Identification of rare microbial colonizers of plastic materials incubated in a coral reef environment

Long-term monitoring of biofilm succession unveils differences between biodegradable and conventional plastic materials

A vast amount of plastic waste enters the ocean every year and the Mediterranean Sea is particularly affected by this issue. Biodegradable polymers like poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), may help mitigate this problem. We investigated bacterial biofilm development and succession on these polymers over one year in the Western Mediterranean Sea. Scanning electron microscopy (SEM) and confocal laser scanning were used to examine microbial colonization and surface erosion, while bacterial community abundance and composition were assessed through culture plate counting and 16S rRNA gene amplicon sequencing. SEM revealed significant surface erosion on PHBV, indicative of microbial degradation, while PLA exhibited minor and irregular erosion. Culture-based quantification showed higher bacterial colonization on PHBV compared to PLA, suggesting that PHBV provides a more favourable surface for bacterial attachment Amplicon sequencing of the 16S rRNA gene revealed high bacterial diversity, with 17,781 operational taxonomic units across all samples. Proteobacteria, Bacteroidota, and Planctomycetota were the dominant phyla, with the Shannon index consistently exceeding 8, corroborating the bacterial diversity across all materials. Temporal shifts in bacterial community composition were significant, with exposure time explaining 29.8 % of the variation, suggesting biofilm succession as a key factor shaping microbial assemblages. While polymer type had a limited impact on bacterial composition, PHBV biofilms exhibited greater bacterial abundance and diversity compared to PLA. This study highlights PHBV's role in shaping biofilms and its relevance in assessing biodegradable plastics in marine environments. Understanding microbial interactions with bioplastics is crucial for evaluating their environmental impact and degradation dynamics.

Mesoplastics: A Review of Contamination Status, Analytical Methods, Pollution Sources, Potential Risks, and Future Perspectives of an Emerging Global Environmental Pollutant

Mesoplastics are emerging environmental pollutants that can pose a threat to the environment. Researching mesoplastics is crucial as they bridge the gap between macroplastics and microplastics by determining their role in plastic fragmentation and pathways, as well as their ecological impact. Investigating mesoplastic sources will help develop targeted policies and mitigation strategies to address plastic pollution. These pollutants are found across aquatic, terrestrial, and agricultural ecosystems. Unlike microplastics, mesoplastics are reviewed in the scientific literature. This paper focuses on existing published research on mesoplastics, determining the trends and synthesizing key findings related to mesoplastic pollution. Research primarily focused on marine and freshwater ecosystems, with surface water and beach sediments being the most studied compartments. Mesoplastics research often offers baseline data, with increased publications from 2014 to 2024, particularly in East Asia. However, certain ecosystems and regions remain underrepresented. Also, mesoplastics can disrupt ecosystems by degrading biodiversity, contaminating soils and waters, and affecting food chains. Mesoplastics can also become vectors for additives and pathogenic microorganisms, highlighting their environmental risks. Various factors influence mesoplastics' prevalence, including anthropogenic and non-anthropogenic activities. With this, future research should expand into less-studied ecosystems and regions, explore mesoplastic interactions with pollutants and organisms, and promote public awareness, education, and policy measures to reduce plastic use and mitigate pollution globally.

Interactions between microplastics and organic contaminants: The microbial mechanisms for priming effects of organic compounds on microplastic biodegradation

The co-presence of plastics and other organic contaminants is pervasive in various ecosystems, particularly in areas with intensive anthropogenic activities. Their interactions inevitably impact the composition and functions of the plastisphere microbiome, which in turn determines the trajectory of these contaminants. Antibiotics are a group of organic contaminants that warrant particular attention due to their wide presence in environments and significant potential to disseminate antibiotic resistance genes (ARGs) within the plastisphere. Therefore, this study investigated the impacts of sulfadiazine (SDZ), a prevalent environmental antibiotic, on the composition and function of the plastisphere microbial community inhabiting micro-polyethylene (mPE), one of the most common microplastic contaminants. Our findings indicated that the presence of SDZ increased the overall plastisphere microbial abundance and enriched populations that are capable of degrading both SDZ and mPE. The abundance of Aquabacterium, a dominant plastisphere population that is capable of degrading both SDZ and mPE, increased over the course of SDZ exposure, while another abundant mPE-degrading population, Ketobacter, remained stable. Accordingly, the removal of SDZ was enhanced in the presence of mPE. Moreover, the results further revealed that not only SDZ but also other labile organic contaminants (e.g., aniline and hexane) could accelerate mPE biodegradation through a priming effect. This investigation underscores the complex dynamics among microplastics, organic contaminants, and the plastisphere microbiome, offering insights into the environmental fate of plastic and antibiotic pollutants.

Microbial communities colonising plastics during transition from the wastewater treatment plant to marine waters

BACKGROUND

Plastics pollution and antimicrobial resistance (AMR) are two major environmental threats, but potential connections between plastic associated biofilms, the 'plastisphere', and dissemination of AMR genes are not well explored.

