Microbes building 'cities' on ocean plastic — metagenomes reveal plastisphere survival strategies

Countless plastic fragments drift through the oceans. On their surfaces, bacteria, viruses, fungi and algae form a unique ecosystem. A joint team from the Helmholtz Centre for Environmental Research (UFZ) and GEOMAR has revealed the survival strategies of this microscopic world known as the 'plastisphere.'

Bigger genomes — a strategy for nutrient-poor seas

The team collected plastic pieces from garbage patches in the North Pacific and North Atlantic and sequenced the metagenomes of attached microbes. They found that plastisphere bacteria have larger genomes and more gene copies than marine plankton.

Analysis of around 340 key functional genes revealed enhanced capabilities for nutrient absorption, carbon source utilisation, UV defence and genome repair. The microbes can also use anoxygenic photosynthesis as an alternative energy source.

The microorganisms in the biofilm have more gene copies, enabling them to absorb nutrients effectively, utilise and break down carbon sources, and either ward off UV radiation or repair genome damage quickly

— Dr Stefan Lips (UFZ, lead author)

Different species in Atlantic and Pacific, same functions

While the bacterial species composition differed between the Atlantic and Pacific plastispheres, the functionally important bacterial groups were shared across both oceans. The functions needed to survive on plastic surfaces are the same everywhere.

They won't break down the plastic

Plastisphere microbes can produce more biomass than surrounding plankton, creating 'eutrophic niches' in the nutrient-poor open ocean. However, since the microbes use plastic as habitat rather than a nutrient source, they will not help remove plastic from the seas.

Because microbes use plastic as a habitat rather than a source of nutrients, it is unlikely that they will help to remove plastic from the oceans

— Dr Erik Borchert (GEOMAR, co-author)

For more on the marine environment, see 'Why is Alaska's coastal ice vanishing so fast?'

A note from the author: The image of microbes building their own 'city' on plastic fragments is honestly a bit unsettling.

And in the end, they don't break down the plastic. For the ocean, they're uninvited tenants.