The plastisphere is a novel, human-made ecosystem that forms on plastic pollution in aquatic environments. This unique habitat consists of diverse organisms living directly on plastic waste, which accumulates in oceans and freshwater systems. Discovered recently, the plastisphere offers insight into microbial ecology and its interactions with human-introduced materials. It is a globally distributed biome, comprising complex microbial and eukaryotic communities that colonize plastic polymers.
Formation of the Plastisphere
The colonization process begins when plastic enters an aquatic environment. Immediately, the plastic surface is coated by a thin layer of organic and inorganic molecules, known as a “conditioning film.” This initial film serves as an adhesive layer, making the surface hospitable for microbial attachment.
Pioneer microorganisms, primarily bacteria, then attach to the plastic surface. These early colonizers, often opportunistic species, proliferate rapidly, establishing the first layer of the developing biofilm. Over time, a more complex, multi-layered community develops through microbial succession, resulting in a stable, tightly adhered microbial community.
Inhabitants of the Plastisphere
The plastisphere hosts diverse microorganisms, forming a micro-ecosystem. These inhabitants include various groups such as bacteria, archaea, fungi, and microalgae. Within this community, different organisms fulfill specific roles, mirroring larger ecosystems.
Microalgae act as primary producers, generating energy through photosynthesis and providing organic matter to the community. Heterotrophic bacteria and fungi consume organic matter, acting as decomposers. High biodiversity has been identified, with over 1,000 kinds of microbes found on a single small piece of plastic. The specific composition of these communities varies depending on factors like plastic type, duration in water, and geographical location.
Ecological and Biogeochemical Roles
The plastisphere significantly influences the fate of plastic debris and environmental processes. Biofilms on plastic surfaces can alter their physical properties, increasing density. This increased density can cause plastics that initially float to sink, changing their distribution to deeper ocean layers or sediments.
Some microbes within the plastisphere can biodegrade plastic polymers, albeit very slowly. This involves breaking down complex plastic macromolecules into simpler metabolites through enzymatic reactions. Beyond plastic degradation, the plastisphere impacts local biogeochemical cycles, including those of carbon, nitrogen, and phosphorus. The microbial communities influence the cycling of these nutrients.
The Plastisphere as a Vector
Plastic debris, once colonized by the plastisphere, can travel vast distances across aquatic environments, carrying its microbial inhabitants to new regions. This mobility raises concerns about the transport of harmful organisms and genetic material. A primary concern is the long-range dispersal of pathogenic microorganisms.
Species like Vibrio have been frequently reported in plastisphere biofilms, even in open ocean waters. This suggests plastic acts as a mobile habitat, introducing potential pathogens to new ecosystems, which could pose risks to marine life and human health. The dense microbial communities within the plastisphere can also act as “hotspots” for horizontal gene transfer, where bacteria exchange genetic material. This exchange can facilitate the spread of traits like antibiotic resistance genes among bacteria, potentially contributing to the global dissemination of antimicrobial resistance.