RESULTS

We conducted mesocosm experiments tracking microbial community changes on plastic surfaces transitioning from wastewater effluent to marine environments over 16 weeks. Commonly used plastics, polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) and polyethylene terephthalate (PET) incubated in wastewater effluent, river water, estuarine water, and in the seawater for 16 weeks, were analysed via 16S rRNA gene amplicon and shotgun metagenome sequencing. Within one week, plastic-colonizing communities shifted from wastewater effluent-associated microorganisms to marine taxa, some members of which (e.g. Oleibacter-Thalassolituus and Sphingomonas spp., on PET, Alcanivoracaceae on PET and PP, or Oleiphilaceae, on all polymers), were selectively enriched from levels undetectable in the starting communities. Remarkably, microbial biofilms were also susceptible to parasitism, with Saprospiraceae feeding on biofilms at late colonisation stages (from week 6 onwards), while Bdellovibrionaceae were prominently present on HDPE from week 2 and LDPE from day 1. Relative AMR gene abundance declined over time, and plastics did not become enriched for key AMR genes after wastewater exposure.

CONCLUSION

Although some resistance genes occurred during the mesocosm transition on plastic substrata, those originated from the seawater organisms. Overall, plastic surfaces incubated in wastewater did not act as hotspots for AMR proliferation in simulated marine environments.

Microbial communities exhibit distinct diversities and assembly mechanisms in rainwater and tap-water storage systems

Roof-harvested rainwater stored for potable and nonpotable usages represent a clean and sustainable water supply resource. However, the microbial dynamics and mechanisms of community assembly in long-termed operated rainwater storage systems remain elusive. In this study, characteristics of microbial communities in different habitats were systematically compared within rainwater and tap-water simulated storage systems (SWSSs) constructed with different tank materials (PVC, stainless steel and cement). Distinct microbial communities were observed between rainwater and tap-water SWSSs for both water and biofilm samples (ANOSIM, p < 0.05), with lower diversity indexes noted in rainwater samples. Notably, a divergent potential pathogen profile was observed between rainwater and tap-water SWSSs, with higher relative abundances of potential pathogens noted in rainwater SWSSs. Moreover, tank materials had a notable impact on microbial communities in rainwater SWSSs (ANOSIM, p < 0.05), rather than tap-water SWSSs, illustrating the distinct interplay between water chemistry and engineering factors in shaping the SWSS microbiomes. Deterministic processes contributed predominantly to the microbial community assembly in cement rainwater SWSSs and all tap-water SWSSs, which might be ascribed to the high pH levels in cement rainwater SWSSs and low-nutrient levels in all tap-water SWSSs, respectively. However, microbial communities in the PVC and stainless-steel rainwater SWSSs were mainly driven by stochastic processes. Overall, the results provided insights to the distinct microbial assembly mechanisms and potential health risks in stored roof-harvested rainwater, highlighting the importance of developing tailored microbial management strategies for the storage and utilization of rainwater.

Marine plastisphere selectively enriches microbial assemblages and antibiotic resistance genes during long-term cultivation periods

Several studies have focused on identifying and quantifying suspended plastics in surface and subsurface seawater. Microplastics (MPs) have attracted attention as carriers of antibiotic resistance genes (ARGs) in the marine environment. Plastispheres, specific biofilms on MP, can provide an ideal niche to spread more widely through horizontal gene transfer (HGT), thereby increasing risks to ecosystems and human health. However, the microbial communities formed on different plastic types and ARG abundances during exposure time in natural marine environments remain unclear. Four types of commonly used MPs (polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC)) were periodically cultured (46, 63, and 102 d) in a field-based marine environment to study the co-selection of ARGs and microbial communities in marine plastispheres. After the first 63 d of incubation (p < 0.05), the initial 16S rRNA gene abundance of microorganisms in the plastisphere increased significantly, and the biomass subsequently decreased. These results suggest that MPs can serve as vehicles for various microorganisms to travel to different environments and eventually provide a niche for a variety of microorganisms. Additionally, the qPCR results showed that MPs selectively enriched ARGs. In particular, tetA, tetQ, sul1, and qnrS were selectively enriched in the PVC-MPs. The abundances of intl1, a mobile genetic element, was measured in all MP types for 46 d (5.22 × 10-5 ± 8.21 × 10-6 copies/16s rRNA gene copies), 63 d (5.90 × 10-5 ± 2.49 × 10-6 copies/16s rRNA gene copies), and 102 d (4.00 × 10-5 ± 5.11 × 10-6 copies/16s rRNA gene copies). Network analysis indicated that ARG profiles co-occurred with key biofilm-forming bacteria. This study suggests that the selection of ARGs and their co-occurring bacteria in MPs could potentially accelerate their transmission through HGT in natural marine plastics.