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The plastisphere is a human-made ecosystem consisting of organisms able to live on plastic waste. Plastic marine debris, most notably microplastics, accumulates in aquatic environments and serves as a habitat for various types of microorganisms, including bacteria and fungi. [1] [2] As of 2022, an estimated 51 trillion microplastics are floating in the surface water of the world's oceans. [3] A single 5mm piece of plastic can host 1,000s of different microbial species. [4] Some marine bacteria can break down plastic polymers and use the carbon as a source of energy.
Plastic pollution acts as a more durable "ship" than biodegradable material for carrying the organisms over long distances. [5] [6] This long-distance transportation can move microbes to different ecosystems and potentially introduce invasive species [1] as well as harmful algae. [7] The microorganisms found on the plastic debris comprise an entire ecosystem of autotrophs, heterotrophs and symbionts. [8] The microbial species found within plastisphere differ from other floating materials that naturally occur (i.e., feathers and algae) due to plastic's unique chemical nature and slow speed of biodegradation. In addition to microbes, insects have come to flourish in areas of the ocean that were previously uninhabitable. The sea skater, for example, has been able to reproduce on the hard surface provided by the floating plastic. [9]
The plastisphere was first described in 2013 by a team of three marine scientists, Linda Amaral-Zettler from the Marine Biological Laboratory, Tracy Mincer from Woods Hole Oceanographic Institution, and Erik Zettler from Sea Education Association. [10] [11] They collected plastic samples during research trips to study how the microorganisms function and alter the ecosystem. They analyzed plastic fragments collected in nets from multiple locations within the Atlantic Ocean. [11] The researchers used a combination of scanning electron microscopy and DNA sequencing to identify the distinct microbial community composition of the plastisphere. [11] Among the most notable findings were "pit formers", crack and pit forming organisms that provide evidence of biodegradation [11] [12] and may also have the potential to break down hydrocarbons. [11] In their analysis, the researchers also found members of the genus Vibrio , a genus which includes the bacteria that cause cholera and other gastrointestinal ailments. [13] Some species of Vibrio can glow, and it is hypothesized that this attracts fish that eat the organisms colonizing the plastic, which then feed from the stomachs of the fish. [14] Studies carried out in the Baltic Sea [15] and in the Mediterranean Sea, [16] also found microorganisms of the genus Vibrio, in plastic films and fragments, and in plastic fibres, respectively.
Plastic was invented in 1907 by Leo Baekeland using formaldehyde and phenol. [17] Since then, plastic use has exploded and is prevalent throughout human society. From 1964 to 2014, the use of plastic increased twenty-fold. It is expected to double from the 2014 levels by 2035. [18] Efforts to curb plastic production through plastic bans have largely focused on packaging and single-use plastics, but have not slowed the pace of plastic pollution. Similarly, plastic recycling rates tend to be low. In the EU, only 29% of the plastic consumed is recycled. [19] Plastic that does not reach a recycling facility or landfill, accumulates in marine environments due to accidental dumping of the waste, losses during transport, or direct disposal from ships. [19] In 2010, it was estimated that 4 to 12 million metric tons (Mt) of plastic waste entered into marine ecosystems. [20]
Smaller, more inconspicuous microplastic particles have aggregated in the oceans since the 1960s. [21] A more recent concern in microplastic pollution is the use of plastic films in agriculture. 7.4 million tons of plastic film are used each year to increase food production. [22] Scientists have found that microbial biofilms can form within 7–14 days on plastic film surfaces, and have the ability to alter the chemical properties of the soil and plants that we are ingesting. [23] Microplastics have been recorded everywhere, even the Arctic due to atmospheric circulation. [24]
Large-scale sequencing studies have found alpha diversities to be lower in the plastisphere relative to surrounding soil samples due to a decrease in species richness in the plastisphere. [25] [26] [27] [28] Polymer film fragments affect microbes in different ways, leading to mixed effects on microbial growth rates in the plastisphere. [25] [28] [29] Certain polymer degrading bacteria release toxic byproducts as a result of the degradation, serving as a deterrent to the colonization of the plastisphere by other species. [25] Phylogenetic diversity is also decreased in the plastisphere relative to nearby soil samples. [25]
