We all know that plastic waste in the oceans is a major problem affecting marine life. It is estimated that around 35 kg per year per person of the world population are produced, and a part of it finds its way into the sea. Most of the studies carried out focus on the threat to marine macrofauna such as turtles and birds (entanglement, ingestions), and this study tried to address the bacteria associated to plastic. Pieces of plastic last much longer in the environment than other types of substrates to which the microorganisms can attach themselves to and it is assumed that plastic represents a vector transporting the microbes over a long distance.
In order to investigate the bacteria associated with the plastic debris, plastics as well as seawater samples were collected and total DNA extracted from the samples. Plastics were identified as polyethylene and polypropylene, and DNA analysis revealed that the microbial communities were consistently distinct from each other between the plastics and were also different from the seawater samples. Cyanobacteria Phormidium and Rivularia sp. occurred on the plastics but not in seawater samples and Pelagibacter sp. dominated the water samples as heterotrophic representatives, and showed varied abundances in the plastic samples. Curiously, the authors found radiolarian OTUs on both plastic types, which is an unusual since these protists are generally not assumed to be substrate associated. The authors furthermore analysed the hydrocarbon degrading bacteria associated with the plastics and discovered among the the taxa identified Oceaniserpentilla, which is one of the major taxa related to the OTUs found in the Deepwater Horizon oil spill. Although the presence of these bacteria does not imply that they are involved in plastic degradation, it offers an opportunity for testing this.
According to the paper, the most striking finding was the abundance of Vibrio OTUs which was found to be as high as 24% of the communities associated with the plastic. Vibrio sp. (with a few exceptions such as V. harveyi) are usually not found in such high concentrations within a community (often not higher than 1%), and the fast growth rate of this genus could be a possible explanation for this. I think this is a very interesting finding; we have recently discussed the persistence of Vibrios in the oceans. The authors have found diatoms attached to some of the plastic samples, and with the background that Vibrio sp. have been found to attach themselves to diatom chitin, the presence of diatoms could be an explanation for the high concentrations of Vibrio OTUs. Plastics could also have an effect on the environmental persistence of other bacteria likewise, and therefore could also influence the spread of harmful pathogens.
Zettler ER, Mincer TJ & Amaral-Zettler LA (2013). Life in the ”Plastisphere”: Microbial Communities on Plastic Marine Debris