Rapid Physicochemical Changes in Microplastic Induced by Biofilm Formation

Abstract

Risk assessment of microplastic (MP) pollution requires understanding biodegradation processes and related changes in polymer properties. In the environment, there are two-way interactions between the MP properties and biofilm communities: (i) microorganisms may prefer some surfaces, and (ii) MP surface properties change during the colonization and weathering. In a 2-week experiment, we studied these interactions using three model plastic beads (polyethylene [PE], polypropylene [PP], and polystyrene [PS]) exposed to ambient bacterioplankton assemblage from the Baltic Sea; the control beads were exposed to bacteria-free water. For each polymer, the physicochemical properties (compression, crystallinity, surface chemistry, hydrophobicity, and surface topography) were compared before and after exposure under controlled laboratory conditions. Furthermore, we characterized the bacterial communities on the MP surfaces using 16S rRNA gene sequencing and correlated community diversity to the physicochemical properties of the MP. Significant changes in PE crystallinity, PP stiffness, and PS maximum compression were observed as a result of exposure to bacteria. Moreover, there were significant correlations between bacterial diversity and some physicochemical characteristics (crystallinity, stiffness, and surface roughness). These changes coincided with variation in the relative abundance of unique OTUs, mostly related to the PE samples having significantly higher contribution of Sphingobium, Novosphingobium, and uncultured Planctomycetaceae compared to the other test materials, whereas PP and PS samples had significantly higher abundance of Sphingobacteriales and Alphaproteobacteria, indicating possible involvement of these taxa in the initial biodegradation steps. Our findings demonstrate measurable signs of MP weathering under short-term exposure to environmentally relevant microbial communities at conditions resembling those in the water column. A systematic approach for the characterization of the biodegrading capacity in different systems will improve the risk assessment of plastic litter in aquatic environments.

Understanding Biofilm Formation in Ecotoxicological Assays With Natural and Anthropogenic Particulates

“…In line with our previous findings ( Ogonowski et al, 2018 ; McGivney et al, 2020 ), high contribution of polystyrene (%PS) significantly stimulated biofilm diversity ( Figure 7 ), whereas high Bdellovibrionaceae contribution decreased it ( Supplementary Figure 7 ). Bdellovibrio and like organisms (BALOs) are a monophyletic group of Gram-negative obligate prokaryotic predators, ubiquitous in the aquatic environment and natural biofilms ( Williams et al, 1995 ; Rotem et al, 2014 ).…”

“…These biofilm communities on plastics often differ from those in the surrounding water and other substrates ( Ogonowski et al, 2018 ). Moreover, plastic surfaces inhabited by biofilms undergo various physicochemical transformations ( McGivney et al, 2020 ), resulting in changing particle capacity to sorb chemicals and aggregate with other particulates. In turn, aggregation affects particle size distribution (PSD) in the environment, altering the plastics uptake by consumers with size-selectivity toward food particles.…”

Human impacts and their interactions in the Baltic Sea region

“…Vibrio, as compared to natural particles, does not occur in the Baltic Sea (Oberbeckmann and Labrenz, 2020). While some physiochemical properties of plastic beads changed significantly after exposure to bacterioplankton from the Baltic Sea (McGivney et al, 2020), the microbial degradation and metabolization of full plastic polymers is unlikely to occur in the Baltic 2245 environment at time scales relevant for human society (Oberbeckmann and Labrenz, 2020). Plastics often contain residual monomers, which are more likely to be degraded by microorganisms than polymers (Klaeger et al, 2019).…”

<em> </em>Current Research on Microbe-Plastic Interactions in the Marine Environment

“…Table S3: The methods used and degradation found by studies including a measurement of biodegradation. Includes references 4,11,21,23,24,30,35,43,45,52,56,59,62,63,65,68,70,72,76,81,84,[92][93][94]102,104,111,[119][120][121][122]134,139,144,149,361 .…”