Microbiological Characterization of the Biofilms Colonizing Bioplastics in Natural Marine Conditions: A Comparison between PHBV and PLA

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.

On the role of bacterial gut microbiota from supralittoral amphipod Talitrus saltator (Montagu, 1808) in bioplastic degradation

Despite the promise of a reduced environmental impact, bioplastics are subjected to dispersion and accumulation similarly to traditional plastics, especially in marine and coastal environments. The environmental impact of bioplastics is attracting increasing attention due to the growing market demand. The ability of the supralittoral amphipod Talitrus saltator to ingest and survive on pristine starch-based bioplastic has already been assessed. However, the involvement of the gut microbiota of this key coastal species in making bioplastics a dietary supplement, remains unknown. In this study, we investigated the modification of T. saltator gut microbiota following bioplastic ingestion and the effect of this change on the modification of their chemical composition. Groups of adult amphipods were fed with: 1 - two different kinds of starch-based bioplastic; 2 - a 50 %/50 % chitosan-starch mixture; and 3 - paper and dry-fish-food. Freshly collected, unfed individuals were used as control group. Faecal pellets from the amphipods were collected and characterized using ATR-FTIR spectroscopy. DNA was extracted from gut samples for metagenomic analysis. Spectroscopic investigation suggested a partial digestion of polysaccharide components in the experimental polymeric materials. The analysis of the gut microbiota revealed that bioplastic feeding induced modification of sandhopper's gut microbial communities, shifting the abundance of specific microbial genera already present in the gut, towards bacterial genera associated with plastic/bioplastic degradation, especially in groups fed with starch-based bioplastics. Overall, our results highlight the involvement of T. saltator's gut microbiota in bioplastic modification, providing new insights into the potential role of microbial consortia associated to sandhoppers in bioplastic management.

Innovations in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and nanocomposites for sustainable food packaging via biochemical biorefinery platforms: A comprehensive review

The substantial build-up of non-biodegradable plastic waste from packaging sector not only poses severe environmental threats but also hastens the depletion of natural petroleum-based resources. Presently, poly (3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV), received enormous attention as ideal alternatives for such traditional petroleum-derived plastics based on their biocompatibility and superior mechanical properties. However, high cost of such copolymer, due to expensive nature of feedstock, inefficient microbial processes and unfavorable downstream processing strategies restricts its large-scale commercial feasibility in the packaging sector. This review explores merits and challenges associated with using potent agricultural and industrial waste biomasses as sustainable feedstocks alongside improved fermentation and downstream processing strategies for the biopolymer in terms of biorefinery concept. Despite PHBV's attractive properties, its inherent shortcomings like weak thermal stability, poor mechanical properties, processability difficulty, substantial hydrophobicity and comparatively higher water vapor permeability (WVP) demand the development of its composites based on the application. Based on this fact, the review assessed properties and potential applications of PHBV-based composite materials having natural raw materials, nanomaterials and synthetic biodegradable polymers. Besides, the review also enlightens sustainability, future prospects, and challenges associated with PHBV-based composites in the field of food packaging while considering insights about economic evaluation and life cycle assessment.

Degradation efficiency of biodegradable plastics in subtropical open-air and marine environments: Implications for plastic pollution

Bioplastics are increasingly used as a solution to tackle plastic pollution problems. However, their degradability in natural environments is currently under debate. To evaluate their degradation efficiencies, we conducted in-situ degradation experiments in an open-air and two marine environments in Hong Kong. Three groups of biodegradable plastic were tested, namely (1) additive-modified low-density polyethylene (LDPE), labelled as oxo-biodegradable or photodegradable plastics, (2) polylactic acid (PLA), and (3) polyvinyl alcohol (PVA)/starch blends. Most biodegradable plastics fail to completely degrade but remain visually present after six months of exposure. Only PLA is able to demonstrate 100 % disintegration in one to three months in marine settings, suggesting that subtropical marine environments may favor PLA degradation. Biodegradable plastics that are bio-based (PLA and PVA/Starch blends) show notably larger mass losses by 23-100 % than the fossil-based ones (modified-LDPE). Our results reveal higher degradation efficiencies of PLA and PVA/Cassava starch blend in marine than open-air settings (with mass losses larger by 50 %, and by 39-41 %, respectively), potentially via biodegradation and hydrolysis. Meanwhile, modified-LDPE and PVA/Corn starch blends in general show higher degradation efficiencies in open-air than marine settings (with mass losses larger by 2 %, and by 17-33 %, respectively), potentially via abiotic oxidation. Since all tested biodegradable plastics exhibit potential fragmentation signs, further investigation is needed to characterize the behaviours of the microplastics generated. The current labelling on biodegradable bags fails to provide comprehensive information regarding their actual environmental degradation behaviours, especially considering their fragmentation risk and limited degradation exhibited in this study. This highlights the imperative for improved messaging to ensure consumers are better informed about these products.