The bacterial and microbial communities in the plastisphere are significantly different from those found in surrounding soil samples, creating a new ecological niche within the ecosystem. [25] [30] [31] The specific growth of bacteria caused by film fragments is a primary cause for the creation of a unique bacterial community. [25] [32] Changes in bacterial community composition over time in the plastisphere have also been shown to drive changes in surrounding land. [25] [28] [33]
In another study which looked at the factors influencing the diversity of the plastisphere, the researchers found that the highest degree of unique microorganisms tended to favor plastic pieces that were blue. [34]
A 2024 paper described an experiment carried out across the Atlantic Ocean and the Mediterranean Sea aimed at studying the colonisation and genetic variety of organisms in the marine plastisphere. The paper identified tardigrades incubating in plastics in situ . [35]
The ability of certain bacteria to degrade polymers facilitates their flourishing within the plastisphere. Phyla of bacteria that have increased presences in the plastisphere relative to soil samples without plastic micro-fragments include Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Planctomycetes, and Proteobacteria. [25] [36] [37] [38] [39] Furthermore, bacteria of the order Rhizobiales, Rhodobacterales, and Sphingomonadales are enriched in the plastisphere. [25] Interactions within the unique bacterial community composition in the plastisphere influence local biogeochemical cycles and ecosystems' food web interactions.
Bacterial communities in the plastisphere have enhanced metabolisms. [25] KEGG Pathway enrichment analyses of plastisphere samples have demonstrated increases in genetic and environmental information processing, cellular processes, and organismal systems. [25] Enhanced metabolic functions for communities in the plastisphere include nitrogen metabolism, insulin signaling pathways, bacterial secretion, organophosphorus compound metabolism, antioxidant metabolism, Vitamin B synthesis, chemotaxis, terpenoid quinone synthesis, sulfur metabolism, carbohydrate metabolism, herbicide degradation, fatty acid metabolism, amino acid metabolism, ketone body pathways, lipopolysaccharide synthesis, alcohol degradation, polycyclic aromatic hydrocarbon degradation, lipid metabolism, cofactor metabolism, cellular growth, cell motility, membrane transport, energy metabolism, and xenobiotics metabolism. [25] [39] [40] [41]
The presence of hydrocarbon-degrading species such as hydrocarbonoclastic bacteria in the plastisphere indicates a direct link between the plastisphere and the carbon cycle. [25] [42] [43]
Metagenome analyses suggest that genes involved in carbon degradation, nitrogen fixation, organic nitrogen conversion, ammonia oxidation, denitrification, inorganic phosphorus solubilization, organic phosphorus mineralization, and phosphorus transporter production are enriched in the plastisphere, demonstrating the potential impact on biogeochemical cycles by the plastisphere. [25] [44] [45] [46] [47] [48] [49] [50] Specific bacterial phyla present in the plastisphere due to their biodegradation abilities and their role in the carbon, nitrogen, and phosphorus cycles include Proteobacteria and Bacteroidetes. [25] [42] [43] [51] [52] Some carbon-degrading bacteria are able to use plastics as a food source. [53] [54]
Research in the southern Pacific Ocean has investigated the plastisphere's potential in CO2 and N2O contribution where fairly low greenhouse gas contributions by the plastisphere were noted. However, it was concluded that greenhouse gas contribution was dependent on the degree of nutrient concentration and the type of plastic. [55]
KEGG Pathway enrichment analyses of plastisphere samples suggest that sequences related to human disease are enriched in the plastisphere. [25] Cholera causing Vibrio cholerae, cancer pathways, and toxoplasmosis sequences are enriched in the plastisphere. [13] [25] Pathogenic bacteria are sustained in the plastisphere in part due to the adsorption of organic pollutants onto biofilms and their usage as nutrition. [25] [39] [40] Current research also aims to identify the relationship between the plastisphere and respiratory viruses and whether the plastisphere affects viral persistence and survival in the environment. [56]
Some microorganisms present in the plastisphere have the potential to degrade plastic materials. [19] This could be potentially advantageous, as scientists may be able to utilize the microbes to break down plastic that would otherwise remain in the environment for centuries. [57] However, as plastic is broken down into smaller pieces and eventually microplastics, there is a higher likelihood that it will be consumed by plankton and enter into the food chain. [58] As plankton are eaten by larger organisms, the plastic may eventually cause there to be bioaccumulation in fish and other marine species eaten by humans. [58] The following table lists some microorganisms with biodegradation capacity. [19]
Microorganism | Plastic type | Degradation capacity |
---|---|---|
Aspergillus tubingensis [59] | Polyurethane | Degraded 90% within 21 days [19] |
Pestalotiopsis microspora [60] | Polyurethane | Degraded 90% within 16 days [19] |
Bacillus pseudofirmus [61] | LDPE | Degraded 8.3% over 90 day observation period [61] |
Salipaludibacillus agaradhaerens [62] | LDPE | Degraded 18.3 ± 0.3% and 13.7 ± 0.5% after 60 days of incubation [62] |
Tenebrio molitor larvae [63] | Polystyrene (PS) | Degradation rates doubled for meal worms with diets that consisted of 10% PS and 90% bran in comparison to meal worms who were exclusively fed PS [63] |
Enterobacter sp. [19] | Polystyrene (PS) | Degraded a maximum of 12.4% in 30 days [19] |
Phanerochaete chrysosporium [19] | Polycarbonate | Degraded 5.4% in 12 months [19] |
Marine microbial consortium [19] | Polycarbonate | Degraded 8.3% in 12 months [19] |
Ideonella sakaiensis [64] | PET | Fully degraded within six weeks [19] |
Activated sludge [65] | PET | Degraded up to 60% within a year [19] |
Galleria mellonella caterpillars [66] | Polyethylene | Degraded 13% within 14 hours [66] Average degradation rate of 0.23 mg cm-2 h-1 [66] |
Zalerium maritimum [67] | Polyethylene | Degraded 70% within 21 days [19] |
Oftentimes the degradation process of plastic by microorganisms is quite slow. [19] However, scientists have been working towards genetically modifying these organisms in order to increase plastic biodegradation potential. For instance, Ideonella sakaiensis has been genetically modified to break down PET at faster rates. [68] Multiple chemical and physical pretreatments have also demonstrated potential in enhancing the degree of biodegradation of different polymers. For instance UV or c-ray irradiation treatments, have been used to heighten the degree of biodegradation of certain plastics. [19]
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradation occurs under a specific set of circumstances.
Geomicrobiology is the scientific field at the intersection of geology and microbiology and is a major subfield of geobiology. It concerns the role of microbes on geological and geochemical processes and effects of minerals and metals to microbial growth, activity and survival. Such interactions occur in the geosphere, the atmosphere and the hydrosphere. Geomicrobiology studies microorganisms that are driving the Earth's biogeochemical cycles, mediating mineral precipitation and dissolution, and sorbing and concentrating metals. The applications include for example bioremediation, mining, climate change mitigation and public drinking water supplies.
Bioremediation broadly refers to any process wherein a biological system, living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment. In comparison to conventional physicochemical treatment methods bioremediation may offer advantages as it aims to be sustainable, eco-friendly, cheap, and scalable.
Microbial ecology is the ecology of microorganisms: their relationship with one another and with their environment. It concerns the three major domains of life—Eukaryota, Archaea, and Bacteria—as well as viruses.
Biological augmentation is the addition of archaea or bacterial cultures required to speed up the rate of degradation of a contaminant. Organisms that originate from contaminated areas may already be able to break down waste, but perhaps inefficiently and slowly.
Biodegradable plastics are plastics that can be decomposed by the action of living organisms, usually microbes, into water, carbon dioxide, and biomass. Biodegradable plastics are commonly produced with renewable raw materials, micro-organisms, petrochemicals, or combinations of all three.
The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. In soil systems, the microbial loop refers to soil carbon. The term microbial loop was coined by Farooq Azam, Tom Fenchel et al. in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.
