Microplastics change soil properties, heavy metal availability and bacterial community in a Pb-Zn-contaminated soil

To understand the ecological impacts of the “Plastisphere”, those microbes need to be identified that preferentially colonize and interact with synthetic polymer surfaces, as opposed to general surface colonizers. It was hypothesized that the microbial biofilm composition varies distinctly between different substrates. A long-term incubation experiment was conducted (15month) with nine different synthetic polymer films as substrate as well as glass using a natural seawater flow-through system. To identify colonizing microorganisms, 16S and 18SrRNA gene tag sequencing was performed. The microbial biofilms of these diverse artificial surfaces were visualized via scanning electron microscopy. Biofilm communities attached to synthetic polymers are distinct from glass associated biofilms; apparently a more general marine biofilm core community serves as shared core among all synthetic polymers rather than a specific synthetic polymer community. Nevertheless, characteristic and discriminatory taxa of significantly different biofilm communities were identified, indicating their specificity to a given substrate.

Mature biofilm communities on synthetic polymers in seawater - Specific or general?By: Kirstein, Inga V.; Wichels, Antje; Krohne, Georg; et al.

Biodegradable plastics in the air and soil environment: Low degradation rate and high microplastics formation.

Particulate plastic fragments (micro and nano-plastics) in aquatic environments provide abundant solid substrates, which serve as an important habitat for a variety of microorganisms. Surfaces of microplastics (MPs) exhibit hydrophobicity that facilitate the adsorption of dissolved organic carbon (DOC) in the aquatic environment. Furthermore, MPs act as substrata, as well as a carbon source including the readily bioavailable DOC, which promote the formation of microbial biofilms. These biofilms have varied metabolic actions that govern the subsequent succession of micro- and meso-organisms habitation of MPs. The assemblage of ecosystems colonising the plastic environment is often referred to as the “plastisphere”. Polymer type, environmental conditions, including nutrient status, salinity, and season, affect the microbial composition of the biofilm. Microbial habitation accelerated by biofilm formation on particulate plastics enables the movement of microorganisms, especially in the aquatic environment, and impacts the transport and toxicity of contaminants associated with these particulate plastic fragments. This review paper describes the processes of microbial habitation and subsequent biofilm formation, the factors affecting biofilm formation, and the implications of biofilm formation on the mobility of microorganisms, degradation of MPs, and the bioavailability of contaminants associated with MPs. 

Biofilm formation and its implications on the properties and fate of microplastics in aquatic environments: A review

Plastic pollution poses a threat to terrestrial ecosystems, even impacting soils from remote alpine and arctic areas. Biodegradable plastics are a promising solution to prevent long-term accumulation of plastic litter. However, little is known about the decomposition of biodegradable plastics in soils from alpine and polar ecosystems or the microorganisms involved in the process. Plastics in aquatic environments have previously been shown to form a microbial community on the surface of the plastic distinct from that in the surrounding water, constituting the so-called ‘plastisphere’. Comparable studies in terrestrial environments are scarce. Here, we aimed to characterize the plastisphere microbiome of three types of plastics differing in their biodegradability in soil using DNA metabarcoding. Polylactic acid (PLA), polybutylene adipate terephthalate (PBAT) and polyethylene (PE) were buried in two different soils, from the Swiss Alps and from Northern Greenland, at 15°C for eight weeks. While physico-chemical characteristics of the polymers only showed minor (PLA, PBAT) or no (PE) changes after incubation, a considerably lower α-diversity was observed on the plastic surfaces and prominent shifts occurred in the bacterial and fungal community structures between the plastisphere and the adjacent bulk soil not affected by the plastic. Effects on the plastisphere microbiome decreased with greater biodegradability of the plastics, from PLA to PE. Copiotrophic taxa within the phyla Proteobacteria and Actinobacteria benefitted the most from plastic input. Especially taxa with a known potential to degrade xenobiotics, including Burkholderiales, Caulobacterales, Pseudomonas, Rhodococcus and Streptomyces, thrived in the plastisphere of the Alpine and Arctic soils. In addition, Saccharimonadales (superphylum Patescibacteria) was identified as a key taxon associated with PLA. The association of Saccharibacteria with plastic has not been reported before, and pursuing this finding further may shed light on the lifestyle of this obscure candidate phylum. Plastic addition affected fungal taxa to a lesser extent since only few fungal genera such as Phlebia and Alternaria were increased on the plastisphere. Our findings suggest that the soil microbiome can be strongly influenced by plastic pollution in terrestrial cryoenvironments. Further research is required to fully understand microbial colonization on plastic surfaces and the biodegradation of plastic in soils.

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Joel Rüthi

Papers

The “Plastisphere” of Biodegradable Plastics Is Characterized by Specific Microbial Taxa of Alpine and Arctic Soils