Recent advances in the relationships between biofilms and microplastics in natural environments

Plastic pollution in the form of microplastics (MPs), poses a significant threat to natural ecosystems, with detrimental ecological, social, and economic impacts. This review paper aims to provide an overview of the existing research on the interaction between microbial biofilms and MPs in natural environments. The review begins by outlining the sources and types of MPs, emphasizing their widespread presence in marine, freshwater, and terrestrial ecosystems. It then discusses the formation and characteristics of microbial biofilms on MPs surfaces, highlighting their role in altering the physicochemical properties of MPs and facilitating processes such as vertical transport, biodegradation, dispersion of microorganisms, and gene transfer. Different methods used to assess these interactions are discussed, including microbiological and physicochemical characterization. Current gaps and challenges in understanding the complex relationships between biofilms and MPs are identified, highlighting the need for further research to elucidate the mechanisms underlying these complex interactions and to develop effective mitigation strategies. Innovative solutions, including bioremediation techniques and their combination with other strategies, such as nanotechnology, advanced filtration technologies, and public awareness campaigns, are proposed as promising approaches to address the issue of MPs pollution. Overall, this review underscores the urgent need for a multidisciplinary approach to combating MPs pollution, combining scientific research, technological innovation, and public engagement to safeguard the health and integrity of natural ecosystems.

Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Effects of poly(3-hydroxybutyrate) [P(3HB)] coating on the bacterial communities of artificial structures

The expanding urbanization of coastal areas has led to increased ocean sprawl, which has had both physical and chemical adverse effects on marine and coastal ecosystems. To maintain the health and functionality of these ecosystems, it is imperative to develop effective solutions. One such solution involves the use of biodegradable polymers as bioactive coatings to enhance the bioreceptivity of marine and coastal infrastructures. Our study aimed to explore two main objectives: (1) investigate PHA-degrading bacteria on polymer-coated surfaces and in surrounding seawater, and (2) comparing biofilm colonization between surfaces with and without the polymer coating. We applied poly(3-hydroxybutyrate) [P(3HB)) coatings on concrete surfaces at concentrations of 1% and 6% w/v, with varying numbers of coating cycles (1, 3, and 6). Our findings revealed that the addition of P(3HB) indeed promoted accelerated biofilm growth on the coated surfaces, resulting in an occupied area approximately 50% to 100% larger than that observed in the negative control. This indicates a remarkable enhancement, with the biofilm expanding at a rate roughly 1.5 to 2 times faster than the untreated surfaces. We observed noteworthy distinctions in biofilm growth patterns based on varying concentration and number of coating cycles. Interestingly, treatments with low concentration and high coating cycles exhibited comparable biofilm enhancements to those with high concentrations and low coating cycles. Further investigation into the bacterial communities responsible for the degradation of P(3HB) coatings identified mostly common and widespread strains but found no relation between the concentration and coating cycles. Nevertheless, this microbial degradation process was found to be highly efficient, manifesting noticeable effects within a single month. While these initial findings are promising, it's essential to conduct tests under natural conditions to validate the applicability of this approach. Nonetheless, our study represents a novel and bio-based ecological engineering strategy for enhancing the bioreceptivity of marine and coastal structures.

Do Microorganisms in Bathing Water in Guadeloupe (French West Indies) Have Resistance Genes?

Waterborne faecal contamination is a major public health concern. The main objectives of this study were to investigate faecal contamination and Escherichia coli (E. coli) antibiotic resistance in recreational fresh water from Guadeloupe and to characterise the microbiome and resistome composition in biofilms from submerged rocks. Significant faecal contamination was observed at 14 freshwater sites. E. coli predominated (62%), followed by Enterobacter cloacae (11%) and Acinetobacter spp. (11%). Of 152 E. coli isolated, none produced extended-spectrum beta-lactamases (ESBLs), but 7% showed resistance to streptomycin and 4% to tetracycline. Biofilm resistome analysis revealed clinically significant antibiotic-resistance genes (ARGs), including those coding for resistance to sulfonamides (sul1), carbapenems (blaKPC), and third-generation cephalosporins (blaCTX-M). Mobile genetic elements (MGEs) (intI1, intI2, intI3) linked to resistance to aminoglycosides, beta-lactams, tetracycline, as well as heavy metal resistance determinants (copA, cusF, czcA, merA) conferring resistance to copper, silver, cadmium, and mercury were also detected. Diverse bacterial phyla were found in biofilm samples, of which Proteobacteria, Bacteroidetes, Planctonomycetes, and Cyanobacteria were predominant. Despite the frequent presence of E. coli exceeding regulatory standards, the low levels of antibiotic-resistant bacteria in freshwater and of ARGs and MGEs in associated biofilms suggest limited antibiotic resistance in Guadeloupean recreational waters.