Wednesday, 25 April 2018

Plastics and good and bad microbes

The media went pretty wild over reports that our plastic problems may be over due to the discovery of microbes which would munch their way through the pollution:
Futures Forum: A solution to our plastic problems: plastic-eating enzymes

However, there are also some rather malignant microbes out there which are latching onto plastics in a potentially very harmful way: 

Bacterial Colonization and Partial Degradation of Plastic Debris in California Coastal Waters

Sunday, Apr 22 12:45 PM

Several studies have addressed the role of microbes associated with plastic marine debris.  However, little is known about the nature of microbes attaching to plastic in coastal areas, and how it could potentially impact humans. 

The goal of this project is to evaluate the microbial diversity on plastic marine debris, specifically the more abundant types of floating plastic (ex. single-use plastic bags) made of polyethylene (PE) and polypropylene (PP) in coastal waters. Our hypothesis is that microbes will colonize plastic and that the diversity and abundance of microbial communities will be directly influenced by plastic resin type. We are also interested in colonization of plastic by pathogenic species and/or species with potential to degrade plastic. 

Three plastic resin types (high density polyethylene (HDPE), low density polyethylene (LDPE), and polypropylene (PP)) were placed in stainless steel cages, submerged to approx. 50 cm depth in Southern California coastal waters and retrieved at 4 different time points between 3 and 40 days along with water samples for comparative purposes. Two sample sets were collected between May 2016 and May 2017. DNA was extracted and 16S rRNA metagenomic tag sequencing was used to differentiate the microbial community. Colonies grown parallel on Salt Water Agar and Vibrio-specific media were characterized by 16S amplicon sequencing. In addition, Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze the breakdown of plastic over time and scanning electron microscopy (SEM) to visualize the biofilms attached to plastic on day 40. 

Our results indicate that over 40% of the sequences obtained are from unclassified organisms. The three plastic resin types exhibited a diverse assemblage of heterotrophic bacterial taxa, while in water samples photosynthetic genera were the most prevalent. There were differences between plastic resin types and the surrounding water, as well as temporal differences. We did not find evidence of Vibrio cholerae either by 16S metagenomic sequencing or by 16S sequencing of colonies isolated on ChromAgar Vibrio. However, other potentially pathogenic genera such as Francisella and Rickettsia were present on plastic at earlier sampling time points. In addition, all three plastic resins showed signs of chemical degradation over time, and SEM revealed a rich biofilm containing diatoms, bacterial, and protist populations. 

Together, this study indicates that there are differences in the microbial communities growing on coastal marine plastic debris with potential implications for human health and the environment. 

Experimental Biology 2018

No comments: