The Restaurant on the polystyrene microparticle

This is a follow up to an earlier post of mine. While I don’t think that you necessarily have to read it before, it does provide some background information

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Recently, the term “Plastisphere” has been coined to describe the new ecological niche found around microplastics. These particles may host diverse microbial communities, which are distinct from the surrounding seawater. Scientists are concerned with the possibility of pathogenic microbes, such as Vibrios, hitchhiking on microplastics. In their paper, Foulon et al. (2016) investigated the ability of Vibrio crassostreae to colonize polystyrene microplastics under different conditions

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The oyster pathogen V. crassostreae strain J2-9 was isolated in 2011 during a disease outbreak in an oyster bed in Brittany. Three different types of polystyrene microparticles were used (i) non-fluorescent smooth spherical microbeads (PS-s), (ii) fluorescent smooth spherical microbeads (PS-f) and (iii) non-fluorescent rough irregular microplastics (PS-i). The fluorescently-labelled Vibrios and Microplastics were incubated in glass culture tubes under continuous stirring. First, the effects of microplastic shape (smooth vs rough) and culture medium (artificial seawater vs. Zobell culture medium) were evaluated. Secondly, the effect of natural microbial communities on the J2-9 colonization process was investigated. The cultures were analysed using confocal and scanning electron microscopy. 

In the first experiment, the Vibrios exhibited rapid movement prior to adhesion to the microplastics. Subsequently, the cells appeared linked to the surface via pili, hair like appendages which attached the Vibrios to the substrate. 

In the artificial seawater, colonization of the microplastics reached its maximum (on average >14%) between 28 min and 2h 45 min. In contrast, Vibrios in the Zobell medium reached their maximum colonization (on average 75%) between 4h 30 min and 6h and 9 min. Overall, the replicates showed high variability despite identical experimental conditions. Higher nutrient availability has been shown to influence adhesion structures positively, therefore likely leading to the higher percentage of colonization in the culture medium. In comparison, the lack of nutrients in the artificial seawater may have led to migration towards an active substrate and thus earlier colonization. However, the microplastics presumably didn’t provide enough nutrients for the bacteria, thus leading to rapid decolonization. In Zobell culture some nutrients may also have been limited, but the exact relationship between nutrient availability and decolonization is yet to be determined. Moreover, hydrodynamic movements and quorum sensing communication between cells might also lead to cell detachment. 

Incubation with rough PS-i particles led to longer colonization. Here, maximum coverage was reached between 3 hours and 10-24 hours, again slightly faster in seawater samples than in Zobell samples. A complete decolonization was observed in Zobell cultures after 24h incubation, while the seawater replicates remained colonized up to 6 days. Microscopy showed the Vibrios to be located in cracks on the PS-i, thus likely being sheltered from turbulence. The PS-i were also up to 10x larger than the smooth particles. Moreover, the effect of any unknown additional chemicals in the particles cannot be discounted. Nevertheless, long-term colonization was not observed in this experiment suggesting that the J2-9 strain was not able use the particle resources. Hence, the authors conclude that V. crassostreae may be secondary colonizers, depending on other microbes to provide nutrients. In any case, further study on possible substrate affinity of Vibrios for specific synthetic polymers is necessary.

In the second experiment with natural seawater, biofouling began in the first 24h of incubation. During the next 7 days, all microparticles were incorporated into natural aggregates (marine snow), harbouring diverse microbial communities. The J2-9 were either found to be vertically structured in a corolla, or as a monospecific biofilm on the aggregates. The authors hypothesize that this could result from interspecies communication or feeding on the nutrients produced by other species in the aggregate. Interestingly, no decolonization was observed. However, after 96h the Vibrios started to disappear either through a loss of fluorescence or predation by ciliates.

The authors conclude, that V. crassostreae strain J2-9 may act as a secondary colonizer, requiring an established microbial community on microplastics. However, the results of this paper merely suggest a possibility open up new areas of research. In regards to my previous blogpost, this paper clearly indicates an upper time limit for Vibrio transport via microplastics. This information could in the future presumably be used to map transport routes and infection

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Reviewed Paper:

Foulon, V., Le Roux, F., Lambert, C., Huvet, A., Soudant, P., & Paul-Pont, I. (2016). Colonization of polystyrene microparticles by Vibrio crassostreae: light and electron microscopic investigation. Environmental Science & Technology, 50(20), 10988-10996. http://pubs.acs.org/doi/abs/10.1021/acs.est.6b02720

References:

Kirstein, I. V., Kirmizi, S., Wichels, A., Garin-Fernandez, A., Erler, R., Löder, M., & Gerdts, G. (2016). Dangerous hitchhikers? Evidence for potentially pathogenic Vibrio spp. on microplastic particles. Marine Environmental Research, 120, 1-8. http://www.sciencedirect.com/science/article/pii/S014111361630112X

Eleni’sReview on: 

Lobelle, D., & Cunliffe, M. (2011). Early microbial biofilm formation on marine plastic debris. Marine Pollution Bulletin, 62(1), 197-200. http://ac.els-cdn.com/S0025326X1000473X/1-s2.0-S0025326X1000473X-main.pdf?_tid=e830865e-b55f-11e6-b984-00000aab0f27&acdnat=1480333600_8074b98c59785186b7da541593992c3d

Zettler, E. R., Mincer, T. J., & Amaral-Zettler, L. A. (2013). Life in the “plastisphere”: microbial communities on plastic marine debris. Environmental science & technology, 47(13), 7137-7146. http://pubs.acs.org/doi/abs/10.1021/es401288x