; long filamentous cell across center = cyanobacteria; blue= general bacteria; yellow rods = Bacteroidetes; red = Alphaproteobacteria; cyan= Rhodobacteraceae. Scale bar is 2 micron. Imaging technology is confocal laser-scanning and CLASI-FISH. [Cathleen Schlundt] 
“We now have a toolkit that enables us to understand the spatial structure of the Plastisphere and, combined with other methods, a better future way to understand the Plastisphere’s major microbial players, what  they are doing, and their impact on the fate of plastic litter in the ocean,” highlights Amaral-Zettler.
During analyses, the researchers observed diatoms and bacteria colonising the microplastics, dominated in all cases by three phyla: Proteobacteria, Cyanobacteria, and Bacteriodetes.
Spatially, the Plastisphere microbial communities were heterogeneously mixed, providing the first glimpse of bacterial interactions on marine microplastics.
(a,b) Scanning electron micrographs and (c–m) CLASI‐FISH images. (a, c) Diatom surrounded by bacteria cells after 1 week in the surface seawater of the North Atlantic Ocean (Vineyard Sound). (b, d) Lower diatom frustules attached to PE after 2–3 weeks of incubation. (b, d, e) Frustules were surrounded and invaded by different bacterial taxa such as Bacteroidetes (yellow), Rhodobacteraceae (cyan) and Gammaproteobacteria (magenta). Colour code is the same as shown in Figure 3. (f) Bryozoan‐like structure surrounded by bacteria after 1 week in the surface seawater of the Tropical Atlantic Ocean (Grenada). (g, h) Bryozoan‐like structure and (i) filamentous Cyanobacteria surrounded by bacteria after 1 week in the surface seawater of the North Atlantic Ocean. (j, k) Filamentous Bacteroidetes surrounded by Alphaproteobacteria and Rhodobacteraceae after 1 week in the tropical Atlantic Ocean. (l) Clusters of Rhodobacteraceae surrounded by Alphaproteobacteria and other bacteria after 1 week in the Tropical Atlantic Ocean. (m) Diverse bacteria embedded in a fluorescent EPS‐like structure after 5 weeks in the North Atlantic Ocean [Cathleen Schlundt et al, 29 November 2019, Molecular Ecology Resources]
The technique has previously been used to study microbial communities in the human mouth and in the digestive tract of cuttlefish and vertebrates.
This study customized and extended the technology, and  Amaral-Zettler now intends to establish a CLASI-FISH microscopy platform in the Netherlands.
Research is published in Molecular Ecology Resources.
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