#FEMSmicroBlog: Some microbes like it hot!

17-12-2020

Plastic pollution is everywhere. Our oceans, in particular, are awash with plastic.  Microplastics – pieces of plastic under 5 mm in size – are concerning because they can be eaten by a very large variety of sea animals. However, the first organisms that are affected by microplastic pollution in the ocean are marine microbes. A new paper in FEMS Microbiology Ecology describes the formation of a reversible plastic-specific microbial community during summer, as co-author Lee Pinnell explains for the #FEMSmicroBlog. #FascinatingMicrobes 

 

Four seasons, two substrates, and two questions

Marine microorganisms in the ocean attach to plastic pollution within a matter of days and soon form a thick biofilm. This plastic-attached community is referred to as the microbial plastisphere. The first thing researchers noticed about the plastisphere was that it was different than the microbial community floating around in the water.

This makes sense since we know that some microbes like living attached to surfaces, but other microbes prefer the free-living lifestyle of floating around in the ocean. But, to find out if certain microbes preferred plastic to other surfaces, we needed to include some other type of reference substrate as a biofilm control.

When we did this (we used ceramic as our reference substrate) and looked at a single time point during the fall we didn’t see any difference between ceramic or plastic communities. However, other researchers have seen that plastic communities differed from their reference substrates.

Other researchers have seen that plastic communities differed from their reference substrates

In the paper “Temporal changes in water temperature and salinity drive the formation of a reversible plastic-specific microbial community” in FEMS Microbiology Ecology, we looked at how the microbial communities on plastic changed over time as environmental conditions varied. We mainly wanted to answer two questions:

  1. Do some microbes prefer living on plastic over another inert surface?
  2. Do the microbes living on plastic change over time?

 

Temperature and salinity as main drivers

To answer these questions, we exposed mesocosms containing plastic and ceramic nurdles to the benthic marine microbial community of a coastal lagoon in south Texas for 424 days. A total of 90 mesocosms (45 plastic, 45 ceramic) were deployed, and we collected triplicate samples every four weeks. We also measured water temperature, salinity, dissolved oxygen, and pH each time we collected our samples. We isolated DNA from our samples on the same day they were collected, and then used 16S rRNA gene sequencing and analysis to characterize the microbial communities at each time point.

During the summer, we found two groups of bacteria (Melioribacteraceae and Cyclobacteriaceae) in particular that seemed to prefer life on plastic versus life on ceramic.

What we found was that during most of the year there was no difference between plastic and ceramic microbial communities. But, in the summer these communities diverged and were actually very different from each other. Surprisingly, during the next fall, the communities reverted back to being similar. During the summer, we found two groups of bacteria (Melioribacteraceae and Cyclobacteriaceae) in particular that seemed to prefer life on plastic versus life on ceramic. One group (Melioribactericeae) got way more abundant on plastic but remained the same on ceramic, while the other group (Cyclobacteriaceae) stayed in the same abundance on plastic but got way less abundant on ceramic.

Barplot showing the relative abundances of plastic-discriminant taxa by season throughout the course of the study. (For more details, see the study.)

In both cases, water temperature and salinity seemed to drive the differential abundance. Whether this effect is direct or indirect remains unknown, however, and we plan on expanding on this work in the future and measure additional factors like light intensity, nutrients, and the activity of bacterial predators that can also be impacted by temperature and salinity.

 

About the author of this blog

Lee J. Pinnell is a Postdoctoral Scientist at the John G. Shedd Aquarium in Chicago, Illinois (US). He received bachelor’s and master’s degrees in Biology from the University of Waterloo (Canada) and a Ph.D. in marine biology from Texas A&M University-Corpus Christi (US) where he studied the impact of plastic and bioplastic pollution on marine microbial communities under Dr. Jeffrey Turner. At Shedd he focuses on the microbial ecology of built environments, host-associated microbiota, and continues to study plastic-microbe relationships in aquatic environments.

About this blog section

The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.

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