Gammaproteobacteria is a class of bacteria in the phylum Pseudomonadota. It contains about 250 genera, which makes it the most genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scientifically important groups of bacteria belong to this class. All members of this class are Gram-negative. It is the most phylogenetically and physiologically diverse class of the Pseudomonadota.
Oxo-degradation is a process of plastic degradation utilizing oxidation to reduce the molecular weight of plastic, rendering the material accessible to bacterial and fungal decomposition. To change the Molecular structure in order to break down under sunlight, the plastic can be broken down and eaten by micro-organisms. Oxo-degradable plastics- composed of polymers such as polyethylene (PE) or polypropylene (PP) -contain a prodegradant catalyst, typically a salt of manganese or iron.
Microbiology is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular, or acellular. Microbiology encompasses numerous sub-disciplines including virology, bacteriology, protistology, mycology, immunology, and parasitology.
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be molded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to their widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives.
The North Atlantic garbage patch is a garbage patch of man-made marine debris found floating within the North Atlantic Gyre, originally documented in 1972. A 22-year research study conducted by the Sea Education Association estimates the patch to be hundreds of kilometers across, with a density of more than 200,000 pieces of debris per square kilometer. The garbage originates from human-created waste traveling from rivers into the ocean and mainly consists of microplastics. The garbage patch is a large risk to wildlife through plastic consumption and entanglement.
Microplastics are fragments of any type of plastic less than 5 mm (0.20 in) in length, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. They cause pollution by entering natural ecosystems from a variety of sources, including cosmetics, clothing, food packaging, and industrial processes.
A microbial consortium or microbial community, is two or more bacterial or microbial groups living symbiotically. Consortiums can be endosymbiotic or ectosymbiotic, or occasionally may be both. The protist Mixotricha paradoxa, itself an endosymbiont of the Mastotermes darwiniensis termite, is always found as a consortium of at least one endosymbiotic coccus, multiple ectosymbiotic species of flagellate or ciliate bacteria, and at least one species of helical Treponema bacteria that forms the basis of Mixotricha protists' locomotion.
Biodegradable additives are additives that enhance the biodegradation of polymers by allowing microorganisms to utilize the carbon within the polymer chain as a source of energy. Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product. Additives are generally in masterbatch formation that use carrier resins such as polyethylene (PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate (PET).
Petroleum microbiology is a branch of microbiology that deals with the study of microorganisms that can metabolize or alter crude or refined petroleum products. These microorganisms, also called hydrocarbonoclastic microorganisms, can degrade hydrocarbons and, include a wide distribution of bacteria, methanogenic archaea, and some fungi. Not all hydrocarbonoclasic microbes depend on hydrocarbons to survive, but instead may use petroleum products as alternative carbon and energy sources. Interest in this field is growing due to the increasing use of bioremediation of oil spills.
The viral shunt is a mechanism that prevents marine microbial particulate organic matter (POM) from migrating up trophic levels by recycling them into dissolved organic matter (DOM), which can be readily taken up by microorganisms. The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM.
Hydrocarbonoclastic bacteria are a heterogeneous group of prokaryotes which can degrade and utilize hydrocarbon compounds as source of carbon and energy. Despite being present in most of environments around the world, several of these specialized bacteria live in the sea and have been isolated from polluted seawater.
Plastic degradation in marine bacteria describes when certain pelagic bacteria break down polymers and use them as a primary source of carbon for energy. Polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are incredibly useful for their durability and relatively low cost of production, however it is their persistence and difficulty to be properly disposed of that is leading to pollution of the environment and disruption of natural processes. It is estimated that each year there are 9-14 million metric tons of plastic that are entering the ocean due to inefficient solutions for their disposal. The biochemical pathways that allow for certain microbes to break down these polymers into less harmful byproducts has been a topic of study to develop a suitable anti-pollutant.
A plastivore is an organism capable of degrading and metabolising plastic. While plastic is normally thought of as non-biodegradable, a variety of bacteria, fungi and insects have been found to degrade it.