Bacterial Abundance, Diversity and Activity During Long-Term Colonization of Non-biodegradable and Biodegradable Plastics in Seawater

Abstract

The microorganisms living on plastics called “plastisphere” have been classically described as very abundant, highly diverse, and very specific when compared to the surrounding environments, but their potential ability to biodegrade various plastic types in natural conditions have been poorly investigated. Here, we follow the successive phases of biofilm development and maturation after long-term immersion in seawater (7 months) on conventional [fossil-based polyethylene (PE) and polystyrene (PS)] and biodegradable plastics [biobased polylactic acid (PLA) and polyhydroxybutyrate-co-hydroxyvalerate (PHBV), or fossil-based polycaprolactone (PCL)], as well as on artificially aged or non-aged PE without or with prooxidant additives [oxobiodegradable (OXO)]. First, we confirmed that the classical primo-colonization and growth phases of the biofilms that occurred during the first 10 days of immersion in seawater were more or less independent of the plastic type. After only 1 month, we found congruent signs of biodegradation for some bio-based and also fossil-based materials. A continuous growth of the biofilm during the 7 months of observation (measured by epifluorescence microscopy and flow cytometry) was found on PHBV, PCL, and artificially aged OXO, together with a continuous increase in intracellular (3H-leucine incorporation) and extracellular activities (lipase, aminopeptidase, and β-glucosidase) as well as subsequent changes in biofilm diversity that became specific to each polymer type (16S rRNA metabarcoding). No sign of biodegradation was visible for PE, PS, and PLA under our experimental conditions. We also provide a list of operational taxonomic units (OTUs) potentially involved in the biodegradation of these polymers under natural seawater conditions, such as Pseudohongiella sp. and Marinobacter sp. on PCL, Marinicella litoralis and Celeribacter sp. on PHBV, or Myxococcales on artificially aged OXO. This study opens new routes for a deeper understanding of the polymers’ biodegradability in seawaters, especially when considering an alternative to conventional fossil-based plastics.

Degradation Rates and Bacterial Community Compositions Vary among Commonly Used Bioplastic Materials in a Brackish Marine Environment

“…Nevertheless, this fragmentation is likely to lead only to the formation of smaller plastic particles and, hence, does not alleviate the plastic pollution load. Thus, on the basis of our results, PLLA is not biodegradable in an open marine environment, as already suggested in previous studies. − …”

“…The consensus is forming toward plastisphere community differences being more dependent upon environmental conditions than polymer type. ,− In contrast, upon biodegradable plastic materials, both bacterial community composition and/or bacterial activity differentiate compared to reference materials, indicating that certain bioplastics could actually harbor communities capable of biodegradation. However, the amount of literature on biodegradable plastics is still limited and have been concentrated mostly on polylactic acid (PLA) and polyhydroxybutyrate (PHB). − Differences in biodegradability between polymer types have also been reported; e.g., in seawater, PHB is more prone to biodegradation than PLA. ,− These studies have provided valuable information on bioplastic behavior and possible degradation in marine environments; however, studies with multiple bioplastic materials combining methodologies on actual biodegradation (biological oxygen demand) and in situ experiments, including both weight attrition and bacterial community composition, are lacking. Also, bacterial community dynamics on bioplastic materials on a yearly scale are still needed.…”

Differences in the Plastispheres of Biodegradable and Non-biodegradable Plastics: A Mini Review

“…Following seawater incubation for 15 months, microbial communities on PLA were significantly different from that of seven other synthetic substrates, with Leptobacterium being the major contributor to the dissimilarity ( Kirstein et al, 2018 ). Odobel et al (2021) reported on the variations in mature biofilms on different polymer surfaces. They observed that Planctomycetaceae (12%) was the most abundant in PLA, whereas Saprospiraceae (19%) was the most abundant in polystyrene (PS; Odobel et al, 2021 ).…”

“… Odobel et al (2021) reported on the variations in mature biofilms on different polymer surfaces. They observed that Planctomycetaceae (12%) was the most abundant in PLA, whereas Saprospiraceae (19%) was the most abundant in polystyrene (PS; Odobel et al, 2021 ). Another study that focused on the freshwater environment concluded that the microbial composition between polyhydroxybutyrate (PHB) and PE varied remarkably, and the PHB surface consisted primarily of unclassified Moraxellaceae, whereas the PE surface hosted a significant amount of Erythromicrobium spp.…”

Biodegradable plastics in the marine environment: a potential source of risk?

“…In a period after entering the natural environment, BPs may pose similar effects on habitats as conventional plastics. It is proven that corn starch-based BP films in the intertidal zone could create anoxic conditions beneath them, reduce primary productivity and organic matter in sediments, and decrease infaunal invertebrate populations, similar to those effects caused by conventional plastics [126] .…”