Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Inga Vanessa Kirstein, Antje Wichels, Elisabeth Gullans, Georg Krohne, Gunnar Gerdts, Nuno Filipe Azevedo.
In order to understand the degradation potential of plastics in the marine environment, microorganisms that preferentially colonize and interact with plastic surfaces, as opposed to generalists potentially colonising everything, need to be identified. Accordingly, it was hypothesized that i.) plastic “specific” microorganisms are closely attached to the polymeric surface and ii.) that specificity of plastics biofilms are rather related to members of the rare biosphere. To answer these hypotheses, a three phased experiment to stepwise uncover closely attached microbes was conducted. In Phase 1, nine chemically distinct plastic films and glass were incubated in situ for 21 months in a seawater flow through system. In Phase 2, a high-pressure water jet treatment technique was used to remove the upper biofilm layers to further, in Phase 3, enrich a plastic “specific” community. To proof whether microbes colonizing different plastics are distinct from each other and from other inert hard substrates, the bacterial communities of these different substrates were analysed using 16S rRNA gene tag sequencing. Our findings indicate that tightly attached microorganisms account to the rare biosphere and suggest the presence of plastic “specific” microorganisms/assemblages which could benefit from the given plastic properties or at least grow under limited carbon resources.
Since the middle of last century the increase of global plastics production is accompanied by an accumulation of plastic litter in the marine environment [1, 2]. Persistent plastic items are rarely degraded but become fragmented over time and are dispersed by currents and wind [1, 3, 4]. Consequently, marine plastic litter can be found in marine waters all over the globe.
Identification of microbes that preferentially colonize and interact with plastics surfaces remains challenging as the differences in community composition of mature biofilms are generally low . Furthermore, young biofilms (2–6 weeks) appear to be rather unspecific between different plastic types or other inert substrates like glass [14, 18, 19]. Here, we present a three phase experimental approach to uncover potential plastic “specific” microbes. Our findings indicate that tightly attached microorganisms might account to the rather rare biosphere and suggest the presence of plastic “specific” microorganisms/assemblages which could possibly benefit from the given plastic properties.
This study represents a systematic and robust experimental approach uncovering potential plastic “specific” microbes and is therefore a step forward in understanding the substrate specificity of the “Plastisphere”. For the first time, a high-pressure water Jet treatment technique was used to remove the cohesive layer of mature biofilms, while leaving the adhesive layer on the plastics surface. Our results indicate the presence of plastic “specific” microorganisms/assemblages which could possibly benefit from the given plastics properties. Furthermore, our findings clearly indicate that plastic “specific” microorganisms might account to the rather rare biosphere and are tightly surface attached. Underrepresentation, due to low read counts, might be an explanation why specificities between plastics biofilms in natural marine environments were not detected so far in young biofilms or seem to be generally low in mature biofilms.